guide to analysis of interference between co-site cdma2000-800mhz and gsm-900mhz base station...

Guide to Analysis of Interference between Co-site CDMA2000-800MHz and GSM-900MHz Base Station SystemsPlease enter the document No.

Huawei Technologies Co., Ltd.

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Guide to Analysis of Interference between Co-site CDMA2000-800MHz and GSM-900MHz Base Station Systems

(For Internal Use Only)

Prepared by:Antenna Feeder TeamDate:2002/07/31

Reviewed by:Date:yyyy/mm/dd

Reviewed by:Date:yyyy/mm/dd

Approved by:Date:yyyy/mm/dd

Huawei Technologies Co., Ltd.

All Rights ReservedRevision Record

DateRevised VersionDescriptionAuthor

2002/04/15V1.0First draft finished.Antenna Feeder Team

2002/07/31V2.0ModifiedAntenna Feeder Team

Table of Contents51 Foreword

2 Relevant Specifications for CDMA2000 1x/IS95A & GSM900MHz Base Station Systems52.0 2.1 Relevant Specifications for CDMA2000 1x 800MHz BTSS52.152.1.1 Frequency band52.1.2 Specifications for out-band spurious emission52.1.3 Blocking specifications52.1.4 Front end of receiver intermodulation specifications62.2 Relevant Specifications for GSM 900MHz BTSS62.2.1 GSM frequency band62.2.2 Spurious emission specifications62.2.3 Intermodulation specifications62.2.4 Blocking specifications73 RF Front-end Modules Structure and Filter Feature Specifications of CDMA2000 & GSM BTS73.1 CDMA2000 Front-End Module83.1.1 CDMA2000 CDU-800MHz83.1.2 CDMA2000 DDU-800MHz93.2 GSM900MHz CDU Front-End Module104 Interference Analysis104.1 Analysis of Interference between CDMA2000 and GSM900 Systems114.1.1 Analysis of Interference of System GSM900MHz by System CDMA2000114.1.2 Analysis of Interference of System CDMA2000 by System GSM900MHz125 Analysis and Calculation of the Influence of Interference on Receiver Sensitivities of GSM and CDMA2000 Systems135.1 Equivalent Noise Level Analysis136 CDMA2000 1x (800MHz) and IS95A BTSs Co-site Interference analyze147 Antenna Isolation Calculations167.1 Horizontal Antenna Isolation Calculation167.2 Vertical Antenna Isolation Calculation197.3 Calculation of Antenna Gain in any Direction20

Guide to the Analysis of Interference between Co-site CDMA2000-800MHz and GSM-900MHz Base Station Systems

Keywords: spurious emission, intermodulation, blocking, receiver sensitivity, antenna, isolation, interference

ABTStract: This document analyzes the interference between co-site CDMA2000-800MHz and GSM-900MHz base station systems through spurious emission, intermodulation and blocking, and sets forth specifications for the mounting of base station antennas on the basis of the analysis.

Abbreviations:

PA: Power Amplifier

LNA: Low Noise Amplifier

TTA: Tower Top Amplifier

List of References:

List of References

ArticleAuthorDocument No.Release DateBy what means to get the articlePublisher

Digital Cellular Telecommunications System Phase (2+)

(GSM 05.05)

1 Foreword

As more new operators emerges and more new mobile communication systems are put into use, multiple different mobile communication systems are more frequently located at the same site. Due to the close distance between antennas of a co-site system, interference will occur between different systems. So to avoid this kind of interference becomes an imminent issue. This kind of interference (or blocking) is resulted from the antenna of a system receiving unwanted (spurious, intermodulation) signals transmitted from another co-site system antenna. This document analyzes this interference in detail, and concludes the mounting specifications of co-site antenna between CDMA-800MHz and GSM-900MHz by calculation (or test data). This specification can serve as a guide or suggestion for the mounting of co-site antennas.

2 Relevant Specifications for CDMA2000 1x/IS95A & GSM900MHz Base Station Systems

Based on the relevant Protocol Specifications for base station systems, the interference between co-site systems can be analyzed through the spurious emission, intermodulation and blocking of receiver.

