1、 Report ITU-R S.2174(07/2010)Guidelines that may be used in the designof satellite networks for assessingthe impact of rain attenuationon the carrier to noise plusinterference ratios of theFSS Plan allotmentsS SeriesFixed satellite serviceii Rep. ITU-R S.2174 Foreword The role of the Radiocommunicat
2、ion Sector is to ensure the rational, equitable, efficient and economical use of the radio-frequency spectrum by all radiocommunication services, including satellite services, and carry out studies without limit of frequency range on the basis of which Recommendations are adopted. The regulatory and
3、 policy functions of the Radiocommunication Sector are performed by World and Regional Radiocommunication Conferences and Radiocommunication Assemblies supported by Study Groups. Policy on Intellectual Property Right (IPR) ITU-R policy on IPR is described in the Common Patent Policy for ITU-T/ITU-R/
4、ISO/IEC referenced in Annex 1 of Resolution ITU-R 1. Forms to be used for the submission of patent statements and licensing declarations by patent holders are available from http:/www.itu.int/ITU-R/go/patents/en where the Guidelines for Implementation of the Common Patent Policy for ITU-T/ITU-R/ISO/
5、IEC and the ITU-R patent information database can also be found. Series of ITU-R Reports (Also available online at http:/www.itu.int/publ/R-REP/en) Series Title BO Satellite delivery BR Recording for production, archival and play-out; film for television BS Broadcasting service (sound) BT Broadcasti
6、ng service (television) F Fixed service M Mobile, radiodetermination, amateur and related satellite services P Radiowave propagation RA Radio astronomy RS Remote sensing systems S Fixed-satellite service SA Space applications and meteorology SF Frequency sharing and coordination between fixed-satell
7、ite and fixed service systems SM Spectrum management Note: This ITU-R Report was approved in English by the Study Group under the procedure detailed in Resolution ITU-R 1. Electronic Publication Geneva, 2010 ITU 2010 All rights reserved. No part of this publication may be reproduced, by any means wh
8、atsoever, without written permission of ITU. Rep. ITU-R S.2174 1 REPORT ITU-R S.2174 Guidelines that may be used in the design of satellite networks for assessing the impact of rain attenuation on the carrier to noise plus interference ratios of the FSS Plan allotments (2010) TABLE OF CONTENTS Page
9、1 Introduction 2 2 The criteria approved in the FSS Plan 2 3 The effect of the limited increase of the space and earth station transmitter power to 8 dB 3 4 The effect of the interference and signal attenuation on the uplink energy balance of the planned allotments 4 4.1 Case where the attenuation u
10、pis less than or equal to 8 dB 4 4.2 Case where the attenuation upis greater than 8 dB . 5 5 The independence of rain events on the uplink and downlink . 6 Annex 1 Effect of rain attenuation on satellite links . 7 1 Introduction 7 2 The effect of the rain attenuation on the earth station thermal noi
11、se (downlink) . 7 3 The effect of uplink rain attenuation on the downlink . 8 3.1 Impact of UPC on downlink . 8 3.2 Impact of ALC on downlink . 8 3.3 Calculation of the impact of uplink rain attenuation on the downlink . 9 Annex 2 Terms and definitions used in this Report 10 2 Rep. ITU-R S.2174 1 In
12、troduction In 2007, the World Radiocommunication Conference (WRC-07) adopted a revised FSS Plan (contained in Appendix 30B to the Radio Regulations), in which a number of technical parameters and criteria were modified. The above-mentioned Plan provides all ITU Members with protected orbital-frequen
13、cy resources. In the FSS Plan, the criterion for the carrier-to-noise ratio (C/N) is defined under rain-faded conditions but the criterion for the carrier-to-interference (C/I) is defined in clear-sky conditions. In some cases, as a consequence of approved technical criteria and unavoidable signal a
14、ttenuation due to rain, the energy balance of planned allotments in the 13/10-11 GHz frequency bands may become substantially worse. All mathematical computations made in this Report are based on the assumption that the uplink power is designed to strictly achieve a C/N ratio of 21 dB under rain-fad
15、ed conditions. It should be noted that test points of some allotments have higher faded C/N values in the uplink (i.e. greater than 21 dB). Throughout this Report, the following notation is used: )1010log(1010/10/dBdBBAdBdBdBdBXBAX+=Annex 1 to this Report provides supplementary information which exa
16、mines two additional impacts of rain attenuation on system margin which are not taken into account by the FSS Plan. Annex 2 contains all the terms and their respective definitions used in the Report and in Annex 1. 2 The criteria approved in the FSS Plan The overall link C/N is set to 14 dB (on the
