1、CCIR RECMN*793 92 4855232 0520034 537 = 7 For the purposes of planning, the WARC-BS-77 adopted a maximum reduction of 0.5 dB of the overall carrier-to-noise (GIN) ratio, to represent the contribution of the feeder link to the CIN ratio for 999 of the worst month. This corresponds to a difference of
2、about 10 dB between the carrier-to-noise ratios of the down links and feeder links. According to an EBU study, the contribution of the noise resulting from the feeder link may be rendered negligible by adopting a relatively small margin in the carrier-to-noise ratio of the down link. This study cons
3、idered the feeder link and down link. I the case of automatic gain control (AGC) in the satellite and was based on a statistical analysis of the attenuations on Numerical applications have been made assuming that the attenuations (in dB) follow a log-normal relationship for which the parameters fit
4、measurements made in Europe. It is seen, first, that the results obtained assuming either total correlation or total independence between feeder-link and down-link fadings, are more or less identical. The influence of a margin of 0.5 dB on the down link, however, is crucial. The improvement due to t
5、his margin is better than that obtained by dimensioning the C/N ratio of the feeder link for 99.99 of the worst month instead of for 99%. Hence, if a down-link C/N ratio of 14 dB for 99%. of the worst month is assumed, the noise contribution from the feeder link to the overall circuit causes the ove
6、rall link CIN to drop below 14 dB, 50% to 10% Rec. 793 145 RECOMMENDATION 793* PARTITIONING OF NOISE BETWEEN FEEDER LINKS FOR AND BSS DOWN LINKS* (Questions 83/11, 86/1 i) THE BROADCASTING-SATELLITE SERVICE (BSS) ( 1992) The CCIR, considering that the broadcasting-satellite service (BSS) is normally
7、 expected to provide service to a relatibely large that in minimizing the effects of feeder-link noise on the overail link noise budget the cost and complexity of that the satellite output e.i.r.p. is maintained at the nominal output level during feeder-link fades by that higher up-link power requir
8、ements would affect only a few feeder-link stations; that in terms of availability, rain fades on the down link would only have a local affect on the performance that a further degradation of the overall link due to thermal noise occurs due to the non-linearity of the a) geographical area encompassi
9、ng a large population of receivers; b the BSS receiver will be minimized; c) employing techniques such as automatic gain control (AGC); d) e) whereas rain fade on the feeder link would affect performance over the whole service area; 0 satellite high power amplifier coupled with WM conversion (see An
10、nex l), recommends that as a guide to system design, for a given service availability objective for analogue-modulated emissions in the BSS, the apportionment of the down-link noise contribution to the feeder-link noise contribution should be of the order of 10: 1 (see Annex 1). ANNEX 1 Partitioning
11、 of noise between feeder links and down links * This Recommendation should be brought to the attention of Study Group 4. Note from the Director, CCIR - Report 952-2 ($ 3.2 and 3.3) was used in preparing Annex 1. * CCIR RECMN*793 92 m 4855212 0520015 475 m 146 Rec. 793 more often (depending on whethe
12、r the feeder link is dimensioned to given CIN ratio of 24 dB for 99% or 99.9% of the worst month). If account is taken of the 0.5 dB margin on the down link, the perccntngc of the time during which the overall CIN drops below 14 dB, including the noise contribution of the feeder link is still smalle
13、r than the specified 1 % of the worst month in both cases. This result cotifms the suitability of the choice, made by the WARC-BS-77, to take account of the feeder link by means of such a margin, even at frequencics of the order of 18 GHz. Similar studies were conducted in C,snlida on the effects of
14、 rain attenuation and satellite transponder characteristics as related to the partitioning of the noise contributions on thc feeder links and down links in 8 broadcasting-satellite service. Some of the results can be found in Fig. 1, wlierc the siune assumptions as in the above-mentioned study were
15、made. The curves in this figure represent the degradation of the down-link CIN due to the noise contribution from the feeder link, (CINd - CINJ as a function of the difference between the GIN of the feeder link and the CIN of the down link (CINU - CINd). Full correlation and independcnec of the fadi
16、ngs on both links are illusuated. All CIN vaiues are specified for 99% of the worst month. FIGURE 1 Nolse contrlbutlon of the feeder link O 4 a 12 16 20 24 (C/NU - C/NJ (dB) A: correlated B: uncorrelatcd CCIR RECMN*793 92 Y855212 0520016 301 I where: D: decrease in post detection signal-to-noise rat