2.1 2.1 Relevant Specifications for CDMA2000 1x 800MHz BTSS

2.1.1 Frequency band

Tx: 869--894MHz

Rx: 824--849MHz

2.1.2 Specifications for out-band spurious emission

Table 1 Spurious emission specifications in the CDMA 2000 1x protocol

Frequency BandSpurious Emission SpecificationsRemark

9kHz--150kHz-13dBm/1kHz

150kHz--3MHz-13dBm/10kHz

30MHz--1GHz-13dBm/100kHz

1GHz --12.75GHz-13dBm/1MHz

2.1.3 Blocking specifications

Table 2 Blocking specifications Offset from center frequencyInterfering signal levelWanted signal levelType of interfering signalRemark

750kHz-67dBm-117dBmCWFor class 0

900kHz-30dBm-117dBmCWFor class 0

2.1.4 Front end of receiver intermodulation specifications

Table 3 Front end of receiver intermodulation specifications

Interfering signal levelOffset from center frequencyType of interfering signal

-45dBm900kHzCW signal

-45dBm1700kHzCW signal

2.2 Relevant Specifications for GSM 900MHz BTSS2.2.1 GSM frequency band

Tx: 935--960MHz

Rx: 890--915MHz

2.2.2 Spurious emission specifications

Table 4 GSM spurious emission specifications

Frequency BandSpurious Emission Specification

9KHz-1GHz-36dBm

1805-1880MHz-47dBm

1-12.75GHz-30dBm

2.2.3 Intermodulation specifications

I. Transmitter intermodulation specifications

Table 5 Intermodulation specifications for a GSM transmitter

Frequency BandSpecification

935-960MHz-36dBm (or 70dBc)

890-915MHz-98dBm

II. Receiver intermodulation specification

Front end of receiver unwanted signal level: (-43dBm

2.2.4 Blocking specifications

Table 6 GSM 900MHz band blocking specifications

Table 7 GSM 900MHz band blocking specifications

3 RF Front-end Modules Structure and Filter Feature Specifications of CDMA2000 & GSM BTS

The front-end module in a CDMA2000 or a GSM BTSS has filters (or duplexer) for transceiver channels, which suppress outgoing spurious signals, incoming out-band signals and interference between Tx and Rx signals in the system, etc. The CDMA2000 BTSS working bands are as follows:

Tx: 870--880MHz

Rx: 825--835MHz

3.1 CDMA2000 Front-End Module

3.1.1 CDMA2000 CDU-800MHz

The CDMA2000 CDU-800MHz front-end module structure is as shown in Diagram 1. Diagram 1 CDMA2000 CDU-800MHz front-end module structure

The suppression index for Tx filter of various frequency bands are shown in Table 8 .

Table 8 Tx filter specifications of a CDMA2000 CDU/800MHz

Frequency bandAttenuations (dBc)Remarks

9~150kHz30

150kHz~30MHz30

921~960MHz44

824~849MHz95

Other band in 30~1000MHz30

1710~1785MHz103

1805~1880MHz44

1880~1920MHz85

1920~1980MHz85

2010~2025MHz73


2110~2170MHz44

2180~12750MHz30

3.1.2 CDMA2000 DDU-800MHz

The composition of a CDMA2000 DDU-800MHz is illustrated below in Diagram 2, and signal attenuation specifications of the Tx duplexer within various frequency bands are listed in Table 9 below.

Functional block diagram of a CDMA2000 DDU-800MHz

Table 9 Tx Duplexer specifications of a CDMA2000 DDU/800MHz


9~150kHz23

150kHz~30MHz23

890~909MHz70

909~915MHz80

921~960MHz44

824~849MHz95


1710~1785MHz103

1805~1880MHz34

1880~1920MHz73

1920~1980MHz85

2010~2025MHz73

2110~2170MHz44


3.2 GSM900MHz CDU Front-End Module

The composition of a GSM900MHz CDU front-end module is illustrated below in Diagram 3, and signal attenuation specifications of the Tx duplexer within various frequency bands are listed in Table 10 below. The duplexer specifications of an EDU are basically the same as those of a CDU.

Diagram2 Block diagram of a GSM900MHz CDU

Table 10 Tx duplexer specifications of a GSM900MHz CDU


9KHz ~ 885MHz 40 dB

890MHz ~ 915MHz 95 dB

1000MHz ~ 1705MHz 40 dB

1710MHz ~ 1785MHz 95 dB

1805MHz ~ 1880MHz 75 dB

1920MHz ~ 3GHz 62 dB

3-6GHz 50 dB

6-12.75GHz 40 dB

4 Interference Analysis

Here below is the analysis of interference between two different co-site base station systems, on the basis of their protocol specifications described in section 2. Please note that none of the calculations below involves any insertion losses (mainly including module insertion losses and feeder losses), because the total insertion loss varies according to actual lengths of feeder cables. However, the total insertion loss can be taken as an isolation margin.

