1、 Recommendation ITU-R P.530-17 (12/2017) Propagation data and prediction methods required for the design of terrestrial line-of-sight systems P Series Radiowave propagation ii Rec. ITU-R P.530-17 Foreword The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient and e
2、conomical 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
3、 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 be
4、 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, radiod
6、etermination, 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
7、 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.530-17 1 RECOMMENDATION ITU-R P.530-17 Propagation data and prediction methods required for the design of terrestrial line-of-sight systems (Question ITU-R 204/3) (1978-1982-1986-1990-1992-1994-19
9、95-1997-1999-2001-2001-2005-2007-2009-2012-2013-2015-2017) Scope This Recommendation provides prediction methods for the propagation effects that should be taken into account in the design of digital fixed line-of-sight links, both in clear-air and rainfall conditions. It also provides link design g
10、uidance in clear step-by-step procedures including the use of mitigation techniques to minimize propagation impairments. The final outage predicted is the base for other Recommendations addressing error performance and availability. The ITU Radiocommunication Assembly, considering a) that for the pr
11、oper planning of terrestrial line-of-sight systems, it is necessary to have appropriate propagation prediction methods and data; b) that methods have been developed that allow the prediction of some of the most important propagation parameters affecting the planning of terrestrial line-of-sight syst
12、ems; 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 applications in system planning, recommends that the pre
13、diction methods and other techniques set out in Annex 1 be adopted for planning terrestrial line-of-sight systems in the respective ranges of parameters indicated. Annex 1 1 Introduction Several propagation effects must be considered in the design of line-of-sight radio-relay systems. These include:
14、 diffraction fading due to obstruction of the path by terrain obstacles under adverse propagation conditions; attenuation due to atmospheric gases; fading due to atmospheric multipath or beam spreading (commonly referred to as defocusing) associated with abnormal refractive layers; fading due to mul
15、tipath arising from surface reflection; attenuation due to precipitation or solid particles in the atmosphere; 2 Rec. ITU-R P.530-17 variation of the angle-of-arrival at the receiver terminal and angle-of-launch at the transmitter terminal due to refraction; reduction in cross-polarization discrimin
16、ation (XPD) in multipath or precipitation conditions; signal distortion due to frequency selective fading and delay during multipath propagation. One purpose of this Annex is to present in concise step-by-step form simple prediction methods for the propagation effects that must be taken into account
17、 in the majority of fixed line-of-sight links, 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 terrestrial line-of-sight systems. Prediction methods based on specific climat
18、e and topographical conditions within an administrations territory may be found to have advantages over those contained in this Annex. With the exception of the interference resulting from reduction in XPD, the Annex deals only with effects on the wanted signal. Some overall allowance is made in 2.3
19、.6 for the effects of intra-system interference in digital systems, but otherwise the subject is not treated. Other interference aspects are treated in separate Recommendations, namely: inter-system interference involving other terrestrial links and earth stations in Recommendation ITU-R P.452; inte
20、r-system interference involving space stations in Recommendation ITU-R P.619. To optimize the usability of this Annex in system planning and design, the information is arranged according to the propagation effects that must be considered, rather than to the physical mechanisms causing the different
21、effects. It should be noted that the term “worst month” used in this Recommendation is equivalent to the term “any month” (see Recommendation ITU-R P.581). 2 Propagation loss The propagation loss on a terrestrial line-of-sight path relative to the free-space loss (see Recommendation ITU-R P.525) is
22、the sum of different contributions as follows: attenuation due to atmospheric gases; diffraction fading due to obstruction or partial obstruction of the path; fading due to multipath, beam spreading and scintillation; attenuation due to variation of the angle-of-arrival/launch; attenuation due to pr
23、ecipitation; attenuation due to sand and dust storms. Each of these contributions has its own characteristics as a function of frequency, path length and geographic location. These are described in the paragraphs that follow. Sometimes propagation enhancement is of interest. In such cases it is cons
24、idered following the associated propagation loss. Rec. ITU-R P.530-17 3 2.1 Attenuation due to atmospheric gases Some attenuation due to absorption by oxygen and water vapour is always present, and should be included in the calculation of total propagation loss at frequencies above about 10 GHz. The
25、 attenuation on a path of length d (km) is given by: dBdA aa (1) The specific attenuation a (dB/km) should be obtained using Recommendation ITU-R P.676. NOTE 1 On long paths at frequencies above about 20 GHz, it may be desirable to take into account known statistics of water vapour density and tempe
26、rature in the vicinity of the path. Information on water vapour density is given in Recommendation ITU-R P.836. 2.2 Diffraction fading Variations in atmospheric refractive conditions cause changes in the effective Earths radius or k-factor from its median value of approximately 4/3 for a standard at
27、mosphere (see Recommendation ITU-R P.310). When the atmosphere is sufficiently sub-refractive (large positive values of the gradient of refractive index, low k-factor values), the ray paths will be bent in such a way that the Earth appears to obstruct the direct path between transmitter and receiver
28、, giving rise to the kind of fading called diffraction fading. This fading is the factor that determines the antenna heights. k-factor statistics for a single point can be determined from measurements or predictions of the refractive index gradient in the first 100 m of the atmosphere (see Recommend
