field study and technical analysis of the potential for interference … · interference would...
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Field Study and Technical Analysisof the Potential for Interference
fromLTE UE Operating in the 700 MHz A Block
toReception of DTV Channel 51, WPWR-TV
Prepared for Laser Inc.by
H. Stephen Berger, President of the General Partner
June 2015
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1. Table of Contents 1. Table of Contents................................................................................................................. i
2. Executive Summary.............................................................................................................1 2.1. Improvements in DTV Technology Have Significantly Lowered the Risk of Interference..........................................................................................................2 2.2. Field Tests in the Chicago Area Corroborate the Improvements in DTV Receiver Performance..............................................................................................2 2.3. LTE UE Operations Are Highly Unlikely to Cause Interference ............................2 2.4. Numerous Factors in This Case Lead to the Conclusion That Interference Will Be De Minimis in Chicago ..............................................................................3 2.5. King Street Wireless’s Adjacent A Block Operations Confirm That Interference Will Be De Minimis ............................................................................4 2.6. In the Unlikely Event of Interference, Simple and Effective Mitigation Options Are Available .............................................................................................4 3. Structure of the Report.............................................................................................4
4. Findings of the Report .........................................................................................................6
5. Technical Evaluation of Adjacent Band Interference........................................................10 5.1. Interference Model.................................................................................................13 5.2. Assessment of Central Viewing Area ....................................................................21 5.3. Operating Experience in Adjacent Market and Related Field Testing ..................24 5.4. Impact of DTV Installation....................................................................................33 5.5. Variation in LTE Transmissions............................................................................33
6. Frequency of Adjacent Band Interference .........................................................................38 6.1. Uplink vs Downlink Traffic...................................................................................42 6.2. Susceptible Portion of the Viewing Area...............................................................43 6.3. Lower 700 MHz A Block Operation .....................................................................45 6.4. LTE UE Maximum Radiated Power......................................................................49 6.5. LTE Power Control................................................................................................50 6.6. Proximity to the DTV Receiving Antenna.............................................................57 6.7. Relative Position and Orientation ..........................................................................57 6.8. LTE Traffic Pattern................................................................................................57 6.9. Impact of Multiple LTE UE...................................................................................57
7. Severity of Adjacent Band Interference.............................................................................58 7.1. Frequency of Impact ..............................................................................................59 7.2. Duration of Impact.................................................................................................60 7.3. Severity of Impact..................................................................................................62
8. Mitigations .........................................................................................................................68 8.1. Network Control ....................................................................................................68
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8.2. DTV Antenna.........................................................................................................69 8.3. DTV Amplifier.......................................................................................................71 8.4. DTV Low-Pass Filter.............................................................................................71 8.5. Cell Placement .......................................................................................................72 8.6. Small Cells .............................................................................................................72
9. Annex - Acceptable Levels of Interference .......................................................................72 9.1. The 10 m Criterion - FCC Part 15 .........................................................................73 9.2. Adjacent Channel DTV Interference .....................................................................74
10. Annex - LTE Signal Strength and D/U Ratios at ToV ......................................................74
11. Annex - Relative Antenna Position and Orientation..........................................................76 11.1. Relative Antenna Position & Orientation ..............................................................77 11.2. Calculating coverage levels ...................................................................................79
12. Annex - Development of Spectrum Management .............................................................82
13. Annex - Measuring Improvements ....................................................................................85
14. Annex - Field Measurements .............................................................................................85 14.1. Measurement System.............................................................................................86 14.2. Initial Field Survey ................................................................................................93 14.3. Assessment of Central Viewing Area ....................................................................97 14.4. Assessment of Border Viewing Area...................................................................100 14.5. Variation in LTE Transmissions..........................................................................108
15. Annex – Relevant Studies & Documents.........................................................................124 15.1. Cricket Waiver Request .......................................................................................124 15.2. Comments on Waiver Request.............................................................................125 15.3. FCC Studies .........................................................................................................126 15.4. Ofcom Studies......................................................................................................127 15.5. PCAST Report .....................................................................................................128 15.6. CSR on Adjacent Band Interference....................................................................128 15.7. 3GPP Standards ...................................................................................................129 15.8. ATSC Standards...................................................................................................130 15.9. NIST Building Propagation Studies ....................................................................130 15.10. Other Relevant Standards ....................................................................................131
16. Laser Team Members ......................................................................................................131
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2. Executive Summary This Report presents a technical analysis of the potential for adjacent band Long Term Evolution (LTE)-to-DTV interference to assess the accuracy of the positions set forth in the Petition filed with the FCC by Laser Inc. (successor to Cricket License Co. LLC) in WT Docket No. 14-17.Specifically, this Report analyzes the potential for inter-service interference to over-the-air (OTA) DTV reception of WPWR-TV, Channel 51 in the Chicago market, from proposed LTE User Equipment (UE) transmissions (i.e., LTE uplink) in the adjacent A Block of the lower 700 MHz band (698-704 MHz). The testing and analyses described in this Report were conducted by a highly experienced team with expertise in wireless communications technologies and broadcast engineering. Biographies for the team members are included in Annex 16.
Based on technical analysis, field measurements, and an assessment of the real world potential for LTE UE interference to DTV reception, this Report concludes that:
the potential for interference from LTE UE transmissions to WPWR-TV broadcast reception on Channel 51 is de minimis, impacting an estimated 46locations and 122 people out of a population of more than 10 million;
in the rare event that interference occurs, it is very likely to be minor and involve no more than loss of a few pixels; and
there are several simple and effective means to mitigate such interference,including LTE network management techniques, and Laser stands ready to cover the costs of any such mitigation measures that may be necessary.
The results of this study, consistent with the other analyses, demonstrate that LTE UEs can operate in the Lower 700 MHz A Block spectrum with only a de minimis risk of interference to the WPWR-TV, Channel 51 station, and that the DTV protection level of -23 dB Desired-to-Undesired (D/U) signal ratio established in Section 27.60 of the FCC’s rules do not serve the purpose of the rule in the Chicago area.
It has been almost 30 years since a Land Mobile Radio/UHF Television Technical Advisory Committee conducted research that led to the -23 dB D/U criteria, and advances in both DTV and wireless technology have resulted in significant improvement in tolerance of adjacent band signals by DTV.
Newer test technology allowed more detailed analysis and a greater understanding of the potential for interference in this case. See Annex 14.
An analysis of the real world impact of LTE uplink transmissions on the population in Chicago viewing the WPWR-TV station signal make clear that there is at most a de minimis risk of interference.
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2.1. Improvements in DTV Technology Have Significantly Lowered the Risk of Interference
The FCC’s current DTV protection criteria, based on a 1986 advisory committee report, do not account for the advances in DTV technology that have significantly improved the tolerance of DTV receivers to wireless LTE operations in the adjacent band.
Over the last three decades, broadcast TV has transitioned from analog to digital ATSC 8VSB and is currently on its sixth generation of chipsets. Each generation of chipsets has improved reception quality and robustness.
Several technical studies, including a report published by the FCC’s Office of Engineering and Technology (OET) in connection with the FCC’s Incentive Auction Order,1 have found that ATSC DTV consistently demonstrates D/U ratios in the -35 to -45 dB range for adjacent band LTE-to-DTV interference—a12 to 22 dB improvement over the -23 dB D/U level established in Section 27.60 of the FCC rules. These improvements arise from improvements in DTV receiver frequency selectivity, error correction, and signal processing.
As a result of these advances in DTV and wireless technology, LTE UE can be operated on a non-interfering basis at much closer distances than were possible in the past with land mobile adjacent to analog TV.
2.2. Field Tests in the Chicago Area Corroborate the Improvements in DTV Receiver Performance
The field testing entailed LTE UEs operating in the Lower 700 MHz A Block spectrum on an LTE network within the WPWR-TV viewing area. This testing allowed observation of the interaction between LTE UE transmissions and Channel 51 DTV reception in a real-world setting, which could then be analyzed and compared to results that had previously been recreated in a lab setting.
In conjunction with this Report, field tests were conducted in locations around the Chicago area. Those tests corroborated the -35 dB to -45 dB D/U ratios for ATSC DTV that were developed in the laboratory-based studies.
The field tests confirmed the expectation that the potential for LTE-to-DTV interference only exists where the WPWR-TV transmitter signal is weak. Even in these areas, the risk of actual interference is de minimis, because several other conditions must exist for interference to occur.
2.3. LTE UE Operations Are Highly Unlikely to Cause InterferenceLike DTV receiver technology, wireless communications technology—in the form of today’s LTE networks using the 3GPP standards—has advanced significantly from the land mobile technology that was studied in 1986 and led to the existing DTV protection criteria.
1 Expanding the Economic and Innovation Opportunities of Spectrum Through Incentive Auctions, Second Report and Order and Further Notice of Proposed Rulemaking, 29 FCC Rcd 13071, Appendix A (2014).
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LTE UE are now limited to 0.2 W ERP,2 under the Third Generation Partnership Program (3GPP) standard, which is a much lower power than land mobile transmitters (4-8 W) or even 2nd generation cellular handsets (1-2 W).
LTE transmissions are very spectrally and energy efficient, due to a combination of LTE automatic transmit power control, transmission scheduling, and dynamic bandwidth allocation.
LTE uses a 10-millisecond frame and the network allocates both time and bandwidth in each frame to individual LTE UEs, meaning that even if an LTE UE were very close to a DTV receiver and interference were to occur, any suchinterference would likely be momentary and imperceptible.
There is a large disparity between uplink and downlink traffic in wireless broadband networks. The consequence is that smartphones transmit much less than they receive, reducing the potential for interference from uplinktransmissions.
2.4. Numerous Factors in This Case Lead to the Conclusion That Interference Will Be De Minimis in Chicago
For LTE UE to interfere with a DTV receiver, at least 11 events must occur simultaneously. The absence of any one of these factors will prevent interference:
1. The TV must be turned on with someone watching it;
2. The LTE device must be in close proximity (in approximately 96 percent of the cases,within 2 meters) to the DTV receiving antenna;
3. The LTE UE must be on and transmitting—i.e., for there to be interference, both the DTV receiver and LTE UE must be turned on and in use at the same time;
4. The viewer must be watching WPWR-TV, Channel 51, which has a peak market share of 1.3 percent and an average market share of 0.7 percent;
5. The viewer must be receiving the WPWR-TV signal over-the-air using an indoor antenna, and not via cable, DBS, streamed over the Internet, or received over-the-air using a rooftop antenna;
6. The DTV receiver must be located in an area with a weak Channel 51 signal.
7. The LTE UE must be operating on a Lower 700 MHz A Block channel (Note that because of Wi-Fi offload and the multiband capability of most LTE UEs, this conditionwill not be met in most cases because users watching over-the-air DTV at home will likely operate their wireless handset on a home Wi-Fi network or the LTE network may assign the UE to a channel outside the A Block);
8. The LTE UE must have a radiated power sufficient to cause interference (Most LTE UEs are certified at maximum A Block power levels somewhat lower than the maximum power specified by the 3GPP standard);3
2 3GPP TS 36.101, clause 6.2.2.
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9. The LTE network power control must have the LTE UE transmitting with full power or sufficiently high power to cause interference;
10. The LTE device must be positioned with an orientation that results in the LTE device’s transmitting pattern coinciding with the indoor antenna’s receiving pattern; and
11. The LTE UE must be transmitting for a long enough duration or with a transmission pattern that is capable of causing interference.
2.5. King Street Wireless’s Adjacent A Block Operations Confirm That Interference Will Be De Minimis
Field testing using King Street Wireless’s network currently operating in the 700 MHz A Block on the fringes of the WPWR-TV viewing area (where the WPWR-TV DTV signal is at its weakest and DTV reception is most susceptible to interference) confirms that LTE UE-to-DTV interference is not a significant risk.
King Street Wireless has advertised a toll-free number for WPWR-TV viewers to report any interference. Laser understands that few, if any, calls have been received.
2.6. In the Unlikely Event of Interference, Simple and Effective Mitigation Options Are Available
In the highly unlikely instance that LTE UE causes interference to DTV reception, several simple and effective mitigation options exist, including using a higher quality indoor antenna, using an outdoor antenna, installing an LTE femtocell, using a home Wi-Fi network that will take LTE UE uplink transmissions off of the 700 MHz A Block, installing filters or amplifiers, as well as network management techniques that can be undertaken by the LTE network operator, and if ultimately necessary, obtaining a cable subscription.
Laser would commit as a condition to the grant of the requested waiver to cover the cost of any such mitigation measures.
3. Structure of the ReportThis report has four major sections:
A technical analysis of adjacent band LTE UE-to-DTV interference (Section 5)
A frequency of interference analysis (Section 6)
A severity of interference analysis (Section 7)
A review of mitigation options (Section 8)
3 The 3GPP standard specify that a band class 12 UE be capable of applying 23 dBm to its antenna. However, for purposes of this report and for an FCC equipment grant, it is the resulting radiated power that is of interest. The radiated power of most devices typically is significantly less due to losses associated with the antenna.
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The technical analysis is a study of the tolerance for adjacent band transmissions based on both laboratory analysis and field testing. The evaluation compares the -23 dB D/U ratio used by47 CFR 27.60 to the tolerance of DTV receivers today to spectrally dynamic, discontinuous, low-powered LTE UE. Multiple prior third-party studies have examined the tolerance of DTV receivers and have found the D/U ratios at which interference occurred to be significantly lower than the -23 dB D/U limit. These studies are summarized in Table 1.
Table 1 - Desired-to-Undesired signal ratios measured in several research studies
Reported Desired-to-Undesired (D/U) Signal RatiosAnalysis Actual Laboratory Testing
Study Done By MSWfor FOX Intertek MSW
for CEA FCC OET
D/U Ratio BeforeInterference Observed -23 dB -35 to -40 dB -46 dB -38 to -45 dB
Study Publication Date May 2013 January 2013 May 2014 6/17/14
The -23 dB D/U ratio was established in the mid-1980s, but that interference criterion is now unreasonably stringent given advances in technology that have improved tolerance of adjacent band signals. Both DTV, represented by ATSC 8VSB, and cellular telephony, represented by LTE, are very different from the technology in use in the mid-1980s when the -23 db D/U criteria was developed. The same logic and level of interference protection that resulted in a -23dB D/U ratio in the 1980s now finds that an LTE uplink is able to operate in the adjacent band to a DTV signal with a 1 MHz guard band4 and still provide sufficient interference protection with a D/U ratio that is at least an order of magnitude more negative. This conclusion is backed up by field tests that demonstrate that DTV receivers will only be susceptible to interference in very few locations at the edges of the WPWR-TV service contour, where LTE UE are located within a few meters of a DTV receiver, and where the LTE UE is relatively far away from a base station, and therefore transmitting at a higher power.
Following the technical evaluation in Section 5, Section 6 examines the frequency of interferencebased on actual LTE UE operation on the A Block adjacent to WPWR-TV’s Channel 51 station.How many people in the WPWR-TV viewing area are likely to be affected? How many locations will need mitigations applied to remedy interference if it does happen? Laser's analysisand field and laboratory work find that there are 11 conditions that must be met for LTE to cause interference to DTV reception. The probability that all 11 factors exist is low, and therefore, few WPWR-TV viewers may be impacted by interference.
Section 7 studies the severity of the interference in the situations where interference could occur.Because LTE transmissions are spectrally and energy efficient, any interference will usually be short in duration and have little impact on DTV reception quality. A combination of LTE automatic transmit power control, transmission scheduling, and dynamic bandwidth allocation results in LTE transmissions that are highly variable, and in most cases, have relatively narrow
4 LTE defines a set of operating bandwidths. The largest bandwidth that would fit into the 6 MHz A block is a 5 MHz LTE bandwidth, leaving a 1 MHz guard band. Because LTE dynamically allocates bandwidth, for most transmissions the active bandwidth would be less than 5 MHz, leaving an even larger guard band.
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bandwidth that are further from Channel 51. Moreover, redundancy in the ATSC signal protocol and error correction can overcome a significant amount of signal degradation when LTE UEs are transmitting in close proximity to DTV receivers.
Section 8 examines mitigation options available to deal with interference. There are multiple simple and effective remedies for locations where interference proves to be a problem, if such locations are found. These include using a higher quality indoor antenna, using an outdoor antenna, installing filters or signal amplifiers, installing an LTE femtocell, or using a home Wi-Fi network that will take LTE UE uplink transmissions off the 700 MHz A Block. Ultimately, if necessary, a cable subscription could be obtained. The network operator can also employ network management techniques to mitigate any interference.
4. Findings of the Report The following were the key findings of the field testing:
1. The D/U ratios found during laboratory testing were confirmed in the field.
2. The "cliff effect"—a sharp transition from no visible impact to total loss of service—was not observed in the field. The combined impact of traffic scheduling and transmit power control in the LTE system results in a 5-8 dB range from the first observable impairment—typically the loss of an occasional pixel—to significant corruption of the picture. Traffic scheduling appears to insert a sufficient break in the LTE uplink that total loss of service never occurs under many conditions.
3. Signal quality of the ATSC signal has a significant influence on the tolerance for adjacent band interference.
Based on these findings, the study concludes that LTE operations on the Lower 700 MHz A Block in Chicago would not cause more than a de minimis level of interference to viewers of WPWR-TV signal, even if the separation distances provided in Section 27.60 of the FCC’s rules are not met.
The field measurements confirmed that, as the ATSC signal improved in amplitude and signal quality, the strength of the LTE UE transmission required to cause interference also increased, as illustrated in Figure 1. This is certainly an expected outcome, and it is important. The D/U ratios do tend to decrease as the DTV signal gets higher and strong signal effects become a factor, as illustrated in Figure 2. However, in scenarios where there is a strong DTV signal, itbecomes increasingly unlikely, and then impossible, for an LTE UE to transmit a signal strongenough to cause interference, even when virtually touching the DTV antenna. The LTE UE are unlikely or totally incapable of interfering in the higher signal regions of Figure 1 and Figure 2.
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Figure 1 - LTE Signal Strength at the Threshold of Visibility5
The field testing confirmed the general “bathtub” shape of the DTV response to an adjacent band LTE transmission, as depicted in Figure 2.6 The significance is that as a practical matter the potential for interference is a fringe area issue. In the central area, where most of the population exists, the DTV signal is strong enough that the potential for LTE UE interference becomes negligible.
In the fringe area, cell coverage is first and most densely located where people make calls, in the larger towns and along major roads, as illustrated in Figure 25. The impact is that, most of the time, LTE UE in these areas will be near a cell tower and as a result operating at lower transmit powers.
What is left is the fringe area that is far from a cell tower. A significant portion of that area also loses the potential for interference, because if the nearest cell tower is far enough away that service is not available, then there will not be an LTE UE transmission and there will be no interference from the LTE UE that isn't getting service.
What remains are those rural areas that are close enough to an LTE cell tower to get service but far enough so that the LTE UE must operate at a higher power and where the WPWR-TV signal is strong enough and of sufficient signal quality to be received but weak enough to be more
5 Intertek, Evaluation Of The RF Coexistence LTE Operation on 700 MHz A Block (Formerly Channels 52 / 57) and TX Channel 51 Reception, January 14, 2013, Report G1002WX445LEX-02, Figure 4. 6 The “bathtub” or “U” shape response seen in the graph show that the tolerance for adjacent band signals degrades at both the low and high end. At the low end of the dynamic range, the DTV signal becomes progressively weaker and thus is more susceptible to other influences, such as an adjacent band LTE UE transmission. The degradation in D/U ratios on the high end of the dynamic range, where the DTV signal is stronger is not a real-world problem. In that region, the DTV signal is so strong that an LTE UE cannot emit enough energy to reach the level required to cause interference. The results shown in the graph were produced in a laboratory setting where LTE signal levels could be injected beyond those an LTE UE could produce.
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sensitive to LTE UE transmissions. The conclusion of this research is that the combination will be relatively rare and is justifiably classified as de minimis.
Figure 2 - Desired-to-Undesired (D/U) Ratio as a function of DTV Signal Level7
The third question to be addressed is whether the D/U ratios measured in the field were consistent with those reported from laboratory measurements.
A key performance metric used by the Commission, also used in this report, and by others is threshold-of-visibility (ToV). ToV is the highest level at which an adjacent band signal does not cause an impairment to the picture or sound. In laboratory testing, using a continuously transmitting signal of constant amplitude on an adjacent band signal above ToV results in severe impairment or total loss of service. In field testing, with discontinuous transmissions of varying amplitude, ToV marks the threshold of a region of increasing impairment.
Table 2 presents the signal strengths and D/U ratios measured in the Intertek study. Table 3compares the conducted and OTA measurements, also using data from the Intertek study. Several observations can be made. The -33 dB D/U used by the FCC in developing Table 8 of FCC DA14-98 appears conservative but consistent with the measurements made in the Intertek study.8 The “U” shape of a plot of D/U ratios is also noteworthy with the ratios degrading at the weak signal and strong signal extremes. It should be noted that at the strong signal extreme, itwill be necessary for the LTE UEs to be extremely close to producing the field strength necessary to reach ToV, or often will be totally incapable of producing these field strengths. Hence, the fact that the D/U ratios degrade under strong signal conditions is not reflective of a realistic interference risk. More detail is provided in Table 15 through Table 18, which are from the findings of the Intertek study.
