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AERONAUTICAL COMMUNICATIONS PANEL (ACP)

THIRTEENTH MEETING OF WORKING GROUP M

Montreal, Canada 18 – 21 November 2008

Agenda Item 1 (c) .

AMENDMENTS TO THE ICAO RF HANDBOOK ON RADIO FREQUENCY SPECTRUM REQUIREMENTS TO INCORPORATE ICAO STUDIES ON COMPATIBILITY BETWEEN VDL

MODE 4 AND FM BROADCASTING

(Presented by Larry Johnsson)

SUMMARY

This paper presents proposals for amendments to the ICAO Handbook on radio frequency spectrum requirements for civil aviation (Doc. 9718) to include the results of ICAO studies on the compatibility between FM broadcasting and VDL Mode 4. Reference material is in working papers 6 and 7 of ACP Working Group F (19th meeting, September 2008).

ACTION

The meeting is invited to take action as in paragraph 3.

1. Introduction

1.1 In September 2008 ACP working group F/19 considered an analysis on the compatibility between FM broadcasting stations and VDL Mode 4, operating in the frequency band 112 – 117.975 MHz. The analysis was presented in working papers 6 and 7 to WG F/19. WG F concluded:

3.1 WP 6 contained details of an analysis of the effect of FM broadcasting on VDL mode 4. The analysis considered the interference modes namely A1, A2, B1 and B2, used in FM compatibility and their effects on VDL mode 4 operating above 112 MHz. During the presentation it was stated that if the meeting could agree to the analysis in the paper then it was hoped that ICAO could submit a contribution to the next meeting of ITU-R WP 5B. Whilst there was no objection by the Secretariat to making such a contribution, it was not possible for the meeting to agree to the

International Civil Aviation Organization

WORKING PAPER

ACP-WGM-13 WP74 November 2008

Handbook on Radio Frequency7-12 Appendix 1Spectrum Requirements for Civil Aviation

analysis since a number of participants felt that they needed more time to review the details. The meeting agreed that a correspondence group led by Mike Biggs (USA) should consider the analysis further and reach a position by 17 October with a view to ICAO making a contribution to ITU-R WP 5B in October 2008. Also within the paper were proposals for modifying certain aspects of VDL mode 4 within Annex 10. These were of an editorial nature and were not objected to by the meeting.

3.2A revised version of WP 7 was introduced and considered by the meeting. The paper contained an analysis of VDL Mode interference into FM broadcast receivers based on physical tests previously undertaken within Germany. The analysis showed the separation distances needed between different types of FM broadcast receivers and VDL mode 4 transmitters before interference occurred with the conclusion that very little interference would be expected from VDL Mode 4. It was agreed by the meeting that they recommend ICAO make a contribution to the next meeting of ITU-R WP 5B based upon WP 7. The meeting was also encouraged to discuss the contents of the paper with broadcasters in their States and provide feedback to the Secretariat by 17 October so that any ITU-R contribution could be suitably refined.

1.2 Following the WG F meeting, the material in the analysis was reviewed and, with editorial corrections, submitted by ICAO to ITU-R Working Party 5B. ITU-R Working Party 5 B is currently reviewing this material.

2. As a result of the ICAO conclusion that no ITU-R Recommendation needs to be developed on compatibility between FM broadcasting and VDL Mode 4, certain material for use by ICAO contracting States needs to be incorporated in the ICAO RF Handbook (Doc. 9718) in the format of guidance material. This paper presents relevant proposals for updating the ICAO RF Handbook, together with other relevant information on the use of the frequency band 112 – 117.975 MHz by VDL Mode 4.

3. Action by the meeting

3.1 The meeting is invited to review the proposed amendments to the ICAO Handbook on radio frequency spectrum requirements for civil aviation (Doc. 9718) as in Appendix 1

Chapter 7. Statement of Frequency Allocations,Technical Details and ICAO Policy Appendix 1 7-11

SECTION 7-II. CIVIL AVIATION FREQUENCYALLOCATIONS — ICAO POLICIES AND

RELATED INFORMATION

This section includes the changes to the Radio Regulations which were adopted at the ITU World Radiocommunication Conference 2007 (WRC-07) and proposed amendments to the ICAO policy statements. Where appropriate, amendments are proposed to the narrative material in this section.

The numbering of the amendments to the Radio Regulations is based on the numbering contained in the provisional Final Acts of WRC-07.


Band: 108–117.975 MHz Service: Aeronautical radionavigation and Aeronautical Mobile (R) (VOR, ILS localizer, GBAS and VDL Mode 4)Allocation:

MHz108–117.975

Allocation to ServicesRegion 1 Region 2 Region 3108–117.975 AERONAUTICAL RADIONAVIGATION

MOD 5.197 MOD 5.197A

Footnotes:

MOD 5.197 Additional allocation: in Japan, Pakistan and the Syrian Arab Republic, the band 108–111.975 MHz is also allocated to the mobile service on a secondary basis, subject to agreement obtained under No. 9.21. In order to ensure that harmful interference is not caused to stations of the aeronautical radionavigation service, stations of the mobile service shall not be introduced in the band until it is no longer required for the aeronautical radionavigation service by any administration which may be identified in the application of the procedures invoked under No. 9.21.

