GSM and UMTS RF Colocation

COSITING BETWEEN UMTS AND GSM SYSTEMS

Dr. Hatem MOKHTARI

Dr. Hatem MOKHTARI, September 2004 /25

T A B L E O F C O N T E N T S

1. INTRODUCTION ......................................................................................................4

1.1. OBJECT .........................................................................................................4

1.2. SCOPE...........................................................................................................4

2. ABBREVIATIONS & DEFINITIONS .........................................................................4

2.1. ABBREVIATIONS...........................................................................................4

2.2. DEFINITIONS.................................................................................................4

4. INTERFERENCE MECHANISMS .................................................................................5

4.1 SYSTEMS AND BRAND TO BE CONSIDERED ................................................5

4.2 TYPES OF INTERFERENCES ...........................................................................5

5. THEORETICAL CONSIDERATIONS............................................................................6

5.1 HYPOTHESIS FOR CALCULATION ..................................................................6

5.2 CO LOCATION BETWEEN GSM SITES AND UMTS SITES .............................7

5.2.1 WIDEBAND NOISE .................................................................................7 5.2.2 SPURIOUS EMISSIONS.........................................................................7 5.2.3 INTERMODULATIONS............................................................................8

Intermodulations generated by the transmitter .........................................8 Intermodulations generated by the transmitter .........................................8

5.2.4 BLOCKING ..............................................................................................8

5.3 CONCLUSION ....................................................................................................9

6. ANTENNA DECOUPLING POSITIONS......................................................................10

6.1 TESTED ANTENNAS...................................................................................10

6.2 TESTED POSITIONS...................................................................................11

6.2.1 HORIZONTAL SEPARATION..........................................................11 6.2.1.1 Basic horizontal separation ...................................................11 6.2.1.2 Horizontal separation with an azimuth divergence ................12

6.2.2 VERTICAL SEPARATION ...............................................................13 6.2.2.1 Basic vertical separation .......................................................13 6.2.2.2 Vertical separation with different azimuths ............................14

6.2.3 DOUBLE SEPARATION..................................................................15 6.2.3.1 Basic horizontal – vertical separation ....................................15 6.2.3.2 Horizontal - vertical separation with different azimuths .........16

7. MEASUREMENT SIGNAL .....................................................................................17

7.1 MEASUREMENT FREQUENCY IN TRANSMISSION BANDWIDTH...........17

7.2 MEASUREMENT FREQUENCY IN RECEPTION BANDWIDTH .................17

8. ANALYSIS OF THE RESULTS ..............................................................................18

8.1 COMMENTS....................................................................................18

8.2 HORIZONTAL SEPARATION WITH AZIMUTH DIVERGENCE...................18

8.2.1 COMMENTS....................................................................................18

8.3 BASIC VERTICAL SEPARATION ................................................................19

8.3.1 COMMENTS....................................................................................19

8.4 VERTICAL SEPARATION WITH DIFFERENT AZIMUTHS .........................19

8.4.1 COMMENTS....................................................................................19

8.5 BASIC HORIZONTAL – VERTICAL SEPARATION .....................................20

8.5.2 COMMENTS....................................................................................20

8.6 HORIZONTAL-VERTICAL SEPARATION WITH A DIFFERENCE OF AZIMUTHS OF 90 DEG...................................................................................................20

8.6.1 COMMENTS....................................................................................20

9 CONCLUSION........................................................................................................22

EXAMPLE...............................................................................................................25

END OF DOCUMENT ...........................................ERROR! BOOKMARK NOT DEFINED.


1. INTRODUCTION

1.1. OBJECT Colocation of UMTS sites with existing GSM-900 / GSM-1800 sites requires the evaluation of potential interference. In the present document, the following points have been treated:

• First of all, the interference mechanisms due to system GSM/ UMTS • Then a theorical study considers each of these latter phenomena and gives the

required isolation between GSM / UMTS In order to evaluate this and deduce the necessary engineering rules, two kinds of antennas characteristics has been studied:

Out of band radiation Decoupling between two antennas

In a first step, these two characteristics have been analyzed through measurements, which was made with the help of a Research Center.

1.2. SCOPE This document only considers the decoupling between GSM-900/UMTS, GSM-1800/UMTS and Dual antenna/UMTS antennas in the UMTS band frequency. This study is done on directive antennas.