7 Ibid., Figure 5.8 FCC DA14-98, Office Of Engineering And Technology Seeks To Supplement The Incentive Auction Proceeding Record Regarding Potential Interference Between Broadcast Television And Wireless Services, ET Docket No. 14-14, GN Docket No. 12-268, released January 29, 2014, pg. 21, footnote 21.
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The values measured in the field study were consistent with these results. D/U ratios in the range of -35 dB to -45 dB were consistently observed.
Table 2 - LTE Signal Strength and D/U Ratio at ToV Measured in Intertek Study
Table 3 - Comparison of Conducted and OTA Measurements from the Intertek Study
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5. Technical Evaluation of Adjacent Band Interference On August 12, 1985 the FCC adopted a Memorandum, Opinion and Order (MO&O) directing that an advisory committee be established to assist the commission in determining land mobile/UHF television sharing criteria.9 The Land Mobile Radio/UHF Television Technical Advisory Committee filed its final report on May 7, 1986 in which the basis for the -23 dB D/U adjacent band protection criterion is set forth.
The -23 dB D/U criteria was applied in 90.545(a)(2) in 1998 for broadcast DTV signals against transmission from adjacent channels in then newly-reallocated public safety spectrum.10 This section has since been removed.
That FCC ruling included the following significant discussion, reviewing the adoption of FCC WT Docket No. 96-86 Adopted September 29, 1998:11
5. TV/DTV Protection from Control and Mobile Stations
160. The Second Notice asked for comments on whether the Commission should establish different separation distances for mobile and fixed stations operating in these bands.12 The only comment we received addressing this request was from Motorola in their letter of May 20, 1998.13 In the preceding paragraphs, we discussed the TV protection requirements needed for base stations operating in a particular TV channel. In the 470-512 MHz band, this was all that was necessary because mobiles operated in the same TV channel as their companion base station.14 Consequently, if you could use the TV channel for high power base station operations, you could also use it for lower-powered mobile operation. For public safety use of the 700 MHz band, however, control station and mobile operation will usually be on a different TV channel from its companion base station (e.g. … base operation on TV channel 63 and mobile operation on TV channel 68 - paired operation). If a particular TV channel is available for base station operations in a geographic area, it does not automatically mean that the paired TV channel is available for mobile operations.15
9 FCC Gen Docket 85-172 NPRM was issued on May 31, 1985.
Amendment of the Rules Concerning Further Sharing of the UHF Television Band by Private Land Mobile Radio Services, GEN Docket No. 85-172, Memorandum Opinion and Order, 50 Fed. Reg. 32,488 (August 12, 1985) (UHF-TV Sharing MO&O).
Gen Docket 85-172 was terminated in late 2001 (FCC 01-385, Termination of Stale or Moot Docketed Proceedings, adopted 12/21/2001) 10 FCC WT Docket 96-86, 1st R&O & 3rd NPRM (FCC 98-191), adopted August 6, 1998. 11 FCC WT Docket No. 96-86 Adopted September 29, 1998, FCC 98-191. 12 See Second Notice, 12 FCC Rcd at 17,804. (Citation in original). 13 See Letter from Motorola to Magalie Roman Salas. Secretary, Federal Communications Commission, dated May 20, 1998, at 2-3 (Motorola ex-parte). (Citation in original). 14 See UHF-TV Sharing NPRM. 101 FCC 2d at 873-874. See also. 47 C.F.R. § 90.311. (Citation in original). 15 Motorola states that there are only 18 cities in the top 50 U.S. markets for which a channel pair (63/68
or 64/69) can be found if TV transmitters must be more than 260 km from the city-center. See Motorola exparte at 4. (Citation in original).
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This discussion is significant because it highlights that at the time the -23 dB D/U ratio was established and first incorporated into the FCC rules, it was common that base station equipment and mobiles operated in the same frequency band. The Motorola comment, footnoted above, is telling:
Motorola states that there are only 18 cities in the top 50 U.S. markets for which a channel pair (63/68 or 64/69) can be found if TV transmitters must be more than 260 km from the city-center.
Understandably, the rule was written to address the primary interference risk, which was from the fixed, high power base station transmitters.
The -23 dB D/U ratio limit was brought to Section 27.60 in 2000, but at the time it only covered747-762 & 777-792 MHz.16 In the order, while presenting the Final Rules for Section 27.60(b)(2)(i), the Commission stated:
Since mobiles and portables are able to move and communicate with each other, licensees must determine the areas where the mobiles can and cannot roam in order to protect the TV/DTV stations.
In 2001, the rules associated with reallocation of 698-746 & 776-794 MHz applied the -23 dB D/U ratio to the 700 MHz A Block.17 Thus, while the -23 dB D/U protection criterion has a long history, the appropriateness of this limit for use in a mobile only scenario has not been deeply explored.
Several recent research efforts have studied the potential for adjacent band LTE UE to interfere with DTV reception. (These research efforts are summarized in Annex 15.) The consensus of these studies is that current ATSC DTV receivers are able to withstand, without interference,adjacent band LTE UE transmissions that result in D/U ratios in the range of –35 dB to –45 dB.This represents a 12 dB to 22 dB improvement over the -23 dB that 47CFR27.60 uses (see Table 4).18 Field measurements, presented in this report, confirm the findings of those laboratory measurements.19
16 FCC WT Docket 99-168 1st R&O, adopted January 6, 2000. 17 FCC GN Docket No. 01-74, Reallocation and Service Rules for the 698-746 MHz Spectrum Band (Television Channels 52-59), Report and Order Adopted December 12, 2001. 18 Recall that the decibel (dB) is a logarithmic measure of a ratio. In this case, at issue is the ratio of the desired to undesired signals at the DTV receiver. The D/U ratio has a negative value if the power level of the Desired signal is less than the power level of the Undesired signal. Thus, a lower D/U ratio is preferred because it means that the DTV receiver is able to successfully decode the desired television signal in the presence of increasing amounts of undesired signal (or noise). A D/U ratio that is -12 dB to -22 dB lower means the receiver can successfully decode a signal that is 4 to 11 times lower in power, respectively. 19 This report summarizes past laboratory measurement efforts and contributes new field measurements in order to improve the understanding of the potential for adjacent band LTE UE for interference with DTV receivers tuned to that station. The specific problem of interest in this report is the potential for LTE UE operating in the 700 MHz A block (698-704 MHz) to cause interference to DTV receivers tuned to channel 51, (692-698 MHz), WPWR in Chicago. To add to the understanding of this question, field measurements were made in early 2015. The purpose of these tests was to supplement laboratory testing and analysis with in-situ field testing, in order to increase the confidence that the potential for interference from LTE UE to DTV receiver is thoroughly understood.
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Table 4 - Desired-to-Undesired signal ratios measured in several research studies20
Reported Desired-to-Undesired (D/U) Signal RatiosAnalysis Actual Laboratory Testing
Study Done By MSWfor FOX Intertek MSW
for CEA FCC OET
D/U Ratio BeforeInterference Observed -23 dB -35 to -40 dB -46 dB -38 to -45 dB
Study Publication Date May 2013 January 2013 May 2014 6/17/14
In addition to the improvement in tolerance of adjacent band transmissions by DTV receivers, LTE UE are designed for much more densely deployed networks than was true of land mobile. Instead of 4 W to 8 W handheld land mobile transmitters, or even the 1 W or 2 W of secondgeneration cellular, LTE UE are limited in the 3GPP standard to 0.2 W ERP (23 dBm ± 2 dB).Even apart from these findings, Laser has found significant overestimation in the laboratory measurements of the impact of LTE to DTV interference. Field measurements showed that in an operating LTE network, a combination of traffic control, transmission pattern, duration of different user activities, and automatic transmit power control, significantly reduce the impact of LTE to DTV interference. The laboratory tests used a continuously transmitting LTE signal and reported a sharp "cliff effect," in which picture quality changed from no visible impairment to total loss of service in a very narrow range, typically within 0.5 to 1.0 dB. However, when operating on a live LTE network, an LTE UE is assigned transmission time and bandwidth by the cellular base, which divides its resources among all LTE UE requesting service. The result is that the LTE UE signal is both dynamic and discontinuous. This of course marks another key distinction between LTE downlink and uplink transmissions (besides the much lower power of uplink transmissions). While downlink transmissions will often be continuous and over the entire 5 MHz channel, particularly during peak traffic periods, uplink transmissions will be sporadic even when the UE is transmitting, which, as discussed below, is relatively rare given the imbalance between uplink and downlink traffic.
20 In October 2014, the Commission issued a Notice of Proposed Rulemaking addressing LTE-to-DTV and DTV-to-LTE inter-service interference issues in the context of the planned incentive auction. See FCC 14-157, Second R&O and FNPRM, ET Docket 14-14, GN Docket 12-268. The FCC proposed rules that are specific to the 600 MHz licenses to be auctioned as part of the incentive auction, and that address a variety of scenarios that are not relevant to Laser’s waiver request and that raise far more complicated interference concerns (such as co-channel and adjacent band LTE base stations transmissions). However, the Commission did address the potential for interference to DTV receivers from adjacent band LTE UE operations, and used a -33 dB D/U ratio for defining adjacent channel LTE UE-to-DTV interference — in other words, 10 dB less restrictive that the -23 dB D/U ratio established in 47 CFR 27.60. Even so, the FCC proposed a rule that would preclude all LTE UE operations within the 600 MHz band within and up to 0.5 km beyond an adjacent TV station’s protected contour. This proposed rule has been criticized as being overly restrictive, including by T-Mobile in an ex parte filing to the FCC in April 2015. The analysis and field testing presented and discussed in this report, which concludes that LTE UE-to-DTV interference is not an issue except for a very small minority of the population at distances closer than a few meters to the DTV receiver, support the claim that the proposed rules in FCC 14-157 are too restrictive. Regardless, the issues raised in Laser’s waiver request and the conclusions in this Report are discreet and apply to proposed LTE UE operations on Laser’s A Block license in the Chicago market, and should not implicate the larger and more complicated set of interference concerns raised in the FCC’s incentive auction proceeding.
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In addition, different user actions have different payloads, particularly for the uplink. The uplink transmission pattern of sending a text message is different from that of a long duration, high definition video call. Other user actions, such as web browsing, reading and sending email, and voice calls, all have different data payloads and different transmission patterns and durations. For many of the most common user actions, such as sending a text message or browsing the Internet (i.e., requesting websites), the data transmitted is small, resulting in short transmission sessions.
There is also a well-known disparity between downlink and uplink traffic with uplink delivering far less data than the downlink. The result is that uplink transmissions from the LTE UE vary widely, based on the payload to be delivered. Generally the uplink transmissions are both less frequent and shorter in duration than downlink transmissions. Sandvine reports21 that in 2014 the mean uplink traffic was only 7% of total traffic and the median uplink traffic was 15%. In mobile networks, uplink traffic is estimated at approximately 10 percent of the total traffic, with the uplink-to-downlink traffic ratio likely to drop as streaming video becomes more popular on mobile networks.22 The impact on the issue being studied here is that the downlink, where there is no risk of interference to DTV, is where the heavy usage will be. The uplink will be used much more lightly, significantly decreasing the probability of interference in real world settings.
Finally, transmission power control results in transmission bursts that vary widely over a transmission sequence. Variation in transmission amplitude of 10 dB or more were commonly observed.
The combined effect of traffic control, variation of data load, and power control results in the real world impact of adjacent band LTE UE operations causing significantly less perceptible interference to DTV receivers than the laboratory estimates would suggest. Tests examining the real world impact on DTV signal reception are discussed in further detail in Section 7.
This Section analyzes those issues in greater detail, using field test results to verify prior laboratory analysis examining adjacent band LTE UE-to-DTV interference.
5.1. Interference ModelThe classic interference model has three elements: a source, a coupling path, and a receptor.When interference is between two radiating services, as is the case here, there are two sources, the DTV transmitter and the LTE UE, each with its own coupling path to the DTV receiver.Hence, there are five elements to LTE UE to DTV receiver interference model: an intended and unintended source, a coupling path to the DTV antenna for each source, and a receptor, the DTV receiver (see Figure 3).
21 Sandvine, Global Internet Phenomena Report, 1H 2014, pg 5, table 1. 22 See What is Going on in Mobile Broadband Networks: Smartphone Traffic Analysis and Solutions, Nokia Networks White Paper, at 4-6, available at networks.nokia.com/system/.../nokia_smartphone_traffic_white_paper.pdf; Kostas Liopiros, Asymmetry and the Impending (US) Spectrum Crisis, Financial Times, May 28, 2013. In 2012, CEPT, the coordinating body of European state telecom regulators, studied the issue of downlink vs. uplink data asymmetry and concluded that due to the growth of download-centric applications such as mobile video and mobile web browsing, download-centric apps would generate more than 90 percent of mobile data traffic by 2016. See CEPT Doc. SE19(12)37, Aug. 28, 2012, available at www.cept.org/documents/se-19/6560/se19.
14
Figure 3 - Elements of LTE UE to DTV receiver interference
5.1.1. Signal Characteristics
LTE and ATSC are both internationally standardized systems, with equipment that requiresinteroperability with other equipment in all installations worldwide. DTV receivers must be capable of receiving a transmission from any DTV station and successfully operating in the wide variety of conditions found throughout the country. LTE is also a widely deployed international system. LTE UE must be able to operate successfully with base station equipment from a wide variety of manufacturers, on networks operated by different companies, using different network management configurations. To achieve this challenging requirement, both LTE and ATSC are rigidly standardized. A consequence of this system interoperability requirement is that both LTE and ATSC equipment exhibit highly reliable and predictable operating characteristics. Within the context of this report, this means that the interference model can rely upon consistent operation of the LTE and ATSC equipment, reducing the likelihood of unpredictable outcomes due to variations in equipment made by different vendors.
This standardization has the effect of keeping the equipment much closer in its operating characteristics than is often found in equipment not governed by a strong set of standards.
15
Figure 4 - The WPWR-TV transmitter and other transmitters on the top of the Willis Tower in Chicago
A specific concern for both DTV and LTE is the ability to successfully operate in crowded spectrum. The TV spectrum in Chicago is very crowded. The WPWR-TV antenna is located on top of the Willis Tower, which is crowded with broadcast antennas (see Figure 4). Crowded TV spectrum is far from unique to Chicago; it is a common condition in other major markets. The result is that DTV receivers are designed to have the ability to successfully receive a channel in the presence of other stations on adjacent channels.
The Illinois Institute of Technology (IIT) has run a spectrum observatory in Chicago for over 7 years. The spectrum observatory is operated by the IIT Wireless Network and Communications Research Center (WiNCom), an initiative of IIT's Computer Science and Electrical and Computer Engineering Departments. A set of permanent spectrum monitors are publiclyavailable over the web to anyone who wants to look at the Chicago spectrum.23
23 The IIT spectrum observatory can be accessed online at:
http://www.cs.iit.edu/~wincomweb/live-monitor.html
16
What stands out is that WPWR-TV operates and has been operating for some time in a crowded spectral environment, as seen in Figure 5 and Figure 6. Every available DTV channel has a station on it.
In major markets, such heavy utilization of broadcast TV spectrum is not at all unusual. Figure 5shows that it is not uncommon for a TV transmission to have a very strong adjacent channel TV signal. For the ATSC standards developers and DTV receiver manufacturers, this creates astrong motivation to improve immunity to adjacent channel transmission.
The measurement results of Intertek, Ofcom and the FCC OET support the conclusion that this industry has successfully met that challenge and has improved immunity to adjacent channel and adjacent band transmissions. Sensitivity to adjacent channel transmissions has been observed to be improved by 10 dB to 20 dB or even more, as compared to the performance measured a few decades ago.
Figure 5 - The WPWR-TV, 692-698 MHz, spectrum viewed from the IIT WiNCom monitor at the IIT building south of downtown Chicago
17
Figure 6 - The WPWR-TV, 692-698 MHz, spectrum viewed from the IIT WiNCom monitor at Harbor Pont, IL, north of downtown Chicago
Comparable dynamics put pressure on cellular technology to improve the ability of user devices to operate without interference in crowded spectrum environments. As with the DTV industry, the cellular industry, represented by the LTE standards and performance of LTE UE, has successfully met the challenge and improved system immunity to adjacent channel transmission.
A study of both the ATSC and LTE standards finds each incorporates powerful mechanisms for ensuring the ability to operate under harsh, crowded signal conditions. Multiple levels of error correction and other mechanisms allow these systems to deliver impressive levels of performance even in crowded spectrum environments.
5.1.2. Energy Injection
There are two mechanisms by which energy from an LTE UE in an adjacent band can enter the signal processing of a DTV receiver, illustrated in Figure 7. Out-of-band energy from the LTE signal that falls within the pass band of the DTV receiver will combine with the intended ATSC signal and become part of the ATSC signal processing. Alternately the filter response and other RF front end circuitry of the DTV receiver will accept energy outside the channel, introducing it into the signal processing path.
Section 6.2.3 of the ATSC A/82 Data Return Link (DRL) standard24 gives the relationship between the Adjacent Channel Rejection Ratio (ACRR), the adjacent channel leakage ratio (ACLR), and the net adjacent channel interference ratio (ACIR), as follows:
ACIR = 1/[(1/ACLR) + (1/ACRR)]
24 ATSC A/82, Automatic Transmitter Power Control (ATPC) Data Return Link (DRL) Standard, 11 February 2008
Available at: http://atsc.org/wp-content/uploads/2015/03/Automatic-Transmitter-Power-Control-Data-Return-Link.pdf
18
ACRR is a measure of a receiver’s selectivity, or ability to reject a non-co-channel signal.
ACLR is also known as out-of-band-emissions (OOBE or OBE).
ACIR is the net impact of adjacent-channel interference; that is, the receiver selectivity plus OBE.
Energy in this area can be filtered out at
the DTV receiver.
Energy in this area cannot be filtered out at the DTV reciever.
DTV Signal Power (dBm in a 6 MHz BW)
10.6 dB – Total Power to Signal Level
LTE UE Signal(5 MHz BW)
6.0 MHzDTV Channel BW
6.0 MHzAdjacent Channel BW
LTE OBE
Per 47CFR27.53(g)43 + 10 log (P) dB
-13 dBm for a 23 dBm LTE UE
Figure 7 - Energy introduction mechanisms for adjacent band transmissions
The FCC rules restrict OBE. For an LTE UE, the limit in 47 CFR 27.52(g) requires that OBE beless than 43 + 10log(P) dB below the LTE UE signal, which for an LTE UE operating at the maximum power specified in the 3GPP standard, or 23 dBm, results in an OBE of 36 dB below the intended UE signal.
The effect of the FCC OBE limit is that LTE UE, per FCC rules, must allow the potential for a D/U ratio of > 36 dB. The D/U ratio from this mechanism will always be >36 dB because the LTE transmission will be positioned as far as possible from the channel boundary, leaving a minimum of a 1 MHz guard band. The ATSC signal, to meet its own OBE requirements, is several hundred kHz from the band edge, leaving an additional guard band. Further, the LTE UE
19
OBE is not flat but continues to fall off with frequency. Thus, the cumulative energy entering the DTV receiver's acceptance band will be less than that calculated from a flat extrapolation of the 36 dB OBE limit.
Another significant factor is that, while the FCC requirement is given in 47 CFR 27.52(g), the majority of LTE UE exceed this limit by large margins. A survey of test reports submitted to the FCC in support of equipment grants for LTE band class 12 devices shows the average device exceeds the FCC requirement by 19 dB (see Table 5). The generally rapid decrease in OBE withfrequency separation from the intended UE signal will further reduce the impact of OBE on DTV reception.
Table 5 - Worst Case OOBE Levels for Recent LTE UE Devices
FCC Requirement: 43 +10log(P) dB-13 dBm for a 23 dBm LTE UE device.
Manufacturer FCC ID BW(MHz)
Modulation OOBEat 698 MHz
(dBm)
Delta to -13 dBm Limit
(dB)
Sony PY7PM-0803 5.0 QPSK -21.0 -8.0Samsung A3LSCHR960 5.0 QPSK -32.6 -19.6LG ZNFUS990 3.0 QPSK -42.3 -29.3Sonim WYPL11V012AA 3.0 QPSK -19.4 -6.4Samsung A3LSMG386T 3.0 QPSK -34.1 -21.1Samsung A3LSMG900R4 5.0 QPSK -46.7 -33.7Samsung A3LSMG900R7 5.0 QPSK -46.7 -33.7Samsung A3LSMN910A 5.0 QPSK -29.8 -16.8VeryKool WA6SL5000 1.4 QPSK -22.5 -9.5ZTE SRQ-MF275U 1.4 16QAM -24.1 -11.1
Average Margin to Limit -18.9
Moreover, the generally rapid decrease in OBE with frequency separation from the intended UE signal will further reduce the impact of OBE on DTV reception. While the FCC OBE measurements consider the OBE at the Channel 51/52 edge, they do not accurately reflect the true impact of LTE OBE because the LTE signal will typically continue to fall with decreasing frequency. For example, two of the phones used in the field testing discussed in this Report, the Motorola Nexus 6 and the Samsung Galaxy Note 4, reported OBE in their FCC equipment grants in the range of -16 to -17 dB to the limit. However, this is the worst case OBE at the band edge. As is clearly seen in Figure 8 the OBE continue to fall from the band edge measurement point and is significantly less through Channel 51. The result is that the ATSC receiver will have lower total OBE than the FCC limit and measurements to it would lead one to expect. In the example shown in Figure 8 the worst case OBE is just beyond Channel 51 and has -16.3 dB margin to the FCC limit. The OBE continues to drop and falls approximately 20 dB by mid-channel at 695 MHz, giving a -36.3 dB margin to the FCC OBE limit.
