1、 Recommendation ITU-R P.619-3 (12/2017) Propagation data required for the evaluation of interference between stations in space and those on the surface of the Earth P Series Radiowave propagation ii Rec. ITU-R P.619-3 Foreword The role of the Radiocommunication Sector is to ensure the rational, equi
2、table, efficient and 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 Radiocommunicatio
3、n Sector are performed 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 Resolutio
4、n ITU-R 1. Forms to 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 datab
5、ase can also be found. 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 se
6、rvice M Mobile, radiodetermination, 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 S
7、pectrum management 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, 2017 ITU 2017 All rights rese
8、rved. No part of this publication may be reproduced, by any means whatsoever, without written permission of ITU. Rec. ITU-R P.619-3 1 RECOMMENDATION ITU-R P.619-3 Propagation data required for the evaluation of interference between stations in space and those on the surface of the Earth (Question IT
9、U-R 208/3) (1986-1990-1992-06/2017-12/2017) Rec. 619-1 Scope This Recommendation provides methods for predicting signal propagation losses for interfering signals between stations in space and stations on (or near to) the surface of the Earth in the overall frequency range of 100 MHz to 100 GHz, exc
10、ept for a few exceptions restricted to lower frequencies which will be specified where they are described. Prediction methods for some of the loss mechanisms are reliable over narrower frequency ranges, and some of the loss mechanisms are not significant at certain frequency ranges. This Recommendat
11、ion provides methods to predict the propagation losses not exceeded for 0.001%-50% of the time. Guidance is given for single entry as well as multiple entry propagation losses in analyses that determine interfering signals, where correlations of temporal variability and location variability may be i
12、nfluential. Keywords Interference, depolarization, beam spreading, scintillation, diffraction, ducting The ITU Radiocommunication Assembly, considering a) that for the assessment of interference between stations based in space and those on the surface of the Earth, it is necessary to have propagatio
13、n data and prediction methods that take account of atmospheric factors, and in some cases terrain, building penetration, multipath and clutter; b) that, given the many possible applications of such evaluation, guidance is required for the selection of appropriate methods; c) that certain analyses of
14、 potential or actual interference may need to determine the aggregate total interfering signal from numerous transmitters, noting a) that Recommendation ITU-R P.526 provides calculation methods for obstacle diffraction; b) that Recommendation ITU-R P.531 provides propagation data and prediction meth
15、ods for ionospheric effects on Earth-space paths; c) that Recommendation ITU-R P.618 provides guidance on the planning of Earth-space links; d) that Recommendation ITU-R P.676 provides methods for calculating attenuation by atmospheric gasses; e) that Recommendation ITU-R P.834 provides information
16、and calculation methods for the effects of tropospheric refraction; f) that Recommendation ITU-R P.836 provides information and calculation methods for the water-vapour content of the atmosphere, including its temporal variability; g) that Recommendation ITU-R P.2040 provides information on the inte
17、raction of radio waves with buildings, 2 Rec. ITU-R P.619-3 recommends that the guidance in Annex 1 be used for the assessment of interference between stations based in space and those on the surface of the Earth. Annex 1 1 Introduction This Recommendation provides guidance and calculation methods t
18、o evaluate interference between a station in space and a station on the surface of the Earth. The phrase “on the surface of the Earth” is intended to cover antennas which are within the atmosphere and not at a great height above the surface, including those installed on radio towers, buildings, land
19、 vehicles, or hand-held. This Earth-based station may be part of a satellite or terrestrial radio system. For brevity, it is sometimes referred to as the “Earth-based station”. The phrase “Earth-space” path refers to the path of radio energy between antennas in either the Earth-to-space or the space
20、-to-Earth direction. All propagation mechanisms are reciprocal with respect to direction unless stated otherwise. 1.1 Temporal and location variability Many propagation losses vary in time, and with the location of Earth-based stations, particularly those located on the surface of the Earth. Many in
21、terference analyses are “statistical” and need to consider potential temporal and spatial variabilities. If a complete cumulative distribution function of Earth-space basic transmission loss is needed, Recommendation ITU-R P.618 should be used for losses exceeded for percentages of time less than 50
22、%. Attenuations and signal power enhancements caused by individual propagation mechanisms on an individual signal path may be treated as independent variables in many cases. Likewise, in analyses where carrier-to-(noise + interference) ratio is a figure-of-merit, interfering and desired signal power
23、 and depolarization effects may be treated as independent variables except for where the desired and interfering signal paths are physically near one another or overlapping and thus have a high degree of correlation. For certain scenarios, there may be a degree of correlation among propagation losse
24、s on the interfering signal paths which can be accounted for by selection of the appropriate methods. 1.2 Apparent and free-space elevation angles The elevation angle of the ray at an Earth-based station to a station in space is higher than it would be in the absence of any atmosphere, due to atmosp
25、heric refractivity. Account should be taken of this effect, particularly at low elevation angles. The elevation angle which would exist in the absence of any atmosphere is referred as the “free-space” elevation angle, and has the symbol 0. The actual angle of the radio path at the Earth-based statio
26、n, including the effect of atmospheric refractivity, is referred to as the “apparent” elevation angle, and has the symbol . Attachment B gives methods to convert between free-space and apparent elevation angles. Rec. ITU-R P.619-3 3 1.3 Relevant propagation mechanisms The principal basic transmissio
27、n loss mechanisms on interfering signal paths occur during clear-air conditions and may include in some cases, tropospheric and ionospheric scintillation, multipath, and mechanisms associated with signal path obstructions (clutter, diffraction over terrain, and building entry loss). Section 2 descri