2. ABBREVIATIONS & DEFINITIONS

2.1. ABBREVIATIONS GSM : Global System for Mobile communications DL : Downlink UL : Uplink UMTS : Universal Mobile Telecommunication System

2.2. DEFINITIONS Antenna decoupling: Signal attenuation between two antennas.


4. INTERFERENCE MECHANISMS

4.1 SYSTEMS AND BRAND TO BE CONSIDERED Obviously, the more systems coexist in a confine zone, the more risky interference is. Thanks to recommendations, it is possible to evaluate the potential jamming generated by one system on another one. In this document, we only consider the following systems: • GSM 900, R-GSM and GSM 1800 • UMTS FDD The evaluation of interference in a system is related to the bands allocated to each interfering and interfered system. • The interfered BTS transmitting in in-band and out-band of its transmitting band

(DL) • The victim BTS receiving in in-band and out-band of its transmitting band. The following tables gives the transmitting and receiving bands of GSM 900 R-GSM, GSM 1800 and UMTS

GSM 900 R-GSM GSM 1800 UMTS Receiving band 890-915 MHz 876-915 MHz 1710-1785 MHz 1920-1980 MHz

Transmitting band 935-960 MHz 921-960 MHz 1805-1880 MHz 2110-2170 MHz

4.2 TYPES OF INTERFERENCES In the analysis of co-location, different interference mechanisms occur:

• Wideband noise

The wideband noise describes unwanted emissions outside the channel bandwith resulting from the modulation process and non linearity in the transmitter but excluding the spurious emissions. So, the jamming transmit part can generate wideband noise in the receive part and can raise the noise level of this latter. Wideband noise depends on the frequency between the transmit carrier and the receiving band.

• Spurious emissions

The spurious emissions are emissions, which are caused by unwanted transmitter effects such as harmonics emissions, parasitic emissions, intermodulation products. So, the spurious emissions issued from the transmit part can jam the receiver, as parasitic signal.

• Blocking

The receiver can be blocked by the normal transmitted carrier of the transmitter, which simply means that reception can be disturbed in presence of a strong interfering signal.


• Intermodulation products

Even if intermodulations products are above all spurious emissions, specifications consider this type of interference in specific paragraph. Indeed: -The transmitter can generate intermodulation products, which can fall in the receiver band and cause jamming. However, since the transceiver is complying the recommendations, the the intermodulation product will have a level below a certain limit: actually the GSM and UMTS recommendations specify some tests to verify that the transmitter is able to restrict the generation of interfering signals in its non linear elements. - High signals, issued from the transmitter, can also induce intermodulation products inside the receiver RF parts and cause degradation in reception. Maximum level of interfering signals have been defined in recommendation, guaranteeing the good reception: actually, the GSM and UMTS recommendations specify some tests to verify that the receiver is able to receive a wanted signal despite the presence of two interfering signals, which have a specific frequency relationship to the wanted signal. These five mechanisms are the only one taken into account in the GSM and UMTS recommendations. Actually, other phenomena might exist, but they are not controlled by any rules. For example, electromagnetic compatibility problems may be encountered in a site between:

- feeders - antennas - transceivers and receivers.

Any way these problems cannot be forecast and must be treated on site, case by case.

5. THEORETICAL CONSIDERATIONS

In this part we only consider the GSM recommendations and the UMTS recommendation to calculate the necessary decoupling between:

- one GSM 900 system and one UMTS system - one R-GSM system and one UMTS system - one GSM 1800system and one UMTS system.

5.1 HYPOTHESIS FOR CALCULATION The following configuration have been assumed for the calculation of the necessary isolation between systems:

- As the channel bandwidths are differents in GSM and in UMTS, we prefer to use all the signal power levels (GSM and UMTS) per Herz

- 43dBm output power (per carrier) is assumed to be at the antenna port of GSM BTS.


- The noise figure of GSM BTS is assumed to be 4 dB, so k.T.F (thermal noisefloor +

noise figure) is equal to –170 dBm/Hz

- 48 dBm output power for one carrier is assumed to be at the antenna port of UMTS BTS. It is the maximum output power we can have with the UMTS BTS, considering a STSR configuration with 2 PA per sector at full power.