20
Figure 8 - OBE for a Motorola Nexus 6
The end result of the improvements in DTV and LTE UE technology, standardization, and strict OOBE requirements have led to far greater rejection of adjacent band signals by DTV receivers than is assumed in the -23 dB D/U ratio set forth in 47 CFR 27.60. For example, Table 15through Table 18 in Annex 10 provide the results from a prior laboratory study by Intertek of the D/U ratios at the threshold of visibility (ToV)25 for a variety of DTV receivers used by consumers today. The Intertek study concludes that D/U ratios of between -35 and -40 dB are typical of DTV receivers used by consumers today.
Practically, as shown in Table 15 through Table 18 in Annex 10, this means that laboratory testing shows that under worst case scenarios of a weak DTV signal typical of the edge of the TV
25 The ToV or threshold-of-visibility is a key performance metric used by the Commission in its measurements, as well as by others. ToV is the highest level at which an adjacent band signal DOES NOT cause an impairment to the picture or sound. In laboratory testing, using a continuously transmitting signal of constant amplitude, an adjacent band signal above ToV results in severe impairment or total loss of service. As explained in Section 7, in field testing, with discontinuous transmissions of varying amplitude, ToV marks the threshold of a region of increasing impairment.
To avoid confusion in the Intertek study, the terms threshold-of-sensitivity (ToS) and threshold-of-visibility (ToV) were differentiated. That study stated the difference as:
To avoid confusion, in this document TOS (Threshold of Sensitivity) is used for the TOV (Threshold of Visibility) level found with only the DTV signal present. TOV is used for the same performance threshold, found using a combination of DTV and LTE signals. This difference in terminology is done to keep the two test conditions clear.
This use of the terms ToS and ToV is continued in this report.
21
station contour and beyond, and with a maximum power and a continuous LTE signal, a consumer may experience some pixel loss as a result of adjacent band LTE UE transmissions at distances closer than approximately 10 meters. In more central locations within the station’s contour, where a stronger DTV signal will be present, a consumer will not begin seeing pixel loss except at distances closer than 1-2 meters—and even less in the area close to the TV station antenna where most of the viewing population will be located.
A key objective of this Report was to study these conclusions regarding the susceptibility of DTV receivers to adjacent band LTE signals using field tests to examine whether the laboratory analysis accurately reflects the real world impact on WPWR-TV viewers in the Chicago market.
5.2. Assessment of Central Viewing AreaDuring the week of April 13, 2015, testing was performed at 20 locations in the Chicago area as shown in Figure 9.
Figure 9 - April 2015 test locations
A recorded LTE UE transmission was replayed through a Universal Software Radio Peripheral(USRP) and combined with the received broadcast Channel 51 signal. The recording had the LTE UE transmitting a continuous 3 MBs uplink transmission (2.5 times the speed of an HD movie transmission).26 The USRP has 30 dB of software adjustable gain, which can be adjusted
26 The LTE UE transmission was created by using iPerf on the device. iPerf is a widely used network testing tool. For more information see: http://www.magicandroidapps.com/wiki/doku.php
22
in 0.5 dB increments. In addition, an 11 dB variable attenuator, with a 1 dB step size, was placed on the output of the USRP. The LTE signal was initially played with a 10 dB gain in the USRP and the full 11 dB of attenuation applied. The USRP gain was increased until ToV was reached. If ToV was not reached at the full 30 dB of gain in the USRP, the external attenuation was increased until ToV was reached.
In some cases where the Channel 51 signal was very strong, an attenuator was placed on the output of the antenna to reduce the signal to more moderate levels. This gave additional insight into how additional architectural loss might impact the ToV threshold. Typically, a 20 dB attenuator was used in such situations, which is roughly the outdoor-to-indoor attenuation for a typical house.
Figure 10 - Test setup used for LTE injection
Table 6 shows the signal strength and D/U ratios measured in the laboratory for a typical DTV receiver. Table 7 presents the results of the field testing, showing the D/U ratios at the 20 locations in the Chicago market that were measured. The Desired-to-Undesired (D/U) ratios measured in the field were found to confirm those measured in laboratory testing, i.e., in the -35dB to -45 dB range. D/U ratios in this range support Laser's finding that, in approximately 96 percent of the cases, the LTE UE must be within 2 meters before interference will occur.
23
Tabl
e 6
- Des
ired-
to-U
ndes
ired
(D/U
) Rat
ios f
rom
Lab
orat
ory
Test
ing
Insi
gnia
NS-
19E3
20A
13(1
9" /
LED
/ 72
0p /
60H
z / H
DTV
)Th
esho
ld o
f Sen
sitiv
ity (T
oS):
-81.
3 dB
mLT
E Si
gnal
Str
engt
h at
Thr
esho
ld o
f Vis
abili
tyD
esire
d-to
-Und
esire
d (D
/U) R
atio
LTE
Sign
al B
andw
idth
(MH
z)&
Res
ourc
e B
lock
s U
sed
-78.
3 (T
OS+
3)-6
8-5
3-2
8-7
8.3
(TO
S+3)
-68
-53
-28
1.4
MH
z 1
RB
-47.
4 dB
m-1
6.5
dBm
-8.7
dB
m8.
0 dB
m-3
0.9
dB-5
1.5
dB-4
4.3
dBTo
V N
R
1.4
MH
z 6
RB
-46.
7 dB
m-1
6.3
dBm
-2.6
dB
m8.
0 dB
m-3
1.6
dB-5
1.7
dB-5
0.4
dBTo
V N
R
3.0
MH
z 1
RB
-48.
3 dB
m-1
8.4
dBm
-5.0
dB
m8.
0 dB
m-3
0.0
dB-4
9.6
dB-4
8.0
dBTo
V N
R
3.0
MH
z 15
RB
-46.
0 dB
m-1
8.5
dBm
-6.0
dB
m8.
0 dB
m-3
2.3
dB-4
9.5
dB-4
7.0
dBTo
V N
R
5.0
MH
z 1
RB
-50.
1 dB
m-2
2.5
dBm
-10.
0 dB
m8.
0 dB
m-2
8.2
dB-4
5.5
dB-4
3.0
dBTo
V N
R
5.0
MH
z 25
RB
-47.
2 dB
m-2
7.9
dBm
-11.
3 dB
m1.
5 dB
m-3
1.1
dB-4
0.1
dB-4
1.7
dB-2
9.5
dB
24
Table 7 - Desired-to-Undesired (D/U) Ratios from Field Testing at 20 locations
Location LTE Signal TV Signal D/U# Power
(dBm)Data Rate
MBsPower(dBm)
Noise Margin(dB)
MER(dB)
(dB)
1 -35.4 3.0 -65.4 -2.0 19.1 -30.02 -24.1 3.0 -63.4 3.0 24.6 -39.32 -20.4 3.0 -57.7 Not Taken Not Taken -37.32 -16.3 3.0 -49.0 Not Taken Not Taken -32.73 -28.4 3.0 -68.1 3.0 24.6 -39.74 -32.4 3.0 -63.1 2.0 24.1 -30.74 -23.5 3.0 -67.3 2.0 24.4 -43.85 -28.7 3.0 -69.1 1.0 23.2 -40.45 -12.8 3.0 -45.6 5.0 26.9 -32.85 -20.2 3.0 -62.6 4.0 26.1 -42.45 -25.2 3.0 -61.4 1.0 22.9 -36.26 -24.4 3.0 -62.3 -8.0 13.7 -37.97 -22.4 3.0 -69.1 2.0 23.3 -46.78 -29.2 3.0 -64.6 2.0 23.6 -35.49 -32.6 3.0 -69.0 2.0 19.5 -36.4
12 -25.5 3.0 -66.2 2.0 23.9 -40.713 -26.1 3.0 -73.6 0.0 21.3 -47.514 -24.6 3.0 -60.6 0.0 19.9 -36.015 -19.5 3.0 -54.7 5.0 27.0 -35.215 -21.6 3.0 -61.5 4.0 25.6 -39.916 -25.6 3.0 -70.1 -2.0 18.6 -44.516 -24.0 3.0 -63.6 2.0 24.7 -39.617 -19.1 3.0 -57.7 4.0 25.9 -38.618 -37.0 3.0 -73.2 0.0 21.0 -36.219 -81.3 No Reception20 -44.3 3.0 -76.6 -3.0 17.4 -32.3
5.3. Operating Experience in Adjacent Market and Related Field Testing
In 2011, King Street Wireless was approved to operate LTE on the 700 MHz A block,27 inside the boundary of the WPWR-TV, Channel 51, viewing area (see Figure 12) based on a consent agreement with WPWR-TV. The areas of operation are on the northern and southeastern fringe of the WPWR-TV viewing area, in southern Wisconsin and northeastern Indiana.
27 FCC ULS File Number 0004950564, call sign WQLE662 and WQLE663, radio service WY - 700 MHz Lower Band (Blocks A, B & E), granted 12/20/2011.
25
The King Street Wireless operation inside the WPWR-TV viewing area creates both a natural experiment and the opportunity to evaluate LTE UE to DTV receiver interference with a live DTV signal and an operating LTE network.
This operating authority includes a large segment of WPWR-TV's potential viewing audience:Based upon 2010 census, population within the WPWR-TV 41 dbu contour is 9,700,436. In the northern area of coverage proposed by King Street Wireless, L.P. ("KSW"), there is a total population of 248,535 within both the 41 dbu of WPWR-TV and within the KSW northern coverage area. Significantly, this area is not covered with a signal strength from WPWR-TV that would allow adequate reliability using an indoor antenna. Using a Yagi system with an overall gain of 10 dbd and located 9.1 meters above ground, the number of people in this area receiving a signal of -80 dbw or greater is 223,464 using the Longley-Rice coverage model.
In the KSW southern area, there is a total population of 58,671 within both the 41 dbu of WPWR-TV and within the KSW southern coverage area. Using the same criteria for the Longley-Rice coverage gives a population of 54,250 receiving signal levels of at least -80dbw. ....
Combining these two coverage figures, there is a population of 277,714 that would receive an adequate signal using an outdoor Yagi antenna from WPWR-TV given no external interference or severe fading. This is only 2.86% of the total WPWR protected coverage population.28
As required in the agreement with WPWR-TV, supporting these grants, King Street Wireless on its website notifies customers who have interference issues that there is a toll free number they can call (notice shown in Figure 11). Laser understands that there have been few, if any,reported cases of interference.
King Street Wireless had a second operation in the KGAN-TV, Channel 51 viewing area, in Cedar Rapids, Iowa, posting a public notice and a contact number on December 30, 2013, Figure 11. KGAN-TV filed its license to change its transmit frequency from Channel 51 to Channel 29 on May 19, 2014. Hence, there was 5.5 months of King Street Wireless operation on the A Block, which KGAN-TV was transmitting on Channel 51. Laser is unaware of any reports of interference resulting from these operations.
Thus, there are at least two operating experiences in which an LTE system has operated in the A Block with no known reports of interference. Perhaps some incidents of interference did occur and went unreported. The impact estimate developed in Section 6 would predict that there were a few incidents of interference. What seems clear is that there were no widespread problems. If there had been widespread problems that had a severe impact, these certainly would have become known. These operating experiences therefore are very strong evidence for the conclusion that interference would be de minimis.
28 FCC ULS File Number 0004850564, call sign WQLE662, radio service WY - 700 MHz Lower Band (Blocks A, B & E), granted 12/20/2011., attachment titled: WPWR-TV Protection from LTE Cell Phone Interference.
26
Figure 11 - King Street Wireless solicitation of interference problems from KGAN29
The results of this natural experiment are important and encouraging, in that they tend to confirm previous laboratory testing and analysis. Further, it created the opportunity to perform an engineering study in the area. In March of 2015, a series of measurements were made in the area to document the performance in a low signal area, on the fringe of the WPWR-TV viewing area.
29 Accessed on June 3, 2015 from:
http://www.kingstreetwireless.com/news.html
27
Figure 12 – King Street Wireless cells operating on the 700 MHz A block
Testing focused on an area near Sturtevant, WI with a significant amount of testing performed in an area off IH-94, Figure 13. Testing focused primarily on three cell sites in this area. One cell tower was just beyond the WPWR-TV service contour but within the +8 km protection contour. The other two cell towers were within the WPWR-TV service contour. This area is believed to be at most risk for interference because it is on the edge of the WPWR-TV viewing area, and also suffers significant signal impairment to the WPWR-TV signal. This area is approximately equidistant from Chicago and Milwaukee, and WPWR-TV reception must contend with an adjacent Channel 50 station based in Madison, WI.
28
Figure 13 - Test area for focused testing in March 2015
The test used an LTE UE operating on the King Street Wireless network and a DTV receiver connected to an indoor antenna, as shown in Figure 14.
29
Figure 14 - Test setup for testing on King Street Wireless network
The results of the field testing show that the real world impact is similar to that expected based on laboratory tests, and illustrate that even at the fringes of the WPWR-TV contour and beyond, viewers will be affected only at very short distances within their personal space. The test results are discussed in greater detail in Annex 14.
The results of this testing are compared to the Intertek testing in Table 8. The Intertek study used DTV signal levels of -68 dBm, which corresponds to a slightly higher power than the expected DTV signal strength at the station contour, as well as a signal level of ToS + 3 dB, which would be a level expected either outside the viewing area or at an indoor location with significant building loss. For the field testing, the DTV signal strength was -61 dBm. The results shown in Table 8 are the distances at which ToV is reached, and are slightly larger than but consistent with the laboratory estimates for this range of signal strength.
In addition to the tests shown in Table 8, seven additional measurement points were tested. These test locations are shown in Figure 15 and Figure 16 with the cell towers the LTE UE were connected to. This testing focused on the distance at ToV as a function of distance from the cellular tower in this weak signal area near the border of the WPWR-TV Viewing area. Two DTV receivers were tested at each location, and a Samsung Galaxy Note 4 was used as the LTE UE. The LTE UE was placed on a call and set to transmit at 3 Mbps, a stronger than normal LTE UE transmission. The LTE UE was then moved toward and away from the DTV antenna until ToV was identified and recorded.
Barring two of the test points where WPWR-TV reception was not possible irrespective of LTE UE use, at each other location WPWR-TV reception was established. The field tests show that even in an area at the boundary of the WPWR-TV viewing area, the ToV distances are very
30
short, as shown in Table 23. In fact it was not possible to get interference in 3 of the tests, evenwith the handset touching the DTV antenna. This was understood as confirming the premise that there is no risk of interference close to cell towers because the LTE power control keeps the phone operating at low power. The testing found that when the LTE UE operated at distances closer than 1.2 km from the LTE base station, the LTE UE signal strength was low enough that ToV was either not reached or reached at very small distances of a few centimeters. When the LTE UE operated at greater distances from the cell tower, the phones did operate at higher power and larger distances were recorded, as reported in Table 9.
31
Figure 15 - Test Locations in Southern Wisconsin on King Street Wireless Network
32
Figure 16 - Detailed View of Test Locations 3-5 in Southern Wisconsin
Table 8 - Comparison of Laboratory to Field Measured Interference Distances30
30 ToS-D is the threshold of sensitivity, descending. The test for ToS-D starts with a signal being received and lowers the signal until reception is lost. ToS-D is the last level before reception is lost. This measurement is made with no LTE interference present.
33
Table 9 - Field test results at 7 locations in Southern Wisconsin
5.4. Impact of DTV InstallationDeficiency in the DTV installation is the most common cause of interference, according to our conversations with those who have worked on other TV interference issues. Common issues included poor reception caused by a poorly oriented, poorly located antenna, use of an inferior antenna, or a damaged coaxial cable. Those issues significantly increased susceptibility to interference. Those, of course, are all easily correctable deficiencies.
During field testing, DTV setups were varied, and a variety of deficiencies introduced. Not unexpectedly, it was found that a defective installation could impact and at time significantly increase the susceptibility to interference. However, in all the locations tested, once the installation was corrected, the susceptibility to interference returned to the range reported by the laboratory measurements and observed during these field measurements.
In all locations where testing was possible, relatively modest improvement in the antenna or antenna placement would successfully eliminate the risk of interference from an LTE UE.
5.5. Variation in LTE TransmissionsAn important observation from the field measurements was the combined effect of traffic control, transmission pattern and duration of different user activities, and automatic transmit power control to significantly reduce the impact of interference. These factors result in dynamic LTE UE transmissions, which have a significant impact on the LTE signal’s potential for causing interference. The overall influence is to create an interference region in contast to the sharp,“cliff effect,” reported in laboratory testing. In contrast to laboratory testing, which has used continual transmissions that are fully loaded with data, in actual operation the LTE UE
34
transmission varies in both time and frequency. Initially, a few packets exceed the interference threshold, causing small loss of data, which will typically be corrected by the ATSC signal recovery process and therefore is not noticable to the viewer. If the LTE UE is brought closer to the DTV's antenna, then more packets will exceed the interference threshold, resulting in more data loss, and eventually exceeding the ability of the ATSC signal recovery process to correct it. At that point the viewer will notice lost pixels. If the LTE UE is brought even closer, signifcant impairment of the picture is possible. However, to have significant impairment the LTE UE must have a long duration data load to transmit. Otherwise, the transmission session will endbefore significant impairment occurs.
In Figure 17 a 3D plot of an LTE UE transmitting at 100 kBs is shown. In Figure 18, the same LTE UE transmission is shown from a perspective that allows the change in amplitude to be clearly seen. At the beginning of the transmission session shown, a high amplitude is frequently used. However, after approxmiately 3 seconds the peak amplitude drops significantly.
Figure 17 - 3D Plot of an LTE UE transmitting at 100 kBs
35
Figure 18 - Time v Amplitude perspective of an LTE UE transmitting at 100 kBs
Figure 18 through Figure 21 show successively closer presentations of this LTE UE transmission. In Figure 19 the variation over a short period of time is noteworthy. In Figure 20and Figure 21 individual frame clusters and then frames are clearly visible.
Figure 19 - Time v Amplitude perspective of an LTE UE transmitting at 100 kBs over 6 seconds
36
Figure 20 - Time v Amplitude perspective of an LTE UE transmitting at 100 kBs over 0.4 seconds
Figure 21 - Time v Amplitude perspective of an LTE UE transmitting at 100 kBs over 0.1 seconds
One can see that there is significant variation in the amplitude of individual transmission packets. It is also clear that there are significant periods where there is no transmission at all. During these periods the DTV receiver will have unhindered reception of the ATSC signal.
In Figure 22, the same transmission is rotated to present amplitude versus frequency. The resource blocks that are loaded with data are clearly seen by their higher amplitude. Near 700.5 MHz vestigial resource blocks, not carrying a data load, can also be observed. Because the data load does not require the full bandwidth, the LTE UE is transmitting on less than the full 5 MHz bandwidth, effectively increasing the guard band.
37
Figure 22 - Amplitude v Frequency perspective of an LTE UE transmitting at 100 kBs
In Figure 23, the view is rotated to show the dynamic nature of the bandwidth allocation. An initial resource block at 701 MHz is in the foreground. A different resource block is next used, slightly more distant in frequency from Channel 51. Succeeding resource blocks fall into a pattern which is both lower in amplitude and further separated in frequency than the initial packet shown in this plot.
Figure 23 - Time v Frequency perspective of an LTE UE transmitting at 100 kBs
All the LTE UE transmissions recorded on operating networks show similar dynamic patterns. The amplitude of resource blocks is actively varied. Resource blocks are used and left idle. The combined result is that both signal amplitude and frequency separation vary in complex ways under the control of the LTE base and then UE.
38
Further, the LTE UE is not observed to transmit continually. Rather, there are significant off times during which no transmission is sent.
A careful study of LTE UE transmissions reveals several characteristics that are significant for the problem being studied.
1. There is a variation in the signal power of individual LTE transmission packets. This means that, at the DTV interference threshold, initially only a small percentage of LTE transmission packets will exceed the threshold and cause interference. This creates a transition range from first detectable interference to service disruption.
2. The duration of transmissions for most user actions is relatively short. Between upload of user data the LTE UE only transmits relatively infrequent control signals to the network. For most user actions, the actual LTE UE transmission will be relatively brief.
3. Even when sending uplink data the LTE UE transmission is divided, providing off periods in which the DTV receiver will receive the ATSC signal without the presence of the LTE UE transmission.
Section 14.5 presents plots of the uplink RF transmission resulting from a variety of common user activities. The RF transmission on/off times are plotted, showing the variation in transmission packet amplitude and total on time density for these activities.
