1、 Report ITU-R SA.2183(10/2010)Method for calculating link performance in the space research serviceSA SeriesSpace applications and meteorologyii Rep. ITU-R SA.2183 Foreword The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient and economical use of the radio-frequ
2、ency 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 policy functions of the Radiocommunication Sector are performed by World and Regional Radiocomm
3、unication 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/ISO/IEC referenced in Annex 1 of Resolution ITU-R 1. Forms to be used for the submission of pate
4、nt 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/IEC and the ITU-R patent information database can also be found. Series of ITU-R Reports (Also a
5、vailable 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 Broadcasting service (television) F Fixed service M Mobile, radiodetermination, amateur and related satell
6、ite 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-satellite and fixed service systems SM Spectrum management Note: This ITU-R Report was approved in Eng
7、lish 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 whatsoever, without written permission of ITU. Rep. ITU-R SA.2183 1 REPORT ITU-R SA.2183 Method fo
8、r calculating link performance in the space research service (2010) TABLE OF CONTENTS Page 1 Introduction 2 2 References 2 3 Types of analysis for frequency selection 2 4 Method for calculating link performance . 3 5 Calculations for atmospheric attenuation (no rain or clouds). 3 6 Calculations for
9、rain attenuation 10 7 Calculations for atmosphere plus rain attenuation . 15 8 Link performance for atmospheric attenuation 17 9 Link performance for atmosphere plus rain attenuation . 18 10 Conclusion 20 2 Rep. ITU-R SA.2183 1 Introduction This Report presents a method of calculating attenuation, n
10、oise temperature, and link performance, based on ITU-R Recommendations concerning the characteristics of radio wave propagation. The method can be extended to include equipment characteristics. The method includes consideration of some effects that become important for systems with noise temperature
11、s below about 30 K when operated in frequency bands below about 15 GHz. These factors are cosmic background noise, galactic noise, and the effect of atmospheric attenuation on their values. For many other systems with higher noise temperatures, these factors may be neglected. The method will be expl
12、ained in the context of providing data for the selection of preferred frequency bands on the basis of link performance. 2 References The method and calculations to be described are based in part on the following Recommendations: Recommendation ITU-R P.837-5 Characteristics of precipitation for propa
13、gation modelling Recommendation ITU-R P.618-9 Propagation data and prediction methods required for the design of Earth-space telecommunications systems Recommendation ITU-R P.676-7 Attenuation by atmospheric gases Recommendation ITU-R P.838-3 Specific attenuation model for rain for use in prediction
14、 methods Recommendation ITU-R P.372-9 Radio noise Recommendation ITU-R P.839-3 Rain height model for prediction methods Recommendation ITU-R P.525-2 Calculation of free-space attenuation. 3 Types of analysis for frequency selection For links between a spacecraft and the Earth, four types of analysis
15、 may be identified: space-to-Earth, as limited only by natural phenomena; space-to-Earth, including the effects of equipment; Earth-to-space, as limited only by natural phenomena; Earth-to-space, including the effects of equipment. For the Earth-to-space link, contributions to the noise temperature
16、of the spacecraft receiving system also include the cosmic and galactic backgrounds, but the contribution from the atmosphere of the Earth may be relatively small. For deep-space probes the Earth occupies such a small portion of the receiving antenna pattern that the noise temperature contribution o
17、f the atmosphere is negligible. The attenuation of the atmosphere must nevertheless be included in the link analysis since it directly affects the received signal power. It is useful to consider links using two types of antennas. The first link assumes fixed diameter transmitting and receiving anten
18、nas. In this case the gain of both antennas varies with frequency. The second type of link assumes the use of one fixed diameter antenna and one fixed beamwidth antenna. In this case the gain of the fixed beam width antenna is nearly independent of frequency. An example of this case is the use of an
19、 omnidirectional antenna on a space station in order to allow communication during course correction maneuvers or loss of attitude control. The shape of link performance curves depends on the antenna types assumed. Rep. ITU-R SA.2183 3 4 Method for calculating link performance The method for calcula
20、ting link performance of space-to-Earth link under conditions of atmospheric attenuation and atmosphere plus rain attenuation is described. Tables 1 to 5 list the several parameters included in the calculation. The tables are: 1. Attenuation by atmospheric gasses and noise temperature as a function