5.197A Additional allocation: the band 108-117.975 MHz is also allocated on a primary basis to the aeronautical mobile (R) service, limited to systems operating in accordance with recognized international aeronautical standards. Such use shall be in accordance with Resolution 413 (Rev.WRC-07).1 The use of the band 108-112 MHz by the aeronautical mobile (R) service shall be limited to systems composed of ground-based transmitters and associated receivers that provide navigational information in support of air navigation functions in accordance with recognized international aeronautical standards. (WRC-07)

The band 108–117.975 MHz may also be used by the aeronautical mobile (R) service on a primary basis, limited to systems that transmit navigational information in support of air navigation and surveillance functions in accordance with recognized international standards. Such use shall be in

1 Resolution 413 (Rev. wrc-07) is in Attachment G


accordance with Resolution 413 (WRC-03) and shall not cause harmful interference to nor claim protection from stations operating in the aeronautical radionavigation service which operate in accordance with international aeronautical standards. (WRC-03)

ICAO POLICY• No change to the current allocation to the aeronautical radionavigation service and the aeronautical mobile (Route) service.• Deletion of Footnote 5.197.• Ensure conformity with ITU-R Recommendation SM.1009 regarding compatibility with FM broadcast services in the band 87.5–108 MHz and ILS/VOR and with ITU-R M.1841@@@ for GBAS. Ensure compatibility with digital broadcasting services in the band 87.5-108 MHz.

(See also Attachment F: ICAO position for the ITU WRC-07.)

AVIATION USE: ILS localizer, VOR, GBAS and VDL Mode 4.

The instrument landing system (ILS) is one of the ICAO standard, non visual aids to final approach and landing. The localizer transmitter, operating on one of the 40 ILS channels within the sub-band from 108 MHz to 111.975 MHz, emits signals which provide course guidance throughout the descent path to the runway threshold.

The VHF omnidirectional radio range (VOR) is the short/medium range navigation aid. The basic navigation guidance derived from a VOR is a radial line of position (magnetic) with respect to a known geographic point (the VOR site). The radial line is read in degrees of azimuth from magnetic North and is technically accurate to within approximately ±3.0 degrees. The overall system accuracy is approximately ±5.0 degrees. Bearing information may be used by aircraft to fly toward or away from the station at any azimuth selected by the pilot. The 180 degrees ambiguity in this indication is resolved by the provision of a “to/from” indicator in the aircraft avionics. A DME is a useful adjunct to, and is normally collocated with, a VOR. In such cases, the VOR is referred to as “VOR/DME”. A DME provides a continuous digital readout of the slant range distance, in nautical miles, between the aircraft and the DME site. When using a VOR/DME, the tuning


of the airborne receiver to the VOR will automatically couple the DME receiver to the associated DME ground station. The VOR/DME is used to provide navigation guidance on ATS routes and specified tracks. Its accuracy allows ATS routes to be kept at reasonable widths and permits the application of comparatively small lateral separation minima between routes, resulting in a more efficient use of the airspace. The VOR/DME route structure is normally established so as to make it possible for aircraft to fly from one VOR direct to the next, or along intersecting radials of two adjacent VORs. Reporting points and/or other significant points are normally established along radials, either together with a given DME distance from an associated VOR, or by an intersection of radials from two different VORs. The VOR can also serve as a landing aid at locations where no precision approach facility is available.

The ground-based augmentation system (GBAS) monitors GNSS signals at an aerodrome and broadcasts locally relevant integrity messages, pseudorange corrections and approach data via a VHF data broadcast (VDB) to aircraft within the range depending upon intended operations.

The sub-band 108–111.975 MHz is shared between ILS localizer and VOR in an interleaved 50 kHz and 100 kHz spaced frequency arrangement (108.1 and 108.15 MHz for ILS, 108, 108.05, 108.2 and 108.25 MHz for VOR, etc.).

The sub-band 112–117.975 MHz is used for VOR, with 50 kHz or 100 kHz channel spacing, depending on regional agreements and requirements.

GBAS is standardized to operate in the band 108–117.975 MHz. GBAS/ILS and GBAS/VHF COM frequency planning criteria are currently under development. Until these criteria are defined and included in SARPs, GBAS frequencies should be selected from the band 112.050–117.900 MHz.

VDL Mode 4 is standardized to operate in the band 112-117.975 MHz. IT will provide data link services for air-ground and air-to-air communications and ADS-broadcast. It operates with 25 kHz channel spacing. VDL Mode 4 frequency assignment planning criteria that secure protection from interference between VDL Mode 4 and ILS/Localizer, VOR and GBAS are currently under development.