6. Frequency of Adjacent Band Interference Having studied the threshold of LTE-to-DTV interference in the previous section, this section examines the probability and the likely impact of LTE interference upon WPWR-TV viewers in the Chicago area. The preceding section demonstrated that the power and transmission characteristics of LTE UE, and the ability of DTV receivers to discriminate between DTV broadcasts and LTE UE transmissions in adjacent frequencies, make it very unlikely that LTE UE operations will interfere with DTV viewing. The possibility of interference in any particular market will also be affected by the geography and population distribution profile of the specific market, the percentage of the population that receives its DTV signal over the air, wireless network design, wireless usage patterns and other user behavior.
For LTE to DTV interference to occur, a number of factors must exist simultaneously. Most significantly, the LTE device must be in close proximity (i.e., within 2 meters, in approximately 96 percent of the cases) to the DTV receiving antenna for any potential for interference to arise.But even in this instance, there are other conditions that must exist to create interference.
The following 11 elements are necessary for an LTE UE in the greater Chicago area to interfere with a DTV receiver tuned to WPWR-TV, Channel 51:
DTV-Related Factors:
1. The TV must be turned on with someone watching it.
2. The viewer must be watching WPWR-TV, Channel 51.
3. The viewer must be receiving the WPWR-TV signal over-the-air using an indoor antenna, and not via cable, DBS, streamed over the Internet, or over-the-air received on a rooftop antenna.
39
4. The DTV receiver must be located in an area with a weak Channel 51 signal.
Handset-Related Factors:
5. The LTE device must be in close proximity to the DTV receiving antenna.
6. The LTE UE must be on and transmitting
7. The LTE UE must be operating on a Lower 700 MHz A-Band channel.
8. The LTE UE must be capable of radiating power on the 700 MHz A-Band sufficient to cause interference.
9. The LTE network power control must have instructed the LTE UE to transmit with full power or sufficiently high power to cause interference.
10. The LTE device must be positioned with an orientation that results in the LTE device’s transmitting pattern coinciding with the indoor antenna’s receiving pattern.
11. The LTE UE must be transmitting for sufficient duration in time or with a transmission pattern that is capable of causing interference.
Figure 24 - The 11 factors necessary for interference
Importantly, as shown in Figure 24, all of these conditions must exist simultaneously for interference to occur.
A number of these factors are estimated in Table 10 below to produce an overall estimate of the number of persons in the greater Chicago area whose viewing of Channel 51 could potentially be affected by LTE UE interference. Table 10 conservatively assumes that:
a wireless device is constantly operating in every household in the greater Chicago area in which TV is viewed over-the-air,
40
all of the wireless devices are operating only in the transmission mode (versus downloading data or receiving voice communications in the downlink mode),
all of the wireless device operations occur on the 700 MHz A-Band (instead of frequently occurring on one of the other multiple bands that are available on virtually every wireless device sold today),
every wireless device is located in close proximity to the DTV,
none of the wireless device are off-loading data on a Wi-fi connection, and
all of the wireless device antennas are oriented toward the DTV receiver antenna, and the device user’s body does not attenuate the signal from the device to the DTV receiver antenna.
Even using these conservative assumptions, Table 10 indicates that only approximately 122persons in the greater Chicago BEA (approximately 46 households) out of over 10 million people may potentially experience interference from wireless operations on the 700 MHz A-Band.31 This result represents less than 0.00122% of the 10 million people who live in the greater Chicago BEA in areas served by WPWR-TV. Said another way, less than 1 in 80,000people will be affected and in most cases the impact will be occasional, annoyance level interference.
At the same time, Table 10 also shows how 3.4 million people could benefit if Band 12 A Block spectrum were used by the largest wireless carrier assuming a penetration of 34% in the coverage area.
31 These 122 persons/46 households are not a static group. Instead, the composition of the group changes during the course of a day as TV viewers turn their televisions on and off, switch channels to and from Channel 51, use their wireless devices, and move closer to and farther from an indoor DTV antenna while using their mobile phone.
41
Tabl
e 10
- Po
tent
ially
Impa
cted
Pop
ulat
ion
42
The following notes provide further documentation and clarification of the table:
1. The population for Chicago and the areas with potential or no LTE interference were based on the 2010 census.
2. The area used to calculate the population is based on standard FCC F(50,90) dipole-adjusted DTV Threshold contour in the viewing area for WPWR-TV.
3. Chicago cable/alternate delivery systems was based on Nielsen data for February 2015.
4. Homes using antennas were 7% of population based on Consumer Electronics Association July 2013.
5. Wireless Carrier market share was the highest for any carrier shown nationally by Statista in 3rd Quarter 2014.
6. WPWR-TV market share was based on Nielsen data.
7. Devices used by people within 1.2 kilometers of a cell site do not transmit at power levels that would cause DTV interference (see Section 6.5 for further discussion).
8. There are 2.63 people per household in Illinois per the 2010 census.
In spite of these small numbers, the very conservative assumptions reflected in Table 10 mean that the results actually over-estimate the number of people who may potentially experience interference from 700 MHz A-Band operations in the greater Chicago BEA. In fact, it would be reasonable to assume instead, for example, that:
1. a wireless device is not always operating in each household that receives a DTV signal over-the-air,
2. such wireless devices are not always operating in the transmit mode, and when they are transmitting, they are not they are not always transmitting on the 700 MHZ A-Band, and
3. the wireless devices are not always in close proximity to a DTV receiver and theirantennas are not always aligned with the DTV receiver antennas.
Reasonable changes in the assumptions, such as those outlined above, would drive down the estimates of potential interference from 700 MHz A-Band operation to even lower levels than the insignificant interference estimated in Table 10.
Further, if any interference were to occur, LTE technology provides multiple paths to eliminate or substantially reduce that interference, and simple actions by any affected viewer can also independently eliminate the interference.
Several of the factors discussed above that affect the possibility of interference from an LTE UEinto an over-the-air broadcast on WPWR-TV Channel 51 are discussed below.
6.1. Uplink vs Downlink TrafficWireless users today download substantially greater amounts of data than they upload from their devices. In early cellular telephony, usage was dominated by voice communication and, as a result, uplink and downlink traffic were roughly equal. However, as reported in Section 5, in wireless uplink traffic is estimated at approximately 10 percent of total traffic, with the uplink-
43
to-downlink traffic ratio likely to drop as streaming video becomes more popular on mobile networks. This disparity is significant when considering the possibility of LTE UE operations potentially interfering with DTV operations on adjacent Channel 51. As previously discussed, 700 MHz A-Band downlink transmissions occur 30 MHz above Channel 51 and thus do not interfere with any DTV transmissions. Thus, because only an estimated 10 percent of total wireless traffic is likely to occur on the uplink channel, the opportunity for LTE UE usage on the A Band to interfere with DTV transmissions is substantially reduced.
6.2. Susceptible Portion of the Viewing AreaTo have a meaningful risk of interference the DTV receiver must be located in an area with a weak Channel 51 signal. Thus, the primary LTE UE interference concern is an “annulus issue”existing on the outer perimeter of the WPWR-TV viewing area.
This point was documented during field testing, which measured the D/U ratio as a function of DTV signal strength. The field testing results are consistent with the laboratory testing results,as the DTV signal strength increases, the strength of the LTE UE signal required to cause interference must also increase.
In addition to the fringe DTV service area, there will also be some locations inside buildings,notably basements that have weak DTV signals in an otherwise strong DTV signal area. LTE UE transmit power is also likely to be stronger in these internal building areas than in nearby outdoor areas. The possibility of interference is higher in these areas than in nearby outdoor or indoor areas closer to the building’s exterior walls.
To account for these indoor areas with weak DTV signal strength, field testing was conducted in an area with a minimum of 20 dB above the FCC's 42.1 dBu contour. The 62.1 dB contour (i.e., 20 dB above the 42.1 dBu contour) was chosen to approximate the DTV signal power loss experienced in moving from an outdoor environment to inside a building. Building loss generally will raise LTE UE power, to overcome the additional loss to the base station, and the WPWR-TV signal to an indoor antenna. Data from US Department of Commerce Spectrum Management Advisory Committee, ITU-R Joint Task Group 5-6 and others report a strong majority of LTE UE operating powers in the range of 9 dBm to 14 dBm. These studies will include the impact of building loss. The conclusion is that in the central part of the viewing area, with a few exceptions for basements and other locations with extreme building loss, interference is not a realistic problem.
Not surprisingly, this central part of the viewing area contains the large majority of the population. The viewing area fringe, where interference is a realistic possibility, is predominantly rural.
Approximately 10.4 percent of the population in the WPWR-TV service area live in locations where the Longley-Rice model estimates that the WPWR-TV signal is below 62.1 dBu. As a first approximation, the portion of the population living in these fringe areas may have the most significant possibility of LTE UE interference.
Not all of this rural population, however, has an equal possibility of interference from LTE UE operations. Network operators do not locate base stations randomly but instead place them where people reside, work, and make calls. Greater Chicago BEA coverage maps show that towns and major roadways outside the 62.1 dBu contour are well covered, and LTE UE
44
operating near a cell tower will operate at lower power and therefore represent a smaller potential for creating interference.
Figure 25 - T-Mobile cellular signal strength in the Chicago market32
Figure 25 shows T-Mobile’s cellular signal strength in the Chicago area. Other network operators show similar coverage patterns. The area of primary concern for interference is the area where the WPWR-TV signal is weak and the LTE UE will be operating at a higher power because it is farther from the base station at the cell site.
As a result, the areas in which the blue fringe areas of cellular coverage in Figure 25 intersect with the areas of weak DTV reception have the greatest potential for LTE UE interference. The blue fringe area in Figure 25 gives a visual view of the research reported by US Department of Commerce Spectrum Management Advisory Committee, ITU-R Joint Task Group 5-6 and others, which report a strong majority of LTE UE powers operate in the range of 9 dBm to 14 dBm.
There is not a risk of LTE UE interference in the outlying areas where there is no LTE coverage. Even though the WPWR-TV signal is weak in those areas, there is no risk of LTE UE interference because LTE UE does not operate in those areas.
32 Source accessed May 23, 2015:
http://opensignal.com/
45
6.3. Lower 700 MHz A Block OperationLTE UE supporting the 70 MHz A-band also support other LTE bands, and often a large number of other bands. As Table 11 illustrates, the supported bandwidth for the current generation ofLTE UE is impressive.
46
Tabl
e 11
- Su
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ted
band
s on
rece
ntly
intr
oduc
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TE U
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Man
ufac
ture
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Nam
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IDSu
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640
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13,
17,
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26,
41
521
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891L
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205
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120
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2, 4
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122
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HTC
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200
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80PJ
A200
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2, 4
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25,
26,
41
416
HTC
HTC
One
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110
NM
80PJ
A110
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2, 4
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, 12,
13,
17,
30
249
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142
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021
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515
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396
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217
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1092
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247
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bly)
4059
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130
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ty42
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Band
5, 4
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4241
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130
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285
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1IH
DP56
NA1
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2, 2
521
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1058
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DT56
PB3
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4, 5
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87M
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4009
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787
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laxy
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2, 4
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H-R9
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515
2
47
Man
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ture
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MG3
86T
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12,
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SM-G
900R
4A3
LSM
G900
R4Ba
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2, 1
7, 5
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147
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sung
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axy
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MG9
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Band
12,
2, 4
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127
Sam
sung
Gal
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Not
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SM-N
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4A3
LSM
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4, 5
, 12,
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152
Sam
sung
Gal
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Not
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Cellu
lar
SM-N
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2, 4
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2, 1
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LSM
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17
147
Sam
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Gal
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H-I4
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LSCH
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147
Sam
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Gal
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H-R8
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LSCH
R830
Band
2, 4
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214
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214
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48
Man
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Band
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12,
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0P82
300
NM
80P8
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Band
17,
5, 4
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212
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Assuming that a network used all available frequencies evenly, the chance that an LTE UE will operate on an A Block channel will be the ratio of the A Block bandwidth, 5 MHz excluding the planned 1 MHz guard band, to the total bandwidth over which the LTE UE can operate. The spectrum over which any specific operator’s LTE UE can operate will be a combination of the network operator's spectrum assets in the Chicago market and the capabilities of each LTE UE.
If both the network and UE support:
the original cellular band (i.e., LTE band 5 with an uplink at 824-849 MHz)
the PCS band (i.e., LTE band 2 with an uplink at 1850-1910 MHz), and
the 700 MHz A-Band (i.e., LTE band 12 with an uplink at 699-716 MHz),
then the network and the UE will be able to utilize 92 MHz of uplink bandwidth. Thus, if calls are assigned evenly across frequencies, the chance of a call being assigned to the band 12 A block is 5/92 or just 5.4%.
In fact, the actual loading on the band 12 A block will depend on the network operator’s spectrum management techniques and the channel conditions in each location. In specific locations, the channel between the LTE UE and base station will favor some frequencies over others. Over a wide frequency range, lower frequencies generally have better propagation characteristics. This is one important reason it is critical to make low frequency spectrum available. However, in a narrow frequency range, local channel conditions may favor a higher frequency over a lower frequency. The base stations continually evaluate channel conditions, assigning UE to channels that best support the communication. For general purposes, however, it is reasonable to assume that only about 5-6% of UE transmissions will be assigned to the band 12 A block, and 94-96% of UE transmissions will be assigned to other bands and frequency blocks. Thus, the availability of multiple bands for LTE UE transmissions reduces the possibility of UE interference into WPWR’s DTV signal.
The probability of interference is further reduced by the fact that the network will assign operating bandwidth as needed. Because an LTE UE seldom needs a full 5 MHz of bandwidth to transmit, it will be assigned 5 MHz for operation infrequently. Instead, an LTE UE will typically operate in a 3 MHz or 1.4 MHz bandwidth and the resource blocks actively utilized by the UE will often occupy only a portion of that bandwidth.
6.4. LTE UE Maximum Radiated PowerWhile the 3GPP standard calls for LTE UE to be capable of applying 23 ±2 dBm to its antenna, test reports in the FCC grants database show that the radiated power for most phones falls under this level. In fact, most phones are only capable of transmitting relatively modest power in band 12.
A survey of the maximum band 12 transmit power for 56 LTE UE, as reported in the test reportsfor their FCC equipment grants, found that the average maximum possible transmit power to be 18.9 dBm (with a range of approximately 14 dBm to 23 dBm). Further, network power control will further reduce the maximum transmit power utilized by these LTE UE in band 12 by keeping the UE transmit power as low as possible while still maintaining communication.
The limitation of the average LTE UE to a transmit power substantially less than 23 ±2 dBm is not surprising in light of all of the spectrum bands these devices must support. The UE antennas
50
must be designed to optimize performance across all of the supported frequencies with the result that maximum efficiency is unlikely to be achieved for any single frequency. And the frequencies nearest the edge of the supported frequency range (such as the 700 MHz A block) will typically suffer the most.
The result is that LTE UE seldom utilize their full theoretical power capabilities when operating on the 700 MHz A block. Thus, the operation of UE at lower than theoretical power levels in the 700 MHz A-block reduces the possibility of interference with adjacent Channel 51 networks such as WPWR-TV.
6.5. LTE Power ControlLTE network power control must instruct the LTE UE to transmit with full power or sufficiently high power to cause interference.
The 58% used in item 7 of Table 10 was derived from 2010 US Census data and represents the number of people in the WPWR-TV fringe area living in towns of over 5,000, where theregenerally is good cellular coverage and significant cell density. Research from Ofcom, CSMAC and ITU-R on the distribution of LTE UE power levels in rural areas shows this percentage to be conservative. In any event, those research studies demonstrate that a high percentage of calls in rural areas use low power levels.
The distribution of LTE UE transmission power levels is shown by the Commerce Spectrum Management Advisory Committee (CSMAC) research.33 Figure 26 illustrates the Cumulative Distribution Function of LTE UE transmission power levels. Table 12 gives the data in tabular form. As shown in Figure 26 and Table 12, CSMAC’s research finds that 60% of the calls in rural areas are under 10 dBm and 85% are under 15 dBm. Thus, the CSMAC data support the58% value arrived at by analyzing the 2010 Census data, and in fact suggest that the 58% figure may be too low.
33 CSMAC, Final Report, Working Group 1 – 1695-1710 MHz Meteorological-Satellite For January 22, 2013. The graph and table reproduced here are from Appendix 3 of that report.
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Figure 26 The Cumulative Distribution Function of LTE UE TX
52
Table 12 Cumulative Distribution Function of LTE UE TX (Data in tabular form)
In an Aerospace and Flight Test Radio Coordinating Council (AFTRCC) report, WHITE PAPER: Sharing between LTE Systems and Aeronautical Mobile Telemetry (AMT) Systems in the Band 1435 - 1525 MHz, AFTRCC cites ITU-R research and states in Section 3.3.1:
The analysis herein is consistent with information published by 3GPP and captured in ITU documents 5D/Temp/171, and more recently in 5D/Temp/232(Rev.1), and in the JTG documents cited previously.34
34 Liaison statement 4-5-6-7/236-E from WP-5D, 18 July 2013, containing Preliminary Draft New Report ITU-R [IMT.ADV.PARAM], Characteristics of terrestrial IMT Advanced systems for frequency sharing/interference analyses. According to JTG5-6/180 Annex 2 (except for small cell indoor scenario, which was not covered in that document).
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A recent Ofcom study reported that LTE UE transmit on average at only 9 dBm, even though the 3GPP standard calls for LTE UE to be capable of transmitting up to 23 dBm. The Ofcom report also found that the average LTE UE power transmission level was only 14-19 dBm at suburban cell edge conditions – conditions that Ofcom judged to be representative of indoor scenarios. Thus, even at cell edge conditions, network power controls generally instruct LTE UE to operate at levels well below their theoretical power limits, thus effectively reducing the possibility that LTE UE will create adjacent channel interference in the real world.
Although Ofcom also found that that LTE UE transmit above 19 dBm in a small portion of edge conditions, those transmissions occurred in the 800 and 1800 MHz bands. As noted above, LTE UE are generally not capable of producing those powers in the 700 MHz A-Band range. Thus, the combination of LTE UE power capability in the 700 MHz A-Band and active network-directed UE power control (even in edge coverage scenarios) result in LTE UE operating below their theoretical power capability which reduces the chance of adjacent channel interference.
In its study, Ofcom concluded:Overall assessment of interference from mobile devices
5.51 Our previous analysis indicated that the impact of 2.3 GHz mobile devices would not be significant, based on the intermittent nature of mobile transmission and because transmit powers are typically low enough that the risk of interference is minimal. Specifically, we calculated a maximum interference range of less than 1 metre, based on a typical transmit power of 3 dBm.
….
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5.53 We have also considered further the transmit power of mobile devices, in response to concerns that our previous assumption of an average transmit power3835 of 3 dBm was too low. In order to address this point we have conducted a series of walk tests in urban and suburban areas recording the transmit power of a mobile device on different existing mobile networks. The results show a range of powers in different areas, depending on the position of the mobile in the cell, as may be expected. As with other tests, the full results are presented in annex 1.
5.54 We use the 50th percentile results from each test, as we believe these are the most relevant for a mobile system, while noting that higher powers are possible in extreme cases. The distribution of transmit power varied depending on the environment and LTE frequency band. As a result the 50th percentile value varied from -2 dBm in areas of good coverage to 19 dBm in more cell edge locations. The median of all the results is 9 dBm which we think is an appropriate value to use in our statistical modelling.
5.55 We understand from informal discussions with a stakeholder that they have seen similar results in walk test campaigns but we have not seen detailed results.
5.56 We note that in a small cell coverage area (including outdoor and indoor pico-cell and in-home femto-cell scenarios described above) mobile devices are more likely to undergo power control, thus reducing the risk of interference from the LTE user equipment (although there may be a risk of interference from the small cell base station to Wi-Fi).
.....
The Ofcom study also noted:.....
Measurements of LTE mobile device transmit power
A1.8 In order to understand the potential impact of interference from 2.3 GHz mobile devices on Wi-Fi, we have undertaken a short set of measurements to record transmit powers36 from LTE mobile devices in other bands (800 MHz and 1800 MHz) in typical environments.
A1.9 Using a Rohde and Schwarz FreeRider system, we carried out a series of walk test in a dense urban and two suburban scenarios. The suburban areas consisted of both good (cell centre) and poor (cell edge) coverage areas that were identified using mobile operators’ coverage checkers and field measurements of signal strength and signal quality.
A1.10 During the walk test, our methodology was to successively run a testing pattern consisting of: an HTTP download; Ping; HTTP browsing; and FTP upload, with 5 seconds pause in between each data task.
A1.11 Measurements were taken on two networks in different bands – one in 800 MHz and one in 1800 MHz.
A1.12 The resulting distributions of the transmit power as reported by the handset are presented in Figure A1.1.1 a�ummarizedsed in Figure A1.2 and Table A1.1.
35 We assume an antenna gain of 0 dBi so this is equivalent to an EIRP value 36 We assume a 0 dBi antenna gain so all values are equivalent to EIRP
55
Figure A1.1: Suburban cell edge 1800 MHz mobile device transmit power distribution
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Figure A1.2: Suburban cell edge 1800 MHz mobile device transmit power distribution
Table A1.1: Summary of walk test results
A1.15 A wide range of transmit powers can be seen in all cases. Transmitting at the maximum value of 23 dBm is shown to be unlikely in all cases.