21、of frequency, elevation angle and water vapour density for atmospheric propagation. 2. Attenuation and noise temperature due to rainfall alone, as a function of frequency, elevation angle, and rain rate. 3. Attenuation and noise temperature for a propagation path including atmosphere plus rain, usin
22、g data from Table 2. 4. Link performance for an assumed set of transmitter, antenna, and distance parameters, and considering the attenuation and noise temperature data from Table 1. 5. Link performance for an assumed set of transmitter, antenna, and distance parameters, considering the attenuation
23、and noise temperature data from Table 3. The tables are merely examples which show the various parameters and values for a few frequencies. Values given in the tables are the result of analytic calculations. It should not be inferred that listing of these values to a precision of several decimal pla
24、ces is an indication of the accuracy or precision of the underlying propagation data or associated analytic expressions. Prediction of actual link performance to the indicated precision is not generally possible. For a space-Earth propagation path through a rainy atmosphere, the attenuation is equal
25、 to the attenuation caused by the clear atmosphere along the path, plus the additional attenuation caused by the rainfall along the path. The attenuation caused by the atmosphere alone, and the attenuation caused by the rainfall alone are separately calculated (see Recommendation ITU-R P.618). The s
26、ky noise temperature attributed to the rainy atmosphere is calculated with respect to the total attenuation, and is not equal to the sum of the noise temperatures that could be calculated for each of the two components of the total attenuation. For each line in each table there is a description of t
27、he parameter or calculation and, usually, a particular information source is referenced. 5 Calculations for atmospheric attenuation (no rain or clouds) Table 1 presents calculated values of attenuation caused by the atmosphere, and of noise temperature caused by the combined effects of the cosmic ba
28、ckground noise, galactic background noise, and the noise temperature related to attenuation by the atmosphere. The calculations shown in Table 1 are for conditions of atmospheric attenuation (no rain or clouds). Referring to the line numbers given at the left side of the table, the calculations are
29、made as follows: Line 7 Water vapour density (g/m3) Water vapour density in the atmosphere that is assumed for the particular calculation. Line 8 Station height above sea level (km) Height of the earth station above sea level. The example given in Table 1 is 0.81 km for the deep-space earth station
30、at Madrid, Spain. Line 10 Frequency (GHz) Radio frequency for the particular calculation. 4 Rep. ITU-R SA.2183 Line 12 h0(km) Equivalent oxygen height at the earth station location. The equivalent oxygen height from sea level up to an altitude of about 10 km is given by: ()3211.10117.011.6tttrhp+=km
31、 ()()()3725266.232223.21102.3101.40169.011061.10001.00247.014.010114.02.2exp031.0)75.118(12.2exp14.09.7exp4.1287.27.59exp066.0164.4ffffffrtrfrtrfrtppppp+=+=+=h0 10.7rp0.3when f , kmcos01.0=rLLgRElse, kmsin)(=srRhhL Rep. ITU-R SA.2183 13 If | | 36, = 36 | | degrees Else, = 0 degrees ()() +=+45.0e131s
32、in112)1/(01.0fLRRLine 26 Effective path length, Le The effective path length is given by: Le= LR0.01km Line 27 Attenuation 0.01% (dB) Rain attenuation exceeded 0.01% of the year, given by: A0.01= RLe See 2.2.1.1, Step 7, Recommendation ITU-R P.618-9. Line 28 Attenuation p% (dB), Ap Rain attenuation
33、exceeded p% of the year, and is given by: If p 1 or | | 36: = 0 If p 1 and | | 36 and 25: = 0.005(| | 36) Otherwise: = 0.005(| | 36) + 1.8 4.25 sin dB01.0)sin)1()n(10.045)n(1033.0655.0(01.001.0+=pApppAA NOTE 1 The selection of a particular percentage of time is based on operational considerations. 0
34、.1% is appropriate for some space research missions and was chosen for this example in order to illustrate the method of calculation. See 2.2.1.1, Step10, Recommendation ITU-R P.618-9. Lines 31-41 and 44-54 are similar to lines 18-28 except for the effects of different elevation angles. 14 Rep. ITU-
35、R SA.2183 1 TABLE 2 2 Data for selection of preferred frequencies Attenuation caused by rainfall alone, without atmosphere 3 4 5 -6 Station latitude (degrees) 40 7 Station height above sea level (km) 0.818 Rain rate (mm/h) 0.01% 32 9 Rain height (km) 3.7 10 11 Frequency (GHz) 1 10 20 30 12 13 Coeffi
36、cient kH0.000026 0.0122 0.092 0.24014 Coefficient H0.969 1.257 1.057 0.94915 Coefficient kV0.000031 0.0113 0.096 0.22916 Coefficient V0.859 1.216 0.985 0.91317 18 Elevation angle (degrees) 15 15 15 15 19 Slant path (km) 11.17 11.17 11.17 11.17 20 Horizontal projection (km) 10.79 10.79 10.79 10.7921
37、Coefficient k 2.835E-5 0.012 0.094 0.235 22 Coefficient 0.909 1.237 1.020 0.93123 R (dB/km) 6.63E-4 0.854 3.218 5.91524 Horizontal reduction 0.01% 1.458 0.731 0.607 0.569 25 Vertical reduction 0.01% 0.470 0.842 1.047 1.138 26 Effective path length (km) 5.248 6.872 7.095 7.23227 Attenuation 0.01% (dB
38、) 0.003 5.867 22.834 42.781 28 Attenuation p = 0.1 (dB) 5.10E-4 1.858 8.324 16.64429 30 31 Elevation angle (degrees) 30 30 30 30 32 Slant path (km) 5.78 5.78 5.78 5.78 33 Horizontal projection (km) 5.006 5.006 5.006 5.00634 Coefficient k 2.835E-5 0.012 0.094 0.235 35 Coefficient 0.909 1.237 1.020 0.