4.1 Analysis of Interference between CDMA2000 and GSM900 Systems4.1.1 Analysis of Interference of System GSM900MHz by System CDMA2000I. Rx in-band spurious interference analysis

If a spurious signal radiating from system CDMA2000 out of band 890--915MHz falls within the Rx working frequency band of system GSM900MHz, the CDMA2000 system would interfere the GSM900MHz system.

The equivalent noise level of a GSM receiver is required to be -113dBm/200k (the GSM protocol requires that the BTS receiver sensitivity be -104dBm with the carrier-interference ratio being 9dB). Hence, The level of the Rx in-band unwanted signal must be less than -120dBm/200k (with a 7dB margin added). As a result, the level of the out-band signal spurious emission from system CDMA2000 within the Rx working frequency band of system GSM900MHz must be less than -120dBm/200k. The level of the out-band signal emitting from Huawei system CDMA2000 power amplifier within the working frequency band of system GSM900MHz is -26dBm/100k (-23dBm/200k). And the suppression of Huawei CDU is greater than 56dB within band 890-915MHz while the suppression of Huawei DDU is greater than 70dB within band 890-915MHz. In the case of Huawei CDU, the antenna isolation is required to be:

-23-56- (-120)=41dB;

In the case of Huawei DDU, the antenna isolation is required to be:

-23-70- (-120)=27dB.2. Intermodulation interference analysis

According to the GSM protocol, the intermodulation interference level from out-band of GSM900 transmitting band should be lower 30dB than the transmitter maximum power output (For GSM is 46dBm). So the CDMA2000 BTS emitting level within GSM900 transmitting band should be less than 45-30=15dBm (45dBm is the CDMA BTS maximum power output). While the requirement of CDMA2000 BTS spurious emission is -13dBm/100k, which is far less than 15dBm. The intermodulation interference within transmitting band can be ignored.

GSM protocols require that the interference level falling into GSM receiver front-end should be less than 43dBm. Here considers the interference from CDMA2000 transmitter with the maximum power output 45dBm, so the system isolation is required to be:

45- (-43)=88dB

The antenna isolation calculation is based on the indexes of GSM receiver front-end module. Because the diversity filter has the lower suppression capability on out-band signal (65dB within 935-960MHz), this filter index is taken to calculate the antenna isolation as follows: 88-65=23dBBecause the maximum spurious signal strength of the CDMA2000 out-band is -13dBm/100k, which is far less than the transmit power. The intermodulation interference within receiving band can be ignored.

3. Blocking analysis

Highest requirements of Blocking level for GSM receiver are: inband -26dBm, out-band: 8dBm.

Because the level of the spurious emission from system CDMA2000 within the GSM900 frequency band is -23dBm/200k, the antenna isolation is required to be:

-23-(-26) = 3dBThe maximum power output of CDMA2000 BTS is 45dBm, and the out-band suppression of the GSM receiver is higher than 65dB. The blocking calculation is based on the signal transmitted from CDMA2000 system as follows:

45-65=-20dBm

Hence, GSM blocking caused by out-band CDMA signals is ignorable.

4.1.2 Analysis of Interference of System CDMA2000 by System GSM900MHzI. Rx inband spurious smission analysis

The equivalent noise level of CDMA receiver is -109dBm/1.23M (with the Noise Figure being 4dB). When 11 dB is added as margin, The interference level caused by spurious emission within the receiving band is required less than or equal to -120dBm/1.23M.According to protocol specifications, the level of the spurious emission from GSM900MHz system within the CDMA2000 frequency band is less than or equal to -36dBm/3M.At present the out-band suppression of GSM frond-end module duplexer within CDMA2000 frequency band is actually greater than 98dB. Hence, according to the power amplifier indexes (the suppression of the amplifier on spurious emission is 70dBc), the spurious emission level fall into the front-end of The receiver is 46-70-98=-122dBm; therefore the required antenna isolation is:

-122-(-120)=-2dB

In other words, the CDMA2000 system shall not be affected even if there is no isolation between antennas.