17、io (SIN) (see Fig. 2) due to increase in post-detection noise in the presence of AMPM conversion I = (clmu I(cIN)d I K2 cc = 1 + (z K: AM/PM conversion factor. K is of the order of 5 to 6 degrees1dB with present-day amplifier technology. This gives a value for CI in the (forfrequencymodulation) regi
18、on of 2.0 to 2.6 dB, which has been demonstrated theoretically and experimentally. The degradation caused by AMPM conversion cannot be observed by means of direct radio-frequency carrier-to-noise (CIA) measurements. However, this degradation can be measured by other means. It must be taken into acco
19、unt when calculating feeder-link budgets and can be compensated for by an increase in C/:VLL of IO log u dB. MPM conversion was not taken into account in the development of the Region 2 Plan. In a plan based on homogeneous characteristics of feeder-link stations which in turn leads to homogeneous no
20、minal (clear sky) power flux-densities at the satellites, the C/NU varies with satellite receive antenna gain. In Region 2, the range of interest of the satellite receive antenna gain at the -3 dB edge of coverage area varies from about 28 dB for a large country-wide feeder-link beam of 3“ x 8“ to 4
21、6 dB for a small spot beam of 0.6. Nith n system noise temperature at the satellite of 1 SOO K, which is readily achievable for satellite receivers at 18 GHz. the range of interest of GIT varies from 4 dB(K-1) to 14 dB(K-1) at the edge of coverage area. The choice of feeder-link Rec. 793 117 Partiti
22、oning of noise need not be specified as a planning element for Region 2 because the overall carrier-to- noise ratio is the applicable criterion when planning feeder links and down links at the same time. Howeler. some assumption of noise partitioning is required in order to determine feeder-link cha
23、racteristics, such as e.1.r.p. needed to satisfy broadcasting-satellite service requirements. As a guidance to the development of all the Plans, the noise contribution of the feeder link to the oerall Iiriii was assumed not to exceed 0.5 dB for 99% of the worst month. Feeder-link carrier-to-noise ra
24、tio Assuming that there is no transponder output back-off, a 0.5 dB noise conmbution of the feeder link to the overall link requires that: is exceeded for 99% of the worst month. Under clear-sky conditions, the (C/N), is then: (ClNu : feeder-link carrier-to-noise ratio (ClNd: down-link carrier-to-no
25、ise ratio LA# : feeder-link rain attenuation exceeded for 1% of the worst month. A margin of 1 dB is also needed for planning purposes for possible mispointing of the earth-station transmitting antenna. Furthermore, the high-power, non-linear amplifier of the repeater introduces, on account of its A
26、XLTX conversion factor, a degradation by the thermal noise in the demodulated signal. The impairment caused to the frequency demodulated signal by the AMPM phenomenon is given by: a+I D =- 1+1 (3, CCIR RECMN*793 92 W 48552l2 0520017 248 148 Rec. 793 power into the transmitting antenna may be in the
27、range of 588 to 1808 W. The Region 2 feeder-link Plcm is based on a maximum radio-frequency power of 1 o00 W delivered at the input of the feeder-link antenna. Table 1 gives a range of C/NU at 17.5 GHz assuming an antenne efficiency of 458, a filter bandwidth of 24 MHz and 1 dB gain loss due to misp
28、ointing of the earth-station antenna for 500 and 1 o00 W transmitted power. In Region 2, the Plan is based on a 5 m antenna dicameter but larger andlor smaller mtennas can be usd. For example, in the case of 14.5 dB CINd on the down link and a possible 1 dB piispointing of the earth- station transmi
29、tter antenna, a very small number of cases in Tabla 1 would give a noise contribution of the feeder link greater than 0.5 dB to the overall noise of the communication channels. These few cases are italicized in the table. In Regions 1 and 3, the Plan is based on 5 and 6 m antenna dimetea for the frc
30、quency bands 17 and 14 GHz, respectively, and 500 W transmitter power. These values correspond to an e.i.r.p. of 84 and 82 dBW, respectivcly, and aim to achieve a c,urier-to-noise ratio (C/NI of 24 dB exceeded for 99% of the worst month. FIGURE 2 Effect OP AM/P,M conversion on the post-deteetion noi
31、se power Link imbalance (C/NU/ C/N ?G. 1 36.1 43. i 38. i ,.- 7 Y. 2 15.2 ?7 - -1 7- 1 - .- 15.2 2i.i 33.3 i33 25 3 31.3 31.3 22.1 28. i 34.1 4!). 1 ?- ? - .- -. b In the case of the feeder link Plan for Regions 1 and 3. the figures in this table should be reduced hy J 5 dtc x;rb l reference bandwidth of 27 MHz.
