1、 Rec. ITU-R SF.1485 1 RECOMMENDATION ITU-R SF.1485*DETERMINATION OF THE COORDINATION AREA FOR EARTH STATIONS OPERATING WITH NON-GEOSTATIONARY SPACE STATIONS IN THE FIXED-SATELLITE SERVICE IN FREQUENCY BANDS SHARED WITH THE FIXED SERVICE (Questions ITU-R 253/4 and ITU-R 219/9) (2000) Rec. ITU-R SF.14
2、85 The ITU Radiocommunication Assembly, considering a) that WRC-95 allocated spectrum to satellite services, on a primary basis, that is used by the FS; b) that the satellite services may operate with space stations in non-GSO orbits; c) that emissions from earth stations operating with space statio
3、ns in non-GSO orbits may produce interference to FS receivers and vice versa; d) that Radiocommunication Study Group 1 is drawing together the results of studies from all concerned Study Groups in the development of text that may be used to revised RR Appendix S7; e) that it is possible to define an
4、 area around a non-GSO earth station outside of which a FS station would cause or be subject to only negligible interference; f) that the pointing of the antenna of an earth station operating with a space station in a non-GSO orbit varies with time and in accordance with the orbital parameters of th
5、e operational non-GSO satellite and the location of the earth station; g) that procedures, similar to those which currently exist, should be established for the determination of coordination area around earth stations operating with non-GSO orbits, recommends 1 that the determination of the coordina
6、tion area around a non-GSO satellite system earth station takes into account the percentage of time that the earth station is pointing in the direction of interest; 2 that, when calculating the basic transmission loss, Lb(p), the percentage of the time, p, during which the interfering power into the
7、 FS station receiver is allowed to exceed the maximum allowable level, Pr(p), is modified by the percentage of time that the non-GSO earth station antenna is pointing in the direction of interest; 3 that the determination of the coordination area should take into account the orbital parameters of th
8、e space stations operating with the non-GSO earth station; 4 that the methods in Annex 1 or Annex 2 should be considered by administrations in determining the coordination area (see Note 1). NOTE 1 The orbital equations in the procedure of Annex 1 are applicable to circular orbits only. _ *This Reco
9、mmendation should be brought to the attention of Radiocommunication Study Groups 1 and 3. Rec. ITU-R SF.1485 2 ANNEX 1 Determination of the coordination area for earth stations operating with non-GSO space stations in the FSS in frequency bands shared with the FS 1 Introduction This procedure has be
10、en developed for determining the coordination area around an earth station operating with a non-GSO space station in frequency bands shared with terrestrial radiocommunication services. The operation of transmitting and receiving non-GSO earth stations and terrestrial stations in shared frequency ba
11、nds may give rise to interference between stations of the two services. 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 interference path, the minimum operational elevation an
12、gle, 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 transmitting or receiving earth station, of a distance
13、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 define a coordination contour around the
14、 earth station, which contains the coordination area. For terrestrial stations located outside the coordination area the probability of causing or experiencing significant interference is considered to be negligible. Although based on technical data, the coordination area is an administrative concep
15、t. Since the coordination area is determined before any specific cases of potential interference are examined in detail, it must therefore rely on assumed parameters of the terrestrial systems, while the pertinent parameters of the transmitting earth stations are known. Stations located outside the
16、coordination area of 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, domes
17、tic and international 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, taki
18、ng into account the antenna discrimination, separation distance and path profile if necessary. For the determination of the coordination area, two cases may have to be considered: a) the non-GSO earth station is transmitting and hence capable of interfering with the reception of terrestrial stations
19、; b) the non-GSO earth station is receiving and hence capable of being interfered-with by emissions from terrestrial stations. Whilst this Annex describes case a) in which the non-GSO earth station is transmitting and the terrestrial station is receiving, the methodologies are applicable to case b)
20、in which the terrestrial station is transmitting and the non-GSO earth station is receiving. 2 General considerations 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
21、 a terrestrial station may be considered negligible, is based on the premise that the attenuation of an unwanted signal is, or can be represented by, a monotonically increasing function of distance. Rec. ITU-R SF.1485 3 The amount of attenuation required between an interfering transmitter and an int
22、erfered-with receiver is given by the minimum permissible transmission loss for p% of the time, a value of transmission loss which should be exceeded by the actual or predicted transmission loss for all but p% of the time (when p is a small percentage of time, in the range 0.001% to 1.0%, it is refe
23、rred to as short-term; if p 20%, it is referred to as long-term): )()( pPPpLrt= dB (1) where: Pt: maximum available transmitting power level (dBW) in the reference bandwidth at the input to the antenna of an interfering station Pr(p): threshold interference level of an interfering emission (dBW) in
24、the reference bandwidth to be exceeded for no more than p% of the time at the terminals of the receiving antenna of an interfered-with station, the interfering emission originating from a single source. Ptand Pr(p) are defined for the same radio-frequency bandwidth (the reference bandwidth) and L(p)
25、 and Pr(p) for the same percentage of the time, as dictated by the performance criteria of the interfered-with system. Only small percentages of the time are of interest here. Considering a specific mechanism of propagation for the interfering emission, the coordination distance can be determined. T
