ITU-R BO 794-1992 Techniques for Minimizing the Impact on the Overall BSS System Performance Due to Rain Along the Feeder-Link Path《将降雨引起的沿馈线链路通道对BSS系统性能的影响降至最小的技术》.pdf
《ITU-R BO 794-1992 Techniques for Minimizing the Impact on the Overall BSS System Performance Due to Rain Along the Feeder-Link Path《将降雨引起的沿馈线链路通道对BSS系统性能的影响降至最小的技术》.pdf》由会员分享,可在线阅读,更多相关《ITU-R BO 794-1992 Techniques for Minimizing the Impact on the Overall BSS System Performance Due to Rain Along the Feeder-Link Path《将降雨引起的沿馈线链路通道对BSS系统性能的影响降至最小的技术》.pdf(11页珍藏版)》请在麦多课文档分享上搜索。
1、CCIR RECMN*794 92 4855232 0520039 010 150 Rec. 794 RECOMMENDATION 794 TECHNIQUES FOR MINIMIZING THE IMPACT ON THE OkTR4LL BSS SYSTEh PERFORMANCE DUE TO RAIN ALONG THE FEEDER-LCVK PATH* (Questions 86/11 and 98/11) 1992) The CCIR, co mide ring a) that any degradation on the feeder links will impact on
2、 the broadcasting-satellite service (BSSI performance over the whole service area; b) that the BSS satellite transponder should be maintained at nominal output level to minimize the impact of feeder-link fading on reducing the down-link e.i.r.p.; c that while excessive use of on-board automatic gain
3、 control (AGC) can result in increasing the inter- and intra-system interference it can maintain the transponder operation at or near nominal output level noting hon.ever that the feeder link carrier-to-noise will not be improved; d) that while feeder iink power control can potentially increase inte
4、r-system interference its application can maintain transponder operation at or near nominal output level without degrading the feeder link UA; e reducing feeder iink fading, particularly in high rain rate areas, that while use of site diversity can lead to complex operational considerations, it is a
5、n effective technique for recommends that the following techniques be used to the extent practicable for alleviating BSS system degradation due to rain fading on the feeder link: - - - on-board satellite AGC (see Annex 1); up-link power control (see Annex 2); site diversity (see Annex 3). ANNEX 1 On
6、-board automatic gain control (AGC) AGC on board spacecraft minimizes the effect of rain fades at the feeder-link station on the dcnvn-iink C/N ratio by keeping the TWTA at saturation. The AGC operates on individual channels and increases the transponder gain of the wanted signal and of any portion
7、of an interfering signal which falls within the filter bandwidth of the wanted channel. Therefore, during rain at the feeder-link station(s) the use of AGC permits the operation of the transponder close to saturation but the ratio of the wanted carrier eo the portion of the interfering adjacent cros
8、s-polarized carrier which falls into the filter bandwidth of the wanted channel remains constant. Therefore, the use of AGC has no effect on the cross-polar C/Z, of the two feeder links under consideration. * This Recommendation should be brought to the attention of Study Group 4. Note from the Dire
9、cor, CCIR - Report 952-2 (9 5.4.1, 5.4.2 and 7) was used in preparing this Recommendation * CCIR RECMN%794 92 m 4855232 0520020 832 m Rec. 794 151 However, the satellite using AGC radiates on the down link a constant level of the wanted signal which is attenuated on the feeder link, but re-radiates
10、on the down link a higher level of the interfering cross-polar signal on the adjacent channel, which is not attenuated when there is no rain on the interfering feeder link. This situation may cause an increase in down-link interference to other systems receiving this re-radiation as Co-channel inter
11、ference. This problem could be significant only for Co-located satellites serving common or adjacent service areas. A limit on the range of AGC, in Co-located satellites with cross-polarized channels, to less than 10 to 15 dB may beneeded to guard against this problem of re-radiation on the down lin
12、k. This problem can be reduced if satellites with cross-polarized channels serving the same service area or adjacent service areas are separated by at least 0.3“ on the geostationary orbit. Non-Co-located satellites with cross-poiatized channels need not be subject to this limit of AGC range. A 10 d
13、B limit on AGC range could be insufficient to maintain a constant TWTA output in some rain climates for certain elevation angles. The use of some other mechanism (power control, site diversity) might be required in these circumstances to maintain a constant signai level on the down link. The Region
14、2 feeder-link Plan is based on a limit of 15 dB on the dynamic range of AGC on board some cross-polarized spacecraft to guard against this problem of re-radiation on the down link. ANNEX 2 Feeder link power control Power control of feeder links is the rapid, automatic adjustment of earth-station tra
15、nsmitter power to compensate for rain-induced attenuation in the path of the desired signai to a satellite. 1. Application of power contrd In the presence of feeder-link power control (PC), the input level of the signai at the satellite transponder is maintained approximately constant and rain atten
16、uation along the feeder-link path is effectively compensated. As a consequence, during rain at the feeder-link station only, the use of feeder-link power control maintains a constant value of CINT as illustrated in Fig. 1. Experiments using the BSE of Japan have shown that power control is effective
17、 in maintaining a nearly constant level of desired carrier during periods of rain. In this experiment, at 14 GHz a variation of power received at the satellite of 6 dB (peak-to-peak) and 1.5 dB r.m.s. without power control, was reduced through the use of power control to 1.5 dB (peak-to-peak) and 0.
18、5 dB r.m.s., respectively. 2. Conditions for use of power control without increased interference I Use of power control to increase the availability of feeder links beyond the values used for planning is 1 andysed in this section. In studying feeder-link interference problems, the geographical locat
19、ions of interfering earth stations and wanted feeder-link beam areas are important factors affecting the feeder-link carrier-to-interference ratio. These factors affect the cross-polarization discrimination (XPZsat) of the wanted-satellite antenna because XPlsar is a function of the ratio of the off
20、-axis angle p to the half-power beamwidth cpo. For the satellite-receiving antenna reference pattern in Fig. 10 of Recommendation 652, the XPZSal can be graphically expressed as in Fig. 2. CCIR RECMN*774 72 W 4B55212 052i21 779 D 152 Rec. 794 FIGURE 1 The effect oPrainfall atenuatlen on ClNr in the
21、presence OP feeder-link power control (PC) 16 14 12 10 h ln 2. k0 i5 6 4 2 O at 17 GHz o24 6 8 10 12 at 12GHt Rainfail attenuation (dB) Clear-sky C/NU - 24 dB Clemsky CINd - 14.5 dB Curves A: rain at feeder-link station only B: correlated rain at feeder-link station and down-link station In order to
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