1、 Recommendation ITU-R P.617-3(09/2013)Propagation prediction techniques and data required for the design of trans-horizon radio-relay systemsP SeriesRadiowave propagationii Rec. ITU-R P.617-3 Foreword The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient and econo
2、mical 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 performed by
3、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 to be use
4、d 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 found. Ser
5、ies 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, radiodeter
6、mination, 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 SNG Sat
7、ellite 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, 2013 ITU 2013 All rights reserved. No part of this publ
8、ication may be reproduced, by any means whatsoever, without written permission of ITU. Rec. ITU-R P.617-3 1 RECOMMENDATION ITU-R P.617-3 Propagation prediction techniques and data required for the design of trans-horizon radio-relay systems (Question ITU-R 205/3) (1986-1992-2012-2013) The ITU Radioc
9、ommunication Assembly, considering a) that for the proper planning of trans-horizon radio-relay systems it is necessary to have appropriate propagation prediction methods and data; b) that methods have been developed that allow the prediction of most of the important propagation parameters affecting
10、 the planning of trans-horizon radio-relay systems; c) that as far as possible these methods have been tested against available measured 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 applicati
11、ons in system planning, recommends that the prediction methods and other techniques set out in Annex 1 be adopted for planning trans-horizon radio-relay systems in the respective ranges of parameters indicated. Annex 1 1 Introduction The only mechanisms for radio propagation beyond the horizon which
12、 occur permanently for frequencies greater than 30 MHz are those of diffraction at the Earths surface and scatter from atmospheric irregularities. Attenuation for diffracted signals increases very rapidly with distance and with frequency, and eventually the principal mechanism is that of tropospheri
13、c scatter. Both mechanisms may be used to establish “trans-horizon” radiocommunication. Because of the dissimilarity of the two mechanisms it is necessary to consider diffraction and tropospheric scatter paths separately for the purposes of predicting transmission loss. This Annex relates to the des
14、ign of trans-horizon radio-relay systems. One purpose is to present in concise form simple methods for predicting the annual and worst-month distributions of transmission loss due to tropospheric scatter, together with information on their ranges of validity. Another purpose of this Annex is to pres
15、ent other information and techniques that can be recommended in the planning of trans-horizon systems. 2 Rec. ITU-R P.617-3 2 Integral digital products The file TropoClim.txt is an ASCII file that provides the identification of the different climatic zones in terms of an integer value and is availab
16、le in the file R-REC-P.617-3-201309-I!ZIP-E. The data is represented as gridded latitude/longitude values in the “standard” ITU-R format. The data format is defined as: TABLE 1 Source Latitude (rows) Longitude (columns) First row (N) Spacing (degrees) Number of rows First col (E) Spacing (degrees) N
17、umber of cols P.2001 89.75 0.5 360 179.75 0.5 720 NOTE 1 The “First row” value is the latitude of the first row. NOTE 2 The “First col” value is the longitude of the first column. The columns represent longitudes increasing from 179.75W to 179.75E inclusive. That is, the longitude increases eastward
18、. NOTE 3 “Spacing” gives the latitude/longitude increment between rows/columns. NOTE 4 The file TropoClim.txt contains integer zone identifiers rather than continuous meteorological variables. Consequently, the values should not be interpolated to obtain a value at a particular latitude/longitude. I
19、nstead the value at the closest gridpoint should be taken. For this file note that the value in the last column is not a duplicate of the first column. Consequently the latitudes of the rows range from 89.75N to 89.75S, and the longitudes of the columns range from 179.75W to 179.75E. 3 Transmission
20、loss for diffraction paths For radio paths extending only slightly over the horizon, or for paths extending over an obstacle or over mountainous terrain, diffraction will generally be the propagation mode determining the field strength. In these cases, the methods described in Recommendation ITU-R P