17、basis of the following balance: an uplink C/N ratio set to 21 dB and a downlink C/N ratio set to 15 dB) for 99.9% of the year on both uplink and downlink directions in the 13/10-11 GHz bands. It should be noted that these values are guaranteed for the carrier-to-thermal noise ratios and not for the
18、carrier-to-noise-plus-interference ratios (C/(N+I). As decided by WARC Orb-88 and confirmed by WRC-07, to increase homogeneity between various allotments, the increase of the space and earth transmitter power, necessary to compensate for the attenuation, is limited to 8 dB. For achieving the same pu
19、rpose, the minimum earth station transmitter power density was limited to 60 dB(W/Hz) averaged over the necessary bandwidth of the modulated carrier. Therefore, on the uplink, while some allotments may not be guaranteed a minimum C/N ratio of 21 dB for 99.9% of the year, others may exhibit a C/N rat
20、io strictly greater than 21 dB even under rain-faded conditions. The carrier to interference ratio C/I for the overall communication link should not be lower than 21 dB for aggregate interference and 25 dB for single-entry interference under free-space conditions. An allotment or an assignment is co
21、nsidered as being affected by a proposed new allotment or assignment if at least one of the following three conditions is not satisfied: 1. the calculated Earth-to-space single-entry carrier-to-interference ratio (C/I)up, SEmust be greater than or equal to a reference value of 30 dB; 2. the calculat
22、edspace-to-Earth single-entry carrier-to-interference ratio (C/I)down, SEmust be greater than or equal to a reference value of 26.65 dB; 3. the calculated overall aggregate carrier-to-interference ratio (C/I)aggmust be greater than or equal to a reference value that is 21 dB. Rep. ITU-R S.2174 3 The
23、 aggregate interference is not specified separately for the uplink and downlink. Taking into account that, for the overall link, the difference between the aggregate and single-entry interference is equal to 4 dB, it is assumed that the minimum downlink aggregate carrier-to-interference ratio (C/I)d
24、own, aggis equal to 22.65 dB and the minimum uplink carrier-to-interference ratio (C/I)up, aggto 26 dB. In this Report, it is assumed that rain fading on the wanted and interfering downlinks is completely correlated since both wanted and interfering signals are received by the earth station at the s
25、ame point on the Earths surface. On the contrary, on the uplink, the wanted and interfering signals are transmitted by different earth stations, which are generally located in geographically separated areas, and rain fading on the wanted and interfering signals is not correlated. 3 The effect of the
26、 limited increase of the space and earth station transmitter power to 8 dB Due to the limited increase of the space and earth station transmitter power to 8 dB, when signal attenuation for any test point is greater than 8 dB, the faded carrier to noise ratio (C/N)fadedis reduced to: (C/N)faded= (C/N
27、)nom ( 8) dB where (C/N)nomis the nominal value for the carrier-to-noise ratio specified in the Plan for this allotment (i.e. at a minimum, the reference value under rain-faded conditions). So, on the uplink, knowing that the nominal value of the carrier-to-noise ratio (C/N)up, nomis equal to 21 dB,
28、 the faded carrier-to-noise ratio (C/N)up,fadedis: (C/N)up,faded= 21 (up 8) = 29 updB On the downlink, knowing that the nominal value of the carrier-to-noise ratio (C/N)down, nomis equal to 15 dB, the faded carrier to noise ratio (C/N)down, fadedis1: (C/N)down, faded= 15 (down 8) = 23 downdB The for
29、mulas below clarify the relationship between and (C/N) for the uplink and downlink: When up 8dB, (C/N)up, faded = (C/N)up, nomWhen down 8dB, (C/N)down, faded = (C/N)down, nom1It is noted that in the equation above when (C/N)down, fadedvalue is calculated under rain-faded conditions, increase of eart
30、h station noise temperature due to increased rain attenuation is not considered. This effect, which is considered in Annex 1, was actively discussed at the WRC-07. In order to keep the entire integrity of the WARC Orb-88 Plan, the Conference decided to apply the same assumptions as the WARC Orb-88 a
31、nd to not consider this effect. 4 Rep. ITU-R S.2174 4 The effect of the interference and signal attenuation on the uplink energy balance of the planned allotments The energy balance of the communication link is defined by the ratio: Cup, faded/(N + Iup, agg) where: Cup, faded: wanted signal power at
32、 the input of the space station receiver with the signal attenuation in the atmospheric gases and precipitation, which corresponds to an availability of 99.9% of the year in the 13/10-11 GHz bands N : thermal noise power of the space station receiver taking into account the Earth noise radiation. In
33、 the FSS Plan, this value is set at N = 550 K in the 13 GHz band Iup, agg: aggregate interference at the input of the space station receiver from all other allotments and assignments in the Plan and List. 4.1 Case where the attenuation upis less than or equal to 8 dB In this case, the value of the u
