1、 Recommendation ITU-R P.617-4 (12/2017) Propagation prediction techniques and data required for the design of trans-horizon radio-relay systems P Series Radiowave propagation ii Rec. ITU-R P.617-4 Foreword The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient and
2、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 performe
3、d 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 to b
4、e 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 found
5、. 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, radio
6、determination, 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 SN
7、G 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, 2017 ITU 2017 All rights reserved. No part of this
8、 publication may be reproduced, by any means whatsoever, without written permission of ITU. Rec. ITU-R P.617-4 1 RECOMMENDATION ITU-R P.617-4 Propagation prediction techniques and data required for the design of trans-horizon radio-relay systems (Question ITU-R 205/3) (1986-1992-2012-2013-2017) Scop
9、e This Recommendation contains a propagation prediction method for the planning of trans-horizon radio-relay systems. Keywords Anomalous/layer-reflection, diffraction, trans-horizon, tropospheric scatter The ITU Radiocommunication Assembly, considering a) that for the proper planning of trans-horizo
10、n 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 the planning of trans-horizon radio-relay systems; c) that as far as possible the
11、se 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 applications in system planning, recommends that the prediction methods and other technique
12、s 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 occur permanently for frequencies greater than 30 MHz are those of diffraction at
13、 the Earths surface and scatter from atmospheric irregularities. In addition propagation due to ducting or layer-reflection may occur occasionally. Attenuation for diffracted signals increases very rapidly with distance and with frequency, and the anomalous propagation probability is relatively smal
14、l, eventually the long term principal mechanism is that of tropospheric scatter. These mechanisms may be used to establish “trans-horizon” radiocommunication. Because of the dissimilarity of the three mechanisms it is necessary to consider diffraction, ducting/layer reflection and tropospheric scatt
15、er paths separately for the purposes of predicting transmission loss and enhancements. 2 Rec. ITU-R P.617-4 This Annex relates to the design 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 the t
16、otal transmission loss due to tropospheric scatter and ducting/layer reflection, together with information on their ranges of validity. Another purpose of this Annex is to present other information and techniques that can be recommended in the planning of trans-horizon systems. 2 Integral digital pr
17、oducts Only the file versions provided with this Recommendation should be used. They are an integral part of the Recommendation. Table 1 gives details of the digital products used in the method. TABLE 1 Digital products Filename Ref. Origin Latitude (rows) Longitude (columns) First row (N) Spacing (
18、degrees) Number of rows First col (E) Spacing (degrees) Number of cols DN50.txt Att.1 Annex 1 P.452 90 1.5 121 0 1.5 241 N050.txt Att.1 Annex 1 P.452 90 1.5 121 0 1.5 241 The “First row” value is the latitude of the first row. The “First col” value is the longitude of the first column. The last colu
19、mn is the same as the first column (360 = 0) and is provided to simplify interpolation. “Spacing” gives the latitude/longitude increment between rows/columns. The files are contained in the Supplement file R-REC-P.617-4-201712-I!ZIP. 3 Transmission loss for diffraction paths For radio paths extendin
20、g 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.526 should be applied. 4 Transmission loss distrib
21、ution due to tropospheric scatter 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 of small-scale irregularities. The slow variations are
22、 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 approximately Rayleigh distributed. In determining the performan
23、ce 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-analytical technique for predicting the distribution o
24、f average annual transmission loss in this range is given in 4.1. The method for conversion of these annual time percentages to those for the average worst month is given in 4.2. Attachment 1 includes additional supporting information on seasonal and diurnal variations in transmission loss, on frequ
25、ency of rapid fading on tropospheric scatter paths and on transmission bandwidth. Rec. ITU-R P.617-4 3 4.1 Average annual median transmission loss distribution The following step-by-step procedure is recommended for estimating the average annual median transmission loss L(p) not exceeded for percent
26、ages of the time p. 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: Obtain the average a
27、nnual sea-level surface refractivity N0 and radio-refractive index lapse-rate dN for the common volume of the link in question using the digital maps of Fig. 1 and Fig. 2, respectively. These maps are available electronically from the ITU-R SG 3 website under the specification in 2. FIGURE 1 Average
28、 annual sea-level surface refractivity, N0 P . 0 6 1 7 - 0 1 5 01LatitudeLongitude0 50 0 01 50 100 150300310320330340350360370380806040200204060804 Rec. ITU-R P.617-4 FIGURE 2 Average annual radio-refractive index lapse-rate through the lowest 1 km of the atmosphere, dN P . 0 6 1 7 - 0 2 5 01Latitud
29、eL o n g i t u d e0 50 0 01 50 100 150253035454055607075806040200204060805065Step 2: Calculate the scatter angle (angular distance) from e t rmmmmmmmrad (1) where t and r are the transmitter and receiver horizon angles, respectively, and e d 103 / kammmmmmmrad (2) with: d : path length (km) a : 6 37
