1、 Recommendation ITU-R P.618-12 (07/2015) Propagation data and prediction methods required for the design of Earth-space telecommunication systems P Series Radiowave propagation ii Rec. ITU-R P.618-12 Foreword The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient a
2、nd 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 policy functions of the Radiocommunication Sector are perfo
3、rmed 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/ISO/IEC referenced in Annex 1 of Resolution ITU-R 1. Forms t
4、o 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/IEC and the ITU-R patent information database can also be fo
5、und. Series of ITU-R Recommendations (Also available online at http:/www.itu.int/publ/R-REC/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, ra
6、diodetermination, 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-satellite and fixed service systems SM Spectrum management
7、 SNG Satellite news gathering TF Time signals and frequency standards emissions V Vocabulary and related subjects Note: This ITU-R Recommendation was approved in English under the procedure detailed in Resolution ITU-R 1. Electronic Publication Geneva, 2015 ITU 2015 All rights reserved. No part of t
8、his publication may be reproduced, by any means whatsoever, without written permission of ITU. Rec. ITU-R P.618-12 1 RECOMMENDATION ITU-R P.618-12 Propagation data and prediction methods required for the design of Earth-space telecommunication systems (Question ITU-R 206/3) (1986-1990-1992-1994-1995
9、-1997-1999-2001-2003-2007-2009-2013-2015) Scope This Recommendation predicts the various propagation parameters needed in planning Earth-space systems operating in either the Earth-to-space or space-to-Earth direction. The ITU Radiocommunication Assembly, considering a) that for the proper planning
10、of Earth-space systems, it is necessary to have appropriate propagation data and prediction techniques; b) that methods have been developed that allow the prediction of the most important propagation parameters needed in planning Earth-space systems; c) that as far as possible, these methods have be
11、en tested against available data and have been shown to yield an accuracy that is both compatible with the natural variability of propagation phenomena and adequate for most present applications in system planning, recommends that the methods for predicting the propagation parameters set out in Anne
12、x 1 should be adopted for planning Earth-space radiocommunication systems, in the respective ranges of validity indicated in Annex 1. NOTE 1 Supplementary information related to the planning of broadcasting-satellite systems as well as maritime, land, and aeronautical mobile-satellite systems, may b
13、e found in Recommendations ITU-R P.679, ITU-R P.680, ITU-R P.681 and ITU-R P.682, respectively. 2 Rec. ITU-R P.618-12 Annex 1 1 Introduction In the design of Earth-space links for communication systems, several effects must be considered. Effects of the non-ionized atmosphere need to be considered a
14、t all frequencies, but become critical above about 1 GHz and for low elevation angles. These effects include: a) absorption in atmospheric gases; absorption, scattering and depolarization by hydrometeors (water and ice droplets in precipitation, clouds, etc.); and emission noise from absorbing media
15、; all of which are especially important at frequencies above about 10 GHz; b) loss of signal due to beam-divergence of the earth-station antenna, due to the normal refraction in the atmosphere; c) a decrease in effective antenna gain, due to phase decorrelation across the antenna aperture, caused by
16、 irregularities in the refractive-index structure; d) relatively slow fading due to beam-bending caused by large-scale changes in refractive index; more rapid fading (scintillation) and variations in angle of arrival, due to small-scale variations in refractive index; e) possible limitations in band
17、width due to multiple scattering or multipath effects, especially in high-capacity digital systems; f) attenuation by the local environment of the ground terminal (buildings, trees, etc.); g) short-term variations of the ratio of attenuations at the up- and down-link frequencies, which may affect th
18、e accuracy of adaptive fade countermeasures; h) for non-geostationary satellite (non-GSO) systems, the effect of varying elevation angle to the satellite. Ionospheric effects (see Recommendation ITU-R P.531) may be important, particularly at frequencies below 1 GHz. For convenience these have been q