28、bes these mechanisms and gives calculation methods. Sub-sections 2.1 to 2.8 describe the mechanisms in detail. Section 3.1 gives the expression for basic transmission loss for a single specific path. Section 3.2 gives the expression for basic transmission loss for multiple sources into a single rece
29、iver. Some evaluations of interference may need to take precipitation effects into account. The relevant mechanisms are described in 3. Sub-sections 2.9 and 2.10 give information and calculation methods for interference caused by rain scattering, and differential rain attenuation, respectively. Thes
30、e mechanisms are considered below and are applied to determine propagation losses that are not exceeded for 50% and smaller percentages of time that are of particular interest in interference analyses. Section 4 discusses correlation between propagation mechanisms. 2 Propagation mechanisms The follo
31、wing sub-sections summarise the mechanisms which in combination determine the attenuation between the (interfering) transmitter and (interfered-with) receiver antennas, with the associated symbols to be used in equations. This overall loss is expressed as basic transmission loss, which is the loss w
32、hich would occur between ideal isotropic antennas. 2.1 Free space basic transmission loss (dB) This is the basic transmission loss assuming the complete radio path is in a vacuum with no obstruction. It depends only on the path length, (km), and frequency, (GHz) according to = 92.45+20log( ) (dB) (1
33、) Attachment A gives a method for calculating the length of an Earth-space path, and the free-space elevation angle at the Earth-based station. It is based on spherical Earth geometry, and ignores the effect of atmospheric refraction. The associated errors are not significant for calculating free-sp
34、ace transmission loss from the path length. must always be included in the calculation of loss over an Earth-space path. It is valid for any frequency and over any Earth-space path length. Attachment B gives methods for converting between the free-space elevation angle and the apparent elevation ang
35、le at the Earth-based station. The method in Attachment A takes no account of any obstruction by the Earth or objects upon it such as buildings. Attachment E gives a method for testing an Earth-space path for obstructions. Diffraction loss due to obstructions is discussed in 2.6. 2.2 Depolarization
36、attenuation (dB) Two propagation mechanisms can cause the polarization angle of a radio signal to change: i) Faraday rotation; ii) Hydrometeor scattering. Polarization mismatch may also be attributed to antenna mismatch without rotation due to propagation effects. This is not considered in this reco
37、mmendation since it involves system considerations rather than propagation. 4 Rec. ITU-R P.619-3 Depolarization effects can be caused either by Faraday rotation or by precipitation scatter. Faraday rotation is only significant below 10 GHz and can be ignored for frequencies at or above 10 GHz. Depol
38、arization loss can be significant in reducing interference. For most multiple-entry Earth-space interference situations where relative polarization orientations can be considered arbitrary, = 3 (dB) assumes that the transmitter and receiver polarization vectors are in the same plane with a uniform d
39、istribution of relative angles. In practice the polarization vectors will be arbitrarily oriented in three-dimensional space which would combine to a higher aggregated loss. = 3 (dB) is thus unlikely to over-estimate the loss. The polarization discrimination from a space-based interference source re
40、ceived by an earth-based station (or vice-versa) depends on the polarization purity of the transmitted wave, as well as the cross-polarization isolation of the receiving antenna. The depolarization loss can be directly calculated in terms of parameters that describe the interfering and receiving ant
41、ennas respective polarization types and polarization purities such as axial ratio in the case of circular polarization or linear cross-polarization isolation in the case of linear polarization. In addition, the polarization sense and tilt angle of the incident wave and the receiving antenna, will ac
42、t to further reduce the net depolarization loss when the actual interfering and interfered-with system parameters are taken into account. 2.2.1 Cross-polar discrimination and cross polar attenuation Polarization mismatch can occur for several reasons, and are sometimes quantified in terms of cross-p
43、olar discrimination (XPD) which is defined as the ratio of co-polar to cross-polar signal strength, normally expressed in decibels. It is a figure-of-merit where frequency sharing is implemented by orthogonal linear polarization. Any degradation of XPD transfers a proportion of the power to the orth
44、ogonal polarization, which can constitute a source of interference. There is a corresponding attenuation of the original signal. Cross- and co-polar attenuations are given by: 0 .11 0 lo g (1 1 0 )x p dRxA (dB) (2a) 0 .11 0 lo g (1 1 0 )x p dRcA (dB) (2b) where is the XPD ratio in dB. Figure 1 shows
45、 co-polar and cross-polar attenuation plotted against XPD. Rec. ITU-R P.619-3 5 FIGURE 1 Co- and cross-polar losses versus XPD P . 0 6 1 9 - 0 1X P D dB ( )C ro s s -p o l arLossdB()5 10 15 20 2 5 300101 52 02 53005C o -p o l arUsually space borne RF systems employ signals with specified polarizatio
46、n depending on their functions. For instance tracking systems, air traffic control systems, and communication systems use vertically polarized signals to minimize interference due to reflection from ground surface. Land surface remote sensing systems use horizontal polarization to ensure maximum cou
47、pling of the transmitted signals with ground surface. Those systems also use different polarizations to get auxiliary detail information. GNSS systems use circularly polarized signals to avoid impacts of Faraday rotation and to relax any restriction on the polarization direction of receiver antennas
48、. Accordingly, it is important to assess values of RF signals with a specified polarization along a specified propagation path. Any reduction in those values can be considered a loss. 2.2.2 Faraday rotation A linearly polarized field propagating through the ionosphere rotates from its initial direct
49、ion by Faraday rotation angle . This means that the field can be split into two components: i) One component oriented along direction of initial polarization and having value proportional to cos; ii) Another component orthogonal to the initial direction and having a value proportional to sin. Figure 2 illustrates transmitted linearly-polarized orthogonal field vectors ( , ) undergoing Faraday rotation to produce received orthogonal vectors ( , ). FIGURE 2
