1、 Rec. ITU-R S.1655 1 RECOMMENDATION ITU-R S.1655 Interference mitigation techniques and frequency sharing in the bands 37.5-42.5 GHz and 47.2-50.2 GHz between geostationary-satellite fixed-satellite service networks and non-geostationary- satellite fixed-satellite service systems (Question ITU-R 231
2、/4) (2003) The ITU Radiocommunication Assembly, considering a) that the 37.5-42.5 GHz and 47.2-50.2 GHz bands are allocated to the FSS; b) that there is an emerging interest in operating GSO FSS networks and non-GSO FSS systems which use low Earth orbit (LEO) or medium Earth orbit (MEO) in these fre
3、quency bands; c) that the FSS systems plan to provide data rates ranging from videoconferencing quality through very high speed transmission of STM-1 (155 Mbit/s) or higher, up to 10 STM-4 (6.22 Gbit/s); d) that most FSS systems planned to operate in these bands are designed to use 3 GHz of spectrum
4、 in the Earth-to-space direction and 3 GHz or higher in the space-to-Earth direction; e) that in some portions of the band 37.5-42.5 GHz, most FSS systems plan to use high gain, narrow-beam earth terminal antennas for their user links, typically 1 m in diameter, and provide at least 99.7% end-to-end
5、 link availability; f) that in some portions of the band 37.5-42.5 GHz, FSS systems may need to use larger earth terminal antennas, of up to 3 m in diameter, for gateway/hub applications involving individually-coordinated earth stations at geographically dispersed points and that these applications
6、require end-to-end link availability of at least 99.9%; g) that some satellite systems are designed to operate in only a small fraction of the satellite field-of-view, and typically provide less than 5% coverage of their satellites field-of-view; h) that the propagation impairments are severe in thi
7、s frequency range; j) that most FSS systems designed to operate in the 50/40 GHz bands are not planned to use dual polarization in the same beam in the same area because the depolarization impairments in adverse propagation conditions are severe; however, dual polarizations for FSS systems operating
8、 in these bands may be used for different beams which are well separated geographically, recommends 1 that one mitigation technique which may be used to facilitate frequency sharing between GSO FSS networks and non-GSO FSS systems in the 37.5-42.5 GHz and 47.2-50.2 GHz bands is operation on opposite
9、 polarizations. Annexes 1 and 2 to this Recommendation describe this mitigation technique (see Notes 1 and 2); 2 Rec. ITU-R S.1655 2 that sharing between non-GSO FSS systems and GSO FSS networks, in a portion of these bands using high gain narrow-beam satellite antennas, can be feasible if appropria
10、te geographical separation between earth stations of the two systems is provided (see Annex 3); 3 that other mitigation techniques, such as those in Annex 3, may be applicable, depending on system characteristics. NOTE 1 Application of the mitigation technique described in Annexes 1 and 2 to non-GSO
11、 FSS systems which use LEO may require further study due to the different time-varying characteristics of LEO and MEO FSS systems. For a non-GSO FSS system to share frequencies with a GSO FSS network on the basis of each using the opposite polarization, all other non-GSO FSS systems covering the sam
12、e geographical area would be obliged to use the same type and direction of polarization as the first system, or to employ a method of avoiding main beam-to-main beam coupling of co-polar interference (such as satellite diversity). Furthermore, as non-GSO FSS systems are often designed for global cov
13、erage and as confinement of GSO FSS networks to a single polarization is a potential constraint, additional study may be necessary to ensure that the use of this technique does not preclude efficient use of 50/40 GHz bands. NOTE 2 For the system studied in Annexes 1 and 2, Annex 3 contains a discuss
14、ion of the advantages and disadvantages of other mitigation techniques. Annex 1 Frequency sharing between non-GSO FSS systems and GSO FSS networks operating in the 50/40 GHz bands using high gain narrow-beam earth antennas 1 Introduction This Annex presents simulation results related to the feasibil
15、ity of co-directional frequency sharing between a non-GSO FSS system and a GSO FSS network in the 47.2-50.2 GHz and 37.5-42.5 GHz bands. In this study, LEO V2 is used as an example non-GSO FSS system. The GSO V1 characteristics are taken as representative of GSO satellite networks. Two interference
16、cases will be summarized. The first case presents the simulation results without an interference mitigation technique when systems operate on same and opposite polarizations. In the second case, satellite diversity is used as an interference mitigation technique to reduce the interference levels at