- The noise figure of GSM BTS is assumed to be 3.3dB so k.T.F (thermal noise +

noise figure) is equal to –170.7dBm/Hz

- Within the receiving channel, there is no specification about the maximum level of any signal disturbing the reception.

Meanwhile, it seems that the GSM spurious emissions level in the UMTS receiving band (new GSM requirement) has been specified so that degradation at the UMTS receiver of 0.8dB has been allowed. So, there is also the UMTS tolerable interference level at the antenna connector ao that the degradation of the thermal noise floor + noise figure (k.T.F) of 0.8 dB is accepted.

- UMTS receiving channel:

Considering the k.T.F equal to –170.7 dBm/Hz, there will be a degradation of 0.8 dB of this level if there is an interfering signal of –178dBm/Hz. It means that the maximum tolerable interference level in the UMTS receiving channel is about –178dBm/Hz

5.2 CO LOCATION BETWEEN GSM SITES AND UMTS SITES

5.2.1 WIDEBAND NOISE

As the frequency separation between the GSM 900/ R-GSM band and the UMTS band and between the GSM 1800 band and the UMTS band is large, we assume that the transmit part (GSM 900 / R-GSM / GSM 1800) do not generate wideband noise in the receive part (UMTS). This assumption is in compliance with the GSM 05.05, which only considers the modulation spectrum (i.e wideband noise) up to 2 MHz either side of the transmit band.

5.2.2 SPURIOUS EMISSIONS

The GSM recommendation 05.05 specifies a maximum level of spurious emisssions in the frequency band 1 – 12.5 GHz, including the UMTS receiving band. This maximum power should not be greater than –30dBm at the base station RF output port, power measured in 3 MHz bandwidth, what is equivalent to –95dBm/Hz Note: According to a new requirement added to the GSM 05.05 in july 2000, which considers the colocation of GSM BTS with UMTS BTS the measured power of the spurious emissions within the UMTS receiving band shall be no more than 96dBm over 100kHz, what is equivalent to –146 dBm/Hz.

To calculate the necessary isolation between antennas we keep the worst case which a spurious emission of –95dBm/Hz.


The difference between the maximum level of the spurious emissions and the maximum level of interfering signal within the UMTS receiving channel gives the required isolation to guarantee to avoid interference.

Jamming system Victim system Tx UMTS Rx UMTS

Specified spurious emissions over 3 MHz

-30 dBm

Specified spurious emissions per HZ

-95dBm

Maximum level of unwanted signal per Hz

-178 dBm

Necessary isolation between antenna connectors

83 dB

5.2.3 INTERMODULATIONS

Intermodulations generated by the transmitter The GSM 05.05 recommendation specifies that the power level of intermodulation products when an interfering signal is injected into the antenna connector at a level of 30 dB lower than that of the wanted signal, shall not exceed the spurious emissions requirements, i.e. –30dBm in the UMTS receiving band at the base station RF outport, power measured in 3MHz bandwidth, what is equivalent to –95dBm/Hz It is the same level than the one specified for the spurious emissions, so we need the same decoupling between antenna connectors.

Intermodulations generated by the transmitter The UMTS TS 25.104 recommendation specifies a test to verify the receiver performance: the reference sensitivity performance shall be met when two interfering signals, with a power equal to –48dBm, are coupled to the UMTS BTS antenna connector.

5.2.4 BLOCKING The UMTS TS 25.104 recommendation specifies that out-of-band, the maximum level of interfering signals (CW carrier) for blocking is equal to –15dBm. The GSM power is assumed to be 43dBm at antenna connector. This power is over 200kHz, rather than a CW interfering source as defined in TS 25.104. Comparing this value to the blocking point, the necessary isolation between the two antennas can be calculated.


Jamming system Victim System Tx GSM Rx UMTS

Transmit output power 43 dBm Blocking point out of receiving

band -15 dBm

Necessary isolation between antenna connectors.

