1、Rec. ITU-R S.1430 1 RECOMMENDATION ITU-R S.1430 DETERMlNATION OF THE COORDINATION AREA FOR EARTH STATIONS OPERATING WITH lN THE REVERSE DIRECTION IN FREQUENCY BANDS ALLOCATED BLDIRECTIONALLY TO THE FSS NON-GSO SPACE STATIONS WITH RESPECT TO EARTH STATIONS OPERATlNG (Questions ITU-R 253/4, ITU-R 231/
2、4 and ITU-R 212/1) (2000) The ITU Radiocommunication Assembly, considering a the space-to-Earth direction of transmission; that some fi-equency bands are allocated to the FSS for use by non-GSO systems in both the Earth-to-space and b) that these fi-equency bands are also available for use by GSO sy
3、stems; c both GSO and non-GSO orbits; that, therefore, there is a possibility of mutual interference between earth stations operating to space stations in 4 that such potential interference may be alleviated or avoided through the coordination of such earth stations; e I) would be subject to only ne
4、gligible interference; s Groups in the development of comprehensive texts that may be used to revise RR Appendix S7; h) stations, that it is desirable to limit the number of coordinations that may have to be undertaken; that it is possible to defiie an area around a transmitting earth station outsid
5、e of which a receiving earth station that Radiocommunication Study Group 1 is drawing together the results of studies fi-om all concerned Study that Recommendation ITU-R P.620 contains a propagation model that is intended for coordination of earth recommends 1 that, in frequency bands allocated to t
6、he FSS in both the space-to-Earth and the Earth-to-space direction of transmission and utilized by both non-GSO and GSO FSS systems, a bidirectional coordination area be determined for each transmitting earth station; 2 that, for that purpose, Annex 1 to this Recommendation should be used. ANNEX 1 D
7、etermination of the coordination area for earth stations operating with non-GSO space stations with respect to earth stations operating in the reverse direction in frequency bands allocated bidirectionally to the FSS 1 Introduction This procedure has been developed for the determination of the bidir
8、ectional coordination area around an earth station operating with a non-GSO space station in fi-equency bands used bidirectionally by earth stations operating to non-GSO space stations and GSO earth stations. 2 Rec. ITU-R S.1430 The operation of transmitting and receiving non-GSO and GSO earth stati
9、ons in bidirectionally allocated frequency bands may give rise to interference between stations of the two FSS applications. The magnitude of such interference depends on the transmission loss along the interfering path which, in turn, depends on factors such as length and general geometry of the in
10、terference path, the minimum operational elevation angle, antenna gain distribution as a function of time, radio climatic conditions and the percentage of time during which the transmission loss should be exceeded. The described procedure allows the determination, in all azimuth directions from a tr
11、ansmitting earth station, of a distance beyond which the transmission loss would be expected to exceed a specified value for all but a specified percentage of the time. A distance so determined is called the coordination distance. The end points of coordination distances determined for all azimuths
12、define a coordination contour around the earth station which contains the coordination area. For earth stations located outside the coordination area the probability of causing or experiencing significant interference is considered to be negligible. Stations located outside the coordination area of
13、a given planned station are eliminated from any coordination consideration. Consequently, the coordination requirements of a station may be strictly domestic, if the coordination area of the planned station lies entirely in the territory of the notifying administration or, domestic and international
14、 if the coordination area also includes the territory of another administration in which case the coordination agreement of that administration is required. Stations located in the coordination area of a planned station need to be examined on a case-by-case basis initially, taking into account the a
15、ntenna discrimination, separation distance and path profile if necessary. Although based on technical data, the coordination area is an administrative concept. Since the coordination area is determined before any specific cases of potential interference are examined in detail, it must therefore rely
16、 on assumed parameters of the receiving earth stations, while the pertinent parameters of the transmitting earth stations are known. Once the coordination area around an earth station has been computed, it can be stated, regarding another earth station to be operated in the reverse direction: - if t
17、he earth station is to be located outside the coordination area, then there will be little risk of interference; - if the earth station is to be located within the coordination area, then it will be necessary to carry out a detailed coordination. The coordination area will normally be determined for