17、the satellite and user terminal receivers. 2 System technical characteristics The orbital characteristics of the LEO V2 system are given in Table 1. Tables 2 and 3 show the satellite communication and user terminal system parameters for both systems, respectively. Rec. ITU-R S.1655 3 TABLE 1 LEO V2
18、orbital parameters TABLE 2 Satellite communication system parameters TABLE 3 User terminal communication system parameters Number of satellites 15 Number of orbital planes 3 Number of satellites per plane 5 Altitude 10 355 km Inclination angle 50 Period of orbit 6 h Plane spacing 120 Plane-to-plane
19、satellite phasing 24 Walker designation 15/3/1 LEO V2 GSO V1 Receive frequency range (GHz) 47.2 to 50.2 Receive bandwidth (GHz) 3 Receive antenna gain (dBi) 46.5 53.0 3 dB beamwidth (degrees) 0.82 0.39 Receive system noise temperature 728 K or 28.6 dBK Transmit frequency range (GHz) 37.5 to 42.5 Tra
20、nsmit bandwidth (GHz) 3 Transmit e.i.r.p. (dBW) 48.9 to 58.9 Depending on data rate 57.5 to 66.4 Depending on data rate and user antenna size Transmit antenna gain (dBi) 46.5 53.0 3 dB beamwidth (degrees) 0.82 0.39 Transmit power density into antenna (maximum) (dB(W/Hz) 81.3 LEO V2 GSO V1 Transmit f
21、requency range (GHz) 47.2 to 50.2 Transmit bandwidth (GHz) 3 Transmit e.i.r.p. (dBW) 54.7 to 78.9 Depending on data rate, propagation condition 56.6 to 80.0 Depending on data rate, propagation condition Transmit antenna gain (dBi) 59.7 59.7 (2.2 m) 60.8 (2.5 m) 4 Rec. ITU-R S.1655 TABLE 3 (end) 3 In
22、terference analysis In the analysis interference computations have been carried out for two distinct cases: with opposite polarization discrimination; and use of satellite diversity as a mitigation technique. Due to the intermittent nature of “in-line” interference, it must be expressed in the form
23、of short-term allowances. Currently, there are no criteria for acceptable interference levels between GSO FSS networks and non-GSO FSS systems in the 38/50 GHz bands. However, the LEO V2 and GSO V1 systems are designed to achieve a minimum link availability of 99.5%. Ten per cent of the 0.5% link ou
24、tage, or 0.05%, is allocated by the designers to short-term interference from other satellite systems, both GSO FSS networks and non-GSO FSS systems operating in these frequency bands. Half of the latter quantity (0.025%) is allocated to interference from GSO satellite systems. The LEO V2 and GSO V1
25、 systems are designed to maintain a 3 dB link margin, i.e. the ratio of carrier power to noise power density, C/N0, is maintained 3 dB above the value corresponding to the requisite link quality. Therefore, the interference criterion appropriate to LEO V2 and GSO V1 is that I0/N0should not exceed 0
26、dB for more than 0.025% of the time. The calculated uplink and downlink interference was based on the following: non-GSO FSS and GSO FSS earth terminals are co-located. The latitude and longitude of the common terminal location are 43.4 N and 70.2 W, respectively; both non-GSO FSS systems and GSO FS
27、S networks use adaptive uplink power control to establish a 3 dB clear-sky margin. There is no downlink power control; user terminal transmit and receive antenna patterns are based on Recommendation ITU-R S.580; LEO V2 GSO V1 3 dB beamwidth (degrees) 0.19 0.19 (2.2 m) 0.17 (2.5 m) Transmit power den
28、sity into antenna (dB(W/Hz) 89.7 to 75.5 Depending on data rate, propagation condition 87.8 to 75 Depending on data rate, propagation condition Receive frequency range (GHz) 37.5 to 42.5 Receive bandwidth (GHz) 3 Receive antenna gain (dBi) 57.8 57.8 (2.2 m) 59.0 (2.5 m) 3 dB beamwidth (degrees) 0.24
29、 0.24 (2.2 m) 0.21 (2.5 m) Receive antenna noise temperature 353 K or 25.48 dBK Rec. ITU-R S.1655 5 user terminal transmit and receive antenna cross-polarized patterns are based on Recommendation ITU-R S.731; satellite transmit and receive antenna patterns are based on Recommendation ITU-R S.672; sa
30、tellite transmit antenna cross-polarized patterns are based on Appendix 30 (WRC-2000) of the Radio Regulations; required Eb/N0is 8.0 dB; clear-sky condition; a 2.2 m diameter transmit and receive antenna earth terminal is used in this study. 4 Simulation results A simulation of 15 non-GSO satellites
31、 and a GSO satellite located at 82.44 W was performed over a 24 h period, with a time interval of 1 s. 4.1 Case 1: Opposite polarization LEO V2 and GSO V1 satellites operate on opposite polarizations. Figures 1 and 2 are a sample of the results obtained in terms of per cent of time that I0/N0at non-
32、GSO and GSO receivers is exceeded when both systems operate on opposite polarizations. Interference levels exceeded for 0.025% of the time at the GSO user terminal and the non-GSO satellite receivers are respectively I0/N0= 9 dB and I0/N0= 17 dB. 1655-01I0/N0(dB)I0/N0(dB)45.0 40.0 35.0 30.0 25.0 20.