The ILS localizer is frequency paired with the glide path frequencies from the band 328.6–335.4 MHz and, where possible, with the microwave landing system (MLS) from the band 5 030–5 150 MHz. DME/N or DME/P from the band 960– 1 215 MHz are also frequency paired with ILS and/or MLS, respectively (see Figure 7-8).


VOR is normally associated with DME and is frequency paired. Short-range airport VOR frequencies are usually taken from the sub-band 108–111.975 MHz.

ILS localizer, VOR, GBAS and VDL Mode 4 receivers are vulnerable to intermodulation and saturation effects from FM broadcast transmissions from the band 87–108 MHz. Material providing guidelines for States when assessing compatibility between assignments for FM broadcasting and aeronautical radionavigation (ILS/VOR) has been agreed in the ITU-R (ITU-R.SM 1009 refers). WRC-03 adopted Resolution 413 (which was amended at WRC-07 to reflect the additional allocation to AM(R)S) S as per MOD 5.179A) and invited ITU-R to further study compatibility issues between AM(R)SGBAS, VDL Mode 4 and FM broadcasting. In particular, compatibility criteria for VDL Mode 4 as well as for new digital sound broadcasting systems, planned to operate in the band 87–108 MHz, need to be developed. ITU-R Recommendation M.1841@@@ on the compatibility between GBAS and FM-sound broadcasting has been adopted in 2007 in ITU-R. ICAO has concluded that no ITU Recommendation on the compatibility between FM broadcasting and VDL Mode 4 needs to be developed (see below)

Frequency congestion for ILS and VOR exists in some high-density areas, such as Western Europe and North America. This applies to ILS and VOR and arises ,partially, from the frequency pairing and planning constraints exercised from MLS and DME.

The band has been used by aviation since 1947. On two occasions, the channel spacing for ILS and VOR was reduced from 200 kHz to 100 kHz in 1963 and from 100 kHz to 50 kHz in 1972 (at the 7th Air Navigation Conference). SARPs for VDL Mode 4 were introduced in 2001 and for GBAS in 2002.

Footnote 5.197 was introduced at WARC-87 in anticipation that ILS would be withdrawn from international service in 1998 and the use of the ILS localizer would be terminated. At WRC-03 most countries removed their names from this footnote since ILS will continue operation for the foreseeable future.

COMMENTARY (ILS): The comprehensive discussion under Agenda Items 1 to 3 of the Special COM/OPS/95 examined the future of ILS in the context of transition to MLS and to GNSS as envisaged in the FANS scenarios. This transition has been much slower than predicted. GNSS has not yet achieved Category II and Category III Capabilities. It is difficult to predict when such capabilities will be widely available.

Most States indicated an intention to retain ILS in service (Special COM/OPS/95, Agenda Item 1, paragraph 1.3.4 refers) for the foreseeable future. In this regard, it


is noted that Annex 10 requires all ILS and VOR receivers to improve immunity standards against interference from FM broadcasts as from 1998.

ILS sustainability is addressed in Appendix B to the Report of the Special COM/OPS/95 meeting on Agenda Item 3. The meeting agreed on Recommendation 3/2 calling for a review of ILS SARPs and guidance material to ensure adequate provision for ILS beyond the year 2000. Other recommendations have called for studies and examinations of various scenarios for transition from ILS to either MLS or GNSS, with important emphasis on the economics of operation.

The introduction of the (generic) mobile service, in accordance with the provision of Footnote 5.197(WRC-07), is not possible in the foreseeable future. In light of the above, it is clear that the ILS allocation will be needed until well beyond 2025.


Figure 7-8. Channel pairing between ILS-localizer and ILS-glide path

. M Hz

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4

COMMENTARY (VOR): The continuing deployment of VOR is dependent on the progress, development and implementation of GNSS; the aviation community may continue to require VOR for some time after implementing GNSS. The GNSS Panel has developed SARPs for GNSS, and ICAO will continue through the NSP developing the measures and principles necessary to evolve towards the use of GNSS as a means of en-route navigation.

Different world regions will have different emphasis on their need for GNSS in the near and medium terms, and decisions will be taken at a regional level.

No definite or tentative dates have been agreed to for the GNSS programmes. In addition, safety requires a backup means of en-route navigation if all GNSS service is temporarily lost. It is therefore necessary to maintain the allocation for VOR until, at least, the year 20202030.

COMMENTARY (GBAS): ICAO has identified the band 108–117.975 MHz to support ground-based augmentation systems (GBAS) operation. WRC-03 reviewed this band and introduced an allocation to the aeronautical mobile (route) service (AM(R)S) limited to systems that transmit navigational information in support of air navigation and surveillance functions. At WRC-07, this allocation was reduced to the band 112 – 117.975 MHz. These systems (currently ICAO has SARPs for VDL Mode 4 operating in this band) shall not cause harmful interference to nor claim protection from international standardized systems operating in the aeronautical radionavigation service (RR 5.197A (WRC-07) refers), including GBAS.

