1、 Recommendation ITU-R P.682-3(02/2012)Propagation data required for the designof Earth-space aeronautical mobile telecommunication systemsP SeriesRadiowave propagationii Rec. ITU-R P.682-3 Foreword The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient and economic
2、al 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 Wor
3、ld 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 used f
4、or 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. Series
5、 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, radiodetermin
6、ation, 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 Satell
7、ite 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, 2012 ITU 2012 All rights reserved. No part of this publica
8、tion may be reproduced, by any means whatsoever, without written permission of ITU. Rec. ITU-R P.682-3 1 RECOMMENDATION ITU-R P.682-3 Propagation data required for the design of Earth-space aeronautical mobile telecommunication systems (Question ITU-R 207/3) (1990-1992-2007-2012) Scope This Recommen
9、dation describes propagation effects of particular importance to aeronautical mobile-satellite systems. Relevant ionospheric and tropospheric propagation impairments are identified, and reference made to ITU-R Recommendations that provide guidance on these effects. Models are provided to predict the
10、 propagation effects caused by signal multipath and scattering from the Earths surface. The ITU Radiocommunication Assembly, considering a) that for the proper planning of Earth-space aeronautical mobile systems it is necessary to have appropriate propagation data and prediction methods; b) that the
11、 methods of Recommendation ITU-R P.618 are recommended for the planning of Earth-space telecommunication systems; c) that further development of prediction methods for specific application to aeronautical mobile-satellite systems is required to give adequate accuracy for all operational conditions;
12、d) that, however, methods are available which yield sufficient accuracy for many applications, recommends 1 that the methods contained in Annex 1 be adopted for current use in the planning of Earth-space aeronautical mobile telecommunication systems, in addition to the methods recommended in Recomme
13、ndation ITU-R P.618. Annex 1 1 Introduction Propagation effects in the aeronautical mobile-satellite service differ from those in the fixed-satellite service and other mobile-satellite services because: small antennas are used on aircraft, and the aircraft body may affect the performance of the ante
14、nna; high aircraft speeds cause large Doppler spreads; aircraft terminals must accommodate a large dynamic range in transmission and reception; aircraft safety considerations require a high integrity of communications, making even short-term propagation impairments very important, and communications
15、 reliability must be maintained in spite of banking manoeuvres and three-dimensional operations. 2 Rec. ITU-R P.682-3 This Annex discusses data and models specifically required to characterize the path impairments, which include: tropospheric effects, including gaseous attenuation, cloud and rain at
16、tenuation, fog attenuation, refraction and scintillation; ionospheric effects such as scintillation; surface reflection (multipath) effects; environmental effects (aircraft motion, sea state, land surface type). Aeronautical mobile-satellite systems may operate on a worldwide basis, including propag
17、ation paths at low elevation angles. Several measurements of multipath parameters over land and sea have been conducted. In some cases, laboratory simulations are used to compare measured data and verify model parameters. The received signal is considered in terms of its possible components: a direc
18、t wave subject to atmospheric effects, and a reflected wave, which generally contains mostly a diffuse component. There is current interest in using frequencies near 1.5 GHz for aeronautical mobile-satellite systems. As most experiments have been conducted in this band, data in this Recommendation a
19、re mainly applicable to these frequencies. As aeronautical systems mature, it is anticipated that other frequencies may be used. 2 Tropospheric effects For the aeronautical services, the altitude of the mobile antenna is an important parameter. Estimates of tropospheric attenuation may be made with
20、the methods in Recommendation ITU-R P.618. The received signal may be affected both by large-scale refraction and by scintillations induced by atmospheric turbulence. These effects will diminish for aircraft at high altitudes. 3 Ionospheric effects Ionospheric effects on slant paths are discussed in
