1、 Recommendation ITU-R S.1857(01/2010)Methodologies to estimate the off-axis e.i.r.p. density levels and to assess the interference towards adjacent satellitesresulting from pointing errors of vehicle-mounted earth stations in the 14 GHz frequency bandS SeriesFixed-satellite serviceii Rec. ITU-R S.18
2、57 Foreword The role of the Radiocommunication Sector is to ensure the rational, equitable, 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 Reco
3、mmendations are adopted. The regulatory and policy functions of the Radiocommunication 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 i
4、n the Common Patent Policy for ITU-T/ITU-R/ISO/IEC referenced in Annex 1 of Resolution 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 th
5、e Common Patent Policy for ITU-T/ITU-R/ISO/IEC and the ITU-R patent information database 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 telev
6、ision BS Broadcasting service (sound) BT Broadcasting service (television) F Fixed service 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 Freq
7、uency sharing and coordination between fixed-satellite and fixed service systems SM Spectrum 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 detaile
8、d in Resolution ITU-R 1. Electronic Publication Geneva, 2010 ITU 2010 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without written permission of ITU. Rec. ITU-R S.1857 1 RECOMMENDATION ITU-R S.1857 Methodologies to estimate the off-axis e.i.r.p. densit
9、y levels and to assess the interference towards adjacent satellites resulting from pointing errors of vehicle-mounted earth stations in the 14 GHz frequency band (Question ITU-R 208/4) (2010) Scope This Recommendation presents the general antenna pointing error characteristics of vehicle-mounted ear
10、th stations with active antenna tracking systems and provides a method to estimate the statistics of off-axis e.i.r.p. variations due to pointing errors. Furthermore, it provides a methodology to assess the potential interference towards adjacent satellites operating in the GSO, FSS systems. The ITU
11、 Radiocommunication Assembly, considering a) that FSS GSO satellites are well suited to provide Internet and data services through a wide range of network configurations; b) that there is an increasing need to support user mobility and broadband services to end-users; c) that vehicle-mounted earth s
12、tation (VMES) terminals can provide a wide range of communication services over FSS satellites in the 14 GHz frequency band; d) that it is necessary to protect networks of the FSS from any potential interference from these VMES terminals; e) that efficient use of the radio-frequency spectrum and the
13、 GSO by VMES terminals can be accomplished through use of a model for the off-axis e.i.r.p. density and interference from such terminals; f) that VMES require statistical approaches to determine their off-axis e.i.r.p. density levels and interference to adjacent satellites; g) that satellite network
14、s using VMES can be designed to comply with the interference limits required by adjacent satellite system operators; h) that it would be useful to have methodologies for assessing the interference levels and impact on link availability of victim satellite networks resulting from variations in off-ax
15、is e.i.r.p. density levels of VMES antennas that are too small in diameter to be meaningfully assessed using currently available methods, noting a) that maximum permissible levels of off-axis e.i.r.p. density from very small aperture terminals (VSATs) are provided in Recommendation ITU-R S.728; b) t
16、hat maximum permissible levels of inter-network interference caused by the earth and space station emissions of all other satellite networks operating in the same frequency band are provided in Recommendation ITU-R S.1323, 2 Rec. ITU-R S.1857 recommends 1 that the methodology and associated model gi
17、ven in Annex 1 can be used to estimate the off-axis e.i.r.p. density levels caused by antenna pointing errors of VMES; 2 that the methodology given in Annex 2 can be used to assess the interference levels resulting from variations in off-axis e.i.r.p. density levels of VMES; 3 that the methodology g
18、iven in Annex 2 can be used to assess the impact to the link unavailability of the interfered system in situations where time-varying antenna pointing errors from VMES antennas of the type described in Note 2 are significant; 4 that the Notes 1 to 5 should be regarded as part of this Recommendation:
19、 NOTE 1 The methodology given in Annex 2 may be used to assess potential interference impacts of VMES. NOTE 2 The methodologies presented in this Recommendation were developed for VMES with directional reflector antennas having equivalent diameters ranging from 0.3 m to 1.0 m; mechanical or electron
