1、 Rec. ITU-R F.1108-4 1 RECOMMENDATION ITU-R F.1108-4 Determination of the criteria to protect fixed service receivers from the emissions of space stations operating in non-geostationary orbits in shared frequency bands (Questions ITU-R 118/9 and ITU-R 113/9) (1994-1995-1997-2002-2005) Scope This Rec
2、ommendation contains various methodologies to determine the criteria to protect fixed service receivers from emissions of space stations operating in non-geostationary orbits in shared frequency bands, including highly elliptical orbits (HEOs). The ITU Radiocommunication Assembly, considering a) tha
3、t the World Administrative Radio Conference for Dealing with Frequency Allocations in Certain Parts of the Spectrum Malaga-Torremolinos, 1992 (WARC-92) has allocated to satellite services, on a co-primary basis, spectrum that is also allocated to the fixed service (FS); b) that the satellite service
4、s may wish to operate with space stations in non-geostationary orbits (non-GSOs); c) that emissions from space stations operating in non-GSOs and sharing the same spectrum may produce interference in receiving stations of the FS; d) that because of the wide geographic visibility of the emissions fro
5、m space stations non-GSOs, frequency coordination with stations in the FS may not be practical; e) that FS systems must meet performance requirements on a worst-month basis; f) that the performance degradation for a FS system depends on the sum of the degradations due to emissions from all space sta
6、tions that are visible to it; g) that studies of the power flux-density (pfd) at the surface of the Earth due to emissions from space stations non-GSO can be carried out by applying statistical methods to results from computer simulations, recommends 1 that frequency sharing criteria for FS systems
7、sharing spectrum with space stations in non-GSOs take into account the aggregate pfd resulting from the emissions of the total complement of space stations visible to FS stations at any point on the Earth; 2 Rec. ITU-R F.1108-4 1.1 that the tolerable interference be specified in terms of a pfd (W/m2
8、) in an agreed bandwidth; 2 that pfd limits be determined on the basis of a statistical application of the principles of Recommendation ITU-R F.758 in the case of digital fixed wireless systems and Recommendation ITU-R SF.357 in the case of analogue fixed wireless systems (method under study); 3 tha
9、t due regard be taken of the fact that ITU-T Recommendation G.826 (from which Recommendations ITU-R F.1397 and ITU-R F.1491 are derived) imposes stricter error performance objectives for digital fixed wireless systems; 4 that the pfd limits take into account the orbital parameters of space stations
10、using the band; 4.1 that the methods in Annex 1 can be used for determining the visibility statistics of space stations operating in circular orbits; 4.2 that the degradation of the performance of analogue systems due to emissions from single or multiple space stations be determined using the method
11、s described in Annex 2; 4.3 that the degradation of the performance of digital systems due to emissions from single or multiple space stations be determined using the methods described in Annex 3 (see Note 1); 4.4 that the effects on digital systems using diversity due to emissions from single or mu
12、ltiple space stations may be determined using the methods described in Annex 4 (see Note 2); 4.5 that the considerations in Annex 5 be used in assessing the non-uniformity of the interference in any month; 4.6 that the methodology given in Annex 6 can be used to develop the cumulative distribution o
13、f the ratio of received power to the sum of noise and interference powers and the associated fade margin loss due to emissions from single or multiple space stations (see Note 3); 4.7 that Annex 7 provides an example methodology that could be used to evaluate the interference to a station in the FS
14、from a non-GSO satellite constellation using circular or elliptical orbits, including highly elliptical orbits (HEOs). NOTE 1 The criterion of fractional degradation in performance (FDP) developed in this Recommendation is applicable to FS systems operating at frequencies where multipath fading is t
15、he principal cause of signal fading. For paths where rain attenuation is the principal cause of fading, further study is required. The assessment of the effect of short-term interference as described in 4 of Annex 3 requires further study. NOTE 2 Diversity is not generally used at frequencies below
16、3 GHz. It is most often employed at frequencies where multipath fading is the principal cause of fading. NOTE 3 The methodology developed in Annex 6 may be used in assessing short-term interference or for evaluating interference potential in bilateral negotiations. Rec. ITU-R F.1108-4 3 Annex 1 Dete