19、uantified for frequencies of 0.1; 0.25; 0.5; 1; 3 and 10 GHz in Table 1 for a high value of total electron content (TEC). The effects include: j) Faraday rotation: a linearly polarized wave propagating through the ionosphere undergoes a progressive rotation of the plane of polarization; k) dispersio
20、n, which results in a differential time delay across the bandwidth of the transmitted signal; l) excess time delay; m) ionospheric scintillation: inhomogeneities of electron density in the ionosphere cause refractive focusing or defocusing of radio waves and lead to amplitude fluctuations termed sci
21、ntillations. Ionospheric scintillation is maximum near the geomagnetic equator and smallest in the mid-latitude regions. The auroral zones are also regions of large scintillation. Strong scintillation is Rayleigh distributed in amplitude; weaker scintillation is nearly log-normal. These fluctuations
22、 decrease with increasing frequency and depend upon path geometry, location, season, solar activity and local time. Table 2 tabulates fade depth data for VHF and UHF in mid-latitudes, based on data in Recommendation ITU-R P.531. Accompanying the amplitude fluctuation is also a phase fluctuation. The
23、 spectral density of the phase fluctuation is proportional to 1/f 3, where f is the Fourier frequency of the fluctuation. This spectral characteristic is similar to that arising from flicker of frequency in oscillators and can cause significant degradation to the performance of receiver hardware. Re
24、c. ITU-R P.618-12 3 TABLE 1 Estimated* ionospheric effects for elevation angles of about 30 one-way traversal* (derived from Recommendation ITU-R P.531) Effect Frequency dependence 0.1 GHz 0.25 GHz 0.5 GHz 1 GHz 3 GHz 10 GHz Faraday rotation 1/f 2 30 rotations 4.8 rotations 1.2 rotations 108 12 1.1
25、Propagation delay 1/f 2 25 s 4 s 1 s 0.25 s 0.028 s 0.0025 s Refraction 1/f 2 20 dB peak-to-peak 10 dB peak-to-peak 4 dB peak-to-peak * This estimate is based on a TEC of 1018 electrons/m2, which is a high value of TEC encountered at low latitudes in daytime with high solar activity. * Ionospheric e
26、ffects above 10 GHz are negligible. (1) Values observed near the geomagnetic equator during the early night-time hours (local time) at equinox under conditions of high sunspot number. 4 Rec. ITU-R P.618-12 TABLE 2 Distribution of mid-latitude fade depths due to ionospheric scintillation (dB) This An
27、nex deals only with the effects of the troposphere on the wanted signal in relation to system planning. Interference aspects are treated in separate Recommendations: interference between earth stations and terrestrial stations (Recommendation ITU-R P.452); interference from and to space stations (Re
28、commendation ITU-R P.619); bidirectional coordination of earth stations (Recommendation ITU-R P.1412). An apparent exception is path depolarization which, although of concern only from the standpoint of interference (e.g. between orthogonally-polarized signal transmissions), is directly related to t
29、he propagation impairments of the co-polarized direct signal. The information is arranged according to the link parameters to be considered in actual system planning, rather than according to the physical phenomena causing the different effects. As far as possible, simple prediction methods covering
30、 practical applications are provided, along with indications of their range of validity. These relatively simple methods yield satisfactory results in most practical applications, despite the large variability (from year to year and from location to location) of propagation conditions. As far as pos
31、sible, the prediction methods in this Annex have been tested against measured data from the data banks of Radiocommunication Study Group 3 (see Recommendation ITU-R P.311). 2 Propagation loss The propagation loss on an Earth-space path, relative to the free-space loss, is the sum of different contri
32、butions as follows: attenuation by atmospheric gases; attenuation by rain, other precipitation and clouds; focusing and defocusing; decrease in antenna gain due to wave-front incoherence; scintillation and multipath effects; attenuation by sand and dust storms. Each of these contributions has its ow
33、n characteristics as a function of frequency, geographic location and elevation angle. As a rule, at elevation angles above 10, only gaseous attenuation, rain and cloud attenuation and possibly scintillation will be significant, depending on propagation conditions. For non-GSO systems, the variation
34、 in elevation angle should be included in the calculations, as described in 8. Percentage of time (%) Frequency (GHz) 0.1 0.2 0.5 1 1 5.9 1.5 0.2 0.1 0.5 9.3 2.3 0.4 0.1 0.2 16.6 4.2 0.7 0.2 0.1 25 6.2 1 0.3 Rec. ITU-R P.618-12 5 (In certain climatic zones, snow and ice accumulations on the surfaces