20、ic tracking systems, and support vehicle speeds up to 100 km/h. However, the methodologies can be applied to other antenna sizes and vehicle speeds. NOTE 3 The parameters and the examples provided in the annexes represent some systems that operate in the 14 GHz frequency band. NOTE 4 The methodology
21、 described in this Recommendation applies when the VMES tracking system is locked to its target satellite. NOTE 5 To use this Recommendation it is necessary to know the representative values of and c, as used in 2 of Annex 1. Annex 1 A model to estimate off-axis e.i.r.p. density levels caused by ant
22、enna pointing errors of VMES 1 Introduction Recent demand for on-the-move communication applications has generated interest in a new type of satellite terminal. These terminals, which are mounted on vehicles, generally consist of small, high-performance antennas, tracking systems with servo controll
23、ers and positioners, and include the respective intermediate-frequency (IF) and RF equipment. The antenna size and other transmission parameters are selected to provide two-way communications under various terrains and operational conditions. The terminals considered in this annex will operate over
24、FSS in the 14 GHz frequency band. Currently these terminals are being tested for use in terrestrial vehicles and trains. The terminals mounted on vehicles, as detailed in this contribution, may cause additional interference to adjacent satellites due to motion-induced antenna pointing errors. From a
25、 satellite operators perspective, this interference should be maintained at a minimum level. On the other hand, service providers will seek to design their systems such that the terminals provide enough transmit power to support end-user applications at reasonable data rates. This annex addresses th
26、ese conflicting demands, i.e. the need to transmit sufficient power to support reasonable data rates while maintaining an interference level that is acceptable to the satellite operators. Rec. ITU-R S.1857 3 In on-the-move communication applications, because of the motion of the antenna platform, er
27、rors in the antenna pointing and tracking system can lead to antenna pointing errors. Typically, these motion-induced antenna pointing errors are small and random, and produce random variations of the off-axis e.i.r.p. density. In order to assess the impact of interference to other satellites it is
28、necessary to model and quantify the e.i.r.p. density from these terminals. This annex presents a statistical model to estimate the e.i.r.p. density levels due to antenna pointing errors and presents an approach to developing an illustrative statistical mask for the e.i.r.p. density in the off-axis d
29、irections. This illustrative statistical mask considers typical operational characteristics of terminals mounted on vehicles and can be used to limit the off-axis emissions from these terminals. For a satellite earth terminal the e.i.r.p. density in its off-axis directions is directly proportional t
30、o the e.i.r.p. density in the boresight1direction. This annex provides a methodology to determine the appropriate levels for the boresight e.i.r.p. density so as to satisfy the above illustrative statistical mask. 2 Motion-induced antenna pointing errors Under certain motion conditions of the antenn
31、a platform the boresight of the antenna will be displaced. The antenna pointing error can be represented by a random variable, , which is the angular distance between the actual and the intended directions of the antenna boresight. In many practical realizations, the antenna pointing error is measur
32、ed in terms of its components: elevation error, , and azimuth error, a. These error components may be represented by mutually independent random variables whose statistical distributions are estimated by measurements carried out over representative drive paths. The probability density function (PDF)
33、 of xis denoted by xf, where x = ,a. For illustrative purposes it is useful to represent these PDFs by well-known statistical distributions. Laboratory measurements of motion-induced antenna pointing errors have indicated that these pointing errors have long-tailed characteristics, that is, the PDF
34、will not decay fast for large values of the antenna pointing error. The symmetric -stable (SS) distribution Shao and Nikias, 1993; Samorodnitsky and Taqqu, 1994, is an example for a distribution with long-tailed characteristics and it is employed to represent, illustratively, the PDFs of the elevati