18、 the case where the non-GSO earth station is transmitting and hence capable of interfering with the reception of other earth stations. It may also be necessary to determine the coordination area for the case where the non-GSO earth station is receiving and hence capable of being interfered-with by e
19、missions from other earth stations. The procedure in this Annex describes the case in which the non-GSO earth station is transmitting. The methodologies apply equally to the case in which the non-GSO earth station is receiving. For the calculation of the coordination area of transmitting earth stati
20、on the necessary parameters can be found in Recommendation ITU-R SM.1448. For a receiving earth station the methodologies can be used on bilateral basis only, since the parameters of the transmitting earth station with respect to which the coordination area is established will have to be provided by
21、 the responsible administration. The coordination area of an earth station operating with a GSO space station in a slightly inclined GSO orbit should be determined for the minimum angle of elevation and the associated azimuth at which the space station is visible to the earth station. 2 General cons
22、iderations 2.1 Concept of minimum permissible transmission loss The determination of the coordination distance, as the distance from a non-GSO earth station beyond which interference from or to a GSO earth station may be considered negligible, is based on the premise that the attenuation of an unwan
23、ted signal is, or can be represented by, a monotonically increasing function of distance. Rec. ITU-R S.1430 3 The amount of attenuation required between an interfering transmitter and an interfered-with receiver is given by the minimum permissible transmission loss for p% of the time, a value of tra
24、nsmission loss which should be exceeded by the actual or predicted transmission loss for all but p% of time: (when p is a small percentage of time, in the range 0.001 % to 1.0%, it is referred to as short-term; ifp 2 20%, it is referred to as long-term): where: P, : maximum available transmitting po
25、wer level (BW) in the reference bandwidth at the input to the antenna of an interfering earth station P,(p) : threshold interference level of an interfering emission (BW) in the reference bandwidth to be exceeded for no more than p% of the time at the terminals of the receiving antenna of an interfe
26、red-with station, the interfering emission originating from a single source. P, and P,(p) are defined for the same radio-frequency bandwidth (the reference bandwidth) and L(p) and P,(p) for the same percentage of the time, as dictated by the performance criteria of the interfered-with system. The co
27、ordination distance can then be determined using a suitable propagation model. The ITU-R has developed propagation models suitable for the determination of the coordination area of earth stations operating with the non-GSO networks. 2.2 The concept of minimum permissible basic transmission loss The
28、transmission loss is defiied in terms of separable parameters, vis-vis basic transmission loss (i.e. attenuation between isotropic antennas) and the effective antenna gains at both ends of an interference path. The minimum permissible basic transmission loss may then be expressed as: where: L this v
29、alue must be exceeded by the actual or predicted basic transmission loss for all but p% of time G, : gain of the transmitting antenna of the interfering station towards the physical horizon on a given azimuth (Bi). If the interfering station is an earth station operating to non-GSO space station, th
30、en G, is a time- varying function G, : gain of the receiving antenna of the interfered-with station towards the physical horizon at a given azimuth (Bi). If the interfered-with station is an earth station operating to non-GSO space station, then G, is a time-varying function. 2.3 Determination of th
31、e threshold interference level P since the entries of interference are not likely to occur simultaneously: p = pdn percentage of time during which the interference from all sources may exceed the threshold value number of equivalent equal level, equal probability entries of interference, assumed to
32、be uncorrelated for small percentages of time link performance margin (dB) (see Note 3) equivalence factor (dB) relating interference from interfering emissions to that caused, alternatively, by the introduction of additional thermal noise of equal power in the reference bandwidth (see Note 4). NOTE
33、 1 - The following earth station receiving system noise temperatures should be used since the location and precise characteristics of the station are unknown: I I I I Frequency range Te (G-1 (KI 75 150 300 NOTE 2 - The factor NL is the noise contribution to the link. In the case of a satellite trans