COMMENTARY (VDL Mode 4): SARPs have also been developed for VDL Mode 4 which supports surveillance (e.g. ADS) applications as well as air-ground data and air-to-air data communications. This system can also only operate in the band 112108–117.975 MHz and 117.975 – 137 MHz. Provisions have been made for such use in Annex 10 and the Radio Regulations (RR 5.197A (WRC-07) and Resolution 413 (Rev. WRC-07) refer).

Allocations to other services

Footnote 5.197 was added by the ITU WARC-87 for mobile services. The footnote introduced the mobile service in the band 108–111.975 MHz in a number of countries. Based on present expectations for the use of the band, it is improbable that this footnote can be considered for implementation for many years (possibly post-2015) in most of the countries in the note. The footnote is not meaningful in practical terms and carries the risk that more country names will be added at future

7-1

Handbook on Radio Frequency7-2 Spectrum Requirements for Civil Aviation

conferences. Hence it should be deleted in its entirety. Furthermore, it should be noted that no guidance exists on how Footnote 5.197 would be applied, or what essential prior agreements are necessary within aviation for mobile service operations to commence on any single frequency or within particular sub-bands. This inexactness compounds the problem, as it leaves room for undesirable interpretations that could be used to allow entry of the mobile service in the band. MThe name of many countries, initially included in this footnote, have been deleted from this footnote in the mean time, leaving the concerns on compatibility and protection of ILS/VOR limited to the two countries mentioned in this footnote. .

WRC-07

At WRC-07 an allocation to the aeronautical mobile (R) service, on a primary basis, was introduced in the band 1`08-117.975 MHz. For the use of this allocation, the conditions of Resolution 413 (Rev. WRC-07) apply.

Important elements of this Resolution include:- AM(R)S shall not cause harmful interference to the aeronautical radionavigation service- AM(R)S systems operating in this band shall meet the FM broadcasting immunity criteria as per ICAO Annex 10 SARPs.- Only GBAS can operate in the band 108-112 MHz- Any AM(R)S operating in this band system shall meet ICAO SARPs (which implies that, in order to operate, ICAO SARPs need to be developed).

This Resolution further stipulates that WRC-11 shall , on the basis of results of ITU-R studies, consider further regulatory measures that will facilitate the introduction of AM(R)S systems in this band. It is not clear what measures could be envisaged.

ITU-R is further invited through this Resolution to study any compatibility issue between the AM(R)S and FM broadcasting as well as the effect of the introduction of digital broadcasting systems in the band below 108 MHz. ICAO has concluded that no ITU material (e.g. in the format of an ITU-R Recommendation needs to be developed for VDL Mode 4. ITU_R Recommendations for ILS, VOR (SM.1009) and GBAS (M.1841) are already in place. New AM(R)S systems that may need to use this band would require an assessment, in ICAO as well as in ITU, of the potential interactions with FM Broadcasting systems. In this regard it is worth noting that these studies do not include the effect of digital broadcasting on ILS/VOR/GBAS/VDL Mode 4. Work on the compatibility between digital broadcasting in the band 87-108 MHz has started in ITU in 2008. Study Groups 5 and 6 are involved in this activity.


TECHNICAL AND OTHER INFORMATION

Band: 108–117.975 MHz Service: Aeronautical radionavigation, Aeronautical Mobile (R)Aviation use:

VOR (108–117.975 MHz)ILS localizer (108–111.975 MHz)GBAS (112.050–117.900 MHz) [108-117.975 MHz]

VDL Mode 4 (112 – 117.975 MHz)Annex 10:

SARPs: Annex 10, Volume I, Chapter 3, 3.1 (ILS), 3.3 (VOR), 3.7 (GBAS) and Volume III, Chapter 6 (VDL Mode 4) Annex 10, Volume III, Part I, Chapter 6, 6.9 (VDL Mode 4)

Frequency plan: Annex 10, Volume I, Chapter 3, 3.1.6 (ILS), 3.7.3.5.4.1. (GBAS)

Channelization: 100 kHz/50 kHz spacing for ILS, VOR and 25 kHz for GBASPlanning criteria:

Annex 10, Volume V, Chapter 4, 4.2Annex 10, Volume I, Attachment C, 2.6 (ILS)Annex 10, Volume I, Attachment C, 3.5 (VOR/ILS)Annex 10, Volume I, Appendix B, 3.6.8.2.2. and Attachment D, 7.2.1

(GBAS) VDL Mode 4 25 kHz channel spacing (Annex 10, Volume III, Part I, CaPTER 6, 6.9.2.1.1 AND 6.9.2.1.2RTCA:

ILS: DO-195, MOPS for Airborne ILS Localizer Receiving Equipment Operating within the Radio Frequency Range of 108–112 MHz (1986)

VOR: DO-180A, MOPS for Airborne Area Navigation Equipment Using a Single Collocated VOR/DME Sensor Input (1990)

VOR: DO-187, MOPS for Airborne Area Navigation Equipment Using Multi-Sensor Inputs (1984)