29、ation ITU-R P.453 on effects of refraction). These gradients need to be averaged in order to obtain the effective value of k for the path length in question, ke. Values of ke exceeded for 99.9% of the time are discussed in terms of path clearance criteria in the following section. 2.2.1 Diffraction
30、loss dependence on path clearance Diffraction loss will depend on the type of terrain and the vegetation. For a given path ray clearance, the diffraction loss will vary from a minimum value for a single knife-edge obstruction to a maximum for smooth spherical Earth. Methods for calculating diffracti
31、on loss for these two cases and also for paths with irregular terrain are discussed in Recommendation ITU-R P.526. These upper and lower limits for the diffraction loss are shown in Fig. 1. The diffraction loss over average terrain can be approximated for losses greater than about 15 dB by the formu
32、la: dB10/20 1 FhA d (2) where h is the height difference (m) between most significant path blockage and the path trajectory (h is negative if the top of the obstruction of interest is above the virtual line-of-sight) and F1 is the radius of the first Fresnel ellipsoid given by: m1 7 .3= 211df ddF(3)
33、 with: f : frequency (GHz) d : path length (km) d1 and d2 : distances (km) from the terminals to the path obstruction. 4 Rec. ITU-R P.530-17 A curve, referred to as Ad, based on equation (2) is also shown in Fig. 1. This curve, strictly valid for losses larger than 15 dB, has been extrapolated up to
34、 6 dB loss to fulfil the need of link designers. FIGURE 1 Diffraction loss for obstructed line-of-sight microwave radio paths P . 0 5 3 0 - 0 140302010010BDAd1 0 1 1 .5 0 .5 0 . 5Diffractionlossrelativetofreespace(dB)N o rmal i ze d cl ea ran ce h / F1B : t h eo ret i ca l k n i fe-ed g e l o s s cu
35、 rv eD k: t h eo ret i ca l s mo o t h s p h eri ca l E art h l o s s cu rv e, at 6 . 5 G H z an d = 4 / 3eAd: emp i ri ca l d i ffract i o n l o s s b as ed o n eq u at i o n (2 ) fo r i n t erme d i at e t errai nh : amo u n t b y w h ich th e rad io p at h cl ea rs th e E art h s s u rfaceF1: rad
36、 i u s o f t h e fi rs t Fres n el zo n e2.2.2 Planning criteria for path clearance At frequencies above about 2 GHz, diffraction fading of this type has in the past been alleviated by installing antennas that are sufficiently high, so that the most severe ray bending would not place the receiver in
37、 the diffraction region when the effective Earth radius is reduced below its normal value. Diffraction theory indicates that the direct path between the transmitter and the receiver needs a clearance above ground of at least 60% of the radius of the first Fresnel zone to achieve free-space propagati
38、on conditions. Recently, with more information on this mechanism and the statistics of ke that are required to make statistical predictions, some administrations are installing antennas at heights that will produce some small known outage. In the absence of a general procedure that would allow a pre
39、dictable amount of diffraction loss for various small percentages of time and therefore a statistical path clearance criterion, the following procedure is advised for temperate and tropical climates. Rec. ITU-R P.530-17 5 2.2.2.1 Non-diversity antenna configurations Step 1: Determine the antenna hei
40、ghts required for the appropriate median value of the point k-factor (see 2.2; in the absence of any data, use k = 4/3) and 1.0 F1 clearance over the highest obstacle (temperate and tropical climates). Step 2: Obtain the value of ke from Fig. 2 for the path length in question. FIGURE 2 Value of ke e
41、xceeded for approximately 99.9% of the worst month (continental temperate climate) P . 0 5 3 0 - 0 210210252ke11 . 10 . 90 . 80 . 70 . 60 . 50 . 40 . 3P at h l en g t h (k m )Step 3: Calculate the antenna heights required for the value of ke obtained from Step 2 and the following Fresnel zone cleara
42、nce radii: Temperate climate Tropical climate 0.0 F1 (i.e. grazing) if there is a single isolated path obstruction 0.6 F1 for path lengths greater than about 30 km 0.3 F1 if the path obstruction is extended along a portion of the path Step 4: Use the larger of the antenna heights obtained by Steps 1
43、 and 3 (see Note 1). In cases of uncertainty as to the type of climate, the more conservative clearance rule (see Note 1) for tropical climates may be followed or at least a rule based on an average of the clearances for temperate and tropical climates. Smaller fractions of F1 may be necessary in St
44、eps 1 and 3 above for frequencies less than about 2 GHz in order to avoid unacceptably large antenna heights. At frequencies above about 13 GHz, the estimation accuracy of the obstacle height begins to approach the radius of the Fresnel zone. This estimation accuracy should be added to the above cle
45、arance. 6 Rec. ITU-R P.530-17 NOTE 1 Although these rules are conservative from the viewpoint of diffraction loss due to sub-refractive fading, it must be made clear that an overemphasis on minimizing unavailability due to diffraction loss in sub-refractive conditions may result in a worse degradati
46、on of performance and availability in multipath conditions. It is not currently possible to give general criteria for the trade-off to be made between the two conditions. Among the relevant factors are the system fading margins available. 2.2.2.2 Two or three antenna space-diversity configurations S
47、tep 1: Calculate the height of the upper antenna using the procedure for single antenna configurations noted above. Step 2: Calculate the height of the lower antenna for the appropriate median value of the point k-factor (in the absence of any data use k = 4/3) and the following Fresnel zone clearan
48、ces (see Note 1): 0.6 F1 to 0.3 F1 if the path obstruction is extended along a portion of the path; 0.3 F1 to 0.0 F1 if there are one or two isolated obstacles on the path profile. One of the lower values in the two ranges noted above may be chosen if necessary to avoid increasing heights of existin
49、g towers or if the frequency is less than 2 GHz. Alternatively, the clearance of the lower antenna may be chosen to give about 6 dB of diffraction loss during normal refractivity conditions (i.e. during the middle of the day; see 8), or some other loss appropriate to the fade margin of the system, as determined by test measurements. Measurements should be carried out on several different days to avoid anomalous refractivity conditions. In this alternative case the diffraction loss can also be estimated using Fig. 1 or equation (2