26、he ITU-R is currently developing propagation models suitable for the determination of the coordination area for earth stations operating with non-GSO satellite networks. 2.2 The concept of minimum permissible basic transmission loss The transmission loss is defined in terms of separable parameters,
27、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: )()( pPGGPpLrrttb+= dB (2) where: Lb(p): minimum permissible basic transmissio
28、n loss (dB) for p% of the time; this value must be exceeded by the actual or predicted basic transmission loss for all but p% of the time Gt: gain of the transmitting antenna of the interfering station (dBi). If the interfering station is a non-GSO earth station, this is the time-varying antenna gai
29、n towards the physical horizon on a given azimuth; in the case of a terrestrial station the maximum expected antenna gain is to be used Gr: gain of the receiving antenna of the interfered-with station (dBi). If the interfered-with station is a non-GSO earth station, this is the time-varying gain tow
30、ards the physical horizon on a given azimuth; in the case of a terrestrial station, the maximum expected antenna gain is to be used. 2.3 Derivation of interference parameters 2.3.1 Determination of the threshold interference level Pr(p) of an interfering emission The threshold interference level (dB
31、W) of the interfering emission in the reference bandwidth, to be exceeded for no more than p% of the time at the receiving antenna terminals of a station subject to interference, from each source of interference, is given by the general formula below: WNBTkpPsMLer+= )( 110log10)(log10)(10/dBW (3) wh
32、ere: k: Boltzmanns constant (1.38 1023J/K)Te: thermal noise temperature of the receiving system (K), at the terminal of the receiving antenna (see Note 1) B: reference bandwidth (Hz), i.e. the bandwidth in the interfered-with system over which the power of the interfering emission can be averaged NL
33、: link noise contribution (see Note 2) Rec. ITU-R SF.1485 4 p: percentage of time during which the interference from one source may exceed the threshold value; since the entries of interference are not likely to occur simultaneously: p = p0/n p0: percentage of time during which the interference from
34、 all sources may exceed the threshold value n: number of equivalent equal level, equal probability entries of interference, assumed to be uncorrelated for small percentages of time Ms: link performance margin (dB) W: an equivalence factor (dB) relating interference from interfering emissions to that
35、 caused, alternatively, by the introduction of additional thermal noise of equal power in the reference bandwidth (see Note 3). NOTE 1 The noise temperature (K) of the receiving system, referred to the output terminals of the receiving antenna, may be determined from: raeeTeTT += 290)1( K (4) where:
36、 Ta: noise temperature (K) contributed by the receiving antenna e: numerical loss in the transmission line (e.g. a waveguide) between the antenna terminal and the receiver front end Tr: noise temperature (K) of the receiver front end, including all successive stages at the front end input. For radio
37、-relay receivers and where the waveguide loss of a receiving earth station is not known, a value of e = 1.0 should be used. NOTE 2 The factor NLis the noise contribution to the link. In the case of a satellite transponder, it includes the up-link noise, intermodulation, etc. For example, in the abse
38、nce of specific interference data, it is assumed: NL= 1 dB for FSS links NL= 0 dB for terrestrial links NOTE 3 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 sa
39、me (reference) bandwidth, would 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 wou
40、ld cause more degradation than thermal noise. When the wanted signal is digital, W is usually equal to or less than 0 dB, regardless of the characteristics of the interfering signal. 3 Determination of the antenna gain of the non-GSO satellite system earth station For an earth station operating with
41、 a non-GSO satellite, the gain of the antenna varies as a function of time. The statistics of the horizon gain of the antenna of a non-GSO earth station can either be provided by administrations or derived based on computer simulations. Using computer simulations, a methodology for calculating the t
42、ime-varying gain of the antenna of a non-GSO earth 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 a valid representation of the antenna ga
43、in 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 avoid certain geometries, e.g. geostationar
44、y orbit arc avoidance. Rec. ITU-R SF.1485 5 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 around the earth station. For each azimuth on the horizon around the earth station, calculate the percenta
45、ge of time each gain value occurs. The probability density function (pdf) of the horizon antenna gain varies over the range Gminto Gmax. It is recommended that increments of s (dB) are used between Gminand Gmax, i.e., G = Gmin, Gmin + s, Gmin + 2s,., Gmax. Derive the gain cumulative distribution fun
46、ction (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. 3.1 Determination of the antenna geometry The following equations are used in the above algorithmic approach to describe the geometry of the boresight
47、of the antenna of the non-GSO earth station as a function of time. For a spherical earth and a circular orbit, the elevation angle (t) to a non-GSO satellite as seen from the non-GSO earth station is given by: )cos(2()cos()sin(22+=gsgsgstrrrrrr(5) where: )(sin)(sin)(sin)(sin)cos()(sin)cos()cos()cos(
48、)cos(fifitftgsgsgg+=G26G26(5a) G26= e G26 e: earth rotation rate = 0.004178 (degrees/s) G26 : rate of precession of the nodes of the non-GSO satellite (degrees/s) : angle between the vectors from the earths centre to the non-GSO satellite and from the earths centre to the non-GSO earth station (degr
49、ees) rs: distance from the earths centre to the non-GSO satellite (km) rg: distance from the earths centre to the non-GSO earth station (km) s: longitude of ascending mode of the non-GSO satellite orbit at time t = 0 (degrees) i: orbit inclination of the non-GSO satellite (degrees) : argument of perigee of the non-GSO satellite orbit at time t (degrees) f: true anomaly of the non-GSO satellite in its orbit at time t (degrees) g, g: longitude and latitude of the non