17、rmination of the visibility statistics of space stations operating in circular non-geosynchronous orbits as seen by a terrestrial station 1 Introduction In order to develop sharing criteria between low-Earth orbiting (LEO) satellites and FS systems, it is necessary to determine how often a satellite
18、 will be visible in any direction for a particular terrestrial station or position and how strong will be the interference received from it. The purpose of this Annex is to develop the equations necessary to simulate the operation of a LEO satellite and thereby the necessary statistics. The developm
19、ent is sufficiently general that the results can be applied either for a random model or for a time evolutionary model. Section 2 of this Annex provides a development of the equations of motion of a satellite, which is in a circular orbit, in an inertial coordinate system. In 3, these equations are
20、transformed to a coordinate system fixed on the Earth. The azimuth and distance of the sub-satellite point from a position on the surface of the Earth are determined in 4. In 5, the expressions for the elevation and off-boresight angle of the satellite are developed, and a simple criterion for testi
21、ng for the visibility of a satellite that is above a particular position on the Earth is given. A right-handed spherical coordinate system is used throughout this development for Earth-centred coordinates with (r, , ) where r is the distance from the origin, is the angular distance from the North Po
22、le, and is the angle around the Pole. 2 The satellite in the inertial frame In order to determine the position of the satellite in the inertial frame, its position in the orbital plane must first be determined. For a body in a circular orbit around the Earth this description involves four Keplerian
23、orbital parameters as follows: Rs : orbital radius, the distance from the centre of the Earth to the satellite I : inclination angle (rad), the angle between the orbital plane and the Earths equatorial plane. It is measured from 0 to and is less than /2 if the satellite is headed eastward as it cros
24、ses the equatorial plane from South to North and greater than /2 if the satellite is headed westward as it crosses the equatorial plane from South to North s: angular distance (rad) along the equatorial plane from the zero reference to the position of the ascending node, the intersection where the p
25、lane of the satellite crosses the equatorial plane from South to North M : mean anomaly (rad), the angular arc in the satellite orbital plane measured from the ascending node to the position of the satellite. To determine the coordinates of the satellite in the inertial spherical coordinate system,
26、one must first determine the position of the satellite referenced to 0, the angular position or longitude of the ascending node, measured East of the first point of Aries. The position of the sub-satellite point is denoted by sand 0. 4 Rec. ITU-R F.1108-4 These coordinates may be determined by spher
27、ical geometry with reference to Fig. 1. Applying the law of cosines to the arc sgives cos s= sin M sin I. Since is defined on the interval (0, ): s= arccos (sin M sin I ) (1) 1108-01M0s/2/2 INorth PoleSub-satellite pointAscending nodeFIGURE 1Spherical triangle of satellite in the inertial frameSimil
28、arly, applying the law of cosines to the arc M gives cos M = sin scos 0. Equation (2) gives the values of 0for the entire range (, 2). RE/ Rs= (13) By using (13) in (9), it is possible to develop an expression for the range of longitudes that are within this circle of visibility for a particular sub
29、-satellite point latitude or mean anomaly. Hence equations (10), (11) and (12) need only be evaluated under conditions that can be predetermined. Annex 2 Simulation of interference into analogue fixed wireless routes from LEO satellites 1 Introduction This Annex describes a computer program which im
30、plements the mathematical relationships developed in Annex 1. The resulting program can be used as an analysis tool for examining interference into simulated analogue fixed wireless networks that share spectrum with LEO satellites representative of those that may operate in bands below 3 GHz. A numb
31、er of example sharing scenario situations and their results are described. 8 Rec. ITU-R F.1108-4 2 Description of the model The program mathematically simulates the path of a constellation of LEO taking into account the Earths rotation and orbit precession effects. Interference is calculated for eac
32、h 1/2 degree movement of the satellite in the constellation into each fixed wireless receiver in a concentration randomly distributed fixed wireless routes. The program accumulates interference density data for each fixed wireless route for the period of the simulation. The program converts this dat
33、a into a probability distribution for each route so that the performance of each route can be separately analysed. The results of the example scenarios described here are compared with the reference performance requirements described in Fig. 1 of Recommendation ITU-R SF.357. Recommen-dation ITU-R SF