A1.16 As may be expected, power control causes a significant reduction in transmit power in urban and suburban cell centre coverage areas. Higher powers closer to the maximum can be seen in cell edge scenarios. We believe the cell edge scenario is also representative of indoor scenarios.
A1.17 We have found no relationship between transmit power level and frequency band, although it is difficult to draw any firm conclusions on this as there are a number of unknown factors to consider, such as possible different network deployment configurations in these areas.
A1.18 As these results show a wide range of distributions in different scenarios, it is difficult to derive one transmit power figure to use in further analysis. However we have taken a simple approximation of 50th percentile results across both bands and all scenarios. This gives a figure of 9 dBm. These figures can then be used as a reasonable
57
representation of typical transmit power, while noting in practice it is heavily dependent on the usage scenario.37
6.6. Proximity to the DTV Receiving AntennaTesting demonstrated that the DTV receiving antenna is the primary point of potential interference. Testing showed that using an LTE UE to illuminate the body of a DTV receiver did not cause interference. Instead, testing showed that the distance of the LTE UE from the DTV antenna is a factor that influences the potential for interference.
6.7. Relative Position and OrientationPotential interference will generally occur only if the LTE UE is positioned with an orientation that results in the UE transmitting pattern coinciding with the DTV indoor antenna’s receiving pattern. About half the time, a user will have the LTE UE positioned so that their body blocks or partially blocks the UE signal from reaching the DTV antenna. Even if the LTE UE signal reaches the DTV antenna, it will almost always have some degree of cross polarization, reducing the coupling efficiency of the LTE signal into the DTV antenna.
In its study, Intertek studied this factor in detail. The Intertek study concluded that there is a 98% probability that the mean alignment coupling loss will be greater than 3.9 dB—which substantially reduces the potential for interference from an UE into an adjacent DTV transmission.
Sections 9.2 and 9.3 of the Intertek report are reproduced as Annex 11 to this Report.
6.8. LTE Traffic PatternFor interference to occur from an LTE UE into adjacent Channel 51, the UE must be transmitting for a sufficient duration in time or with a transmission pattern that is capable of causing interference.
The impact of variations in LTE UE transmission duration and traffic pattern are discussed earlier in this Report. The specific characteristics of LTE transmission patterns are significant variables that tend to reduce the frequency, duration and severity of interference below what would be expected from a continually transmitting power source.
6.9. Impact of Multiple LTE UEA concern that might be raised is the impact of more than one LTE UE operating at the same time and location. There are of course multiple scenarios in which many people will be at the same place and using their phones. One can think of a party or other social gathering and some event motivates several people to make calls at the same time.
What saves this scenario is that the base station must support all of these UE and will separate them in time and frequency. To the observer, it may appear that there are many people talking on their phones at the same time. To the base station that is receiving the calls and from an
37 Ofcom, Award of the 2.3 and 3.4 GHz spectrum bands: Update on the coexistence of 2.3 GHz LTE with Wi-Fi in the 2400 to 2483.5 MHz range and other coexistence issues, Dec. 3, 2014.
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interference viewpoint, it is one UE at a time on each channel. Several channels may be simultaneously in use but those other channels will be more distant in frequency and so not a problem for adjacent band interference.
The people calling may be using different networks and so connecting to different base stations. However, to separate their calls, since they are at the same location those base stations will separate their channel assignments. At this point it must be remembered that handsets typically, almost universally support multiple frequency bands. The base station traffic schedulers involved will have a number of channel options to assign and will do so in a way that separates the LTE UE in frequency and time. For a DTV receiving the WPWR-TV signal, this means the risk of interference will be only from one LTE UE at a time.
7. Severity of Adjacent Band Interference Section 5 examined the threshold at which an adjacent band LTE UE transmission would impair DTV reception and the transition zone from first observable impairment to severe impairment. Section 6 then looked at the probability that the conditions for LTE UE interference would exist. In section 6 an estimate in terms of people and locations was developed. This Section 7 looks at the frequency, duration, and severity of interference. In locations where the conditions allow interference, how often will it occur? When interference does occur, how long will it last? Finally, when interference occurs, how severe is it likely to be?
As IEEE 1900.2:2008, IEEE Recommended Practice for the Analysis of In-Band and Adjacent Band Interference and Coexistence Between Radio Systems, explains, interference can be evaluated from two perspectives. The first perspective is the number of viewers potentially impacted by interference. That perspective was studied in Section 6. The perspective studied in this section focuses on the second perspective, the degree of impact on users who experience interference. A complete understanding of the impact of a particular kind of interference requires that both perspectives be understood.
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Figure 27 - Interference Impact from two perspectives, percentage of viewers impacted and impact on individual viewers38
Of the 11 factors identified in Section 6 as being necessary or interference to occur, five factors give insight into the frequency, duration and severity of LTE interference:
TV viewing habits
LTE usage and uplink transmission
Variation in LTE UE maximum transmit power
Separation between LTE UE and DTV antenna
Relative orientation of LTE UE, DTV and user's body
Some aspects of these factors have been discussed previously in this report. In this section they will be explored further in an effort to understand the impact of interference on WPWR-TV viewers, when interference does occur.
7.1. Frequency of ImpactLTE UE interference cannot happen more frequently than an LTE UE transmits. While some routine control traffic between the network and LTE UE is continuous, this traffic is widely spaced in time and short in duration. Longer duration events that result in significant uplink data determine the likelihood of interference.
38 IEEE 1900.2:2008, IEEE Recommended Practice for the Analysis of In-Band and Adjacent Band Interference and Coexistence Between Radio Systems, Figure 7.
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However, when an LTE UE does transmit uplink, it will not always cause interference. It must be close to the DTV antenna and oriented in a way that allows its transmission to couple into the indoor DTV receiving antenna. A number of factors may result in shielding the DTV antenna from the LTE UE signal, including the body position of the user being between the LTE UE and the DTV antenna, use of the LTE UE in an adjacent room, etc.
A significant factor will be the relative position of the user’s body. If the LTE user is holding the device such that their body is between the device and the DTV antenna, a large loss is introduced, which in almost all cases will effectively prevent interference. The probability that the user's body will totally or partially shield the DTV receiving antenna from the LTE UE transmission is expected to be random and therefore 50%. There is no reason for an LTE user to have their body in any particular position relative to the DTV antenna and so it is likely that half the time they will be positioned to block or partially block the signal.
It will certainly be common for LTE UE to be used in the same location where a DTV is being watched. It also appears certain that in most cases the LTE UE will be transmitting with a frequency that will depend on the habits of its user. The top 1% of users are much more active than the majority of users. User activities also vary significantly with some users making more voice calls, others using text messaging or web browsing more commonly.
In addition, the LTE device must be operating on Lower 700 MHz A Block frequencies. As previously discussed, this will only occur a small portion of the time because of the multiple wireless bands that a network can instruct a wireless device to utilize. In addition, because of Wi-Fi offloading, wireless devices will not be radiating on Lower 700 MHz A Block frequencies in most cases because users watching over-the-air DTV at home will likely operate their wireless handset on a home Wi-Fi network. Mobile analytics provider Mobidia estimates that approximately 80 percent of wireless data traffic was off-loaded to Wi-Fi in the 3rd quarter of 2014, with that percentage rising over time. The percentage is slightly higher for iOS users than Android users, and is relatively consistent across the wireless carriers. Mobidia also found that 98-99 percent of iOS users and between 92 and 97 percent (depending on the carrier) of Android users offload data to Wi-Fi networks.39 Mobidia has also noted that the vast majority of data offload to Wi-Fi happens at home and in the office -- the former, of course, being the location where users are most likely to watch over-the-air television. In other words, the locations where Wi-Fi offload is most likely to occur are also the locations where users watch television, significantly lowering the likelihood of adjacent band LTE UE-to-DTV interference.
In the next section the impact of various user profiles will be explored further.
7.2. Duration of ImpactAs noted above, interference can only occur when the LTE UE is transmitting. Thus, the duration of use of the LTE UE is an important variable. A short control message or data transmission may cause momentary signal levels at which interference could theoretically occur,but the impact will be short and it is very likely that the viewer will be totally unaware that a pixel or small group of pixels was blocked.
39 See Mobidia, Network Usage Insights, Nov. 2014, available at http://www.mobidia.com/network-usage-insights-report-0.
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The distribution of the duration of LTE UE use is important in predicting the probability of significant interference.
In a 2014 study, Ofcom stated:5.10 In order to better understand the time domain effects of LTE uplink signals we have collaborated with stakeholders in conjunction with the Wireless TIC group2640 to record signals from a live 2.3 GHz LTE network. A range of recordings were taken looking at different usage profiles. We focussed on the following cases for use in further measurements:
1. Light loading based on a user downloading data and only sending acknowledgements on the uplink. We believe this represents the most typical usage case for mobile devices;
2. Heavy loading based on a user uploading a large file for a long duration. This represents the assumed worst case in terms of interference, but is not likely to represent typical user behaviour for long periods of time;
3. Continuous video streaming based on a Skype call. We believe this represents a typical case of persistent uplink usage.41
Extending the thoughts of Ofcom, the dominant uses that result in long duration uplink transmission are voice calls and video calls. Other kinds of user action, such as web browsing, downloading streaming video, and texting, result in short uplink transmissions separated by relatively long periods with only control signaling being returned uplink.
Voice calls require relatively small amounts of data, which results in smaller bandwidth and transmission time being assigned. Further, technical challenges are delaying the deployment of VoLTE. Even on networks that currently provide VoLTE, it is used for higher quality audio which also requires better signal to noise and generally better channel conditions. When the LTE channel is not clean enough, calls are switch over to simpler protocols, meaning they are moved back to pre-LTE protocols, which results in their being moved to the traditional bands. Hence, currently most voice calls are moved to the cellular or PCS band. However, as VoLTE comes into wider use, it will still use a smaller bandwidth signal, resulting in larger frequency separation from WPWR-TV.
Video calls are the other long-duration call type. Video calls do have large data loads, especially for high definition video, and accordingly require more spectral resources. However, video calls are relatively rare when viewed in conjunction with active viewing of a DTV receiver, and so present a small risk of interference when viewed from the perspective of the full population.
Other types of LTE UE use will result in short uplink transmissions. The interference impact, if the LTE UE is close enough to have any impact, will be nothing more than momentary annoyance.
40 The Wireless TIC group is a collaborative test and measurement forum as part of the techUK Future Technologies Network. 41 Ofcom, Award of the 2.3 and 3.4 GHz spectrum bands: Update on the coexistence of 2.3 GHz LTE with Wi-Fi in the 2400 to 2483.5 MHz range and other coexistence issues, Dec. 3, 2014.
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7.3. Severity of ImpactIn this section we look at the question, "When interference does occur, how bad is it?" With an operating LTE network, interference is at first minimal but can increase if the LTE UE is brought closer. A range of 5 to 7 dB was observed between the first noticeable picture impairment, Figure 25, and severe impairment to reception, Figure 28. As discussed elsewhere in this Report, in approximately 96 percent of cases, interference will not occur until the LTE UE is closer than 2 m. If we consider a case were the ToV distance is exactly 2 m, then a 1 dB increase in the signal will start to cause some impairment. And even then, the other factors discussed above must be present for interference to occur. The handset would need to be moved from 2.0 m to 1.8 m. At that point, there would be occasional pixel loss if the LTE UE is transmitting.However, to get to the kind of signal loss shown in Figure 28 would require the handset to be brought to with 1.1 m, for a 5 dB increase, or 0.9 m, for a 7 dB increase in the LTE UE signal arriving at the DTV antenna.
The severity of the interference, in terms of its impact on TV viewing, extends over a range. This finding arose from the field testing and is in contrast to most laboratory tests performed. Once identified, the reason for this difference is relatively easy to understand. Laboratory tests are usually performed with signals of even amplitude and fully loaded with data. Using such signals results in a sharp "cliff effect" where there is no interference up to a threshold and then a very small increase in amplitude results is severe impairment or total loss of service. However, when testing on a live LTE network, at the initial stages, interference is barely noticeable. The most commonly observed impairment would be a pixel loss, as shown in Figure 28, with additional examples in Figure 29.
MomentaryPixel Loss
Figure 28 - Initial LTE UE interference is likely to result in occasional pixel loss
This observation of a transition region is important for several reasons.
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Having a transition region of increasing severity will let viewers know that they have reception but that there is a problem. It is likely to prompt them to think about what might be causing the interference and take steps available to them to remedy the situation. If a person is using their phone, he or she will likely begin to associate use of the handset with interference. If the person is moving around they are likely to discover that the interference gets better, gets worse or disappears entirely at certain distances and positions with respect to the DTV antenna.
The transition region also means that the most likely manifestation of interference will be an annoyance at seeing a few pixels lost. An LTE is more likely to be farther away from the DTV antenna simply because the area away from the antenna is greater. The result is that when interference happens, it will most often be relatively minor.
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PixelLoss
MomentaryPixel Loss
Figure 29 - Additional examples of momentary pixel loss
As more transmission packets exceed the interference threshold the severity will rise, becoming moderate, Figure 30, and eventually may become severe or even completely block reception, as in Figure 31.
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Figure 30 - As an LTE UE comes close to a DTV antenna the number of transmission packets above the interference threshold increase and reception gets worse
Figure 31 - Severe interference occurs when a number of transmission packets go over the interference threshold over a long enough time to overcome the ATSC error correction capability
The laboratory tests used a continuously transmitting LTE signal and reported a sharp "cliff effect," in which picture quality changed from no visible impairment to total loss of service in a very narrow range, typically within 0.5 to 1.0 dB. However, this was not what was observed during the field testing. It is worth considering why this difference may exist.
In an operating LTE network, a combination of traffic control, transmission pattern, duration of different user activities and automatic transmit power control significantly reduce the impact of
66
interference. However, when operating on a live LTE network, an LTE UE is assigned transmission time and bandwidth by the cellular base, which divides its resources among all LTE UE requesting service. The result is that the LTE UE signal is both dynamic and divided (rather than continuous). The impact on interference is that as an LTE UE is brought close to a DTV receiving Channel 51, at first only a few of its transmission packets exceed the interference threshold. There is then a transition region, shown in Figure 32. As the LTE UE is brought even closer, a growing number of transmission packets exceed the interference threshold resulting in increasing impairment to the received picture.
The laboratory testing suggests that interference would occur at the upper line in Figure 32.However, only the highest transmission packet reaches that level. So the DTV would only have a very short time, the duration of that one packet, when it was over its ToV level. It may well be that the ATSC error correction is able to restore the data and the viewer may see no impairment at the upper threshold. All the other packets are several dB lower. The LTE UE would need to be brought much closer, perhaps to as little as half the distance, before the viewer would notice any significant impairment. It is not until the lower threshold shown in Figure 32 is reached that a number of transmission packets are over the ToV level.
If someone were walking toward the DTV antenna with an LTE UE active on the lower 700 MHz A Block, at first there would only be occasional pixel loss and the viewer might not even notice any impairment. As the LTE UE gets closer more transmission packets will be high enough to cause interference and eventually there will be very noticable interference. This transmission region was found to be 5-7 dB—which translates to half the distance. So if the first pixel loss happens at 4 m, then there would be a significant degradation until the LTE UE comes to 2 m. If the first pixel loss is at 1.5 m, then significant impairment is likely to only happen when the LTE UE is at 0.75 m. From a user impact perspective lab testing with a continuous transmission at level amplitude overestimates the threat distance by a significant margin.
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Observed interference level in field testing
Interference level predicted from laboratory testing
Figure 32 - Interference level predicted from laboratory testing vs level observed in the field
In addition, different user actions have different payloads, particularly for the uplink. The uplink transmission pattern of sending a text message is different from that of a long duration, high definition video call. Other user actions, such as web browsing, reading and sending email, voice calls, all have different data payloads and different trasmission patterns and durations.
The end result is a transition region in which the impact of interference increases as a function of the number of transmission bursts that exceed the interference threshold and the tramission pattern generated by the user's activity.
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8. Mitigations Earlier sections of this Report have demonstrated the de minimis possibility of interference from Chicago 700 MHz A-Band operations into WPWR TV Channel 51 operations. In the unlikely event of interference, however, there are multiple mitigation paths that individual users or a network operator can employ to eliminate the interference.
Because the possibility of interference is a function, among other things, of the distance and orientation of the LTE UE in relation to the DTV receiver antenna, UE users can effectively eliminate virtually all interference that may occur simply by moving away from the DTV antenna or by turning the orientation of the LTE UE so that its antenna is no longer oriented toward the antenna of the DTV receiver. These actions will be particularly effective to address any interference that may occur because, as demonstrated earlier, interference occurs gradually and is likely to have minor impacts to picture quality. Thus, position adjustments can be made as interference is beginning to minimize its effect.
Additional mitigation paths are discussed briefly below.
8.1. Network Control LTE is an extremely versatile protocol. It can be modified to operate in a number of ways, and many of those modifications can be employed on a cell-by-cell basis. If interference proves problematic in a specific area, the cell base station controlling that area can implement local interference reduction techniques to address the situation. Several interference issues have been successfully addressed in other bands using this set of techniques.
One technique is to utilize the location and density of base stations to minimize interference. In the central part of Chicago, this will happen naturally because large urban areas are increasingly capacity limited. A denser configuration of cells is a core technique for increasing capacity. If concerns about adequate capacity do not already solve the problem installing an additional cell, which might be a micro, pico or femtocell, will lower LTE UE transmit power and resolve the issue.
Perhaps the most common transmission, which is constant although spaced in time and short in duration, is the control signaling between a base station and LTE UE. These communications are typically located at the out edges of a channel. However, they are under software control of the network operator and may be moved away from a frequency area where there is concern about interference.
Another technique that can be employed is to use the most distant resource block first and only use the resource block closest to Channel 51 when absolutely necessary. This technique does not withhold the spectrum from the network but only prioritizes it use.
A variety of other techniques are available to the network operator for minimizing interference to the adjacent band. As T-Mobile noted in a filing to the FCC in April 2015, “[o]perators have gained experience in successfully deploying broadband uplinks adjacent to television stations” and “[s]oftware solutions in the LTE network, such as blanking resource blocks and power controls in user equipment, can be used to prevent harmful interference to broadcast
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operations.”42 The LTE system provides the network operator the tools to modify the network operation to best meet its needs. The network operator can use these tools and apply them, as needed, to any cells where interference proves to be a problem.
8.2. DTV AntennaAnother simple solution to address interference that may occur is to deploy an improved antenna. In a 2009 study for Ofcom, Aegis Engineering43 concluded that 5% of UK households that used antennas for TV reception could benefit from an upgrade to improve reception. While the data from the UK is not directly applicable to the United States, it does illustrate that improvement in the quality of households’ antenna can improve their TV reception and thus decrease the possibility of interference from a UE operating on the 700 MHz A-Band.
To quantify the benefit that new, higher-quality antennas could provide, a test was conducted of multiple antennas sold at major consumer outlets.
42 Ex Parte filing by T-Mobile USA, Inc., GN Docket No. 12-268, ET Docket No. 14-14, at 18 (filed Apr. 24, 2015). 43 Aegis Engineering, Domestic TV Aerial Performance, research for Ofcom, 2106/HAC/R/3.0, December 14, 2009.
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This straight-forward test of DTV reception demonstrated the large improvements in DTV reception that consumers can achieve by purchasing better quality (but still retail grade) antenna.
In addition to improved indoor antenna, consumers who watch DTV over-the-air can substantially improve DTV reception by deploying a rooftop antenna. A rooftop antenna both improves reception and moves the antenna 8-10 meters away from the most likely location of an LTE UE, in the house. In addition, ceiling and roof materials further attenuate the LTE UE signal and reduce its strength at the antenna.
Each of these actions to enhance reception through improved antenna also reduces the possibility of interference. As previously noted, as a DTV signal improves (or its reception improves), it takes a more powerful LTE transmission to cause interference.
8.3. DTV AmplifierThe Aegis Engineering study44 also found that:
29% of UK household aerials have some form of amplification in the system (33% for DTT homes, 19% for analogue only homes). Where amplification is used, it improves both the system gain and the C/N or MER.
Users who experienced interference from 700 MHz A-Band operations could improve their DTV reception and decrease the possibility of future interference by utilizing a DTV amplification device.
8.4. DTV Low-Pass Filter A company named at80045 was established in the UK to address interference problems arising from deployment of LTE in a band adjacent to a UK DTV channel. The UK band plan utilizes a wireless spectrum band adjacent to a DTV station to operate the downlink, with the LTE UE uplink occurring in a more distant frequency. This is the reverse of the U.S. band plan and a more difficult interference scenario to deal with because base station transmissions are adjacent to the DTV channel and operate at power levels that can be on the order of 1,000 times an LTE UE.
One of the mitigation strategies used in the UK to minimize the possibility of adjacent channel interference is to put a filter on the antenna input of the DTV receiver. at800 identifies a number of commercially available filters that have proven effective at minimizing adjacent channel interference. See Table 14.
