1、ITU-R RECMN*S. SERIES 95 = 4855232 O527707 006 Rec. IW-R S.728-1 1 SECTION 4B: SYSTEMS ASPECTS - PERFORMANCE AND AVAILABILITY 4B 1: Systems aspects RECOMMENDATION ITU-R S.728-1 MAXIMUM PERMISSIBLE LEVEL OF OFF-AXIS e.i.r.p. DENSITY FROM VERY SMALL APERIWRE TERMINALS (VSATs) (Question ITU-R 23/4) (19
2、92-1995) The ITU Radiocommunication Assembly, considering that geostationary-satellite networks in the fixed-satellite service (FSS) operate in the same frequency bands; that interference between networks in the FSS contributes to noise in the network; that it is necessary to protect a geostationary
3、-satellite network in the FSS from interference by other such a) b) c) networks; d) stations, to promote harmonization between geostationary-satellite networks; e) 0 spectrum and the geostationary-satellite orbit (GSO); 8) are widely available; h) e.g. using high gain forward error correction scheme
4、 for demodulation or using the spread-spectrum technique; j) may transmit simultaneously in the same frequency channel, that it is necessary to specify the maximum permissible levels of off-axis e.i.r.p. density from VSAT earth that networks in the FSS may receive interference into the space station
5、 receiver; that the use of antennas with good off-axis performance will lead to the most efficient use of radio-frequency that progress in the development of VSAT antennas indicates that improved side-lobe performance antennas that off-axis e.i.r.p. density levels can be limited through the choice o
6、f antenna and/or transmission parameter, that in some VSAT systems the code division multiple access (CDMA) scheme is used so that multiple VSATs recommends 1 that VSAT earth stations operating with geostationary satellites in the 14 GHz frequency band used by the FSS be designed in such a manner th
7、at at any angle cp specified below, off the main-lobe axis of an earth-station antenna, the maximum e.i.r.p. in any direction within 3“ of the GSO should not exceed the following values: Angie off-axis Maximum e.i.r.p. in any 40 kHz band 2“ IcpS 7O 7“ 48“ 33 - 25 log p dBW 12 dBw 36 - 25 log p dBW -
8、6 dBW COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling ServicesIn addition, the cross-polarized component in any direction cp degrees from the antenna main-lobe axis should not exceed the following limits: Angle ofl-axis Maximum e.i.r.p.in any
9、40 kHz band 2“ I cpl7“ 23 - 25 log p dBW 2 dBw 7 e cp I; 9.2“ 2 NOTE 1 - Maximum e.i.r.p. density values in Q 1 above may need to be decreased up to 8 dE in the systems where the satellite spacing is near 2“. NOTE 2 - For the systems in which the earth stations are expected to transmit simultaneousl
10、y in the same 40 kHz band, e.g. for the systems employing CDMA, the maximum e.i.r.p. values in Q 1 above should be decreased by 10 log N (dB), where N is the number of earth stations which are expected to transmit simultaneously on the same frequency. NOTE 3 -Recommendations for VSATs operating in t
11、he 6 GHz and other frequency bands are under study. Provisionally Recommendation IT-R S.524 should be applied for these bands. NOTE 4 - The values given in 1 may be exceeded over the range of angles for which the particular feed system may give rise to relatively high levels of spill-over. NOTE 5 -
12、The limits given in Q 1 could be increased up to the limits of Recommendation IT-R S.524 in case of very large service areas. NOTE 6 - Annex 1 describes the calculation of permissible off-axis e.i.r.p. density for VSATs. NOTE 7 - Earth station antennas with DA ratios less than 50 are likely to have
13、main beams which extend beyond an off- axis angle of 2“ to 3“. Annex 2 shows examples of the main beamwidths of some of these antennas. The off-axis e.i.r.p. limitations at the lower off-axis angles in Q 1 can be met by constraining the transmit power spectral flux-density of these antennas. that th
14、e following Notes should be regarded as part of this Recommendation. NOTE 8 - This Recommendation applies to protection between geostationary-satellite networks in the FSS. Potential interference between geostationary-satellite systems and non-geostationary-satellite systems is to be addressed by ot