VOR: DO-196, MOPS for Airborne VOR Receiving Equipment Operating within the Radio Frequency Range of 108–117.95 MHz (1986)

GBAS: DO-246C, GNSS Based Precision Approach Local Area Augmentation System (LAAS) – Signal-in-Space Interface Control Document (ICD) (2005)Eurocae:

ILS: ED-46B, MOPS for Airborne Localizer Receiving EquipmentILS: ED-74, MOPS for Combined ILS and MLS Airborne Receiving

Equipment, Amend. 1 (1997)ILS: ED-88, MOPS for MMR including ILS, MLS, and GPS used for


Supplemental Means of NavigationVOR: ED-22B, MPS for Airborne VOR Receiving Equipment (1988)VOR: ED-27, MOPR for Airborne Area Navigation Systems Based on VOR

and DME as Sensors (1979)VOR: ED-28, MPS for Airborne Area Navigation Computing Equipment

Based on VOR and DME as SensorsVOR: ED-52, MPS for Conventional and Doppler VOR Ground Equipment

(1984)GBAS: ED-95, MASPS for GBAS to Support CAT 1 Operations (1999)GBAS: ED-114, MOPS for GBAS Ground Facility to Support CAT 1

Approach and Landing (2003)VDL Mode 4: ED-108, MOPS for VHF VDL Mode 4 Aircraft Transceiver for

ADS-B (2001)ARINC characteristics:

ILS: 578-4, Airborne ILS ReceiverILS: 710-10, Mark 2 Airborne ILS ReceiverVOR: 579-2, Airborne VOR ReceiverVOR/ILS: 711-10, Airborne VOR ILS Receiver

ITU Res./Rec.: Res. 413; Use of the band 108-117.975 MHz by the aeronautical mobile (R) serviceITU-R:

• ITU-R M44-1: Signal-to-interference ratios and minimum field strengths required in the aeronautical mobile (route) service above 30 MHz

• ITU-R.SM 1009: Compatibility between the sound broadcasting service inthe band 87–108 MHz and the aeronautical services in the band 108–137 MHz

ITU-R.M 1841: Compatibility between FM sound-broadcasting in the band of about87-108 MHz and the aeronautical ground-based augmentation system in the band about 108-117.975 MHz

Other material:• Receiver susceptibility to FM broadcast:

— DO-176, FM Broadcast Interference related to Airborne ILS, VOR and VHF Communications (1981)

— Annex 10, Volume I, Chapter 3, 3.1.4 (ILS)— Annex 10, Volume I, Attachment C, 2.2.10 (ILS)— Annex 10, Volume I, Chapter 3, 3.3.8 (VOR)— Annex 10, Volume I, Attachment C, 3.6.5 (VOR)— Annex 10, Volume I, Appendix B, 3.6.8.2.2 (GBAS)— Annex 10, Volume III, Part I, 6.3.5.4 (VDL)


• RTCA DO-117, Standard Adjustment Criteria for Airborne Localizer and Glide Slope Receivers (1963), Errata

• RTCA DO-217, MASPS for DGNSS Instrument Approach System: Special Category 1 (SCAT-1) (1993), Change 1 to DO-217 (1994), Change 2 to DO-217 (1996)

INTERFERENCE FROM NON-AERONAUTICAL SOURCES

COMPATIBILITY BETWEEN ILS/VOR AND FM BROADCASTING

General: The ITU WARC in 1979 allocated the band at 100–108 MHz to broadcasting services in Region 1. This band was previously allocated in that way only in Regions 2 and 3. The band is adjacent to the VOR/ILS band at 108 to 117.975 MHz, and interference effects have been experienced due to transmissions of broadcast stations, particularly those operating on frequencies close to the band edge and in areas where there is a high density of both FM stations and ILS or VOR. In many countries, FM sound broadcasting services of both low and high power are operated in this band. In some countries, the broadcast services also include analogue television transmissions. Compatibility problems due to intermodulation products, generated by both FM transmitter stations and in ILS/VOR receivers as well as overloading of the front end of aircraft ILS/VOR receivers, became apparent when broadcast stations commenced use of the frequencies in the band 100– 108 MHz in the mid-seventies in Region 2. Studies on a suitable planning methodology initiated by the CCIR (now ITU-R) in a joint aeronautical/ broadcasting group have documented a viable methodology for broadcast and aeronautical frequency assignment planning with a view to ensuring a safe situation for air operations.

Any resolution of this problem through planning and coordination automatically restricts both services. In high-density areas, such as Western Europe and North America, the full potential of the frequency band for either service cannot be realized. Both services tend to be at their greatest density in areas of high population, which places a severe constraint on the full utilization of the potential of the 40 channels available for use by ILS (see Annex 10, Volume I, 3.1.6). VOR services are also affected but not to the same critical degree. VHF communications, because of their greater frequency separation, are also affected, but to a lesser degree than ILS/VOR.