33、0 15.0 10.0 5.0 0.00.0010.0100.1001.00010.000% timeI0/N0isexceededI0/N0at GSO earth station receiver(opposite polarization)FIGURE 1% time I0/N0at GSO earthstation receiver is exceeded50.0 45.0 40.0 35.0 30.0 25.0 20.0 15.0 10.0 5.0 0.00.0010.0100.1001.00010.000% timeI0/N0isexceededI0/N0at non-GSO sa
34、tellite receiver(opposite polarization)FIGURE 2% time I0/N0at non-GSO satellite receiver is exceeded6 Rec. ITU-R S.1655 4.2 Case 2: Satellite diversity Satellite diversity can be used to reduce the interference levels at satellite and user terminal receivers. In this case, systems are assumed to ope
35、rate on the same polarization. It is productive to explore the practicality of using satellite diversity to reduce the interference levels at the non-GSO and GSO satellite and earth terminal receivers. This technique specifies that to avoid in-line interference when the separation angle between a no
36、n-GSO satellite and a GSO satellite as seen from an earth station is less than X, the non-GSO user switches the traffic to an alternate in-view satellite. In this study, the GSO satellite system is assumed to have dual coverage provided by at least two satellites in different orbital locations. In g
37、eneral, it is not usual for GSO satellite systems to have dual coverage provided by at least two satellites in different orbital locations. For non-GSO FSS systems using circular orbits, dual coverage by at least two satellites in different orbital locations is more usual. Also, both systems are ass
38、umed to operate on the same polarization, and the user of its system can communicate with any of the systems satellites in view. Figures 3 and 4 show the interference levels at the GSO earth terminal and non-GSO satellite receivers when the satellite diversity technique is used. In this study, when
39、the separation angle, X, between a non-GSO satellite and a GSO satellite as seen from an earth station falls to below 0.5, the GSO FSS user switches the traffic to an alternate satellite. Interference levels at the non-GSO and GSO FSS user terminal and satellite receivers are below the interference
40、criteria. A sample of the results are provided in Figs. 3 and 4. 1655-03I0/N0(dB)I0/N0(dB)40.0 35.0 30.0 25.0 20.0 15.0 10.0 5.0 0.00.0010.0100.1001.00010.000% timeI0/N0 isexceededI0/N0at GSO earth station receiver(same polarization)FIGURE 3% time I0/N0at GSO earth stationreceiver is exceeded (X = 0
41、.5)50.0 45.0 40.0 35.0 30.0 25.0 20.0 15.0 10.0 5.0 0.00.0010.0100.1001.00010.000% timeI0/N0isexceededI0/N0at non-GSO satellite receiver(same polarization)FIGURE 4% time I0/N0at non-GSO satellite receiver is exceeded (X = 0.5)X: the minimum separation angle between the non-GSO and GSO satellite as s
42、een from an earth station.Rec. ITU-R S.1655 7 5 Conclusion A summary of the simulation results is provided in the following Table: Based on results of the studies, we can draw the following conclusions: Frequency sharing between non-GSO FSS systems and GSO FSS networks operating in the frequency ban
43、ds 47.2-50.2 GHz and 37.5-42.5 GHz may not be feasible, without imposing complex interference mitigation techniques on both GSO FSS networks and non-GSO FSS systems, if both systems operate on the same polarization. However, when the systems operate on opposite polarization, frequency sharing may be
44、 feasible. If satellite diversity is used as an interference mitigation technique, frequency sharing between non-GSO FSS systems and GSO FSS networks is feasible even when they operate on the same polarization. Frequency sharing between non-GSO FSS systems and GSO FSS networks operating in the band
45、47.2-50.2 GHz and 37.5-42.5 GHz is feasible if the systems operate on opposite polarizations or use satellite diversity with a diversity switching angle, X, at the earth station is 0.5 or greater. Annex 2 Frequency sharing between non-GSO FSS systems and GSO FSS networks operating in the 50/40 GHz b
46、ands using small earth terminal antennas 1 Introduction This Annex presents simulation results related to the feasibility of co-directional frequency sharing between non-GSO FSS systems and GSO FSS networks operating with small earth terminal antennas. I0/N0(exceeded for 0.025% of the time) I0/N0(ex
47、ceeded for 0.025% of the time) Same polarization: no mitigation technique (dB) Opposite polarization(dB) Same polarization: use of satellite diversity (at 0.5) mitigation technique (dB) Non-GSO user terminal receiver 11 13 6 Non-GSO satellite receiver 6 17 9 GSO user terminal receiver 15 9 2.5 GSO s
48、atellite receiver 0 24 16 8 Rec. ITU-R S.1655 Studies have shown that without mitigation techniques, such as satellite diversity, geographic isolation, etc., the frequency sharing between non-GSO FSS systems and GSO FSS networks is not feasible when they operate on the same polarization. This Annex
49、only presents the simulation results when the systems operate on opposite polarizations. 2 System technical characteristics The orbital characteristics of a non-GSO FSS system are given in Table 1. Tables 4 and 5 show the satellite communication and user terminal parameters for both a non-GSO FSS system (LEO V2) and for a GSO FSS network (GSO V1), respectively. TABLE 4 Satellite communication system parameters TABLE 5 User terminal communication system parameters Parameters Non-GSO (LEO V2) GSO