2. Intermodulation interference analysis

The intermodulation attenuation out of CDMA2000 transmitting band is required to be less than 30dB. In other words, the interference level is required to be less than 45-30=15dBm. The spurious emission from GSM900MHz system within band 869-894MHz is less than or equal to -36dBm/3M(-40dBm/1.23M), so the requirement is met.

The intermodulation interference specifications of CDMA2000 receiver require that the interference level falling into the frond-end of the receiver should be less than or equal to -45dBm. Here considers the interference from GSM transmitter with the maximum power output 46dBm, and the diversity filter of CDMA2000 CDU frond-end module has the lower suppression capability on out-band signal (65dB within GSM transmitting band), so the system isolation is required to be: ((46-65)-(-45)=25dB. The suppression of CDMA2000 DDU front-end module within GSM transmitting band exceeds 90dB, so it can be ignored.3. Blocking analysis

The blocking level specification for a CDMA2000 receiver is: -30dBm (for both in-band and out-band signals).

The level of the spurious emission from the GSM system within CDMA2000 receiving is less than or equal to -40dBm/1.23m, and therefore the blocking caused by GSM spurious emission is quite weak.

The maximum power output of GSM BTS is 46dBm, and the out-band suppression of the CDMA2000 receiver is higher than 65dB. The blocking calculation is based on the signal transmitted from GSM system as follows:

46-65-(-30)=11dBm

5 Analysis and Calculation of the Influence of Interference on Receiver Sensitivities of GSM and CDMA2000 Systems

5.1 Equivalent Noise Level Analysis

Suppose the Rx intermediate frequency bandwidth of BTS is Bw (MHz), and the receiving noise figure of BTS is Nf (dB).

Then the equivalent noise level of the BTS receiver is:

No=-114+10log (Bw)+Nf (dBm)

Suppose the demodulation carrier-interference ratio of the BTS receiver is C/I (dB).

The theoretical BTS receiver sensitivity is So=No+(C/I)m, wherein the (C/I)m is the minimum carrier-interference ratio. According to this equation, the equivalent noise level directly affects the BTS receiver sensitivity, namely, with the equivalent noise level increasing by 1dB, the BTS receiver sensitivity would deteriorate by 1 dB.

Typical values of the above mentioned parameters of the current GSM and CDMA (IS95, CDMA2000, WCDMA) systems are respectively listed in the following table.

Table 1 Values of typical parameters of various mobile communication systems

IF Bandwidth (Bw) (MHz)BTS Noise Figure

(dB)BTS Equivalent Noise Level (dBm)Minimum Demodulation Carrier-Interference Ratio (dB)Theoretical Receiver Sensitivity (dBm)

GSM0.24-1179-108

IS951.254-109-14-123

CDMA20001.254-109-16-125

WCDMA54-103-19-122

in most cases, the actual minimum demodulation carrier-interference ratios are basically the same as those values in the table.

The external co-channel spurious interference within the receiving band is supposed to be additive white Gaussian noise. The influence of this noise on the system is to be superimposed to the previous equivalent system noise level, and to increase the receiving noise level. Listed in the following table are values of the system receiver equivalent noise level raised under influences of several noise levels (all in dB).

Table 2 Influence of noise levels on the equivalent system noise level

The noise level is less than equivalent system noise level in dB201612109630

The total noise level increases in dB after the external noise interfering 0.040.10.370.40.50.971.763

the receiver sensitivity deteriorates in dB after the external noise interfering0.040.10.370.40.50.971.763

According to the above table, if the previous receiver sensitivity is allowed to deteriorate by 0.5dB, the permissible noise level must be 9dB less than the previous equivalent system noise level; if the previous receiver sensitivity is allowed to deteriorate by 0.1dB, the permissible noise level must be 16dB less than the previous equivalent system noise level; and if the noise level is equal to the previous equivalent system noise level, the receiver sensitivity would deteriorate by 3dB.

Taking a GSM BTS as an example, here below is the calculation of the permissible external noise level.