ITU-R Studies: After many studies on the compatibility between ILS/VOR and FM broadcasting were initiated in ITU, ITU-R approved Recommendation


SM.1009 in 1994.

The three Annexes of Recommendation SM.1009 deal comprehensively with the subject and are:

Annex 1: Interference mechanism, system parameters and compatibility assessment criteria;

Annex 2: General assessment method; andAnnex 3: Detailed compatibility assessment and practical verification.

The report comprehensively covers the treatment of conflict situations for the four interference modes:

Type A:FM broadcasting-transmitter-generated interference products falling within the ILS/VOR bands. The two sub-types are:

Type A1: spurious or harmonic intermodulation products generated by one or more FM transmitters within the aeronautical band; and

Type A2: non-negligible components of the FM broadcasting signal, operating near the band edge 108 MHz, within the aeronautical band (affecting only aeronautical frequencies near the 108 MHz band edge).

Type B:ILS/VOR-receiver-generated interference caused by high-level broadcast signals operating outside the ILS/VOR band. The two sub-types are:

Type B1: interference that may be generated in the aeronautical receiver being driven into non-linearity due to high-power broadcasting signals outside the aeronautical band. The effect on the receiver resulting in the generation of intermodulation products in the receiver; and

Type B2: performance degradation due to high-power overload and desensitization without any frequency relationship.

This Recommendation, with its three detailed Annexes, provides the essential requirements for the identification and analysis of interference situations and for the coordination between broadcasting and aeronautical interests within a country or between countries. The criteria and methods have been developed and reviewed by a group of experts and represent the best available information on the subject. Furthermore, the Recommendation is recognized by aeronautical and telecommunication authorities as the definitive guidance for planning and coordination purposes.


In 2007 ITU-R Recommendation M.1841 on “Compatibility between FM sound-broadcasting in the band of about 87-108 MHz and the aeronautical ground-based augmentation system in the band about 108-117.975 MHz” was approved. This Recommendation provides the necessary material for assessing compatibility between FM broadcasting and GBAS systems operating in the band 108 – 117.975 MHz. The principles for protection of GBAS from harmful interference from FM broadcasting signals are similar to those for ILS/VOR. This Recommendation is in line with the FM-immunity criteria developed for GBAS by ICAO.

In 2008 ICAO reviewed potential interference from FM broadcasting stations into VDL Mode 4, operating in the band 112-117.975 MHz. Although at relative short distances from high-powered FM broadcasting stations (less than 1 km) harmful interference could be caused in some cases to VDL Mode 4, it was concluded that no international coordination criteria between FM broadcasting assignments and VDL mode 4 assignments would be necessary. A technical analysis of compatibility between FM broadcasting and VDL Mode 4 is in Part II of this Handbook

ICAO Studies

Handbook for evaluation of electromagnetic compatibility (EMC) between ILS and FM broadcasting stations using flight tests (1997)

This ICAO handbook is the result of considerable flight testing programmes and provides detailed guidance on this activity. It addresses the methods of flight testing for analysing and resolving cases of FM interference to aircraft ILS localizer receivers. It describes test equipment, test procedures and interference assessment criteria. The material is also generally applicable to VOR or communications systems. The areas covered in the handbook are:

a) Description and operation of airborne equipment;b) Interference assessment methodology; andc) Flight test procedures.

with six explanatory appendices.

Note.— This handbook is available from the Secretariat on request.

SARPs on FM-immunity for ILS, VOR, GBAS, VDL and VHF communications

Since 1984, Annex 10 incorporates provisions covering the FM-immunity performance of airborne receivers. These performance requirements are a considerable improvement compared to those of unmodified receivers. In many cases, compliance with these SARPs will require equipment replacement. These


SARPs were incorporated to standardize the FM-immunity performance of ILS, VOR and VHF communication receivers to FM broadcast signals. While the SARPs were incorporated in the Annex with Amendment No. 65 in 1984, implementation was not required until 1998, allowing fourteen years for modification or refit. In some areas of the world, implementation is not necessary due to the lower level of implementation of both ILS/VOR and FM broadcasting stations. Implementation of these SARPs took place in Europe by 2001 and is foreseen in other Regions.

The FM-immunity SARPs are contained in:

(i) for ILS: Annex 10, Volume I, 3.1.4, Interference immunity performance for ILS localizer receiving systems and Annex 10, Volume I, Attachment C, 2.2.9, providing guidance material;(ii) for VOR: Annex 10, Volume I, 3.3.8, Interference immunity performance for VOR receiving systems;

(iii) for GBAS: Annex 10, Volume I, Appendix B, 3.6.8.2.2;

(iv) for VDL: Annex 10, Volume III, Part I, 6.3.5.4 (VDL); and

(v) for VHF Com: Annex 10, Volume III, Part II, 2.3.3, Interference immunity performance and Annex 10, Volume III, Part II, Attachment A, 1.3.