21、 Recommendation ITU-R P.531. These phenomena are important for many paths at frequencies below about 10 GHz, particularly within 15 of the geomagnetic equator, and to a lesser extent, within the auroral zones and polar caps. Ionospheric effects peak near the solar sunspot maximum. Impairments caused
22、 by the ionosphere will not diminish for the typical altitudes used by aircraft. A summary description of ionospheric effects of particular interest to mobile-satellite systems is available in Recommendation ITU-R P.680. For most communication signals, the most severe impairment will probably be ion
23、ospheric scintillation. Table 1 of Recommendation ITU-R P.680 provides estimates of maximum expected ionospheric effects at frequencies up to 10 GHz for paths at a 30 elevation angle. 4 Fading due to surface reflection and scattering 4.1 General Multipath fading due to surface reflections for aerona
24、utical mobile-satellite systems differs from fading for other mobile-satellite systems because the speeds and altitudes of aircraft are much greater than those of other mobile platforms. Rec. ITU-R P.682-3 3 4.2 Fading due to sea-surface reflections Characteristics of fading for aeronautical systems
25、 can be analysed with procedures similar to those for maritime systems described in Recommendation ITU-R P.680, taking careful account of Earth sphericity, which becomes significant with increasing antenna altitude above the reflecting surface. 4.2.1 Dependence on antenna height and antenna gain The
26、 following simple method, based on a theoretical model, provides approximate estimates of multipath power or fading depth suitable for engineering applications. The procedure is as follows: Applicable range: Frequency: 1-2 GHz Elevation angle: i 3 and G(1.5i) 10 dB where G() is the main-lobe antenna
27、 pattern given by: G() = 4 104(10/10mG 1) 2dB (1) where: Gm: value of the maximum antenna gain (dB) : angle measured from boresight (degrees). Polarization: circular and horizontal polarizations; vertical polarization for i 8 Sea condition: wave height of 1-3 m (incoherent component fully developed)
28、. Step 1: Calculate the grazing angles of the specular reflection point, sp, and the horizon, hr, by: sp= 2 sp+ idegrees (2a) hr= cos1Re/(Re+ Ha) degrees (2b) where: sp= 7.2 103Ha/taniRe: radius of the Earth = 6 371 km Ha: antenna height (km) Step 2: Find the relative antenna gain G in the direction
29、 midway between the specular point and the horizon. The relative antenna gain is approximated by equation (1) where = i+ (sp+ hr)/2 (degrees). Step 3: Calculate the Fresnel reflection coefficient of the sea: iiiiHR+=22cossincossin(horizontal polarization) (3a) 2222/)cos(sin/)cos(sin+=iiiiVR (vertica
30、l polarization) (3b) 2VHCRRR+= (circular polarization) (3c) 4 Rec. ITU-R P.682-3 = r(f) j60 (f) where: r(f): relative permittivity of the surface at frequency f (from Recommendation ITU-R P.527) (f): conductivity (S/m) of the surface at frequency f (from Recommendation ITU-R P.527) : free space wave
31、length (m). Step 4: Calculate the correction factor C(dB): =7for2/)77for0spspspC (4) Step 5: Calculate the divergence factor D (dB) due to the Earths curvature: +=)(sincossin21log10ispspspD(5) Step 6: The mean incoherent power of sea reflected waves, relative to the direct wave, Pr, is given by: Pr=
32、 G + R + C+ D dB (6) where: R = 20 log iRwith Ri= RH, RVor RCfrom equations (3). Step 7: Assuming the Nakagami-Rice distribution, fading depth is estimated from: A + 10 log ( )10/101rP+(7) where A is the amplitude (dB) read from the ordinate of Fig. 1 of Recommendation ITU-R P.680. Figure 1 below sh
33、ows the mean multipath power of the incoherent component obtained by the above method as a function of the elevation angle for different gains. By comparing with the case of maritime mobile-satellite systems (Fig. 2 of Recommendation ITU-R P.680), it can be seen that the reflected wave power Prfor a
34、eronautical mobile-satellite systems is reduced by 1 to 3 dB at low elevation angles. Rec. ITU-R P.682-3 5 FIGURE 1 Mean multipath power relative to direct signal power as a function of elevation angle for different antenna gains 46810121416182022Elevation angle, (degrees)iFrequency = 1.54 GHzCircul