According to GSM0505 protocol specifications, the sensitivity of a GSM BTS receiver must excel -104dBm. If the minimum signal demodulation carrier-interference ratio is 9dB, the equivalent receiver noise level would then be -113dBm. Suppose at the frond-end of the receiver there is now an external noise with a noise distribution similar to a white noise. If the previous GSM receiver sensitivity is allowed to deteriorate by 3dB, the noise level can be equal to the previous equivalent receiver noise level, i.e. 113dBm. If the receiver sensitivity is allowed only to deteriorate by 0.5dB, the noise level must be 9dB less than the previous receiver noise level, i.e. -122dBm/200KHz. If the receiver sensitivity is allowed only to deteriorate by 0.1dB, the noise level must be 16dB less than the previous receiver noise level, i.e. -129dBm/200KHz.

6 CDMA2000 1x (800MHz) and IS95A BTSs Co-site Interference analyzeInterference analysis of CDMA2000 and IS95 co-site mainly in cases of these configurations mainly includes the following three cases:

(1) Influence of the BTS transmitting with f1 on the BTS receiving with f2;

(2) Influence of the BTS transmitting with f1 on the MS receiving with f2;

(3) Influence of the MS transmitting with f2 on the BTS receiving with f2.

There are two cases that CDMA2000 BTS and IS95 BTS work with adjacent frequencies. The first is they both have two carriers with the same two adjacent frequencies f1and f2 respectively. The another is CDMA2000 BTS works with f1 and IS95 BTS works with f2.

Case 1: Influence on BTS receivers itself when this BTS works with adjacent frequencies f1 and f2

In this case, at least two TRXs are configured with a sector, respectively working with frequency f1 and f2. Because each carrier must ensure the -117dBm receiver sensitivity, the spurious emission of each carrier falling within the BTS Rx frequency band is at least less than -110dBm to guarantee the receiver sensitivity. Hence, interfering sources are mainly the dividers crosstalk and inter-transmitter intermodulation. As for the dividers crosstalk, because full consideration has been given to the crosstalk issue during system designs, and there are specifications for the in-band spurious emission of each TRX and for the isolation of the dividers port. This issue is nonexistent (the receiver sensitivity and other receiving specifications must be complied with). As for the inter-transmitter intermodulation, because the duplex space between Tx and Rx in CDMA800MHz system is 45MHz, and the intermodulation of two frequencies at an interval of 1.23MHz, falling into the Rx frequency band, is already below order 45, the intermodulation of adjacent frequencies can be ignored.Conclusion: No influence, ignorable.Case 2: Influence on BTS receivers when different BTSs work respectively with adjacent frequencies f1 and f2In this case, BTS A works at f1 and has its own transmitting & receiving antenna, while BTS B works at f2 and has another transmitting & receiving antenna.(1) Co-channel spurious interference of receiversAccording to specifications for CDMA base station systems, the maximum level of the out-band spurious emission of a transmitter is in theory -13dBm/100KHzRBW (equivalent to -3dBm/1MHzRBW). If this spurious signal falls within the Rx frequency band, it would severely interferes the receiver of another BTS. To ensure the minimum 117dBm receiver sensitivity, the spurious signal level of the transmitter, falling into the front-end of receiver within the Rx frequency band, is definitely less than -110dBm.

Suppose the BTS receiver sensitivity is the typical -123dBm/1MHzRBW, and its equivalent receiver noise level is -109dBm/1MHzRBW. If the receiver sensitivity is allowed to deteriorate by 3dB, the permissible co-channel interference level is-109dBm/1MHzRBW.

Hence, the requirement for the isolation between the transmitting antenna of one BTS and the receiving antenna of another is: the relative net gain being no greater than 1dB.

(2) Blocking of receivers

According to specifications for CDMA base stations, the receiver blocking level is required to be at least -30dBm (for both in-band and out-band signals). To comply with this specification, BTS must have a Tx/Rx isolation of more than 80dB at least. In other words, the level of the Tx signal falling into the receiver must be less than -30dBm. Because the Tx/Rx working frequency bands of the two BTSs are completely identical with each other, Tx/Rx isolation between different BTSs is complied with each other. Hence, the blocking issue is nonexistent so far as there is no net gain between antennas of the two BTSs (e.g. none face-to-face emission).

Conclusion: Because the Tx/Rx working frequency bands of the two BTSs are completely identical with each other, and both comply with the same protocol specifications, the blocking is nonexistent so far as there is no net gain between antennas of the two BTSs due to a face-to-face emission.

Case 3: Influence on the MS receiving when adjacent frequencies f1 and f2 are employed for one same sector.