(vi) for VDL Mode 4: Annex 10, Volume III, Part I, 6.9.5.6

LEGBAC consultative arrangements

In Europe, the Limited European Group on Broadcasting Aeronautical Compatibility (LEGBAC) has developed a methodology, including software tools, to assess compatibility of assignments to FM broadcasting stations and ILS/VOR assignments. This methodology has been accepted as the European-wide assessment method. It is compliant with the provisions of the Final Acts of the 1984 ITU Broadcasting Conference, the ITU-R Recommendation SM.1009 and the relevant SARPs.

==========================================================Material for incorporation in Part II of the Handbook (Details on Frequency assignment planning and coordination)

NEW TEXT

1 Compatibility between FM Broadcasting stations and VDL Mode 4.

1.2 In ITU-R criteria have been established on the compatibility between FM broadcasting stations operating in the band 87-108 MHz and aeronautical radionavigation systems (ILS, VOR and GBAS) operating in the band 108-117.975 MHz. These criteria are contained in ITU-R Recommendations SM.1009 (ILS and VOR) and M.1841 (GBAS). For assessing interference between VDL Mode 4 and FM Broadcasting no specific ITU-R material (such as an ITU-R Recommendation) has been developed as the interference that can occur is a local matter that can be solved nationally.

1.3 The analysis below examines the interference mechanisms for type A1, A2, B1 and B2 interference for VDL Mode 4. Reference material is taken from ITU-R Recommendation M.1841and ICAO Annex 10. It provides guidance to ICAO Contracting States when assessing compatibility between FM broadcasting transmissions and VDL Mode 4.

2. Type A1 interference.

2.1 Type A1 interference is (mainly) caused by spurious emissions or inter-modulation products generated by several FM broadcasting transmitters (normally operating from the same FM broadcasting transmitter site. These emissions fall within the pass-band of the aeronautical receivers and cannot be suppressed by these receivers. Suppression is only possible at the FM broadcasting site and is normally achieved through filtering of the spurious emissions.

2.2 For FM broadcasting transmitters typical suppression of spurious emissions from co-sited broadcasting transmitters in the aeronautical band 108-117.975 MHz, including intermodulation products, is as in Table 1.

7-1


Maximum e.r.p. (dBW) for FM broadcasting transmitters

Suppression relative to maximum e.r.p

(dB)

≥48 8530 76

≤30 46 + max. e.r.p (dBw)Table 1

Note 1: linear interpolation is used between maximum e.r.p. values of 30 and 48 dBW.

Note 2: Implementation of FM broadcasting stations needs to secure that at least these values are met.

2.3 The protection ratio (D/U) that may be used to assess type A1 interference for VDL Mode 4 receivers is as in Table 2:

Frequency difference between wanted signal and spurious emission

(kHz)

Protection ratio (dB)

0 1450 7100 -4150 -19200 -38

Table 2Note: These protection ratios are the same as those for ILS, VOR and GBAS. Manufacturers need to ensure to comply with these.

2.4 Calculation of interference margin for type A1 interference

2.4.1 Paragraph 3.2.5 of Recommendation M.1841 shows that the type A1 interference margin should be calculated as:

(Re. (13) in Rec. M.1481)

where:IM: A1 interference margin (a positive margin implies no

interference) N: number of inter-modulation components (N=2 or 3)

Ei : field strength (dB(µV/m)) of the (unwanted) FM broadcasting transmission i


Si : Type A1 suppression (dB) of broadcasting transmitter I (See Table 1)PR:protection ratio as per Table 2 (in the analysis only the co-channel

case whereby the inter-modulation product coincides with the desired aeronautical frequency was used; this was considered to present the worst case)

Ew: field strength (dB(µV/m)) of the aeronautical signal (at least 37.5 dB(µV/m) for VDL Mode 4)

2.4.2 E can be calculated as follows:

E=76.9+P-20logd (Re. (1) in Rec. M.1481)where:

E : field strength (dB(µV/m)) of the (unwanted) FM broadcasting transmission

P: maximum e.r.p (dBW) of the broadcasting stationd: distance between the broadcasting station and the aeronautical receiver

Note: Both the FM Broadcasting signal as the VDL Mode 4 signal are vertically polarized.

2.4.3 Reference (13) in paragraph 2.4.1 above can be re-written as follows:

=0

2.4.3.1 In the following example: the radiated power of the FM broadcasting transmitter P=100 kW; type A1 suppression S =85 dB as per Table 1; the spurious emission or inter-modulation product coincides with

the aeronautical frequency in use (PR=14 dB) and Ew is 37.5 dB(µV/m) (minimum fieldstrength for VDL Mode 4),

the interference margin of 0 dB will be reached at a minimum interference of separation distance of 8.3 km. This can be considered too large for most operational situations where VDL Mode 4 is being used.

2.4.3.2 Should the type A1 suppression be increased to 103.4 dB, the interference distance would be reduced to less than 1 km.