58 dB

5.3 CONCLUSION

The isolation required to protect UMTS from GSM interference is 83 dB. This value is very high, it is explained by the fact that GSM standard was fixed without thinking about protection of UMTS. (cositing UMTS /GSM has been taken into account in the UMTS standard and there should not be problem of interference from UMTS in GSM Rx Band.) This high value of 83dB concerns the BTS installed before july 2000, the BTS installed after this date should comply with the new GSM recommendation which fix the level of spurious emissions lower than –146 dBm/Hz, so the isolation required for this equipment is 32 dB. Now all these calculations have been done only considering the GSM and UMTS specification. But often, the products have better performances than these specifications. It means that the necessary isolation to avoid any disturbance between systems will be reduced. So it is important to get the real performances of the products. The next part of the document is a study regarding the possibility to reach the necessary isolation by antenna decoupling.


6. ANTENNA DECOUPLING POSITIONS 6.1 TESTED ANTENNAS

The following set of antennas was considered : In 900 MHz band :

• directive crosspolar antenna, 65° horizontal aperture , 17 dBi max. gain: named antenna900X

In 1800 MHz band :

• directive crosspolar antenna, 65° horizontal aperture , 17 dBi max. gain: named antenna1800X

Dual band 900 / 1800 MHz :

• directive crosspolar antenna, 65° horizontal aperture , 17 dBi max. gain: named dualantennaX

In UMTS band :

• directive crosspolar antenna, 65° horizontal aperture, 17 dBi max. gain: named antenna2000X

For the Dualantenna, two cases must be studied : - GSM-900 transmission - GSM-1800 transmission For the GSM-900 transmission case, the CW signal generator is connected to the GSM-900 port, and for the GSM-1800 transmission case it is connected to the GSM-1800 port.


6.2 TESTED POSITIONS

6.2.1 HORIZONTAL SEPARATION

6.2.1.1 Basic horizontal separation The following mutual position was tested (figure 1):

d

Antenna 1 Antenna 2

d

Antenna 1 Antenna 2 front view top view

Figure 1 : Basic horizontal separation

Antenna 1 and 2 are the following ones and d varies in the following range :

Antenna 1 Antenna 2 d (m) Antenna900X Antenna2000X 0.5 1 1.5 2 2.5 3 3.5 4 Antenna1800X Antenna2000X 0.5 1 1.5 2 2.5 3 3.5 4 DualantennaX Antenna2000X 0.5 1 1.5 2 2.5 3 3.5 4

In that default case, both antennas are oriented in the same direction, perpendicular to the axe of the study. Measurements for distance lower than 0.5 m was not feasible due to the mechanical aspects of the system.


6.2.1.2 Horizontal separation with an azimuth divergence The mutual position correspond to the previous separation distance, except that both antennas are not oriented in the same direction (figure 2):

d

α

Antenna 1 Antenna 2

top view

Figure 2 : Horizontal separation with an azimuth divergence

Antenna 1 Antenna 2 α

(deg) d (m)

Antenna900X Antenna2000X 30 0.5 1 1.5 2 2.5 3 3.5 4 Antenna900X Antenna2000X 60 0.5 1 1.5 2 2.5 3 3.5 4 Antenna900X Antenna2000X 90 0.5 1 1.5 2 2.5 3 3.5 4 Antenna900X Antenna2000X 120 0.5 1 1.5 2 2.5 3 3.5 4 Antenna1800X Antenna2000X 30 0.5 1 1.5 2 2.5 3 3.5 4 Antenna1800X Antenna2000X 60 0.5 1 1.5 2 2.5 3 3.5 4 Antenna1800X Antenna2000X 90 0.5 1 1.5 2 2.5 3 3.5 4 Antenna1800X Antenna2000X 120 0.5 1 1.5 2 2.5 3 3.5 4 DualantennaX Antenna2000X 30 0.5 1 1.5 2 2.5 3 3.5 4 DualantennaX Antenna2000X 60 0.5 1 1.5 2 2.5 3 3.5 4 DualantennaX Antenna2000X 90 0.5 1 1.5 2 2.5 3 3.5 4 DualantennaX Antenna2000X 120 0.5 1 1.5 2 2.5 3 3.5 4


6.2.2 VERTICAL SEPARATION

6.2.2.1 Basic vertical separation The following mutual position was considered (figure 3):

d

Antenna 2

Antenna 1

Figure 3 : Basic vertical separation

Both antennas are pointing in the same horizontal direction. The distance d between the two antennas varies in the following range :

Antenna 1 Antenna2 d (m) Antenna900X Antenna2000X 0.5 1 1.5 2 2.5 3 Antenna1800X Antenna2000X 0.5 1 1.5 2 2.5 3 DualantennaX Antenna2000X 0.5 1 1.5 2 2.5 3

In that case, both antennas are not tilted. Measurements for distance lower than 0.5 m was not feasible due to the mechanical aspects of the system.