39、93136 R (dB/km) 6.63E-4 0.854 3.218 5.91537 Horizontal reduction 0.01% 1.504 0.885 0.758 0.717 38 Vertical reduction 0.01% 0.491 0.877 1.127 1.246 39 Effective path length (km) 2.836 4.487 4.934 5.16440 Attenuation 0.01% (dB) 0.002 3.831 15.878 30.54 41 Attenuation p = 0.1 (dB) 2.585E-4 1.161 5.574
40、11.4842 43 44 Elevation angle (degrees) 75 75 75 75 45 Slant path (km) 2.992 2.992 2.992 2.992 46 Horizontal projection (km) 0.774 0.774 0.774 0.77447 Coefficient k 2.835E-5 0.012 0.094 0.235 48 Coefficient 0.909 1.237 1.020 0.93149 R(dB/km) 6.627E-4 0.854 3.218 5.915 50 Horizontal reduction 0.01% 1
41、.392 1.109 1.024 0.99451 Vertical reduction 0.01% 0.522 0.957 1.259 1.429 52 Effective path length (km) 1.563 2.864 3.768 4.25253 Attenuation 0.01% (dB) 0.001 2.445 12.126 25.153 54 Attenuation p = 0.1 (dB) 1.340E-4 0.707 4.140 9.262Rep. ITU-R SA.2183 15 7 Calculations for atmosphere plus rain atten
42、uation Table 3 presents calculated values of attenuation caused by the clear atmosphere plus rain, and of noise temperature caused by the effects of the cosmic background noise, galactic background noise, and the noise temperature related to attenuation by the combination of atmosphere and rain. Ref
43、erring to the line numbers given at the left side of the table, the calculations are made as follows: Lines 1 through 26 are as explained for Table 1. Line 27 Rain attenuation (dB) Attenuation due to rain along a path at the specified elevation angle. The value given is the attenuation that is excee
44、ded 0.1% of the time at Madrid and is obtained from Table 2. Line 28 Total attenuation (dB) B = Sum of the attenuation due to the atmosphere and the attenuation due to rain. Line 29 Atmospheric + rain noise temperature (K) Noise temperature due to the total attenuation, given by: 280 (1 10B/10) K wh
45、ere 280 is the mean radiating temperature (K) of the atmosphere and B (dB) is the one-way total attenuation along the path. Line 30 Background noise temperature (K) Sum of the cosmic and galactic noise temperatures, as reduced by the attenuation at the particular elevation angle, given by: (Cosmic +
46、 Galactic temperature) / 10B/10K where B (dB) is the one-way attenuation through the atmosphere in the direction of the elevation angle. Line 31 Noise temperature (K) Sum of the atmospheric and rain noise and the background noise for the particular elevation angle. Line 32 Noise power spectral densi
47、ty (dB(W/Hz) Noise power spectral density corresponding to the noise temperature, given by: 228.6 + 10 log(noise temperature (K) dB(W/Hz) where 228.6 is the logarithmic expression of Boltzmans constant, 1.3806 1023 (J/K). Lines 34-50 are similar to lines 25-32 except for the effects of different ele
48、vation angles. 16 Rep. ITU-R SA.2183 1 TABLE 3 2 Data for selection of preferred frequencies Attenuation and noise temperature, atmosphere plus rain 3 4 -5 Water vapour density (g/m3) 7.506 Station height above sea level (km) 0.81 7 Frequency (GHz) 1 10 20 308 9 h0 (km) 5.213 5.2005.181 5.15610 0 (dB/km) 0.005 0.0080.011 0.02011 hw(km) 1.665 1.6751.963 1.69612 w(dB/km) 5.668E-5 0.0070.101 0.08013 14 Galactic temperatu