44 Ibid. 45 https://at800.tv/
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Table 14 - Filters recommended by at800 in the UK
Company Product Code / Model Number
Filtronic UK-PSD006-V3-P UK-PSD008-V5-P
Lynx 14.00551.19.00LM 14.00555.19.00LM
Labgear F4GA Televes 404401Telecam 316259Triax 314080Vision V25-259
8.5. Cell PlacementAs previously discussed in this Report, LTE UE interference to DTV Channel 51 is primarily a concern in fringe coverage areas. A viewer at the fringe of the WPWR-TV viewing area may receive a weak or poor quality signal, perhaps with severe fading.46 In addition, at the fringe of cell site coverage, an LTE UE may also be operating at the upper range of its power capability. Decreasing the distance between a UE and the nearest cell through the construction of additional cell sites is an effective remedy for LTE UE interference because the LTE UE will be closer to the base and operate at lower power.
Operators who experience interference into adjacent DTV channels, particularly because of increased usage in the fringe of an area of coverage, can address the increase in customer usage and decrease the probability of interference by constructing additional cell sites.
8.6. Small CellsThe use of small cells is a major trend in cellular telephony. As networks are increasingly limited by capacity rather than by coverage, operators’ use of more cells increases capacity and improves network performance. As a further advantage, cells that are more closely packed allow LTE UE to operate at lower power thus decreasing the risk of potential interference.
9. Annex - Acceptable Levels of Interference The FCC has found certain levels of interference acceptable. Various levels have been used in different parts of the FCC rules. What unifies them is the finding by the FCC that at some point the value of the services enabled outweighs, and generally far outweighs, the negative impacts of interference caused by the new service.
A significant factor in its determination of acceptable levels of interference is the availability and ease of application of mitigation measures. If any interference that does occur can be dealt with easily, then it is more reasonable to allow a new service.
46 It should be understood that the fringe of the viewing area is not strictly defined geographically. There are other areas where the DTV signal will be weak, such as when multiple walls block the signal or the signal is degraded by local conditions. Hence, in this report the fringe area means the area of marginal WPWR-TV signal reception.
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When the FCC allows a new service even though there is some probability of interference to an incumbent service it is essentially making a public policy value judgment that the societal benefit of the new service outweighs the potential for negative impact.
A variety of interference levels and ways of evaluating interference have been used. Some of those are discussed here.
9.1. The 10 m Criterion - FCC Part 15The FCC has used a 10 m threshold as an acceptable interference threat distance. In establishing the Part 15 rules for unintended emissions, the FCC used the 10 m distance as the dividing line at which the FCC would assume that both devices were under the control of a single household, making a number of mitigation options available. Our testing showed that there were no issues if the user was 10 m or more away from the DTV. As an example in FCC 79-555 the Commission states:
54. We are most interested in protecting an individual who is receiving interference from his neighbor's computer. To a lesser extent, we are concerned about devices in the same household. In a household, the homeowner or apartment dweller can choose which device he wants to operate. For example, if a second TV set in the same house is receiving interference from a computing device in a adjacent room, there are a number of steps he can take to remedy or minimize the problem, or as a last option, he can always choose which is most important to operate—the TV set or the computing device. One of the first and easiest corrective steps he can take is to move the two pieces of equipment further apart. Another step is to reorientate the receiving antenna. Since there is a lobing effect associated with all antennas, by reorientating the antenna he can reduce the interfering signal picked up by the antenna. Reorientation of the equipment is another easy remedy, since radiated emanations from most electronic equipment is directional. These simple corrective steps can help correct such interference problems in most households. On the other hand, these remedies may not work when a second party is receiving the interference.
55. Assuming a separation distance of 10 meters, our analysis (as given in Appendix C)shows that the minimum limit necessary for protection of TV reception from a computing device operated in an adjacent household is essentially the limit that had been proposed in Section 15.13(b)--100 μV/m at 3 meters. The Commission recognizes, of course, that there will be instances when the separation distance is less than 10 meters. In many such cases, we anticipate there will be mitigating circumstances which will counteract the shorter separation distance, such as greater attenuation due to additional walls between the computer and the TV receiver. We also anticipate that, in many cases, the orientation of the TV receiver with respect to the computer will help reduce pickup of the undesired computer signal.47
This basis makes the distance of 10 meters a significant benchmark to be considered for other situations. The underlying logic is that, if the probability is high that both devices will be under the control of the same user, and that easily applied mitigation options are available to the user,then some probability of interference is acceptable. This essentially reasons that it is good public policy to allow consumers to have the benefits of both services because, if there are problems, the consumer has the ability to remedy those problems.
47 First Report and Order in Gen Docket 20780, FCC 79-555, released October 11, 1979, 44 Fed. Reg. 59530 (October 16, 1979), Appendix C.
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9.2. Adjacent Channel DTV InterferenceA third level of interference the Commission has found acceptable is the level allowed between adjacent channel DTV stations.
§73.616 Post-transition DTV station interference protection.
....
(e) An application will not be accepted if it is predicted to cause interference to more than an additional 0.5 percent of the population served by another post-transition DTV station. For this purpose, the population served by the station receiving additional interference does not include portions of the population within the noise-limited service contour of that station that are predicted to receive interference from the post-transition DTV allotment facilities of the applicant or portions of that population receiving masking interference from any other station.
By setting this threshold the FCC demonstrates that it finds interference between two DTV stations acceptable if it impacts less than 0.5% of viewers. For Chicago, with 11 million viewers, this calculates to an acceptable interference population something on the order of 55,000.
An important point when considering this criterion for LTE UE interference is that, becauseDTV stations are constant transmitters, this interference is continuous, whereas LTE interference will be sporadic, only occurring when an LTE UE is operating nearby. If impacting 0.5% of viewers with continuous interference from a constantly transmitting DTV station is acceptablethen the intermittent interference caused by an LTE UE should certainly be acceptable.
10. Annex - LTE Signal Strength and D/U Ratios at ToV Table 15 through Table 18 present the findings of the Intertek study. The measurements were performed conducted. The interference distances shown are calculated based on the signal strength at ToV.
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Table 15 – TOV Levels (LTE UE signal bandwidth 5.0 MHz with 25 Resource Block / DTV Signal at TOS+3 dB)48
Table 16 – TOV Levels (LTE UE signal bandwidth 5.0 MHz with 25 Resource Block / DTV Signal at -68 dBm)49
48 Ibid.., Table 52. 49 Ibid., Table 53.
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Table 17 – TOV Levels (LTE UE signal bandwidth 5.0 MHz with 25 Resource Block / DTV Signal at -53 dBm)50
Table 18 – TOV Levels (LTE UE signal bandwidth 5.0 MHz with 25 Resource Block / DTV Signal at -28 dBm)51
11. Annex - Relative Antenna Position and Orientation The portion of the Intertek report52 dealing with relative antenna location and coverage levels, Sections 9.2, Relative Antenna Position & Orientation, and 9.3, Calculating coverage levels, is reproduced here to document the relative magnitude of this factor.
50 Ibid., Table 54. 51 Ibid., Table 55. 52 Intertek, Evaluation Of The RF Coexistence LTE Operation on 700 MHz A Block (formerly channels 52 / 57) and TV Channel 51 Reception, Report G1002WX445LEX-02, May 24, 2015.
filed as Annex B to the Cricket waiver request:
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11.1.Relative Antenna Position & OrientationBoth DTV and LTE UE antennas have directional patterns with significant variation. The testing performed in this project sought to maximize the coupling between antennas by positioning and aligning the antennas for maximum coupling of LTE energy into the DTV antenna. However, normally the relative position and orientation of the antennas will be arbitrary. The DTV antenna will be placed and presumably oriented to maximize DTV reception. The LTE UE will be used at a location of the user’s choosing and quite possibly be in motion, both moving and changing orientation during a conversation. It must be assumed that the coupling between these antennas will be arbitrary and have an equal probability to be in any possible relative position and orientation.
In this discussion orientation refers to the degree to which the antennas are aligned or misaligned. For any given position the LTE UE can be rotated to be aligned for maximum (worst case) coupling to the indoor DTV receiving antenna for a given position and separation distance, or can be aligned to be cross-polarized and have significantly reduced coupling. For antennas of the type used for indoor reception of a DTV signal and LTE UE devices the minimum impact of orientation is 0 dB of isolation, meaning aligned for best possible reception at that position and there is no loss due to misalignment. Theoretically, if the antennas are cross polarized there will be no coupling and the misalignment will be large. However, in actuality all antennas have some physical aspect in the orthogonal direction, and while a null may be deep, itis never perfect. Figure 33 shows a typical antenna pattern for a retail DTV antenna and for an LTE UE. As can be seen in Figure 33, there is considerable variation depending on the location in the antenna pattern. In the calculations provided later in this section a mean alignment coupling loss of 3.9 dB will be calculated.
Petition of Cricket License Company, LLC (Cricket) for a Waiver of DTV Protection Criteria, Attachment, Universal Licensing System (ULS) File No. 0006046277 (filed Dec. 6, 2013) (Cricket Waiver Request).
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DTV Receiving Antenna LTE UE Transmitting Antenna
Antenna Pattern in the Horizontal Plane
Antenna Pattern for Elevation
Figure 33– Variation in relative placement can influence the coupling efficiency between an LTE UE and DTV antenna
A calculation was performed of the coverage levels for a DTV and UE antenna used in a significant number of the measurements made. While worst case coupling between antennas is clearly possible, additional coupling loss will be present most of the time.
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11.2.Calculating coverage levelsThe relative position of two antennas (rabbit ear and LTE UE) will add loss to the LTE UE signal received by DTV receivers. The higher the loss the lower the interference the DTV receiver will be experienced. In other words, LTE UEs can operate closer to the DTV receiver before it will interfere with DTV. There are several steps required to calculate the coverage level. Standard statistical 98th PERCENTILE was utilized to calculate the coverage level. At the end, a ratio is calculated from the coverage level calculation. This ratio will be a multiplier to the worst case to acquire the new TOV distance. Since 98th PERCENTILE is used, that means the TOV distance will represent 98% of the times TOV distance will be lower and only 2% of the times the TOV distance will be great. But the TOV distance will not exceed the worst case TOV distance. Here are steps to calculate the additional loss in dB:
1. Create loss matrix from TRP testing (rabbit ear and LTE UE)
a. 275x275 loss matrix
2. Calculate the Minimum Value (X) of these 275x275 loss matrix
3. Calculate the 98 PERCENTILE Value (Y) for the loss matrix
a. 98 PERCENTILE value present 98% of the loss will be below and 2% of the loss will be above
4. Calculate Delta Value by (Z) by subtract the 98 PERCENTILE value from the Minimum Value (Z = X-Y)
5. Include the polarization mismatch of 2.06 dB (W = Z - 2.06dB)
6. Calculated the delta distance:
where d1 = worst case distanced2 = new distance
7. Calculate the multiplier ratio of change:
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The multiplier ratio based on all 12 sets of antenna is listed in Table 19.Table 19 – Coverage levels shown in terms of the
fraction of the maximum for the 12 combinations tested
Antenna Combination Percentile97.75%
BANDRICH C525 vs GE Enhance 0.45
BANDRICH C525 vs Generic 0.53BANDRICH C525 vs RCA Flat 0.54BANDRICH C525 vs RCA1 0.53BANDRICH C525 vs RCA2 0.58BANDRICH C525 vs Zenith 0.49SAMSUNG R930 vs GE Enhance 0.45
SAMSUNG R930 vs Generic 0.54SAMSUNG R930 vs RCA Flat 0.54SAMSUNG R930 vs RCA1 0.54SAMSUNG R930 vs RCA2 0.59SAMSUNG R930 vs Zenith 0.49
Average 0.52Max 0.49Min 0.45
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Figure 34 – Plot of DTV receiving antennas with coverage levels shown
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12. Annex - Development of Spectrum Management Spectrum management is following a course of development comparable to that of electromagnetic compatibility (EMC). As it was for EMC, the movement is from isolation to coexistence. Spectrum management has been leaving its early stage of development, in which transmit power, frequency, and geographic separation were the only mechanisms for coordinating the use of spectrum. Increasingly, new variables allow spectrum efficiency never before possible.
In the early days of EMC, both emissions and immunity problems were almost exclusively treated by shielding and grounding. Metal boxes were put around circuits to prevent them from causing interference or from falling victim to interference. Personal computers (PC) with heavy metal cases, enhanced with copper-beryllium gaskets, were once the norm. Such remedies were too expensive and soon were widely replaced by metal coatings, conductive plastics and other reduced cost shields. However, today devices typically use shielding in far more limited ways, having developed a variety of circuit and component improvements that allow better control of emissions and immunity than shielding was able to provide.
In a parallel, development spectrum management is transitioning from a time when the only ways to coordinate spectrum were by either:
1. Reducing transmit power,
2. Increasing the geographic separation, or
3. Increasing frequency separation.
Today, a variety of mechanisms allow dramatic improvements in spectrum utilization. For example, cordless phones operating with no frequency separation from cellular phones and base stations have operated successfully for many years. In addition, when the FCC established the Personal Communications Services (PCS) band, there was a need to separate the uplink from the downlink of the cellular system. When the service was first established, the separation needed was 20 MHz. Rather than allow that spectrum to go unused, the FCC created the Unlicensed Personal Communications Services (UPCS) band. The UPCS band was located at 1910-1930MHz, separating the PCS uplink, below it in frequency, from the downlink, above it in frequency. Later, with technological improvements the UPCS band was reduced to 10 MHz, to its current 1920-1930 MHz. The cordless phone industry moved in mass into the UPCS band, using the Digital Enhanced Cordless Telecommunication (DECT) protocol. Although DECT is not required by the FCC rules, currently all UPCS devices also use the DECT protocol.
What is of great interest is that there are multiple possible interference scenarios. PCS User Equipment (UE) potentially could interfere with DECT UE, or DECT UE could interfere with PCS UE. On the PCS downlink side DECT UE has the potential for interfering with signal reception by nearby PCS UE. However, no interference problems exist. An important question is how do two different services operate with no frequency separation on an interference free basis?The PCS band is dominated by two RF protocols, Code Division Multiple Access (CDMA) andGlobal System for Mobile Communication (GSM). CDMA spreads its signal and retrieves its signal in the presence of interference by encoding the signal over a wide bandwidth. It is therefore understandable that CDMA will be somewhat tolerant of adjacent band energy, so long
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as enough of its signal is unencumbered to allow successful recovery of the intended transmission.
However, GSM, like DECT, is a Time Division Multiple Access (TDMA) service. Why are there not problems with GSM and DECT interference? In the case of a GSM-based PCS device each 60 mS period is divided into 13 frames of 8 time slots. Control information and data is interleaved and spread over the 13 frames to support a very robust error tolerance. Each frame occupies a 4.6 mS period or frame cycle time. Each timeslot is assigned 1/8 of the frame, or a 0.58 mS period.
DECT devices use 1 of 24 time slots divided over a 10 mS period. Each timeslot occupies a 0.42 mS period.
Figure 35 shows two 60 mS cycles of the worst case time alignment between a GSM and DECT transmission. Both begin transmission at exactly the same time. It is assumed that all overlapping bits are lost. As can be seen, most of the first timeslot in the first GSM frame is lost. However, there are no other collisions until a new cycle begins, at the 60 mS boundary. This chart shows that 6% data loss is the worst case overlap of transmissions. Hence, at the maximum possible collision rate between GSM and DECT, at most 6% of the GSM data can be lost. This is well within the error correction ability of the system, but even that rate can only occur if the UPCS energy is sufficient to completely destroy a PCS transmission. Hence, a combination of offset relative timing with error correction allows adjacent band operation with no frequency separation.
In the case of ATSC and LTE similar but different mechanisms produce similar results. ATSC is designed to operate over an extraordinary range of signal conditions. Multiple error correction and signal recovery mechanisms allow it to successfully provide service over a very impressive range of environments. Further, each of the now six generations of DTV chips has improved the sophistication and operating capability of ATSC receivers. Improvements in both ATSC tuners and signal recovery software have delivered impressive improvements in reception reliability.
The LTE system utilizes three mechanisms, which together maximize spectrum efficiency. LTE UE are dynamically allocated transmission time and bandwidth to service (but not over-supply)their needs. Transmission power is controlled by an aggressive system of automatic power control. In addition the base equipment by each cell gates the transmission from each LTE UE in order to facilitate service to all LTE UE seeking to use the cell. Together these three mechanisms work together to fundamentally change the impact of an LTE UE transmission on an ATSC receiver.
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Figure 35 - Analysis of Potential for Transmission Conflict between GSM and DECT
LTE has a very flexible and spectrally efficient signaling methodology. The fundamental unit in the LTE signal is a resource block (RB). Each RB is a time and frequency unit that can be loaded with data. RBs are dynamically allocated by the cellular base, which balances the need to service all current users of a cell with the transmission requests of each LTE UE. LTE UE with larger data loads to transmit will be given more RB's, if they are available. An LTE signal can expand, through the use of additional RB's in both signal bandwidth and transmission time, to allow very impressive data rates to be achieved. Conversely, small data transmission requirements are only given enough RB's to service their need successfully.
What was discovered during the recent field measurements in the Chicago area is that the combination of flexible bandwidth, transmit power control and traffic scheduling fundamentally changes how LTE UE can interfere with ATSC. Previous laboratory testing, including the Intertek study, used a fully loaded, continuous LTE signal and found a dramatic, all-or-nothing“cliff effect.” The ATSC signal was received without visible degradation until the error correction and signal recovery mechanisms of the ATSC receiver were overwhelmed, at which point all service was lost. Within the space of 1 dB or even 0.5 dB of LTE signal amplitude, the DTV receiver went from a perfect picture, without visible flaws, to no picture at all. This is notthe case with an operating LTE network.
LTE transmit power control continuously adjusts the LTE UE power, keeping it as low as possible while maintaining communication integrity. When viewed with instrumentation that allows frame-by-frame analysis, the constantly changing transmit power can clearly be seen. When viewing a DTV receiver the importance of this is quickly understood. As the threshold of interference is exceeded, at first only a few transmission packets exceed the threshold. So at first there are minor impairments, and a few pixels are occasionally lost. As the LTE UE is brought closer to the DTV receiver, more of its transmission packets will exceed the threshold, resulting in a growing number of impairments. The result is that LTE UE to ATSC interference covers a
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range, starting with very minor, almost unnoticeable, loss of a few pixels and building with reduced LTE UE to DTV antenna distance, and so LTE UE signal strength, until the interference is very noticeable and after that highly disruptive.
A different mechanism is created by the LTE traffic scheduler and use of dynamic resource assignment. The LTE UE does not transmit continuously, even when transmitting very high speed data. The transmission is intermittent. For most user actions, which only need to transmit a small or moderate amount of data the transmission bursts are widely spaced. This results in quiet intervals in the transmission during which the ATSC signal receives unimpaired reception. This discontinuous LTE transmission has positive and negative impacts. Negatively, the ATSC adaptive equalization circuitry has a harder time setting the correct level for reception. However, positively and more important for the adjacent band situation, the DTV receiver has periods of reception with no LTE transmission present, allowing its error correction algorithms to restorelost data. Hence, for low and some moderate data rate transmission from the LTE UE the ATSC error correction can recover the data, and there is no impact visible to the TV viewer.
13. Annex - Measuring Improvements As new techniques are used to improve spectrum utilization efficiency new instrumentation is required to measure interference performance. Under the old approach to spectrum management,a simple energy-on-energy analysis was sufficient. If the peak signal strength of an adjacent band transmission exceeded the adjacent band, rejection of device interference occurred. However, with newer techniques, an energy-on-energy analysis is not enough. The instrumentation must follow the signal transmission and recovery techniques if an accurate understanding is to be gained.
An accurate understanding of the situation requires not only a much finer view of what is happening in the physical domain, but also a grasp of how what is happening in the RF impacts, or fails to impact the ability at the MAC layer to recover the intended signal.
If spectrum utilization is to be realized, it is essential that old, energy-on-energy measurements be replaced by measurements that allow a full understanding of the actual interference mechanism(s). Many of the most important advances in spectrum efficiency are not taking place at the physical layer. If only the physical layer is measured, the benefits of these techniques willnot be recognized with the result that spectrum will wastefully go unused, not because the systems using the spectrum actually interfere with each other but because outdated instrumentation results in an inaccurate understanding of the true situation.
14. Annex - Field Measurements Between January and April 2015, field measurements were made in the WPWR-TV viewing area. These measurements were made to address several important issues. The primary purpose was to deepen the understanding of these issues and advance the understanding of the potential impact of an adjacent band LTE network on adjacent band DTV reception.
The first issue was to determine how well the laboratory work compared when dealing with the actual WPWR-TV transmission and an operating LTE network. Other variables are involved in actual field situations. An objective was to understand the impact of these variables and perhaps most important to determine if there were any important variables that were not considered in the laboratory measurements.
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A second objective was to use some newer RF record-and-playback technology to inject LTE signals in areas where they do not currently exist and to evaluate the impact. This was accomplished by recording as IQ files LTE transmissions on an operating network. These recordings were then injected, using a signal combiner, into the coax from an antenna receiving WPWR-TV. The combined signal was then presented to a TV broadcast receiver and its response observed. Using this method, the impact of a deployed LTE network was recreated in areas of the WPWR-TV viewing area where no LTE network operating on the lower 700 MHz A block currently exists.