6.2.2.2 Vertical separation with different azimuths The following mutual position was considered (figure 4):

d

Antenna 2

Antenna 1

Figure 4 : Vertical separation with different azimuths

Both antennas are pointing in their own direction separated by an angle α. The distance d between the two antennas varies in the following range:

Antenna 1 Antenna 2 α (deg) d (m) Antenna900X Antenna2000X 90 0.5 1 1.5 2 2.5 3 Antenna1800X Antenna2000X 90 0.5 1 1.5 2 2.5 3 DualantennaX Antenna2000X 90 0.5 1 1.5 2 2.5 3

In that case, both antennas are not tilted.


6.2.3 DOUBLE SEPARATION

6.2.3.1 Basic horizontal – vertical separation This position is a combination of vertical and horizontal separation (figure 5).

d

d’

Antenna 2

Antenna 1

Figure 5 : Basic horizontal – vertical separation

Both antennas are pointing in the same direction, the d' axis study.

Antenna 1 Antenna 2 d (m) d' (m) Antenna900X Antenna2000X 1.5 0.5 1 1.5 2 2.5 3 3.5 4 Antenna900X Antenna2000X 2 0.5 1 1.5 2 2.5 3 3.5 4 Antenna900X Antenna2000X 2.5 0.5 1 1.5 2 2.5 3 3.5 4 Antenna900X Antenna2000X 3 0.5 1 1.5 2 2.5 3 3.5 4 Antenna1800X Antenna2000X 1.5 0.5 1 1.5 2 2.5 3 3.5 4 Antenna1800X Antenna2000X 2 0.5 1 1.5 2 2.5 3 3.5 4 Antenna1800X Antenna2000X 2.5 0.5 1 1.5 2 2.5 3 3.5 4 Antenna1800X Antenna2000X 3 0.5 1 1.5 2 2.5 3 3.5 4 DualantennaX Antenna2000X 1.5 0.5 1 1.5 2 2.5 3 3.5 4 DualantennaX Antenna2000X 2 0.5 1 1.5 2 2.5 3 3.5 4 DualantennaX Antenna2000X 2.5 0.5 1 1.5 2 2.5 3 3.5 4 DualantennaX Antenna2000X 3 0.5 1 1.5 2 2.5 3 3.5 4


6.2.3.2 Horizontal - vertical separation with different azimuths The mutual position correspond to the previous separation distance, except that both antennas are oriented differently (figure 6) :

d

d’

Antenna 2

Antenna 1

d'

α

Antenna 2

Antenna 1

Figure 6 : Horizontal – vertical separation with different azimuths

Antennas are not tilted.

Antenna 1 Antenna 2 α (deg)

d (m) d' (m)

Antenna900X Antenna2000X 90 1.5 0.5 1 1.5 2 2.5 3 3.5 4 Antenna900X Antenna2000X 90 2 0.5 1 1.5 2 2.5 3 3.5 4 Antenna900X Antenna2000X 90 2.5 0.5 1 1.5 2 2.5 3 3.5 4 Antenna900X Antenna2000X 90 3 0.5 1 1.5 2 2.5 3 3.5 4 Antenna1800X Antenna2000X 90 1.5 0.5 1 1.5 2 2.5 3 3.5 4 Antenna1800X Antenna2000X 90 2 0.5 1 1.5 2 2.5 3 3.5 4 Antenna1800X Antenna2000X 90 2.5 0.5 1 1.5 2 2.5 3 3.5 4 Antenna1800X Antenna2000X 90 3 0.5 1 1.5 2 2.5 3 3.5 4 DualantennaX Antenna2000X 90 1.5 0.5 1 1.5 2 2.5 3 3.5 4 DualantennaX Antenna2000X 90 2 0.5 1 1.5 2 2.5 3 3.5 4 DualantennaX Antenna2000X 90 2.5 0.5 1 1.5 2 2.5 3 3.5 4 DualantennaX Antenna2000X 90 3 0.5 1 1.5 2 2.5 3 3.5 4


7. MEASUREMENT SIGNAL CW signal S at frequency f was entered at antenna 1 input and received at antenna 2 output (figure 7). For crosspolar antenna, only one antenna 1 input was tested. Antenna 2 outputs were both measured. Since antenna2000X is crosspolar, always two measurements were done in reception.