The following two interference cases should be considered.

(1) Co-channel receiving interference

According to CDMA specifications, the receiving sensitivity of CDMA MS is required to be no worse than -104dBm/1MHz. If the receiving noise figure is the typical 7dB, the equivalent noise level would be -97dBm/1MHz. If the receiving sensitivity is allowed to deteriorate by 3dB, the permissible co-channel interference level is -97dBm/1MHz.

There is an ACPR (Adjacent Channel Power Ratio) for each CDMA BTS carrier (less than 45dBc if the offset from the center frequency is 750KHz, and less than 60dBc if the offset from the center frequency is 1.98MHz). If two adjacent frequencies are employed for one cell, because the SNR of the signal arriving at a MS would be more than 45dB, the interference level of the f2 signal received by a MS working at f1 would be far less than 97dBm, thus not resulting in co-channel interference.

(2) Blocking interference

The MS receiving level is required within the range from -20dBm to its sensitivity. If the received signal level exceeds 20dBm, the MS may be blocked.

As analyzed in (1), if the two adjacent frequencies are employed for one cell, because there is almost no difference in propagation loss between them, it is impossible that the f1 signal would block the MS working at signal f2.

But, if the two adjacent frequencies come from two different cells, and the MS has been restricted to a certain working frequency, it is possible that the MS may be blocked by the invalid frequency signal.

Conclusion: If a MS is able to select the stronger signal to get online, the interference issue is nonexistent. If MS has been restricted to one certain working frequency, and the location of the MS is within the coverage area of an invalid signal, the MS may not be able to get online.

7 Antenna Isolation Calculations

In this section, equations used to calculate the antenna isolation based on the antenna gains and mounting distance between antennas are given..

7.1 Horizontal Antenna Isolation Calculation

Here below are values of relative gains of antenna emissions at various angles.

The angle of the antenna beam in the direction of maximum emission is defined as 0. Relative gains of antenna emissions at different angles in column Angle a, with reference to the gain in the direction of maximum emission, are listed below in Table 13 (which applies to all 824-960MHz BTS antennas. When angles are greater than 90, relative gains of antennas in similar types made by different manufacturers may have an error of about 3dB):

Table 3 Relative gains of antenna emissions at different angles

Angle a6590120

00 (dB) same below0 (dB) same below0 (dB) same below

5-0.100

10-0.3-0.2-0.1

15-0.7-0.4-0.2

20-1.2-0.7-0.3

25-1.9-1.1-0.5

30-2.7-1.5-0.7

35-3.6-2-0.9

40-4.6-2.6-1.2

45-5.8-3.3-1.6

50-7-4-2

55-8.3-4.8-2.4

60-9.7-5.7-2.9

65-11.2-6.6-3.5

70-12.6-7.6-4.1

75-14-8.6-4.7

80-15.4-9.7-5.5

85-16.5-10.8-6.3

90-17.6-11.9-7.1

95-18.5-12.8-7.8

100-19.5-14-8.5

105-20.5-15.3-10.1

110-21.5-16.7-11.7

115-22.4-18.3-14.2

120-23.5-20-16.5

125-24.7-21.8-18.6

130-26.8-23.4-20

135-27.7-25-21.6

140-29.2-26.2-22.9

145-30.1-26.6-22.9

150-31.6-26.4-22.7

155-30.5-26.1-22.5

160-30.8-26-22.4

165-29.9-26.3-22.7

170-28.8-26.4-22.9

75-27.9-26.4-23.0

180-27.0-26.4-23.1

With the above data, following equations can be used to calculate the isolation between two antennas.

When two antennas are placed in the horizontal direction, the isolation between them depends upon their emission patterns, distance between them and gains. The gain in the direction of maximum emission of antenna 1 is G1 (dBi), and the level of the side lope at angle a1 is SL1 (in dBp, a negative value relative to the gain of the main beam). The gain in the direction of maximum emission of antenna 2 is G2 (dBi), and the level of the side lope at angle a2 is SL2. The horizontal distance between the two antennas is d. a1 is the angle from the line in the direction of maximum emission of antenna 1 to the connecting line between antenna 1 and antenna 2, a2 is the angle from the line in the direction of maximum emission of antenna 2 to the connecting line between antenna 2 and antenna 1. Then, the horizontal isolation between antennas is:

HI=-22-20log(dh/ (dB) (negative value)........(1)

If they are both omnidirectional antennas, SL1=SL2=0(dB). Variable in the above equation stands for working wavelength (similar to the far field analysis).