15、her Recommendations. NOTE 9 - The revision in Q 1 above to reduce the minimum off-axis angle from 2.5“ to 2“ applies to earth stations brought into service after the end of 1995 for all geostationary-satellite networks. ANNEX 1 Calculation of permissible off-axis e.i.r.p. density for VSATs 1 System
16、noise budget According to Recommendation -R S.523 which deals with permissible interference level in digital satellite transmission, 20% of the total noise power at the demodulator input is allocated to the interference caused by other networks in frequency bands in which the networks practice frequ
17、ency re-use. Also, 6% of the total noise power is allocated for the single entry interference. While the off-axis emissions from earth stations cause up-link interference to the adjacent satellites, the emissions from the adjacent satellites cause down-link interference to the receiving earth statio
18、ns. Therefore, the single entry allocation of 6% should be further divided into up-link and down-link interference. The antenna diameter of the receiving earth station affects the division. If it is larger, the down-link interference becomes less because of its better off-axis isolation, while the u
19、p-link interference becomes severer because the total system thermal noise decreases due to increased earth-station GR. COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling ServicesITU-R RECMN*S- SERIES 95 q855232 0527709 989 D Ra ITU-R S.728-1 3 I
20、n considering the off-axis e.i.r.p. limit of VSATs, it may be appropriate to assume that the antenna diameter of the receiving earth station of the interfered network is around 5 m. In this case the budget for the single entry down-link interference can be assumed as less than 1% considering the off
21、-axis gain performance of the antenna. Then the budget for the single entry up-link interference can be assumed as 5%. Further, the total system noise budget can be assumed as follows: Thermal noise (up link + down link) Interference from other satellite networks 50% 20% (Recommendation -R S.523) In
22、terference due to cross-polarization 5% Intermodulation noise due to transponder Therefore, the ratio of 5%/50% can be used in comparing the up-link single entry interference power density with the thermal noise density. 25% 2 In calculating the system total thermal noise, both the up-link and the d
23、own-link thermal noise should be considered. The up-link carrier-to-noise density ratio (c/No)u, the down-link carrier-to-noise density ratio (C/NO)D and the total carrier- to-noise density ratio (C/NO)T can be calculated as follows: Derivation of system total thermal noise (C/No)u = e.i.r.p.g - Lu
24、- LUA - LUR + (G/T)s + 228.6 (1) (C/NO)D = e.i.r.p.g - OB0 - LD - LDA - LOR + (G/T)E + 228.6 = e.i.r.p.E - Lu - LUA - LVR + Gs - LD - LDA + LDR + (G/T)E + 228.6 (2) where: e. i. r.p. E : e. i. r.p. s : Lu: LD : LUA : LDA : LDR : (Gms LUR : (Gfl)E : OB0 : Gs : where: SFD : IBO : GI: e.i.r.p. of the t
25、ransmit earth station of wanted signal saturation e.i.r.p. of the satellite up-link free-space loss down-link free-space loss up-link clear-air attenuation down-link clear-air attenuation up-link rain fade down-link rain fade Gfl of the satellite G/T of the receiving earth station of wanted signal o
26、utput back-off of the satellite small signal gain of the transponder Gs = GI + (e.i.r.p.s - SFD) f (IBO - OBO) saturation flux-density of the satellite input back-off of the satellite gain of an ideal antenna area of 1 m* G1 = 44.4 dB at 14 GHz (4) COPYRIGHT International Telecommunications Union/IT
27、U RadiocommunicationsLicensed by Information Handling ServicesITU-R RECMNmS- SERIES 95 4855232 0527730 bTO = 4 Rec ITU-R S.728-1 If the effective Gfl of the receiving earth station at the satellite input is defined as: and the total effective G/T of the satellite is defined as: (G/T)T = - 10 log (lo
28、“(- (G/T)s / 10) + lo“(- (GIT)EE / 10) then the down link C/NO and the total C/No can be expressed as: (C/NO)D = e.i.r.p.E - Lu - LUA - LUR + (G/T)EE + 228.6 (C/NO)T = e.i.r.p.E - Lu - LUA - LUR + (G/T)T + 228.6 3 Derivation of permissible off-axis e.i.r.p. density It is assumed that the off-axis e.