30、0 km radius of the Earth k : effective earth radius factor for median refractivity conditions (k = 4/3 should be used unless a more accurate value is known). Step 3: Estimate the aperture-to-medium coupling loss Lc from: Lc = 0.07 exp 0.055(Gt Gr)mmmmmmdB (3) where Gt and Gr are the antenna gains. S
31、tep 4: Estimate the average annual transmission loss associated with tropospheric scatter not exceeded for p% of the time from: 2 2 l o g 3 5 l o g 1 7 l o gb s c pL p F f d L Y dB (4) where 00 . 1 8 e x p 0 . 2 3sbF N h h d N dB(5) Rec. ITU-R P.617-4 5 0 . 6 7000 . 6 7000 . 0 3 5 e x p l o g 5 0 5
32、00 . 0 3 5 e x p l o g 1 0 0 5 0 5 0bqbN h h q pYN h h q p (6) 0 = 181062 (7) with: hs: height of the Earths surface above sea level (km) hb: scale height (km) which can be determined statistically for different climates conditions. For reference purpose a global mean of the scale height may be defi
33、ned by hb=7.35 km. 4.2 Average worst-month median transmission loss distribution 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:
34、Step 1: If the annual statistics time percentage is given, calculate the time percentage conversion of annual statistics to worst-month statistics for tropospheric scatter from Recommendation ITU-R P.841. If the worst-month time percentage is given, an inversion calculation is needed. Step 2: Calcul
35、ate the worst-month median transmission loss for the given time percentage, substituting the given or solved annual statistics time percentage into 4.1. 5 Transmission loss and enhancement distribution due to ducting/layer reflection Ducting and layer reflection may cause an enhancement of the signa
36、l which can effect system design. The following calculation is the same as Recommendation ITU-R P.2001-2, Attachment D: Anomalous layer reflection model. 5.1 Characterize the radio-climatic zones dominating the path Calculate two distances giving the longest continuous sections of the path passing t
37、hrough the following radio-climatic zones: dtm: longest continuous land (inland or coastal) section of the path (km) dlm: longest continuous inland section of the path (km). Table 2 describes the radio-climatic zones needed for the above classification. TABLE 2 Radio-climatic zones Zone type Code De
38、finition Coastal land A1 Coastal land and shore areas, i.e. land adjacent to the sea up to an altitude of 100 m relative to mean sea or water level, but limited to a distance of 50 km from the nearest sea area. Inland A2 All land, other than coastal and shore areas defined as “coastal land” above. S
39、ea B Seas, oceans and other large bodies of water (i.e. covering a circle of at least 100 km in diameter). 6 Rec. ITU-R P.617-4 Large bodies of inland water A “large” body of inland water, to be considered as lying in Zone B, is defined as one having an area of at least 7 800 km2, but excluding the
40、area of rivers. Islands within such bodies of water are to be included as water within the calculation of this area if they have elevations lower than 100 m above the mean water level for more than 90% of their area. Islands that do not meet these criteria should be classified as land for the purpos
41、es of the water area calculation. Large inland lake or wet-land areas Large inland areas of greater than 7 800 km2 which contain many small lakes or a river network should be declared as “coastal” Zone A1 by administrations if the area comprises more than 50% water, and more than 90% of the land is
42、less than 100 m above the mean water level. Climatic regions pertaining to Zone A1, large inland bodies of water and large inland lake and wetland regions, are difficult to determine unambiguously. Therefore administrations are invited to register with the ITU Radiocommunication Bureau (BR) those re
43、gions within their territorial boundaries that they wish identified as belonging to one of these categories. In the absence of registered information to the contrary, all land areas will be considered to pertain to climate Zone A2. For maximum consistency of results between administrations it is rec
44、ommended that the calculations of this procedure be based on the ITU Digitized World Map (IDWM) which is available from the BR. 5.2 Point incidence of ducting Calculate a parameter depending on the longest inland section of the path: 41.241012.4e1 lmd (8) Calculate parameter 1 characterizing the deg
45、ree to which the path is over land, given by: 2.0)77.148.2(6.6161 1010 tmd(9) where the value of 1 shall be limited to 11. Calculate parameter 4, given by: 70f o r1070f o r1011l o g3.0l o g)0176.0935.0(4mnmnmn (10) where mn is the path mid-point latitude. The point incidence of anomalous propagation
46、, 0 (%), for the path centre location is now given by: 70f o r%17.4 70f o r%10 41 4167.1015.00 mnmnmn (11) 5.3 Site-shielding losses with respect to the anomalous propagation mechanism Corrections to transmitter and receiver horizon elevation angles: ltt dg 1.0 (12) lrr dg 1.0 (13) Rec. ITU-R P.617-
47、4 7 where dlt, dlr (km) are the terminal to horizon distances. For LoS paths set to distances to point with largest knife-edge loss The losses between the antennas and the anomalous propagation mechanism associated with site-shielding are calculated as follows. Modified transmitter and receiver hori
48、zon elevation angles: ttst g mrad (14) rrsr g mrad (15) Transmitter and receiver site-shielding losses with respect to the duct: 3/12/1 264.0361.01l o g20 fdfA stltstst dB st0 (16) 0stA dB otherwise (17) 3/12/1 264.0361.01l o g20 fdfA srlrsrsr dB sr0 (18) 0srA dB otherwise (19) 5.4 Over-sea surface duct coupling corrections Obtain the distance from each terminal to the sea in the direction of the other terminal: dct = coast distance from transmitter km (20) dcr = coast distance from receiver km (21) The over-sea surface duct coupling corrections for the transmitter and receiver, Act and A