35、 of antenna reflectors and feeds can produce prolonged periods with severe attenuation, which might dominate even the annual cumulative distribution of attenuation.) 2.1 Attenuation due to atmospheric gases Attenuation by atmospheric gases which is entirely caused by absorption depends mainly on fre
36、quency, elevation angle, altitude above sea level and water vapour density (absolute humidity). At frequencies below 10 GHz, it may normally be neglected. Its importance increases with frequency above 10 GHz, especially for low elevation angles. Annex 1 of Recommendation ITU-R P.676 gives a complete
37、 method for calculating gaseous attenuation, while Annex 2 of the same Recommendation gives an approximate method for frequencies up to 350 GHz. At a given frequency the oxygen contribution to atmospheric absorption is relatively constant. However, both water vapour density and its vertical profile
38、are quite variable. Typically, the maximum gaseous attenuation occurs during the season of maximum rainfall (see Recommendation ITU-R P.836). 2.2 Attenuation by precipitation and clouds 2.2.1 Prediction of attenuation statistics for an average year The general method to predict attenuation due to pr
39、ecipitation and clouds along a slant propagation path is presented in 2.2.1.1. The method to predict the probability of non-zero rain attenuation along a slant path is described in 2.2.1.2. If reliable long-term statistical attenuation data are available that were measured at an elevation angle and
40、a frequency (or frequencies) different from those for which a prediction is needed, it is often preferable to scale these data to the elevation angle and frequency in question rather than using the general method. The recommended frequency-scaling method is found in 2.2.1.3. Site diversity effects m
41、ay be estimated with the method of 2.2.4. 2.2.1.1 Calculation of long-term rain attenuation statistics from point rainfall rate The following procedure provides estimates of the long-term statistics of the slant-path rain attenuation at a given location for frequencies up to 55 GHz. The following pa
42、rameters are required: R0.01: point rainfall rate for the location for 0.01% of an average year (mm/h) hs: height above mean sea level of the earth station (km) : elevation angle (degrees) : latitude of the earth station (degrees) f: frequency (GHz) Re: effective radius of the Earth (8 500 km). If l
43、ocal data for the earth station height above mean sea level is not available, an estimate can be obtained from the maps of topographic altitude given in Recommendation ITU-R P.1511. The geometry is illustrated in Fig. 1. 6 Rec. ITU-R P.618-12 FIGURE 1 Schematic presentation of an Earth-space path gi
44、ving the parameters to be input into the attenuation prediction process P . 0 6 1 8 - 0 1A : fro zen p reci p i t at i o nB: rai n h ei g h tC: l i q u i d p reci p i t at i o nD : E art h -s p ace p at hBADChRh sLGL s()hhRsStep 1: Determine the rain height, hR, as given in Recommendation ITU-R P.83
45、9. Step 2: For 5 compute the slant-path length, Ls, below the rain height from: kms in )( sRs hhL (1) For , kmc o s 01.0 rLL GRElse, kms in )( sRR hhLIf | | 0). It relies on the following input parameters: 0(,): probability of rain at the earth station, (0 P0 1)where: : elevation angle (degrees) and
46、 LS: slant path length from the earth station to the rain height (km). Step 1: Estimate the probability of rain, 0(,), at the earth station either from Recommendation ITU-R P.837 or from local measured rainfall rate data. Step 2: Calculate the parameter : = 1(0), (9) where: () = 12 22 (10) Step 3: C
47、alculate the spatial correlation function, : = 0.59|31 +0.41|800, (11) where: = .cos (12) and Ls is calculated in equation (2). Step 4: Calculate the complementary bivariate normal distribution, 1: = 1212 22+22(12) (13) Step 5: Calculate the probability of rain attenuation on the slant path: 000200
48、1110pB PP PcPAP (14) 2.2.1.3 Long-term frequency and polarization scaling of rain attenuation statistics Frequency scaling is the prediction of a propagation effect (e.g. rain attenuation) at one frequency from knowledge of the propagation effect at a different frequency. Typically, the frequency of
49、 the predicted propagation effect is higher than the frequency of the known propagation effect. The ratio between the rain attenuation at the two frequencies can vary during a rain event, and the variability of the ratio generally increases as the rain attenuation increases. 1 NOTE is the same bivariate normal integral used in 2.2.4.1. An approximati
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