Antenna 2

Antenna 1

Signal generator

Input

S

S’

Network analyser

Figure 7

7.1 MEASUREMENT FREQUENCY IN TRANSMISSION BANDWIDTH Frequency used for transmitting varies from 0.5 to 2.5 GHz.

7.2 MEASUREMENT FREQUENCY IN RECEPTION BANDWIDTH At antenna 2 output, S’ is measured in UMTS frequency band. As a consequence, when GSM frequency was used for transmission, measured decoupling corresponds to :

- antennas separation attenuation - band attenuation (antenna filtering effects)


8. ANALYSIS OF THE RESULTS

8.1 COMMENTS The results show that there is no difference between the S’ measurements when the signal is taken from the output +45° and the signal measured at the output –45° of the UMTS antenna. Consequently, decoupling is independent on polarization aspects. Only the signal measured at the +45° output port will be taken into account for the following results.

8.2 HORIZONTAL SEPARATION WITH AZIMUTH DIVERGENCE

8.2.1 COMMENTS Decoupling increases with the growth of the angle and the horizontal distance

between the two antennas. This is due to basic separation distance effects. The reason of the decoupling increase with the angle is that in every case the

antenna 1 is a directive antenna. So, when angle exceeds 30 degrees, the radiation from the antenna 1 to antenna 2 decreases.

We can notice that the decoupling between the UMTS antenna and GSM-900 antenna is the greatest.

Decoupling values for the dual antenna in case of GSM-1800 transmission and for the GSM-1800 antenna are very closely.

The minimum decoupling measured for each antenna is in the case of 0.5m horizontal distance and for the basic horizontal separation (corresponding to the worst radiation case).

Isolation measured for the dual band antenna in case of GSM-900 transmission is roughly 10-15 dB below than the one of GSM-900 antenna.

The minimum and maximum decoupling for each antenna are noted in the following table:

Antennas Min decoupling function of

the separation distance Max decoupling function of the separation distance

GSM 900 - UMTS 65 dB (α = 0°) 80 dB (α=0°) to 90 dB (α=120°) GSM 1800 - UMTS 50 dB (α = 0°) 65 dB (α=0°) to 80 dB (α=120°) Dualband - UMTS GSM-1800

50 dB (α=0°) GSM-900 50 dB (α=0°)

GSM-1800 65 dB (α=0°) to 85 dB (α=120°)

GSM-900 70 dB (α=0°) to 85 dB (α=120°)


8.3 BASIC VERTICAL SEPARATION

8.3.1 COMMENTS S' decreases with the growth of the vertical distance between the two antennas. This

is due to basic separation distance effects. Compared to horizontal separation, higher decoupling is obtained thanks to limited antenna vertical radiation pattern.

The decoupling between the UMTS antenna and GSM-900 antenna is always the greatest.

The minimum decoupling measured for each antenna is in the case of closed antennas.

There is no much gain to obtain in widely separating antennas: 10 dB from 0.5m to 3m.



Antennas Min decoupling (d=0.5m) Max decoupling (d=2.5m) GSM 900 - UMTS 70 dB 80 dB GSM 1800 - UMTS 55 dB 65 dB Dualband - UMTS GSM-1800

60 dB GSM-900 65 dB

GSM-1800 65 dB

GSM-900 70 dB

8.4 VERTICAL SEPARATION WITH DIFFERENT AZIMUTHS

8.4.1 COMMENTS Decoupling increases with the growth of the vertical distance between the two

antennas. The decoupling between the UMTS antenna and GSM-900 antenna is always the

greatest. The comparison between the results of the basic vertical separation and of this

position shows that the second position gives a better decoupling between the antennas. This is due to radiation filtering in angles.



There is no much gain to obtain in widely separating antennas: 10 dB from 0.5m to 3m.