2.3.4.3 Mitigating factors that can be considered include the consideration of the vertical antenna diagram of the broadcasting transmitter and the efficiency of the FM broadcasting antenna to radiate signals above 112 MHz. It should also be considered that this type of interference normally occurs in cases where two broadcasting antennas are co-located (or in their near vicinity) and the radiated


signal of one transmitter can be coupled into the other the antenna of the other transmitter (or when one FM-broadcasting antenna is used for two transmitters)

2.5 As a result, it was concluded that Type A1 interference is a local issue that can be solved by technical means as required, including frequency assignment planning, as an implementation measure. The attention of the possibility of Type A1 interference needs to be considered by aviation and the broadcasting community.

3. Type A2 interference.

3.1 Type A2 interference is caused by non-negligible components of the FM signal nearby (about +/- .5 MHz) the FM broadcasting operating frequency. This type of interference from FM broadcasting transmitters will in practice only occur in the aeronautical band near the band-edge (108 MHz).

3.2 For VDL mode 4, operating above 112 MHz, type A2 interference is not expected.

4. Type B1 interference.

4.1 Type B1 interference is interference caused by third order inter-modulation products that are generated inside an aeronautical receiver resulting from (high powered) broadcasting transmissions outside the aeronautical frequency band. (See also Rec. M.1841, paragraph 2.2.2). These inter-modulation products can involve two or three broadcasting frequencies. 4.2 For the assessment of type B1 interference (two frequencies, fintermod= 2f1-f2)The following formula can be used:

(4)

Note: This formula is derived from formula (13) in ITU-R Recommendation M.1841

4.3 From formulas (1) and (2) in Recommendation M.1841) the value for N (which is the (dBm) of the FM-broadcasting signal at the input of the aeronautical receiver) can be calculated as follows:

(5)


In these formulas:

N (N1 or N2): broadcasting signal level (dBm) at the input of the aeronautical receiver

P: maximum e.r.p. (dBW) of the broadcasting stationd: distance from the broadcasting station to the aeronautical

receiver Ls: signal splitter loss of 3.5 dB

Lf: antenna system frequency dependent loss at broadcasting frequency f (MHz) of 1.2 dB per MHz below 112 MHz

La: antenna system fixed loss of 9 dBK: 78Lc: correction factor (dB) to account for changes in wanted signal

level.S: 3 dB

Formula (5) can be re-written when Ls =3.5 dB and La=9 dB as

When P =100 kW (or 50 (dBW))

4.3.1 The correction factor Lc in this example is assumed to be 0 (no correction as the wanted VDL Mode 4 signal is assumed to be at the minimum value).

4.3.2 Calculation of minimum separation distance between VDL Mode 4 receivers and an FM broadcasting station with the following characteristics:

f1 = 107.9 MHzf2 = 103.8 MHzP1=P2=100 kW (50 dBW)

In this example, the FM-Broadcasting antennas are co-located; the combination of f1 and f2 is the worst case capable of generating an inter-modulation product on the aeronautical frequency 112 MHz (ie. the FM broadcasting frequencies are the closest possible to generate an intermodulation product on the lowest assignable VDL Mode 4 frequency (112 MHz).

4.3.3 The minimum separation distance between VDL Mode 4 receivers and FM broadcasting transmitters in the above case would be about 550m. For two FM broadcasting stations, operating on the same frequencies and an e.r.p of 300 kW, this distance would increase to about 960 m.


4.4. As this has been considered as the worst case, type B1 interference has been considered to not cause a threat that would cause harmful interference to the reception of VDL Mode 4 signals as normally the separation between an aircraft and a high-power FM broadcasting station would be more than 1 km.

5. Type B2 interference. 5.1 Type B2 interference is characterized as desensitization of the RF section of an aeronautical receiver when it is subject to overloading by one or more high powered broadcasting transmissions. Annex 10, Volume III, Part I, paragraph 6.9.5.6.2.2 provides B2 immunity criteria for the VDL Mode 4 receiver.

5.2 In accordance with formula (10) of Recommendation M.1841, the maximum level of an FM broadcasting signal at the input of a VDL Mode 4 receiver can be established as follows:

(re. (10) in Rec. M.1481)

For f=107.9 MHz, =15-3=12 dB (correction factor Lc is not applied)

Compatibility is achieved at a distance of about 165m from the FM broadcasting transmitter.

5.3 It has been concluded that type B2 interference will not cause harmful interference from FM broadcasting stations into VDL Mode 4 receivers.

6. Assessment of potential interference

6.1 VDL Mode 4 frequencies are used on a national, Regional or Global basis, throughout a large designated operational coverage area. It has been concluded that only type A1 interference can be identified as an interference mechanism that can potentially cause harmful interference to VDL Mode 4. Type A1interference has its maximum value at the transmitter site. For assessing potential type A1 interference into VDL Mode 4 it is therefore sufficient consider each site from which more than one FM broadcast transmitter is operating as a test point and perform the analysis as described in paragraph 2 above.


END OF NEW TEXT

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