34、plink carrier-to-noise ratio (C/N)up, nomis determined in order to achieve the required C/N of 21 dB under rain-faded conditions: =+up, aggup, fadedup, fadedup, aggup, fadedICNCINCor equivalently: =+upaggupnomupup, aggup, fadedICNCINC,where: up, nomNC= 21 dB and up, aggIC= 26 dB. For example when up
35、= 5 dB: dB21=up, aggup, fadedICand =+up, aggup, fadedINC18 dB which is 3 dB less than the C/N value established in Appendix 30B. See also Fig. 1. Rep. ITU-R S.2174 5 4.2 Case where the attenuation upis greater than 8 dB In this case the value of the uplink carrier-to-noise ratio (C/N)up,nomis partly
36、 restored, only by 8 dB, therefore: ()=+upup, aggupup, nomup, aggup, fadedICNCINC8 or equivalently: ()()upupup, aggup, fadedINC=+6292 because dB21=up, nomNCand dB26=up, aggIC. For example, if up= 10 dB: dB19=NCup, faded, dB16=up, aggup, fadedICand dB2.14=+up, aggup, fadedINCwhich is 6.8 dB less than
37、 the C/N value of 21 dB established in RR Appendix 30B for the uplink planned allotments. As another example, if up= 21 dB: dB8=NCup, faded, dB5=up, aggup, fadedICand dB2.3=+up, aggup, fadedINCwhich is 17.8 dB less than the C/N value of 21 dB established in RR Appendix 30B for the uplink planned all
38、otments. See also Fig. 1. 6 Rep. ITU-R S.2174 FIGURE 1 Display for the case where the attenuation upis less than or equal to 8 dB C(Cf/N)u(C/Iag)u(N/I)CfNIag u21 dB 26 dBFIGURE 2 Display for the case where the attenuation upis greater than 8 dB 5 The independence of rain events on the uplink and dow
39、nlink Section 2.2.4.1 of Recommendation ITU-R P.618-10 provides a methodology to estimate the joint probability that it is raining at both the uplink and downlink sites. This methodology can be used to determine the probability that both the uplink and downlink margins will be required to overcome r
40、ain attenuation. It should be noted that such probability is normally low for FSS satellite links for the cases where the uplink station is far from the downlink station. Rep. ITU-R S.2174 7 Annex 1 Effect of rain attenuation on satellite links 1 Introduction When the FSS Plan was developed, two add
41、itional impacts on system margin due to rain attenuation were not taken into account. These two impacts are: 1 the effect of rain attenuation on the earth station thermal noise from a rain fade on the downlink, and 2 the effect of uplink rain fading on the downlink. The increase in earth station noi
42、se temperature during a downlink rain fade causes a decrease in the downlink carrier-to-noise ratio that was not taken into account in the development of the Plan. The impact of uplink rain fading on the downlink is also not taken into account in the Plan. The Plan does not distinguish whether conve
43、ntional transparent transponders or remodulating transponders with onboard signal processing are used. At the time of preparation of this Report, conventional transparent transponders are widely used on most satellite networks. Section 3 of this Annex considers the effect of uplink rain fading on th
44、e downlink on satellite networks when transparent transponders are used. In addition, the calculation of uplink margins for satellite networks when using Recommendation ITU-R P.618-10 should take into account the effect of uplink rain attenuation on the downlink as per 3. In many cases, the use of u
45、plink fade compensation techniques, where feasible, will mitigate the impact of not taking into account the effect of uplink fading on the downlink carrier-to-noise plus aggregate interference. 2 The effect of the rain attenuation on the earth station thermal noise (downlink) Since the earth station
46、 noise TESincreases as a result of the raining conditions according to the formula: ( )10/,101downmclear-skyESrainESTTT+= the downlink carrier-to-noise ratio (C/N)down, rainis reduced to: +=skyES, clear-mskyES, clear-downr-skydown, cleadown, rainTTTNCNCdown)10(1log10 /10where: (C/N)down, clear-sky :
47、value of the downlink carrier-to-noise ratio in clear-sky conditions determined in the Plan for this allotment ES, clear-sky:equal to 125 K in the 10-11 GHz band Tm:effective temperature of the medium, usually 260-280 K (Recommendation ITU-R P.618). For simplicity it has been assumed that the temper
48、ature of the medium is constant during rain and clear-sky conditions down:downlink attenuation due to rain. 8 Rep. ITU-R S.2174 It should be noted that this effect was not taken into account when determining required satellite e.i.r.p. levels for downlink planned allotments during the development of the FSS Plan. 3 The effect of uplink rain attenuation on the downlink Many modern satellite communications networks using transparent transponders implement one or more methods for mitigating the effects of fading (typically due to rain) on the uplink to improve overall end-to-end link per