34、ponder, it includes the up-link noise, intermodulation, etc. In the absence of specific interference data, it is assumed NL = 1 dB for fiied-satellite links. NOTE 3 - M, is the factor by which the link noise under clear-sky conditions would have to be raised to produce the specified minimum performa
35、nce. It is the dB sum of two margins MO (the natural performance margin) and AM (the operational excess margin). The natural performance margin MO is the dB difference between the two CIN values that would just produce the specified nominal (long term) and the specified minimum (short term) performa
36、nces, respectively. The excess margin AM is the dB difference between the actual clear-sky CIN and the value which would produce the nominal specified performance; it may be equal to O dB. Thus, M, is the real fade margin but it is also the margin by which the clear-sky noise floor could be raised (
37、e.g. as the result of interfering emissions) to produce minimum performance conditions. In analogue systems of the FSS, MO is given by Mo = 10 log (50 OOOI10 000) = 7 dB. Since this is sufficient to deal with fading at least below about 17 GHz, AM is taken as O dB, and M, = 7 dB. For frequencies abo
38、ve about 17 GHz, AM may have to assume some value greater than O dB. In digital systems of the FSS, Mo can be as little as 1 dB for practical satellite circuits. In real satellite circuits, due to the presence of FEC codes, the BER versus CIN curve is very steep. In addition, at BER as low as 1 x th
39、e modems decoder can lose synchronization to the incoming bit stream as the modem FEC algorithm begins to break down. Especially for very low bit rates, the recovery time could be significantly large. Thus, a degradation in CIN as small as 1.0 dB, when the BER is 1 x lop7, could result in degraded p
40、erformance and/or downtime to the end-user anywhere from Rec. ITU-R S.1430 5 17 a few seconds to several minutes. The low value of Mo, i.e. 1 dB, is not likely to be sufficient to deal with fading on real links, hence, M, is to be estimated directly from the expected fading depth for the real percen
41、tages of the time of concern. Practical values for M, are therefore: 2 4 6 NOTE 4 - The factor W (dB) is the level of the radio-frequency thermal noise power relative to the received power of an interfering emission which, in the place of the former and contained in the same (reference) bandwidth, w
42、ould produce the same interference (e.g. an increase in the voice or video channel noise power, or in the BER). The factor W generally depends on the characteristics of both the wanted and the interfering signals. The factor W is positive when the interfering emissions would cause more degradation t
43、han thermal noise. When the wanted signal is digital, W is usually equal to or less than O dB, regardless of the characteristics of the interfering signal. 3 Determination of the antenna gain of the non-GSO earth station For an earth station operating with non-GSO satellites, the antenna gain varies
44、 as functions of the time. The statistics of the horizon gain of the antenna of an earth station operating to a non-GSO space station can either be provided by administrations or derived based on computer simulations. Using computer simulations, a procedure for calculating the time-varying gain of t
45、he transmitting or the receiving antenna of an earth station operating to a non-GSO space station is as follows: - Simulate the non-GSO satellite constellation over a sufficiently long period (e.g. one repetition cycle of the constellation) with a time step appropriate for the orbit altitude to have
46、 a valid representation of the antenna gain variations. - At each time step, record the earth station azimuth and elevation angles of all satellites which are visible at the earth station and are above the minimum operational elevation angle. Criteria in addition to elevation angle could be used to
47、avoid certain geometries, e.g. geostationary orbit arc avoidance. - Use the actual earth station antenna pattern or a formula giving a good approximation of it to calculate the gain towards the horizon at each azimuth and elevation angle around the earth station. - For each azimuth on the horizon ar
48、ound the earth station, calculate the percentage of time each gain value occurs. The probability distribution function (pdf) of the horizon antenna gain varies over the range Gmin to G- It is recommended that increments of s dB are used between G, and G, i.e. G = Gminy Gmin + s, Gmin + 2s, ., Gm. A
49、value of s = 0.1 to 0.5 dB is recommended. - Derive the gain cumulative distribution function (cdf) by integrating the gain density function; this cdf gives the percentage of time that the gain is less than or equal to a specific value. The following equations should be used in the above algorithmic approach to describe the geometry of the boresight of the antenna of the earth station operating to a non-GSO space station as a function of time. For a spherical Earth and a circular orbit, the elevation angle (E,) to a non-GSO satellite as seen from the earth station operating to a non-GS