21、.526 should be applied. 4 Transmission loss distribution on tropospheric scatter paths Signals received by means of tropospheric scatter show both slow and rapid variations. The slow variations are due to overall changes in refractive conditions in the atmosphere and the rapid fading to the motion o
22、f small-scale irregularities. The slow variations are well described by distributions of the hourly-median transmission loss which are approximately log-normal with standard deviations between about 4 and 8 dB, depending on climate. The rapid variations over periods up to about 5 min are approximate
23、ly Rayleigh distributed. In determining the performance of trans-horizon links for geometries in which the tropospheric scatter mechanism is predominant, it is normal to estimate the distribution of hourly-median transmission loss for non-exceedance percentages of the time above 50%. A simple semi-a
24、nalytical technique for predicting the distribution of average annual transmission loss in this range is given in 4.1. A graphical technique for translating these annual time percentages to those for the average worst month is given in 4.2. Finally, guidance is given in 4.3 on estimation of the tran
25、smission loss distribution for small percentages of time for use in obtaining receiver dynamic ranges required. Appendix 1 includes additional supporting information on seasonal and diurnal variations in transmission loss, on frequency of rapid fading on tropospheric scatter paths and on transmissio
26、n bandwidth. Rec. ITU-R P.617-3 3 4.1 Average annual median transmission loss distribution for time percentages greater than 50% The following step-by-step procedure is recommended for estimating the average annual median transmission loss L(q) not exceeded for percentages of the time q greater than
27、 50%. The procedure requires the link parameters of great-circle path length d (km), frequency f (MHz), transmitting antenna gain Gt(dB), receiving antenna gain Gr(dB), horizon angle t(mrad) at the transmitter, and horizon angle r(mrad) at the receiver: Step 1: Determine the appropriate climate for
28、the common volume of the link in question using the climate map of Fig. 1. This map, TropoClim.txt, is an integral digital part to this Recommendation (see 2). FIGURE 1 Climate zone classification P.0617-011LatitudeLongitude234 56If the troposcatter common volume lies over the sea, the climates at b
29、oth the transmitter and receiver locations are determined. If both terminals have a climate zone corresponding to a land point, the climate zone of the path is given by the smaller value of the transmitter and receiver climate zones. If only one terminal has a climate zone corresponding to a land po
30、int, then that climate zone defines the climate zone of the path. If neither terminal has a climate zone corresponding to a land point, the path is assigned a “sea path” climate zone. Step 2: Obtain the meteorological and atmospheric structure parameters M and , respectively, and the equation to be
31、used for calculating Y(90) from Table 2 for the climate in question. 4 Rec. ITU-R P.617-3 TABLE 2 Values of meteorological and atmospheric structure parameters Climate 1 2 3 4 5 6 Sea* M (dB) 39.60 29.73 19.30 38.50 29.73 33.20 26.00 (km1) 0.33 0.27 0.32 0.27 0.27 0.27 0.27 Y(90) Equation 9 7 10 11
32、7 7 8 * Sea is coded as 0 in the TropoClim.txt Step 3: Calculate the scatter angle (angular distance) from: = e+ t+ rmmmmmmmrad (1) where tand rare the transmitter and receiver horizon angles, respectively, and e= d 103/ kammmmmmmrad (2) with: d : path length (km) a : 6 370 km radius of the Earth k
33、: effective earth radius factor for median refractivity conditions (k = 4/3 should be used unless a more accurate value is known) Step 4: Estimate the transmission loss dependence LNon the height of the common volume from: LN= 20 log(5 + H ) + 4.34 hmmmmmmdB (3) where: H = 103d / 4mmmmmmkm (4) h = 1
34、062k a / 8mmmmmkm (5)and is the atmospheric structure parameter obtained in Step 2. Step 5: Estimate the conversion factor Y(q) for non-exceedance percentages q other than 50% from: Y(q) = C(q) Y(90)mmmmmmdB (6) Here Y(90) is the conversion factor for q = 90% given by the appropriate equation (7-11)
35、 as indicated in Table 2 for the climate in question: () ()hfY 137.0exp4000,1000min103.21.82.2490=(7) ()hY 1370exp35990= (8) 2.890=Y ds 100 (9a) Rec. ITU-R P.617-3 5 2.10224.010569.210006.1253890+=sssdddY 100 ds 1000 (9b) 4.390=Y otherwise (9c) 845.1090=Y ds 100 (10a) 645.2122.01045.4105.4243790+=ss