34、.357 proposes reference interference sharing criteria for analogue systems only. 2.1 Input The simulation allows operator selection of the following parameters: frequency, latitude and longitude of the centre of the fixed wireless route trendlines, fixed wireless receive antenna gain, number of radi
35、o-routes to be analysed, satellite orbit altitude (same for each satellite), number of satellite orbital planes, longitude of the ascending node for each plane, orbit inclination (same for each plane), number of satellites per plane (same for each plane), high angle satellite pfd level, low angle sa
36、tellite pfd level, length (in days) of the simulation. The assumptions that are built into the model include: For the fixed wireless system model: 50 hop, 2 500 km routes, hop directions are selected by Monte Carlo methods. Receiver noise temperature of 1 750 K. Baseband 4 kHz bandwidth thermal nois
37、e per hop is 25 pW. Receive antenna characteristics per Recommendation ITU-R F.699. Losses (feeder, conversion) of 3 dB. For the satellite system model: Circular orbit only. pfd constrained to the following mask: pfdlowfor 0 5 pfd = pfdlow+ 0.05 (pfdhi pfdlow) ( 5) for 5Interference (pW0p)Frequency
38、= 1.5 GHzFrequency = 2.0 GHzFrequency = 2.5 GHzFIGURE 5FS interference versus frequency(800 km, 50 hop routes, 33 dB antenna gain, 40 latitude, pfd = 154/144 dB(W/(m2 4 kHz)Rec. ITU-R F.1108-4 11 1108-0611025252525252510 110 210 310 410 52511010210310410525 25 25 2510FIGURE 6Interference versus alti
39、tude and pfd(50 hop routes, 40 latitude, 2 GHz)ProbabilityI Interference (pW0p)pfd = 154/144 dB(W/(m2 4 kHz), altitude = 800 kmpfd = 154/144 dB(W/(m2 4 kHz), altitude = 10 300 kmpfd = 144/144 dB(W/(m2 4 kHz), altitude = 800 kmpfd = 144/144 dB(W/(m2 4 kHz), altitude = 10 300 kmThe lower group of thre
40、e curves in Fig. 7 represent the distributions of received interference distributions at different latitudes from single orbiting satellites that have high orbit angles (80). It is interesting to note here that if the curve plots were extrapolated back to the y axis for X = 0 it would approximately
41、represent the percent of time that the satellites were visible to the FS systems at the indicated latitudes. Conversely the inverse of that number would also approximate the number of satellites needed to achieve constant single satellite visibility. It follows from a close observation of these curv
42、e plots in Fig. 7 that fewer satellites would be needed to continuously illuminate higher latitudes systems since the distribution for the 65 latitude fixed wireless routes does appear to intercept the y axis at a much higher point. 12 Rec. ITU-R F.1108-4 1108-0711025252525252510 110 210 310 410 525
43、11010210310410525 25 25 2510FIGURE 7Interference (i) pW in 4 kHz bandwidthProbabilityILatitude = 65Latitude = 40Latitude = 15Interference (pW0p)FS interference versus latitude(50 hops, 33 dB antenna gain, pfd = 154/144 dB(W/(m2 4 kHz), 2 GHz)This might be verified intuitively by considering that for
44、 every orbit of a highly inclined satellite system each satellite in the plane would be visible for a percentage of time to terrestrial sites at more northern or southern latitudes, whereas terrestrial sites at mid or lower latitudes may not bevisible to any portion of some orbits. This would sugges
45、t that LEOs optimized to serve medium and lower latitudes would cause more interference into higher latitude terrestrial systems since a larger percentage of the satellites in orbit would be visible to the higher latitude terrestrial sites. Rec. ITU-R F.1108-4 13 Finally, Figs. 8 and 9 illustrate th
46、e interference effects into the FS from constellations of satellites that might represent practical operating systems. Both systems are arranged such that 3 to 6 satellites are continually visible to the terrestrial site requiring service. Figure 8 investigates a satellite constellation consisting o
47、f 6 circular orbit planes with 11 satellites per plane. All planes have the same inclination (86.5) and the same satellite altitude (780 km). Figure 9 shows the interference distribution that might be expected from a 12-satellite constellation operating at an altitude of 10 370 km. The satellites ar
48、e arranged in 3 orbit planes separated by 120 with inclinations of 56 and 4 satellites per plane. 1108-0811025252525252510 110 210 310 410 52511010210310410525 25 25 2510FIGURE 8Interference (i) pW in 4 kHz bandwidthProbabilityI pfd = 152/142 dB(W/(m2 4 kHz)pfd = 152/137 dB(W/(m2 4 kHz)pfd = 152/132
49、 dB(W/(m2 4 kHz)66 LEOs/780 km interference into FS(86.5 inclination, FS antenna gain = 33 dB, 2 GHz, latitude 40)Interference (pW0p)14 Rec. ITU-R F.1108-4 1108-0911025252525252510 110 210 310 410 52511010210310410525 25 25 2510FIGURE 9Interference (i) pW in 4 kHz bandwidthProbabilityI pfd = 152/142 dB(W/(m2 4 kHz)pfd = 152/137 dB(W/(m2 4 kHz)pfd = 152/132 dB(W/(m2 4 kHz)12 LEOs/10 370 km interference into FS(56 incli