35、on and azimuth antenna pointing errors. The SS distribution has many parameters that can be used to generate different PDFs and the Gaussian distribution is a special case. The characteristic function of the SS distribution with zero location parameter is given as: e)(=cxx (1) where c 0 is the scale
36、 parameter or the dispersion and , 0 ERef(), is expressed as: )(1d)()()(Pr)(= RefRefEFxxfEEEEERef(6) This is the complementary CDF (CCDF) of the off-axis e.i.r.p. density level computed at ERef() and is a function of the off-axis angle, ; boresight e.i.r.p. density, EB; and the locations of the eart
37、h terminal and the satellite represented by the sum and difference of elevation and azimuth angles and,+SSSSSSa . Intuitively, it is clear that by reducing EBthe above probability can be reduced, and it is instructive to express this probability so that EBis an explicit parameter. To accomplish this
38、 equation (3) may be written as E() = EBG (BS), where G(BS) is the normalized antenna gain pattern such that G(0) = 1. The probability in equation (6) can be written as: ) / )(1 / )()(Pr)(BRefGBRefBSEEFEEGBS=(7) where )(BSGF is the CDF of G(BS) and is not a function of EB. The probability that the e
39、.i.r.p. density level exceeds the reference level ERef() is as given above; however, this does not address the level of excess e.i.r.p. density above ERef(). This aspect can be addressed by examining the probability that the off-axis e.i.r.p. density level exceeds (EIRPexcess ERef(), where EIRPexces
40、s 1 is a scale factor. Using this in equation (7) the required probability is: ) / EIRP )(1) / EIRP )( )(Pr)EIRP )( )(Pr)(BexcessRefGBexcessfReBSexcessRefEEFEEGEEBS=(8) The above probability is the CCDF of G(BS) computed at (ERef() EIRPexcess/ EB).The procedure for computing the probability in equat
41、ion (8) is as follows: Step 1: The underlying random variables here are the antenna pointing error components, and a, whose PDFs, for illustrative purposes, are assumed to be known as in 2. Step 2: For known locations of the earth terminal, satellite and the off-axis direction, the sum and differenc
42、e of elevation and azimuth angles, +SSSSSSaand, , are computed as described in 3. These angles are then be used in equation (5) and the result substituted in equation (4) to express BSin terms of the random variables, and a. The PDF of BScan then be determined using the PDFs of and a. Making use of
43、the relationship in equation (2), the PDF of BSso determined is then used to compute the CCDF of the random variable G(BS). 8 Rec. ITU-R S.1857 Step 3: Finally, the desired probability in equation (8) is determined from the CCDF of G(BS) with EBand e.i.r.p.excessas parameters. 5 An illustrative stat
44、istical e.i.r.p. density mask to limit off-axis emissions In order to limit off-axis emissions, in the presence of motion-induced antenna pointing errors, an upper bound on the probability that the e.i.r.p. density level exceeds a reference level may be used. However, it is clear that the probabilit
45、y computed in equation (8) depends on the locations of the earth terminal and the satellite, and the off-axis angle. Since the earth terminal may be located anywhere on the Earths surface it is highly desirable to limit the off-axis emissions using a function that is independent of the earth termina
46、l and satellite locations. Ideally, it is instructive to derive an upper bound for the probability PrE() (ERef () EIRPexcess) by a single function, Pmax(EIRPexcess), which is applicable anywhere on the Earths surface and for all off-axis angles. This desired probability function, Pmax(EIRPexcess), l
47、imits the off-axis e.i.r.p. density emissions and constitutes a statistical mask on the e.i.r.p. density level. To obtain a statistical e.i.r.p. density level mask as discussed above consider the special case when the points S and Sare on the GSO and the earth terminal is placed on the equator and d
48、irectly below S. For this configuration, S= 90, )90( =S, 270or90and90 =sSaa , and it follows that 180or0and,)801(=+SSSSSSa . Using these expressions in equation (5) and substituting the result in equation (4), BScan be written as: 2sin)cos( )(cos()cos(cos2 aBS=(9) The CDF of G(BS) obtained using the
49、 above BSwill not be a function of the specific elevation and azimuth angles from the earth terminal to the satellite; however, this CDF will be a function of the off-axis angle, . To derive a function that is applicable to all off-axis angles consider the maximum of the probability in equation (8) over all off-axis angles. From equation (8) this desired maximum probability is expresse