Equation 1 is applicable under far field conditions. The distance between the two antennas must meet the following requirement (in which case, the error is about 0.5dB):

dh>((L1+L2)2/); wherein, L1 and L2 are respectively the maximum sizes of the two antennas.

If the distance between them is close, the HI calculated by means of equation 1 has a relatively great error (about 6-10dB less than the HI actually measured). Please refer to Antenna Isolation Test and Analysis.Examples:

Example 1: There is an omnidirectional antenna (900MHz, 11dBi) and a directional antenna (900MHz, 65, 18dBi); the distance between them, d, is 300m; a=60. Here below is how we calculate the isolation between the two antennas. The antennas are placed as illustrated below in Figure 5.

Figure 2 Relative positions of the omnidirectional and directional antennas

Therefore, G1=11, SL1=0, dh=300, G2=18, SL2=-9.7 (found in Table 13 above), =300/947.5=0.317. Substitute variables in equation 1 with these values:

HI= -22-20log(dh/ = -22-20log(300/0.317)+(11+18)+(0-9.7) = -62.2 (dB).

Hence, the antenna isolation is 62.2dB.

Example 2: There is a directional antenna (900MHz, 90, 15dB) and another (900MHz, 120, 15dBi); the distance between them, d, is 300m; a1=90; a2=60. Here below is how we calculate the isolation between the two antennas. The antennas are placed as illustrated below in Figure 6.

Figure 3 Relative positions of the two directional antennas

Therefore, G1=15, SL1=-11.9 (found table 17 above), dh=300, G2=15, SL2=-2.9 (found in Table 13 above), =300/947.5=0.317. Substitute variables in equation 1 with these values:

HI = -22-20log(dh/ = -22-20log(300/0.317)+(15+15)+(-11.9-2.9) = -66.3 (dB).


Example 3: there is a directional antenna (1800MHz, 65, 15dBi) and another (1800MHz, 65, 15dBi); the distance between them, d, is 300m; a1=90; a2=60. Here below is how we calculate the isolation between the two antennas. The antennas are placed as illustrated below in Figure 7.

Figure 4 Relative positions of the two directional antennas

Therefore, G1=15, SL1=-11.9 (found in Table 13 above), dh=300, G2=15, SL2=-2.9 (found in Table 13 above), =300/1842.5=0.163. Substitute variables in equation 1 with these values:

HI= -22-20log(dh/= -22-20log(300/0.163)+(15+15)+(-11.9-2.9)= -72.1(dB).


7.2 Vertical Antenna Isolation Calculation

If two BTS antennas are mounted on the same tower but different levels, they are placed in the vertical direction. The following equation is used to calculate the isolation between two antennas in the vertical direction and aligned (see the diagram on the left in Figure 8):

VI=-(28+40log(dv/))+(g1+g2) dB ........(2).

Herein, g1 stands for the gain of antenna 1 in the direction of antenna 2, while g2 stands for the gain of antenna 2 in the direction of antenna 1. Usually, the approximate value, g1=g2=0dBi, can be assumed.

The following equation is used to calculate the isolation between two antennas in the vertical direction but not aligned (see the diagram on the right in figure 8):

SI=(VI-HI)angle/90+HI .......... (3)

Figure 5 Relative positions of two antennas Placed in the vertical direction

7.3 Calculation of Antenna Gain in any Direction

During the interference analysis, we usually wish to know what is the antenna gain in a certain direction, but antenna suppliers in most case only provide the horizontal and vertical emission patterns. If a point is located on neither the horizontal nor the vertical patterns, the following equation, equation 4, can be used to calculate the antenna gain at this point.

Suppose the antenna gain is G (dBi), and the normalized horizontal and vertical emission patterns of the antenna are illustrated below in Figure 9. The following equation can be used to calculate the gain at point P. The location of Point P in the horizontal direction is illustrated in the diagram on the right in Figure 9.

G (p)=G+10log (10eh/1010ev/10); wherein, ev is the vertical emission pattern normalized value (-dB)

=G+10log (10-3/1010-10/10)=G-13 (dB); wherein, eh is the horizontal emission pattern normalized value (-dB).

Figure 6 Emission patterns of the antenna

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