A third set of objectives was to study a variety of factors and determine the range of variability. A set of consumer grade DTV receiver antennas was evaluated. A variety of LTE transmissions during various user activities were recorded and analyzed. In various locations different DTV setups were used both to understand their sensitivity to LTE interference but also to evaluate how well various mitigation measures could be used to increase the immunity to adjacent band transmissions.
A fourth objective was to both understand the actual field situation but also to make a number of IQ spectrum records so that further experimentation could be done in the laboratory. Using actual IQ recordings of the ATSC and LTE transmission allows for their recreation. A wide variety of combinations can be created by modifying their frequency or amplitude, or by simulating various channel impairments. In addition, mitigation strategy can be explored in an efficient manner to identify additional options for improving the immunity to adjacent band interference.
The field measurements made were successful in accomplishing all of these objectives. The laboratory testing of Laser, the FCC's engineers, and others was confirmed in the field. D/U ratios in the -35 dB to -45 dB range were observed. The “U-shaped” response with decreasing immunity at both the strong and weak signal extremes was also seen. Additionally, the importance of signal quality was clear. In particular, ATSC signals impaired by deep fades were also more sensitive to interference than those without such impairments. Importantly, the ability to address these situations was confirmed. Small movements of the antenna were often sufficient to remedy a deep fade situation. In weak signal areas, the use of an amplified antenna was typically effective. However, in very strong signal areas an amplified antenna occasionally had poorer immunity to LTE, and removing the unneeded amplifier improved the immunity.
The conclusion was that the variables influencing interference from LTE UE in an adjacent band to DTV transmission are understood. The degree of interference is both understood and minimal. Where interference does occur, the mitigations identified are effective.
14.1.Measurement SystemThe opportunity created by King Street Wireless operating on the A Block inside the WPWR-TV viewing area created the challenge of how best to utilize this fact to advance the understanding of adjacent band LTE UE interference to WPWR-TV. The measurement system(s) needed to be able to do the following:
Measure and record for further analysis the interaction of LTE UE on the King Street Wireless network with WPWR-TV reception.
Move the live LTE UE and DTV signals to areas where they do not exist.
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o It was useful to move the LTE UE transmission to parts of the WPWR-TV viewing area where King Street Wireless does not operate, particularly the more central part of the viewing area, so that its impact there could be evaluated.
o It was also desired that both transmissions be recorded in a way that would allow further analysis and experimentation in the laboratory, where neither King Street Wireless, nor WPWR-TV transmissions, were available.
Accurately measure the extremely dynamic LTE signal and its influence on the ATSC reception in the physical layer. An accurate measurement requires instruments that are equally dynamic and able to record signals in frequency, amplitude and time with resolution appropriate to the transmissions.
Allow the transmissions to be not only accurately recreated in the laboratory but to be modified in various ways so that their interaction could be more fully understood. For example it was useful to move the LTE signal in frequency closer to or farther from the ATSC signal and observe the variation in response.
These objectives were met by using software-defined instrumentation with real-time capability for recording what was really happening, replaying the spectrum, to allow experimentation and analysis of it. The use of newer test technology, software-defined, real-time instrumentation, with its record-and-playback capability and software implementation of the decoding process allowed a much more detailed and nuanced understanding of the problem than has been the case in the past.
Software defined instrumentation brings new capabilities. When compared to traditional instruments on the basis of these new capabilities software defined instruments provide generational improvement and in many cases make possible measurements that were not possible in the past. The task facing the test engineer is to understand the instruments available and use the best instrument for the task. For the current project, measurements were repeatedly checked using both newer software defined instruments and traditional instruments to ensure measurement accuracy. In the current measurements a Sencore SLM1476 DTV meter was used extensively along with the USRP's for just this reason. Replayed files were routinely measured for frequency and amplitude fidelity using traditional spectrum analyzers.
The initial RF survey was performed using Averna RF Studio software and a NI USRP™ (Universal Software Radio Peripheral), specifically the NI USRP-2930. This system is equipped with a GPS receiver, allowing location to be recorded with the measurements. During drive testing both the WPWR-TV signal and current location were recorded.
The antennas used in the initial RF survey were calibrated at an accredited antenna calibration lab.
Later tests used an NI USRP-2920 or Ettus Research B210 USRP controlled by software in GNURadio or test loops written in Python. Ettus Research is now a National Instrumentscompany and produces the NI USRP, which is a version of its own USRP. The USRP family of products is a leading example of how software radio is being utilized to allow real-time signal analysis, spectrum record-and-playback and other advanced spectrum measurements.
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Figure 36 - Simplified Diagram of an NI USRP-2920
Software radio, or as it is commonly known software defined radio (SDR), is an approach to solving wireless communications problems by moving more of the processing from traditional hardware components into software. Software defined instrumentation utilizes the same techniques for measurement and analysis. The use of software processing means that an SDR gets the full benefits of a computing platform, including flexibility and reuse through software engineering principles. It has also allowed us in the field to evolve new ways of handling signals through the full use of logic and numerical processing for our advanced mathematical work.
Measurement verification by other laboratories is greatly assisted through implementation of SDR on widely available hardware and computing platforms. These measurements can also be compared to those made by others in the same or other locations as further confirmation of the findings.
SDR has also significantly reduced the barrier to entry for analyzing spectrum, and for developing sophisticated radio systems and interference mitigation techniques. For the current project it allows an understanding of how the LTE UE signal is interacting with the ATSC decoding process. With that understanding, options for minimizing the interference can be explored and coexistence solutions developed.
The most popular SDR tool is GNU Radio as a software processing framework along with the Ettus Research Universal Software Radio Peripherals (USRP). GNU Radio is an open source project. The software may be downloaded without cost and used by any engineer wishing to use it. The open source aspect makes it particularly helpful when multiple laboratories want to collaborate on the same problem. Being open source also allows detailed scrutiny of the measurement process to insure accuracy in the results.
The use of SDR is widespread and covers many areas of radio signal processing as well as other forms of signal processing such as optical and acoustic. In this report, we focus on SDR as a new tool for enabling more advanced signal collection and analysis techniques. In the case of GNU Radio, one of its strengths is the ability to use it both with hardware for live data processing as well with files for offline development and analysis.
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For signal collection purposes and the ability to do interference analysis, this combination of live field studies and easy offline analysis and back again are powerful. In this instance, we are able to collect ATSC and LTE uplink signals individually and together, post-process to manage the signal levels and filtering as we want to, and the rebroadcast within a controlled environment to study the different effects and situations.
The combination of GNU Radio and a USRP provide a dynamic and powerful collection system. The data collection process with this system setup is very similar to other data acquisition systems. The USRP is a radio front end that connects an antenna to a transceiver. Here we consider the receiver side. The antenna connects to the receiver through either the RX1 or RX2 ports as shown in the Figure 36. The signal goes through typical receiver stages of amplification,heterodyning, and filtering and then is sampled by two analog to digital converters (ADCs). The ADC samples are run by the same clock, and then the samples from one ADC are rotated by ninety degrees in the digital down conversion (DDC) stage. The result is a single sample that contains an in-phase and a quadrature component from the two ADCs. We represent these values as complex numbers as the in-phase (call it the real part) is ninety degrees offset in phase from the quadrature (or imaginary part).
A secondary part of the DDC is to down-sample and filter the signal. In the case of a USRP N210, the original signal is sampled by the two ADCs at 100 megasamples per second (Msps). However, that amount of data does not fit across the bandwidth of a GigE bus. At most, a GigE bus can handle about 30 Msps of a complex sample with 16 bit resolution for the real and imaginary parts. The DDC performs integer down-sampling, so the smallest amount of down-sampling possible is 4 to produce a new sample rate of 25 Msps. Because we have two components per sample, the complex valued 25 Msps signal satisfies a Nyquist rate to represent the information in 25 MHz of spectrum. Because the system uses 14 bit ADCs, the receiver can also handle up to about 88 dB of spurious free dynamic range (SFDR). Because the signalgathered fits within 25 MHz and 88 dB of dynamic range, this data collection system represents the entire signal with some amount of added noise within the receiver.
During a collection campaign, we typically want to first run a spectrum monitoring application to confirm that we are seeing the signal of interest at the intended center frequency and that the receiver settings are correct. In particular, we need to make sure that the bandwidth of the receiver is large enough to properly capture the entire signal of interest. Another important aspect is to set the receiver gain correctly to maximize the signal power without overloading the receiver.
With the system settings established, it is easy to create a collection script that saves the signal to file. This is often done by using the "uhd_rx_cfile" script that is distributed with GNU Radio as a command-line tool. Because of the SDR technology, the monitoring and collection stages are handled by the same hardware and software framework setup and by simply switching between applications.
The file captured in this process is binary samples of the sampled spectrum. The file then represents the exact signal captured at the full bandwidth set during the collection, and so we have full control over the signal as it is received to do in-depth analysis, signal processing, and even playback of the files for future tests. These files, stored as IQ files, made up of the complex number that define the measured spectrum, can then be played back, either exactly as originally recorded or with adjustments in frequency, amplitude or channel characteristics. Figure 37shows one example of a replay flowgraph.
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Because the collection process captures the full signal of interest, we can replay these samples at any time to recreate the system collected. The GNU Radio framework has the ability to source data from these files and play the samples through another SDR application. We can make example scripts to measure properties of the signal such as the power of the ATSC signal and the power and duty cycle of the LTE UE. We can also play the signals through different processing stages, use software decoders on the ATSC signals, and even retransmit the signals through a USRP connected via a cable to the television input line to continue to study effects of our manipulations.
The maximum output power of a USRP N210 with the WBX daughterboard as used in these experiments is 100 mW. We then use simple GNU Radio applications to adjust the power of the transmitted signal, both by scaling the amplitude of the digital signal and then by adjusting the gain of the analog transmission stages of the USRP. The digital scaling allows us to adjust the signal levels such that the total signal going into the USRP is within the linear range of the transmit chain or risk clipping in the DAC and driving the transmit amplifiers into compression.
An example of this use of GNU Radio to retransmit different capture files is shown in Figure 37.The top row of blocks are the default parameters to be used in replaying the captured file. The bottom row are controls that are made available and can be adjusted while the captured signal is being replayed. In the middle program blocks show the flow from left to right. The file is accessed from the computer's disk. Then the ATSC and LTE signals are separated and filtered to allow them to be treated separately. This separation of the signals allows either to be individually raised or lowered in amplitude or moved in frequency. Channel impairments such as fading or noise can also be introduced to evaluate their impact. Channel impairments are not shows in this flowgraph but could be added in software. After adjustment, the signals are recombined and delivered to the driver for the USRP for generation.
The blocks in the center with the blue ports make up the actual GNU Radio signal processing path. The file is read in with the File Source. It is then split into two paths. The upper path filters the ATSC part of the signal while the lower path filters the LTE UE part of the signal. The filtered signals are then put into the Add block to sum them back together, and then the entire signal is digitally scaled by the Multiple Const block, which is how we prevent transmitter overloading and non-linearities from occurring. The digital signal is then pushed into the USRP Sink block where it is passed over the GigE connection to the hardware device itself and transmitted.
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Figu
re 3
7 - E
xam
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dio
Flow
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layb
ack
92
This application has many knobs that we can turn to alter the behavior. Each knob is represented by one of the QT GUI Range blocks along the bottom. We can adjust the transmitter frequency and the analog gain. The gain0 and gain1 parameters allow us to adjust the individual scaling of the two channels in the filters. We do this by applying these settings to the filter coefficients, which means we can easily change the relative power levels of either the ATSC or LTE signal relative to the other. Turning these gains to zero turns the signal in that channel off entirely, which means we can easily observe the ATSC signal reception with no interference at all.
The “total_gain” parameter is the digital adjustment for the overall signal level. If either or both of the signals have their gains increased dramatically, the sum of that signal may now be over the linear region of the transmit chain, so we can use this to scale down the signal. Finally, the filters used to isolate and adjust the gains of each channel also allow us to move the signal around in frequency. This stage is done using a complex multiply with a sine wave within those filter blocks. We then have the ability to move the signals individually around in frequency. For example, we can slide the LTE signal closer or farther away from the DTV channel to adjust the proximity of the adjacent channel.
We can perform many more signal manipulations with the captured signal, such as add more noise or add shaped noise to approximate multipath. The example given here explains the scenario used to explore the adjacent channel interference caused by LTE UE signals.
Captured files can also be analyzed in programs like MatLab, LabVIEW, or open source alternatives, such as Octave and Scilab. We produced the plots and graphs in Section 14.5 using Octave to analyze the USRP captures of various LTE transmissions. These tools bring the ability to extend the analysis of the measurements and present the findings in a wider variety of presentations.
Using software defined instrumentation not only makes field measurements easier to perform, it allows them to be done in a way that leads to a better understanding of the interference problem. An effective bridge can be built from the overly conservative interference estimates of the past to what is actually occurring in the field. Using the methods and instruments available in the past,much greater interference distances would be expected than those reported here and in other recent research studies. The foundational difference is that there is something different to be measured. Technology has improved and manifested itself in greater adjacent band immunity. Given that there is an improved situation to be measured, we can now compare the differences in measurement methodology and understand why different conclusions might be possible among those studying the issue.
In addition to having more detailed measurements, more nuanced solutions can be crafted. It is no longer necessary to make one-size-fits-none rules. Spectrum can be managed to require interference mitigation where there is a significant probability of interference. The cells in a strong signal area can be operated differently than those in weak signal areas. The frequency placement, power management and traffic control can all be adjusted to reduce adjacent channel impact. Those measures might only be needed in the outlying areas but they are available and effective for use in those areas. A network operator can be made responsible to be a good spectrum neighbor and has the tools to fulfill that obligation.
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14.2.Initial Field SurveyAn initial survey was performed on January 6-9, 2015, to measure the WPWR-TV signal strength throughout its viewing area. The purpose of these measurements was to provide initial signal strength measurements in preparation for the field testing performed in March and April 2015. This information then supported planning for the upcoming field tests and also provided acontext to help understand those results. With the signal strength data, it is possible to judge how representative measurements at specific locations are. One objective was to conduct testing in locations that are representative of a portion of the WPWR-TV viewing area to confirm in the field what would be anticipated in other locations with similar signal conditions.
Initial measurements were made in the downtown Chicago area, Figure 38. These measurements gave insight into the strong signal area, near the WPWR-TV transmission tower (on top of the Willis Tower in downtown Chicago). This data helped quantify the strongest WPWR-TVsignals and confirmed the expected slight shadowing in the downtown area. The WPWR-TVmain beam is slightly tilted downward to increase its penetration. The result is that the strongest signals are a short distance from the tower, rather than immediately around the broadcast antenna.
The testing continued to the northwest, as far as Rockford, IL, Figure 41. This data gave a radial extending from the central Chicago area to the edge and slightly beyond the WPWR-TV viewing area.
The survey then explored the outer border of the viewing area, going from the edge of the viewing area west of Chicago north into southern Wisconsin. Figure 42 shows the drive routes followed in relation to WPWR-TV, its service contour and protection distance, which is 8 km beyond the service contour. Also shown in Figure 42 is the calculated Longley-Rice WPWR-TVsignal strength.53
53 The Longley-Rice calculated signal strength overlay for Google Earth was obtained from tvfool.com, at:
https://www.tvfool.com/index.php?option=com_content&task=view&id=15&Itemid=41
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Figure 38 - Measurement route in central Chicago area
95
Figure 39 - Survey route west of Chicago and Rockford, IL
96
Figure 40 - January 2-15 drive testing routes shown with WPWR service and protection contours and Longley-Rice calculated signal strength
The measurement system used had a dynamic range of ~50 dB and measured differences in signal strength over that range.
The maximum signal strength measured was -9.4 dBm, which compares well with a -13.5 dBmLongley-Rice calculated signal strength for the same location.
The measurements followed the expected reduction with distance but were generally somewhat higher than Longley-Rice predicts, particularly in the fringe areas.
Over the course of the survey, as expected, the WPWR-TV signal fell below the threshold of sensitivity, about -86 dBm, in some locations near the service and protection contours and sometimes beyond the predicted service contour. These measurements again compared favorably with Longley-Rice but were frequently noticeably higher.
Over the middle portion of the service area the signal strength was generally in the -50 dBm to -60 dBm range.
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14.3.Assessment of Central Viewing AreaDuring the week of April 13, 2015 testing was performed at 20 locations in the Chicago area, Figure 41.
Figure 41 - April 2015 test locations
A recorded LTE UE transmission was replayed through a USRP (Universal Software Radio Peripheral) and combined with the received broadcast Channel 51 signal. The USRP has 30 dB of software adjustable gain, which can be adjusted in 0.5 dB increments. In addition, an 11 dB adjustable attenuator, with a 1 dB step size, was placed on the output of the USRP. The LTE signal was initially played with a 10 dB gain in the USRP and the full 11 dB of attenuation applied. The USRP gain was increased until ToV was reached. If ToV was not reached at the full 30 dB of gain in the USRP, the external attenuation was increased until ToV was reached.
In some cases where the Channel 51 signal was very strong an attenuator was placed on the output of the antenna to reduce the signal to more moderate levels. This gave additional insight into how additional architectural loss might impact the ToV threshold. This method also gave some insight as to whether strong signal effects were starting to become significant.
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Figure 42 - Test setup used for LTE injection
The Desired-to-Undesired (D/U) ratios measured in the field were found to be equivalent to those measured in laboratory testing. In Table 20 the signal strength and D/U ratios measured in the laboratory are shown for the DTV receiver used. Table 21 presents the D/U ratios at the locations measured.
99
Tabl
e 20
- De
sire
d-to
-Und
esire
d (D
/U) R
atio
s fro
m L
abor
ator
y Te
stin
g
Insi
gnia
NS-
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/ 72
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z / H
DTV
)Th
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ld o
f Sen
sitiv
ity (T
oS):
-81.
3LT
E Si
gnal
Str
engt
h at
Thr
esho
ld o
f Vis
abili
tyD
esire
d-to
-Und
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d (D
/U) R
atio
LTE
Sign
al B
andw
idth
(MH
z)&
Res
ourc
e B
lock
s U
sed
-78.
3 (T
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3)-6
8-5
3-2
8-7
8.3
(TO
S+3)
-68
-53
-28
1.4
MH
z 1
RB
-47.
4 dB
m-1
6.5
dBm
-8.7
dB
m8.
0 dB
m-3
0.9
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1.5
dB-4
4.3
dBTo
V N
R
1.4
MH
z 6
RB
-46.
7 dB
m-1
6.3
dBm
-2.6
dB
m8.
0 dB
m-3
1.6
dB-5
1.7
dB-5
0.4
dBTo
V N
R
3.0
MH
z 1
RB
-48.
3 dB
m-1
8.4
dBm
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dB
m8.
0 dB
m-3
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9.6
dB-4
8.0
dBTo
V N
R
3.0
MH
z 15
RB
-46.
0 dB
m-1
8.5
dBm
-6.0
dB
m8.
0 dB
m-3
2.3
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9.5
dB-4
7.0
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V N
R
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5.5
dB-4
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R
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RB
-47.
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m1.
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1.1
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0.1
dB-4
1.7
dB-2
9.5
dB
100
Table 21 - Desired-to-Undesired (D/U) Ratios from Field Testing at 20 locations
Location LTE Signal TV Signal D/U# Power
(dBm)Data Rate
MBsPower(dBm)
Noise Margin(dB)
MER(dB)
(dB)
1 -35.4 3.0 -65.4 -2.0 19.1 -30.02 -24.1 3.0 -63.4 3.0 24.6 -39.32 -20.4 3.0 -57.7 -37.32 -16.3 3.0 -49.0 -32.73 -28.4 3.0 -68.1 3.0 24.6 -39.74 -32.4 3.0 -63.1 2.0 24.1 -30.74 -23.5 3.0 -67.3 2.0 24.4 -43.85 -28.7 3.0 -69.1 1.0 23.2 -40.45 -12.8 3.0 -45.6 5.0 26.9 -32.85 -20.2 3.0 -62.6 4.0 26.1 -42.45 -25.2 3.0 -61.4 1.0 22.9 -36.26 -24.4 3.0 -62.3 -8.0 13.7 -37.97 -22.4 3.0 -69.1 2.0 23.3 -46.78 -29.2 3.0 -64.6 2.0 23.6 -35.49 -32.6 3.0 -69.0 2.0 19.5 -36.4
12 -25.5 3.0 -66.2 2.0 23.9 -40.713 -26.1 3.0 -73.6 0.0 21.3 -47.514 -24.6 3.0 -60.6 0.0 19.9 -36.015 -19.5 3.0 -54.7 5.0 27.0 -35.215 -21.6 3.0 -61.5 4.0 25.6 -39.916 -25.6 3.0 -70.1 -2.0 18.6 -44.516 -24.0 3.0 -63.6 2.0 24.7 -39.617 -19.1 3.0 -57.7 4.0 25.9 -38.618 -37.0 3.0 -73.2 0.0 21.0 -36.219 -81.3 No Reception20 -44.3 3.0 -76.6 -3.0 17.4 -32.3
14.4.Assessment of Border Viewing AreaKing Street Wireless has a waiver and operates some cells on the northern border of the WPWR viewing area on the 700 MHz A block, as shown in Figure 45. King Street Wireless customers are operating on the 700 MHz A block when connected to these cells. They then have the potential for interfering with reception of WPWR. On its website, King Street Wireless notifies customers who have interference issues that there is a toll free number they can call. Laser understands that, to date, there have been few, if any, reported cases of interference.