Antennas Min decouplig (d=0.5m) Max decoupling (d=2.5m) GSM 900 – UMTS 70 dB 80 dB GSM 1800 – UMTS 60 dB 75 dB Dualband – UMTS GSM-1800

60 dB GSM-900 65 dB

GSM-1800 75 dB

GSM-900 75 dB


8.5 BASIC HORIZONTAL – VERTICAL SEPARATION The following figures (figure 19 to figure 22) shows the variation of S’ in function of the horizontal and vertical distances between the two antennas. These two antennas are oriented in the same direction (Figure 5 : ).


antennas, but doesn't fluctuate very much with the horizontal distance. 1.5m vertical distance is enough to reach basic attenuation. Between 0.5m and 1.5m horizontal separation 10 dB are to gain, not more is expected.

The decoupling between the UMTS antenna and GSM-900 antenna is always the greatest.

Decoupling values for the dual antenna in case of GSM-1800 transmission and for the GSM-1800 antenna are very closely.



Antennas Min decoupling(d=0.5m) Max decoupling(d=3m) GSM 900 – UMTS 70 dB 85 dB GSM 1800 – UMTS 60 dB 70 dB Dualband – UMTS GSM-1800

60 dB GSM-900 65 dB

GSM-1800 70 dB

GSM-900 70 dB

8.6 HORIZONTAL-VERTICAL SEPARATION WITH A DIFFERENCE OF AZIMUTHS OF 90 DEG


antennas, but doesn't fluctuate very much with the horizontal distance. The decoupling between the UMTS antenna and GSM-900 antenna is always the

greatest. Decoupling values for the dual antenna for the two cases of transmission and for the

GSM-1800 antenna are very closely. The comparison between the results of the basic horizontal – vertical separation and

of this position shows that first position gives a better decoupling between the antennas.



1.5m vertical distance is enough to reach basic decoupling. Between 0.5 and 1.5m horizontal separation 10 dB are to gain.



Antennas Min decoupling (vert. sepa. = 1.5m)

Max decoupling (vert. Sepa.=3m)

GSM 900 - UMTS 70 dB 80 dB GSM 1800 - UMTS 60 dB 70 dB Dualband - UMTS GSM-1800

60 dB GSM-900 60 dB

GSM-1800 70 dB

GSM-900 70 dB


9 CONCLUSION The decoupling between UMTS antenna and the others antennas is always higher than 50 dB, and increases with the distance between the antennas. The best decoupling is the one between the GSM-900 and UMTS antenna, and the worst one is with the GSM-1800 antenna. We can deduce some position recommendations of each antenna for a decoupling bandwidth from these measurements:

If a lower decoupling of 50-60 dB is needed, the horizontal separation is enough. If a minimum decoupling of 70-80 dB is required, a vertical separation is

recommended with a minimum separation of 1.5 m. The association of a horizontal separation and a vertical separation doesn’t have a

great influence on the antenna decoupling. To summarize, the minimum and maximum decoupling for each antenna are noted in the following table: α = azimuth difference

Position Antennas Min decoupling Max decoupling GSM 900 - UMTS 65 dB (α = 0°, hor.sep. = 0.5m) 80 dB (α=0°) to 90 dB

(α=120°) ( hor.sep.=4m) GSM 1800 - UMTS

50 dB (α = 0°, hor.sep. = 0.5m) 65 dB (α=0°) to 80 dB (α=120°) ( hor.sep.=4m)

Horizontal separation

with azimuth

divergence Dualband - UMTS

GSM-1800 50 dB (α=0°, hor.sep. = 0.5m)

GSM-900 52 dB (α=0°, hor.sep. = 0.5m)

GSM-1800 65 dB (α=0°) to 85 dB (α=120°) (hor.sep.=4m)

GSM-900 70 dB (α=0°) to 85 dB (α=120°) (hor.sep.=4m)

GSM 900 - UMTS 70 dB (vert.sep.=0.5m) 80 dB (vert.sep.=3m)

GSM 1800 - UMTS

55 dB (vert.sep.=0.5m) 65 dB (vert.sep.=3m) Basic vertical

separation Dualband - UMTS

GSM-1800 60 dB (vert.sep.=0.5m)


GSM-1800 65 dB (vert.sep.=3m)


GSM 900 - UMTS 70 dB (vert.sep.=0.5m) 80 dB (vert.sep.=3m)

GSM 1800 - UMTS

60 dB (vert.sep.=0.5m) 75 dB (vert.sep.=3m)