35、ar polarization= 10 kmHa Multipathpower,(dB)PrGm = 0 dBi10 dBi5 dBi15 dBi18 dBi21 dBi24 dBi2 4 6 8 10 12 14 16 18 20NOTE 1 Analytical as well as experimental studies have shown that for circularly polarized waveforms at or near 1.5 GHz and an antenna gain of 7 dB, multipath fade depth for rough sea
36、conditions is about 8 to 11 dB for low and moderate aircraft heights and about 7 to 9 dB for high altitudes (above 2 km). Multipath fade depth is about 2 dB lower for a 15 dB antenna gain. 4.2.2 Delay time and correlation bandwidth The received signal consists of the direct and the reflected wavefor
37、ms. Because the reflected component experiences a larger propagation delay than the direct component, the composite received signal may be subject to frequency-selective fading. Signal correlation decreases with increasing frequency separation. The dependence of correlation on the antenna gain is sm
38、all for gains below 15 dB. Figure 2 shows the relationship between antenna height and the correlation bandwidth, defined here as the frequency separation for which the correlation coefficient between two radio waves equals 0.37 (1/e). The correlation bandwidth decreases as the antenna altitude incre
39、ases, becoming about 10 to 20 kHz (delay time of 6 to 12 s) for an antenna at an altitude of 10 km. Thus, multipath fading for aeronautical systems may have frequency-selective characteristics. 6 Rec. ITU-R P.682-3 FIGURE 2 Correlation bandwidth vs antenna altitude for antenna gain of 10 dBi Coheren
40、t componentIncoherent component (rough sea conditions)G m= 10 dBi1051041031021011Correlation bandwidth(kHz)101102103104105Antenna altitude (m) = 10 = 54.3 Measurements of sea-reflection multipath effects Extensive experiments have been conducted in the 1.5 to 1.6 GHz band. Results of these measureme
41、nts are summarized in this section for application to systems design. Table 1 summarizes the oceanic multipath parameters observed in measurements, augmented with results from an analytical model. The delay spreads in Table 1 are the widths of the power-delay profile of the diffusely-scattered signa
42、l arriving at the receiver. The correlation bandwidth given in Table 1 is the 3 dB bandwidth of the frequency autocorrelation function (Fourier transform of the delay spectrum). Doppler spread is determined from the width of the Doppler power spectral density. The decorrelation time is the 3 dB widt
43、h of the time autocorrelation function (inverse Fourier transform of the Doppler spectrum). Rec. ITU-R P.682-3 7 TABLE 1 Multipath parameters from ocean measurements Parameter Measured range Typical value at specified elevation angle 8 15 30 Normalized multipath power (dB) Horizontal polarization Ve
44、rtical polarization 5.5 to 0.5 15 to 2.5 2.5 14.5 1 9 1.5 3.5 Delay spread(1)(s) 3 dB value 10 dB value 0.25-1.8 2.2 -5.6 0.6 2.8 0.8 3.2 0.8 3.2 Correlation bandwidth(2)3 dB value (kHz) 70-380 160 200 200 Doppler spread(1)(Hz) In-plane geometry 3 dB value 10 dB value 14-190 13-350 45 44 40(3)70 180
45、 140 350 Cross-plane geometry 3 dB value 10 dB value 179-240 180-560 179 180 180(3)110 280 190 470 Decorrelation time(2)(ms)3 dB value 1.3-10 7.5 3.2 2.2 (1)Two-sided. (2)One-sided. (3)Data from multipath model for aircraft altitude of 10 km and aircraft speed of 1 000 km/h. Normalized multipath pow
46、er for horizontal and vertical antenna polarizations for calm and rough sea conditions are plotted versus elevation angle in Fig. 3, along with predictions derived from a physical optics model. Sea condition has a minor effect for elevation angles above about 10. The agreement between measured coeff
47、icients and those predicted for a smooth flat Earth as modified by the spherical-Earth divergence factor increases as sea conditions become calm. 8 Rec. ITU-R P.682-3 FIGURE 3 Oceanic normalized multipath power vs elevation angle at 1.6 GHz 20151050Normalizedmultipath power(dB)0 5 10 15 20 25 30 35E
48、levation angle (degrees) : :horizontal polarization measurementsvertical polarization measurementshorizontal polarization prediction, calm seahorizontal polarization prediction, rough seavertical polarization prediction, calm seavertical polarization prediction, rough seaCurvesA :B :C :D :ABCDMultip
49、ath data were collected in a series of aeronautical mobile-satellite measurements conducted over the Atlantic Ocean and parts of Europe. Figure 4 shows the measured mean and standard deviations of 1.6 GHz fade durations as a function of elevation angle for these flights. (A crossed-dipole antenna with a gain of 3.5 dBi was used to collect these data. The aircraft flew at a nominal altitude of 10 km and with a nominal g