29、i.r.p. density from the interfering VSAT is expressed as E - 25 log (p CLB(W/40 kHz). Then the up-link carrier-to-interference density ratio in 40 kHz bandwidth can be expressed as follows: ClIo = e.i.r.p.E - LUR - (E- 25 log cp) (9) Note that it is assumed only the wanted signal suffers the up-link
30、 rain fade. Then the interference to thermal noise ratio in 40 kHz bandwidth can be derived as: = (E- 25 lg p) - Lu - LUA + (G/T)T + 228.6 - 10 log B where B = 40 kHz. As described in 0 1, the value of Zo/No should be less than 5%/50% to satisfy the single entry interference criteria. Then the permi
31、ssible value of E can be derived as: E = lo/No + 25 lg cp + Lu + LUA - (G/T)T - 228.6 + 10 lg B (1 1) In the case when the up-link frequency is 14 GHz: E = 25 lg p - (G/T)T + 14.5 + LUA (12) Note that the up-link rain fade does not affect the interference to noise ratio. However, the effect of the d
32、own-link rain fade should be taken into account in the calculation of (G/T)r because the interference budget is defined as a portion of the total noise power which would give rise to a bit error ratio of 1 in lo6 and usually the system is designed so that the bit error ratio of 1 in lo6 can be achie
33、ved even during the fade condition. COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling ServicesITU-R RECMN*S- SERIES 95 = 4855212 0527711 537 RC. ITU-R S.728-1 5 4 Derivation of the required e.i.r.p. from VSATs The permissible level of E can be d
34、erived by the expressions in the previous section. However, it should be checked if VSAT systems can operate with good performance even under that condition. If it is assumed that the transmit antenna gain of the VSAT earth station is GT, and that the side-lobe performance of the antenna can be expr
35、essed by 29 - 25 log p. then the e.i.r.p. of the VSAT, e.i.r.p.E, in 40 kHz bandwidth can be expressed as: e.i.r.p.E = E - 29 + GT (13) Then, from expression (8). the carrier power density-to-thermal noise density ratio can be derived as: (CO/NO)T = E - 29 + GT - Lu - LUA - LUR + (G/T)T + 228.6 - 10
36、 log B (14) As explained in 8 1 of this Annex, the thermal noise is assumed to be 50% of total noise. Therefore, if required overall energy-per-bit-to-noise density ratio is (EblNo) and the conversion factor from ColNo to T of the receive earth station in clear weather C/T of the receive earth stati
37、on in rainy weather Down-link rain fade Up-link rain fade Down-link clear-air attenuation 5m 31 dB 30 dB 4 dB 3 dB 0.5 dB Up-link clear-air attenuation 0.5 dB Small signal satellite gain increase BO-OBO) VSAT antenna diameter VSAT antenna transmit gain Required &/No with rate 1/2 FEC Required EbINO
38、with rate 314 FEC 4 dB 1.2 m 42.7 dB 6.4 dB 7.4 dB Required overall system margin 1.5 dB COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling ServicesITU-R RECMN*S* SERIES 95 48552112 0527732 473 6 RC. ITU-R S.728-1 Also the topocentric angle is us
39、ed for the off-axis angle 9. It is assumed that the topocentric angles are 1.1 times of the geocentric angles and that the satellites are located at their nominal positions. To calculate the down-link free-space loss, the frequencies shown in Table 1 are used. TABLE 1 Permissible and required values
40、 of E Satellite system Region Down-link frequency (GHz) Satellite Gf (dB(K-) SFD (dB(W/m2) Satellite e.i.r.p. (dBW) Small signal satellite gain (dB) Equivalent total Gfl (DL clear) Equivalent total Gf (DL rain) Permissible E - 25 log cp Permissible E (cp = 2.2) Permissible E (cp = 3.3) Permissible E
41、 (cp = 4.4) Required E (BPSK 3/4 FEC) Required E (BPSK 1/2 FEC) GSTAR USA 11.7 1 .o -85.0 42.0 175.4 -2.3 -5.7 20.7 29.3 33.7 36.8 27.3 24.6 EUTELS AT-II Europe 12.5 2.0 -82.8 44.0 175.2 -2.4 -6.1 21.1 29.7 34.1 37.2 27.4 24.7 INTELSAT-VI West-spot 10.95 4.3 -81.3 41.7 177.4 0.6 -3 .O 18.0 26.6 31.0
42、 34.1 24.4 21.7 AUSSAT Australia 12.5 -1.0 -88.0 42.0 178.4 -2.5 4.7 19.7 28.2 32.6 35.8 27.5 24.8 As shown in the table, E = 33 (dB(W/40 kHz) may be adequate when the satellite spacing is not less than 3”. When the satellite spacing is 2” less value of E. e.g. 25, may need to be used, although only
43、 BPSK transmission with rate 1/2 FEC may be feasible in this case. ANNEX 2 Ultra small aperture terminal antenna characteristics 1 Introduction With the recent introduction of FSS space stations with substantial transmission power capabilities, it has become possible to use “ultra-small aperture ter
44、minals (USATs)” for applications formerly relegated to “very small aperture terminals (VSATs)”. However, these USATs have large or wide main beams which, when transmitting in the Earth-to-space direction, could impinge upon adjacent space stations in the GSO. Likewise, Co-frequency, Co-coverage tran
45、smissions from space stations adjacent to the wanted space sation could introduce high levels of interference into these USAT networks. The resultant increase in interference between neighbouring FSS networks will have a negative effect on the communication capacity of the existing GSO/spectnim reso
46、urces. Thus it is necessary to constrain the interference potential of USAT networks, particularly in the magnitude of uplink off-axis e.i.r.p. densities. COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling ServicesRec. -R S.728-1 7 Radio frequenc
47、y Antenna diameter (GW (m) - 14 50 1 .O5 14 40 0.84 14 30 0.63 - 2 USAT antenna beam sizes Table 2 shows the growth in main beamwidths (MBWs) for antenna sizes with DAS below 50. For antennas designed with low side lobe gains and efficiencies around 60% (by incorporating special feed distribution designs), the MBWs shown in Table 2 are likely to be in the higher range. Half-MBWd) (degrees) 1.4-2.3 1.7-2.9 2.4-3.9 TABLE 2 Off-axis angular range of antenna haif-main beamwidths COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling Services