While the results of this natural experiment are very important because they tend to confirm previous laboratory testing and analysis, we also performed a separate engineering study in theChicago area. In March of 2015, a series of measurements was made in the area to document performance in a low signal area, i.e., on the fringe of the WPWR-TV viewing area.
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Figure 43 – King Street Wireless cells operating on the 700 MHz A block
The March 2015 testing focused on an area near Sturtevant, WI, with a significant amount of testing performed at a local motel just off IH-94, as shown in Figure 46. There were three cell sites in the area that were primarily used for testing. One cell tower was just beyond the WPWR-TV service contour but within the +8 km protection contour. The other two cell towers were within the WPWR-TV service contour.
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Figure 44 - Test area for focused testing in March 2015
The test was performed using an LTE UE operating on the King Street Wireless network and a DTV receiver connected to an indoor antenna, as shown in Figure 47.
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Figure 45 - Test setup for testing on King Street Wireless network
This field testing was performed in Southern Wisconsin at the edge of the WPWR-TV viewing area. This area is believed to be at most risk for interference because it is on the edge of the WPWR-TV viewing area but in addition suffers significant signal impairment to the WPWR-TV signal. In this area there are the typical issues of fading and noise, common in outlying areas. However, the area is approximately equidistant from Chicago and Milwaukee. In addition, Madison, WI is only a little further and its channel 50 station is strong enough to put adjacent band pressure on the WPWR-TV signal from the low frequency side of that channel.
The field data is remarkably consistent with the laboratory measurements. This conclusion is strengthened if the signal impairments are taken into account, which are well understood and documented in the Intertek report as degrading immunity to adjacent band transmissions.
The estimates shown from the Intertek study are provided for 3 dB above each DTV receiver's threshold of sensitivity (ToS + 3 dB) and -68 dBm.54 The WPWR-TV signal in this area was in this range. -68 dBm converts to -39 dBu, which is slightly higher than the 42.1 dBu that defines the contour and is therefore a level expected inside but near the edge of the viewing area. The ToS + 3 dB would be a level expected either outside the viewing area or at an indoor location with significant building loss.
The field measurements were made with a variety of antennas. Sometimes amplifiers were used and other times they were not. This was done to survey the range of configurations a user might
54 The weak (-68 dBm), moderate (-53 dBm) and strong (-28 dBm) DTV signal strengths are defined in ATSC A/74-2010 Table 5.2 and have been used in both the FCC’s work in this area and in the Intertek study.
104
have. The minimum and maximum values are the results over the range of antennas and amplifiers tested.
The LTE handsets were operating on the King Street Wireless network during these tests.
Converter boxes are commonly available to equip analog TVs to be equipped to receive DTV signals. The models used were purchased at major consumer retail store and are typical of what is currently on the market.
The results of this testing is compared to the Intertek testing in Table 22. The signal strength was -61 dBm with a noise margin of 5 dB and modulation error ratio (MER) of 27.2 dB. The results are slightly larger than but consistent with the laboratory estimates for this range of signal strength.
Three converter boxes were also tested and those results are also shown in Table 22. However, these units were not tested in the laboratory and so that comparison is not available.
In addition to the tests shown in Table 22 seven additional measurement points were tested. These test locations are shown Figure 46 and Figure 47 with the cell towers the LTE UE were connected to. This testing focused on the distance at ToV as a function of distance from the cellular tower in this weak signal area near the border of the WPWR-TV viewing area. Two DTV receivers were tested at each location. At two of the test points WPWR-TV reception was not possible. A Samsung Galaxy Note 4 was used as the LTE UE. At each location WPWR-TV reception was established. The LTE UE was placed on a call and set to transmit at 3 Mbps. The LTE UE was then moved toward and away from the DTV antenna until ToV was identified and recorded.
Even in this area, at the boundary of the WPWR-TV viewing area, the ToV distances are very short, as shown in Table 23. In fact it was not possible to get interference in 3 of the tests, even with the handset touching the DTV antenna. This was understood as confirming the premise that close to cell towers there is not a risk of interference because the LTE power control keeps the phone operating at low power. When more distant from the cell tower, the phones did operate at higher power and larger distances were recorded, as reported in Table 23.
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Figure 46 - Test Locations in Southern Wisconsin on King Street Wireless Network
106
Figure 47 - Detailed View of Test Locations 3-5 in Southern Wisconsin
107
Table 22 - Comparison of Laboratory to Field Measured Interference Distances55
Table 23 - Field test results at 7 locations in Southern Wisconsin
55 ToS-D is the threshold of sensitivity, descending. The test for ToS-D starts with a signal being received and lowers the signal until reception is lost. ToS-D is the last level before reception is lost. This measurement is made with no LTE interference present.
108
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15. Annex – Relevant Studies & Documents This section identifies and provides an overview of studies and documents most relevant to the Cricket/Laser waiver request seeking approval to operate LTE on the lower 700 MHz A Block in Chicago. Its purpose is to provide a guide to the relevant literature with some commentary on the importance of each item to the questions addressed in this report.
The topic of LTE to DTV interference has international relevance, and, as a result, a number of research studies have been conducted. While each study has its unique characteristics, taken as a group, they create a body of literature that builds confidence in the conclusions reached in this report.
15.1.Cricket Waiver RequestOn December 6, 2013, Cricket filed a waiver request seeking the FCC’s permission to operate in the lower 700 MHz A Block in the Chicago area:
Cricket FCC Waiver Request56
In the opening sentences of that request they stated:Cricket License Company, LLC, together with its parent companies, Cricket Communications, Inc. and Leap Wireless International, Inc. (collectively “Cricket”), hereby request a waiver of the Section 27.60 digital television (“DTV”) signal protection criteria to allow the deployment of commercial service on Cricket’s Lower 700 MHz A Block license (call sign WQJQ707) (the “License”) in the Chicago-Gary-Kenosha, IL-IN-WI BEA (BEA064) (the “Market”). The potential for interference into the adjacent Channel 51 DTV broadcast station, WPWR-TV (Gary, Indiana) (the “Station”) operated by Fox Television Stations, Inc. (“Fox”), is de minimis, and the probability that viewers of the Station’s signal will suffer from interference is highly unlikely.
In support of the assertion that only a de minimis level of interference would be experienced, atest report by Intertek Laboratory and a statistical analysis by Newfield were filed:
Intertek, Evaluation Of The RF Coexistence LTE Operation on 700 MHz A Block (Formerly Channels 52 / 57) and TX Channel 51 Reception, January 14, 2013, Report G1002WX445LEX-02.
That report was filed as annex B to the waiver request.
Newfield Wireless, Chicago Channel 51 Interference Probability Study. Dec. 27, 2012, Version 1.4.
That report was filed as annex C to the waiver request.
56 Petition of Cricket License Company, LLC (Cricket) for a Waiver of DTV Protection Criteria, Attachment, Universal Licensing System (ULS) File No. 0006046277 (filed Dec. 6, 2013) (Cricket Waiver Request). Cricket’s supporting exhibits can also be accessed in ULS under Application Search (File No. 0006046277) through the “Admin” tab, followed by “All Attachments.”
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The area in question is shown in Figure 48, which depicts the FCC’s calculation of the WPWR-TV 41 dBu contour and its protection boundary, which is 8 km beyond the 41 dBucontour.
The FCC issued a public notice seeking comments on the Cricket Waiver Request:
FCC Public Notice DA 14-113, Wireless Telecommunications Bureau Seeks Comment On Request by Cricket License Company For Waiver Of Section 27.60 For Lower 700 MHz A Block License, WT Docket 14-17, released January 31, 2014.
Figure 48 - WPWR-TV viewing area and protection contours
15.2.Comments on Waiver RequestThere are 57 documents filed with the FCC in WT Docket 14-17, excluding the original waiver request and FCC public notice. Fox Broadcasting, which operates WPWR-TV, the National Association of Broadcasters, T-Mobile, and others filed significant comments on the Cricket Waiver request. These comments can be accessed at www.fcc.gov by searching the FCC's Electronic Comment Filing System for WT Docket 14-17.
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On March 4, 2014, Fox Broadcasting filed extensive comments on the Cricket waiver request. Attached to those comments as Exhibit A is the following analysis report by Meintel, Sgrignoli, & Wallace (MSW):
Meintel, Sgrignoli, & Wallace, A Report to FOX Television Stations Inc. Regarding Severe Impairments to WPWR CH 51 Chicago, IL From Proposed Cricket Wireless Block "A" LTE Signals, June 7, 2013.
In May 2014, MSW prepared a report for the Consumer Electronics Association (CEA) which was filed with the FCC:
Meintel, Sgrignoli, & Wallace, LLC, "A Report To The Consumer Electronics Association Regarding Laboratory Testing of Recent Consumer DTV Receivers With Respect To DTV & LTE Interference" (May 22, 2014), filed as an ex parte of the Consumer Electronics Association in GN Docket No. 12-268 and ET Docket No. 14-14
Laser Inc., successor to Cricket Communications, found the new MSW report relevant and filed comments on it in WT Docket 14-17. MSW filed, also in WT Docket 14-17 a rebuttal to those comments:
FCC WT Docket 14-17, Laser Inc., filed July 3, 2014.
FCC WT Docket 14-17, Meintel, Sgrignoli, & Wallace, LLC, Supplemental Ex Parte Comments of Meintel, Sgrignoli, & Wallace, LLC, Filed August 13, 2014.
15.3.FCC StudiesOver the years, the FCC has conducted a number of studies that are relevant to this issue.
In support of the incentive auction process, the FCC conducted studies and held workshops on the potential for inter-service interference. As part of that proceeding, Commission staff conducted studies and held workshops discussing methodologies for predicting potential interference between broadcast television and licensed wireless services after repacking.
OET Report TA-2014-01, released June 20, 2014, focused on the interference potential, measured in terms of D/U ratios of overlapping DTV and LTE signals. However, one of the test cases had the LTE signal immediately adjacent to the DTV signal, but with no guard band. An important finding for the purposes of the waiver was:
The adjacent-channel selectivity of all of the receivers tested appears to be much better than FCC rules anticipate in the presence of a single interferer.
OET Report TA-2014-01, Measurements of LTE into DTV Interference (released June 20, 2014).
A very important item is the rationale given in FCC 79-555 for using a 10 m separation distance as the basis for setting the unintentional emissions limits:
FCC 79-555 discussing separation distance of 10 m.
The key FCC OET bulletins on this topic are:
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OET BULLETIN No. 69, Longley-Rice Methodology for Evaluating TV Coverage and Interference, July 2, 1997.
OET BULLETIN No. 69, Longley-Rice Methodology for Evaluating TV Coverage and Interference, Feb. 6, 2004.
OET BULLETIN No. 71, Guidelines for Testing and Verifying the Accuracy of Wireless E911 Location Systems, April 12, 2000.
Other important FCC OET reports and studies are:
Report To Congress: The Satellite Home Viewer Extension and Reauthorization Act Of 2004: Study of Digital Television Field Strength Standards and Testing Procedures, ET Docket No. 05-182, FCC 05-199, Adopted: December 6, 2005.
FCC OET Report R-6602, Development of VHF and UHF Propagation Curves for TV and FM Broadcasting, September 7, 1966.
FCC/OET TR 05-1017, Tests of ATSC 8-VSB Reception Performance of Consumer Digital Television Receivers Available in 2005, November 2, 2005.
FCC/OET 07-TR-1003, Interference Rejection Thresholds of Consumer Digital Television Receivers Available in 2005 and 2006, March 30, 2007.
FCC/OET 07-TR-1005, Direct-Pickup Interference Tests of Three Consumer Digital Cable Television Receivers Available in 2005. July 31, 2007.
FCC/OET 07-TR-1006, Initial Evaluation of the Performance of Prototype TV-Band White Space Devices, July 31, 2007.
FCC/OET 9-TR1003, DTV Converter Box Test Program--Results and Lessons Learned, October 9, 2009.
15.4.Ofcom StudiesOfcom has coordinated a significant body of work studying the LTE to DTV issue.
Ofcom, Coexistence of new services in the 800 MHz band with digital terrestrial television, June 2, 2011.
Ofcom, Technical analysis of interference from mobile network base stations in the 800 MHz band to digital terrestrial television, June 10, 2011.
In a March 8, 2014, email from Mark Waddell of the BBC, Mr. Waddell made the following useful comments:
Simulating the impact of LTE interference on TV reception requires knowledge of:
1. Coupling gain between LTE BS and victim DTV
1. This includes characteristics of DTV antennas (VRP/HRP)
2. Appropriate propagation models accounting for clutter (Hata or terrain based models)
2. Knowledge of the DTT Field strength and statistical variations over each coverage pixel. In the UK we use a terrain model with clutter data and 100m
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resolution. We assume a log normal variation within each pixel, with a standard deviation of 5.5dB.
3. Protection ratio performance data for TV receivers (e.g. ITU-R BT.1368.9), defining at what ratio (Wanted/Unwanted) the receiver will fail.
1. The performance is strongly influenced by receiver AGC characteristics and LTE traffic characteristics. Silicon tuners are more susceptible to LTE than CAN tuners.
4. Details of the OOB characteristics of the LTE-BS as this affects the receiver protection ratios
The most comprehensive piece of work is the Ofcom study:
http://stakeholders.ofcom.org.uk/binaries/consultations/949731/annexes/DTTCo-existence.pdf
Statistical analysis is required to determine the probability of interference and there can be considerable uncertainty in the calculations.
It is often difficult to know details of consumer installation, receiver performance, antenna performance, BS characteristics, BS antenna patterns, power control algorithms. As a consequence, errors can quickly accumulate. I hope this helps you.
In a 2014 study, Ofcom reports its evaluation of the range and average transmit power for LTE UE devices:
Ofcom, Award of the 2.3 and 3.4 GHz spectrum bands: Update on the coexistence of 2.3 GHz LTE with Wi-Fi in the 2400 to 2483.5 MHz range and other coexistence issues, Dec. 3, 2014.
15.5.PCAST ReportFACT SHEET: Executive Office of the President, FACT SHEET: Freeing up Spectrum for Wireless Broadband, July 20, 2012.
PCAST ReportExecutive Office of the President, President’s Council of Advisors on Science and Technology, Report To The President Realizing The Full Potential Of Government-Held Spectrum To Spur Economic Growth, JULY 2 01 2.
15.6.CSR on Adjacent Band InterferenceAdjacent band interference is an important challenge that must be addressed in the study of LTE and DTV interaction.
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Figure 49 - DTV & LTE adjacent band interference
As Figure 49 illustrates, the adjacent band problem has two separate interference mechanisms.
CSR has done some important work on the adjacent band problem between LTE operating in the 2.3 GHz band and unlicensed devices, such as Wi-Fi, operating in the 2.4 GHz ISM band:
1st public release of this reportCSR, Bluetooth Performance with 2.3 GHz LTE Interference Report, CS-324419-RPP5, Issue 5, Jan. 26, 2015
15.7.3GPP StandardsThe 3GPP standards specify LTE equipment parameters, including maximum transmit power and other relevant parameters.
Table 24 - 3GPP User Equipment Specification
Document Number Title Revision/Date
3GPP TS 36.101 3rd Generation Partnership Project;Technical Specification Group Radio Access Network;Evolved Universal Terrestrial Radio Access (E-UTRA);User Equipment (UE) radio transmission and reception (Release 11)
2012
3GPP TS 36.104 3rd Generation Partnership Project;Technical Specification Group Radio Access Network;Evolved Universal Terrestrial Radio Access (E-UTRA);
2014
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Base Station (BS) radio transmission and reception(Release 12)
15.8.ATSC StandardsThe ATSC standards specify ATSC equipment parameters and performance requirements.
Table 25 - Relevant ATSC Standards
Document Number Title Revision/Date
ATSC A/54A Recommended Practice:Guide to the Use of the ATSC Digital Television Standard, including Corrigendum No. 1
04 DEC 2003Cor No 120 DEC 2006
ATSC A/64B ATSC Recommended Practice:Transmission Measurement and Compliance for Digital Television
26 MAY 2008
ATSC A/74:2010 ATSC Recommended Practice:Receiver Performance Guidelines
07 APR 2010
ATSC A/174:2011 ATSC Recommended Practice:Mobile Receiver Performance Guidelines
26 SEP 2011
15.9.NIST Building Propagation StudiesBoth NIST and ITS have and continue to actively research in-building propagation, path loss and RF channel characteristics. The following are some of the NIST technical notes in this area:
NIST Technical Note DateNIST Technical Note 1792: Performance Analysis of RF-Based Electronic Safety Equipment in a Subway Station and the Empire State Building 2013
NIST Technical Note 1540: Propagation and Detection of Radio Signals Before, During and After the Implosion of a 13 Story Apartment Building 2005
NIST Technical Note 1541: Propagation and Detection of Radio Signals Before, During and After the Implosion of a Large Sports Stadium (Veteran's Stadium in Philadelphia)
2005
NIST Technical Note 1542: Propagation and Detection of Radio Signals Before, During and After the Implosion of a Large Convention Center 2006
NIST Technical Note 1545: Attenuation, Coupling, and Variability of Radio Wave Signals Into and Throughout Twelve Large Building Structures 2008NIST Technical Note 1546: Measurements to Support Modulated-Signal Radio Transmissions for the Public-Safety Sector 2008
NIST Technical Note 1547: Electromagnetic Airframe Penetration Measurements for the FAA Bombardier Global 5000 2008NIST Technical Note 1548: Electromagnetic Airframe Penetration Measurements of a Beechcraft Premier IA 2008
NIST Technical Note 1549: Electromagnetic Airframe Penetration 2008
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Measurements of the FAA's 737-200NIST Technical Note 1550: NIST Tests of the Wireless Environment in Automobile Manufacturing Facilities 2008
NIST Technical Note 1552: Measurements to Support Public Safety Communications: Attenuation and Variability of 750 MHz Radio Wave Signals in Four Large Building Structures 2005NIST Technical Note 1557: Measurements and Models for the Wireless Channel in a Ground-Based Urban Setting in Two Public Safety Frequency Bands 2011
15.10. Other Relevant StandardsSome additional industry standards relevant to this issue are:
Table 26 - Other Industry Standards Relevant to the Issue
Document Number Title Revision/Date
IEEE 1900.2-2008 IEEE Recommended Practice for the Analysis of In-Band and Adjacent Band Interference and Coexistence Between Radio Systems
2008
TIA 916 Recommended Minimum Performance Specification for TIA/EIA/IS-801-1 Spread Spectrum Mobile Stations
APR 2002
16. Laser Team Members
Doug Hutcheson - CEO
Previously CEO of Leap Wireless InternationalCurrently serves as Chairman of the Board of Directors, InterDigital and member of the Board of Directors, Pitney BowesAlso serves as a Senior Advisor, Searchlight Capital PartnersB.S. in Mechanical Engineering, California State Polytechnic University, San Luis Obispo; MBA, UC - Irvine
Tim Ostrowski - SVP – Business Development
Previously VP – Business Development, Leap Wireless InternationalFormerly served as Chief Financial Officer for Verizon Public Communications Group B.S. in Finance, MBA, Northern Illinois University
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Stephen Berger - Consultant – TEM Consulting
Chair of several standards adopted by the FCCANSI C63.17 (47CFR15.31(a)(2))ANSI C63.19 (47CFR20.19(a))
Convener and 1st
Chair IEEE Standards Coordinating Committee on Dynamic Spectrum Access Networks
Panel co-moderator FCC-FDA Wireless Test Beds workshop
Dr. Paul Kolodzy
Currently consults government and commercial customers on areas such as spectrum policy, and technology development Member of the spectrum management advisory committee for U.S. Department of CommerceFormer Senior Spectrum Policy Advisor to the FCCPh.D. in Chemical Engineering from Case Western Reserve University
Tom Rondeau
Maintainer and lead developer for GNU RadioConsults through Rondeau ResearchVisiting Researcher at UPenn with Prof. Jonathan SmithAdjunct Professor at Center for Communications Research, Princeton
Dr. David Reed
Currently the Faculty Director of the Interdisciplinary Telecommunications Program at the University of Colorado at BoulderWorked for 18 years at Cable Television Laboratories, including as Chief Technical Officer and Chief Strategy OfficerServed at the FCC as senior staff member participating in the design, technical standards and auction format of the PCS spectrum band planPh. D in Engineering and Public Policy from Carnegie Mellon University
Dr. Ken Baker
Currently a Scholar in Residence at the University of Colorado at BoulderHas over 30 years of experience in the wireless industry, including various positions related to RF network planning and new product research and development at both Nortel and QualcommHolds sixteen patents in wireless communication system technologyPh.D. in Electrical Engineering from Virginia Tech