Vertical separation

with azimuth







GSM 900 - UMTS

70 dB (vert.sep.=1.5m, hor.sep. = 0.5m)

85 dB (vert.sep.=3m, hor.sep. = 4m)

GSM 1800 - UMTS



Basic horizontal – vertical separation Dualband

- UMTS

GSM-1800 60 dB (vert.sep.=1.5m, hor.sep. = 0.5m)


GSM-1800 70 dB (vert.sep.=3m, hor.sep. = 4m)


GSM 900 - UMTS



GSM 1800 - UMTS



Horizontal – vertical separaion

with azimuth






Using the above information, we can draw some guidelines to enable the engineer to determine his antenna locations where other operators are already present. Firstly, line of sight between antennas should be avoided. This can be achieved by using available masks on the rooftop (eg. penthouse, chimney). Wall mounting the antennas should be considered where possible. The design of the site should not compromise its quality. Secondly, where line of sight between antennas cannot be avoided, the engineer should prioritize the vertical decoupling with or without azimuth divergence (there is a better isolation with azimuth divergence) a minimum distance of 1 m between antennas is needed. If vertical decoupling is not possible then a vertical / horizontal decoupling should be used with priority given to vertical decoupling which is much more effective than the horizontal one (minimum vertical distance =1m). The measurements regarding the Vertical + Horizontal decoupling were only done on the GSM antenna’s axis.

GSM Ante

a

Dr. Hatem MOKHTARI, Septem

Axis Y

d’

a

Axis X

nna

ber 2004

ß

GSM antenn

UMTS antenn

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The axis Y represents the axis where the GSM antenna gain is maximum, then the isolation of a UMTS antenna place on this axe (0,Y) is lower than the isolation of an antenna place on (X,Y) with X<>0. Therefore the measurements on Horizontal + Vertical decoupling show the worse case, where the attenuation is the lowest, in order to reach an higher isolation the engineer should look for a relative azimuth (ß) between antenna higher than 0 degrees. However the results of the measurements (figure 5) should be used as a base to calculate the attenuation.

α = 60 d’=1,5m A

Thirdly horizontal decoupling alone should be chosen as a last option with a minimum distance of 3m and an azimuth divergence if possible. Assuming that the other operator is using a 65 degrees horizontal aperture antenna, the engineer has to put his antenna away from +/- 60 degrees around the azimuth of the GSM antenna (orange zone in the diagram below). In the red zone no antenna should be placed within a radius of 3m In the green zone, the azimuth must be as follows: On the right hand side whilst looking from behind the antenna, and assuming that the antenna is pointing at 0 degrees, the range in which you may place your antenna is from 0 to 180 degrees, relative to the theoretical 0 azimuth. On the left hand side, it may be placed in the range of 180 to 360 degrees also based on the theoritical azimuth.

-6 +60 +90 -90

There is no restriction in the white area.

Dr. Hatem MOKHTARI, September 2004

0

For a minimum vertical distance d=1m,we can define three horizontal zones: with d’< d*1,5 Zone A: no restriction of distance and azimuth. Zone B: The antenna placed in this zonemust have an azimuth between 240 and120 degrees (clockwise), assuming that the GSM antenna is pointing north. Zone C: No antenna should be placed in this zone. This rule should be applied within a radius of 20m (no interference measuredbeyond this point).

GSM Antenna

Zone

Zone B

Zone C

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EXAMPLE

d2

d1

The GSM antennas are in white, first the engineer should look for the vertical decoupling solution. Then if it is not possible the Vertical/Horizontal decoupling should be chosen (blue antenna) with minimum vertical distance = 1m.There is no restriction on d2 since the UMTS

d

d

Dr. Hatem MOKHTARI, Sep

distance d1>3m and an azimuth divergence

antenna is not in the main beam (+/- 60 deg) around the GSM azimuth. Finally if the vertical decoupling alone is not possible, the horizontal one should be chosen (orange antenna) with a minimum

(see restrictions above).

In this case the best decoupling can be achieve by placing the UMTS antenna ( in red) as showed in the sketch. If vertical decoupling can be used then there is no restriction on d, otherwise, in case of horizontal decoupling alone, d must be greater than 3m.

d

tember 2004 /25

GSM and UMTS RF Colocation

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