36、sdddY 100 ds 550 (10b) 0.490=Y otherwise (10c) 5.1190=Y ds 100 (11a) 1.121018.410444.710519.84253890+=sssdddY 100 ds 465 (11b) 4.890=Y otherwise (11c) where: 1000kasd = km (12) The coefficient C(q) for the non-exceedance percentage of time q in question can be obtained from Table 3. TABLE 3 Values o
37、f C(q) of interest q 50 90 99 99.9 99.99 C(q) 50 91 91.82 92.41 92.90 Step 6: Estimate the aperture-to-medium coupling loss Lcfrom: Lc= 0.07 exp 0.055(Gt+ Gr)mmmmmmdB (13) where Gtand Grare the antenna gains. Step 7: Estimate the average annual transmission loss not exceeded for q% of the time from:
38、 L(q) = M + 30 log f + 10 log d + 30 log + LN+ Lc Gt Gr Y(q)mmmmmmdB (14) NOTE 1 Equation (14) is an empirical formula based on data for the frequency range between 200 MHz and 4 GHz. It can be extended to 5 GHz with little error for most applications. 6 Rec. ITU-R P.617-3 4.2 Average worst-month me
39、dian transmission loss distribution for time percentages greater than 50% For reasons of consistency with the average annual transmission loss distribution, this distribution is best determined from the average annual distribution by means of a conversion factor. The procedure is as follows: Step 1:
40、 Obtain the average annual distribution for the non-exceedance percentages (50, 90, 99, 99.9) and climate(s) of interest using the technique in 4.1. Step 2: Obtain the basic transmission loss difference between the average annual distribution and the average worst-month distribution from the curves
41、of Fig. 2. Since owing to lack of measurement data curves are not available for climates 2 or 5, the curves for climate 3 should be used for climate 2 and the curves for climate 6 should be used for climate 5. The equivalent distance used in Fig. 2 is defined as: ()rtqdd += 5.8 km (15) Where the sym
42、bols have the same value as evaluated in 4.1. Step 3: Add the difference in Step 2 to the corresponding average annual values obtained in Step 1 to obtain the average worst-month transmission losses for the non-exceedance percentages (50, 90, 99, 99.9). Step 4: Average worst-month transmission losse
43、s not exceeded for 99.99% of the time can be estimated from the values above by logarithmic extrapolation (i.e. extrapolating from a plot on normal probability paper). 4.3 Average annual median transmission loss distribution for time percentages less than 50% For percentages of time between about 20
44、% (as low as 1% in some dry climates over land) and 50%, the average annual transmission loss distribution can be considered symmetrical and the transmission loss values estimated from the corresponding values above the median, i.e. L(20%) = L(50%) L(80%) L(50%) (16) However, for dynamic range calcu
45、lations requiring estimates of the distribution for lower time percentages, pure tropospheric scatter cannot be assumed. The transmission loss values not exceeded for very small percentages of time will be determined by the duct propagation mechanism. These values are best estimated by the technique
46、 given in Recommendation ITU-R P.452. 5 Diversity reception The deep fading occurring with tropospheric scatter propagation severely reduces the performance of systems using this propagation mode. The effect of the fading can be reduced by diversity reception, using two or more signals which fade mo
47、re or less independently owing to differences in scatter path or frequency. Thus, the use of space, angle, or frequency diversity is known to decrease the percentages of time for which large transmission losses are exceeded. Angle diversity, however, can have the same effect as vertical space divers
48、ity and be more economical. Rec. ITU-R P.617-3 7 FIGURE 2 Curves giving the difference between worst-month basic transmission loss and annual basic transmission loss P.0617-0250%90%99%99.9%50%90%99%99.9%50%90%99.9%50%90%99%99.9%99%6024681042064208642081012Basic transmission lossdifference(dB)Equival
49、ent distance d (km)q200100 500 1 000Equivalent distance d (km)qEquivalent distance d (km)qEquivalent distance d (km)qa) climate 1b) climate 3, can also be used for climate 2c) climate 4d) climate 6 and sea, can also be used for climate 55.1 Space diversity Diversity spacing in the horizontal or vertical can be used depending on whatever is most convenient for the location in question. Adequate diversity spacings h and v in either the horizontal or vertical, r
