1、STD-ITU-R RECMN SaL25b-ENGL 2997 = 4855232 053035b b37 1 Rec. ITU-R S.1256 RECOMMENDATION ITU-R S.1256 METHODOLOGY FOR DETERMINING THE MAXIMM AGGREGATE POWER FLUX-DENSITY AT THE GEOSTATIONARY-SATELLITE ORBIT IN THE BAND 6700-7075 MHz FROM FEEDER LINKS OF NON-GEOSTATIONARY SATELLITE SYSTEMS IN THE MO
2、BILE-SATELLITE SERVICE IN THE SPACE-TO-EARTH DIRECTION (Question IT-R 206/4) (1 997) The ITU Radiocommunication Assembly, considering a) that the band 6 700-7 075 MHz is allocated to the fixed-satellite service (FSS), in the space-to-Earth direction, on a primary basis, for the use by feeder links o
3、f non-geostationary satellite networks in the mobile-satellite service (MSS); b) that the band 6 700-7 075 MHz is also allocated to the FSS in the Earth-to-space direction, on a primary basis, and the band 6725-7025 MHz is subject to the Allotment Plan of Appendix 30B of the Radio Regulations (RR) f
4、or geostationary satellite networks; c) that, under No. S22.5A of the RR, the maximum aggregate power flux-density (pfd) produced within i 5“ of the geostationary-satellite orbit (GSO) by a non-geostationary satellite system in the FSS shall not exceed -168 dB(W/m2) in any 4 kHz band; d) that Resolu
5、tion i 15 of the World Radiocommunication Conference (Geneva, 1995) (WRC-95) invites ITU-R to establish a methodology to determine the maximum aggregate power flux-density at the GSO from a non-geostationary satellite network; e) that non-geostationary satellite networks of the mobile-satellite serv
6、ice have orbital and transmission parameters available as specified in 5 A.3 vii) of Annex 1 to Resolution 46 (Rev.WRC-95), recommenh 1 that the methodology given in AMeX 1 shall be followed to determine the maximum level of aggregate power flux-density (dB(W/m2) in any 4 kHz band), at any location
7、within f 5O inclination of the GSO, from the feeder links of a non-geostationary satellite network operating in the band 6 700-7 075 MHz, in the space-to-Earth direction. ANNEX 1 Methodology 1 Description of methodology To calculate the aggregate pfd from a non-geostationary orbiting satellite (non-
8、GSO) network to a single test location at the GSO, computer modelling of the full non-GSO constellation and a test location at the GSO is needed. Basically, noting that in an ordinary situation a GSO satellite will orbit the geostationary orbit with a period of about TGSO = 24 h and that the orbital
9、 period of a non-GSO satellite (TnOn-so) is not necessarily a submultiple of TGS, extensive time-consuming statistical simulations may be needed to assess the worst-case scenario that would lead to the maximum pfd level at the GSO location. STD-ITU-R RECMN SmL25b-ENGL 1997 4855232 0530357 575 = 2 Re
10、c. ITU-R S.1256 A simple and very much less time-consuming simulation can be performed to assess the maximum pfd at any GSO location. Instead of a real orbiting GSO satellite, a fixed test location at the GSO is considered whose orbital position is fmed with respect to a Oxyz Cartesian reference sys
11、tem (see Fig. I) but not with respect to the rotating Earth reference system. With this in mind, since the non-GSO satellites have an orbital period TnOn-so, it implies that the position of the non-GSO satellites, as seen from the fixed GSO test location (see Fig. i), will be repeated at least once
12、every orbital period TnOn-so. Moreover, in the case where the non-GSO satellites are uniformly distributed on each orbital plane, the same geometrical disposition of the non-GSO satellites will be repeated with a period equal to Tnon-s0/Ns (where N, is the number of non-GSO satellites uniformly dist
13、ributed on one plane). With these basic considerations, the aggregate pfd level (aggregated over the visible non-GSO satellites) at the GSO test location will have values that will be repeated within this period. FIGURE 1 GSOInon-GSO constellation geometry to calculate pfd: Ail = Oo t“ The aggregate
14、 pfd can be calculated for each time step and a maximum aggregate pfd, for the chosen GSO test location, can be derived during the simulation period from To to To + Tnons/Ns. The value found for the particular GSO test location in Fig. 1 is not necessarily the maximum pfd level. In order to find the
15、 highest possible maximum aggregate pfd level, the same procedure must be repeated to the other GSO test locations by incrementing the angle AO (see Fig. 2) between the GSO test location and the non-GSO line of nodes. This second iteration will be done for angles of AO between O“ and AO, = 36O0/NP,
16、where Np is the number of non-GSO satellite orbital planes. In cases where Np is even (as per LEO-F and LEO-D) then AOma = 180/Np. The method can also apply to any non-GSO constellation which does not meet the orbital requirements as stated above (e.g. non-uniform satellite distribution, elliptical
17、orbits). In such cases the time simulation will be performed for a period of time equal to the minimum repeatability period of the constellation configuration, which in many cases is equal to the constellation period Tnon-cso. The 5 2 reports all the basic equations needed to arrive at the aggregate
18、 pfd level from a given non-GSO network to a given test location at the GSO and Fig. 3 shows the flow chart for the software implementation of the methodology here described. _ _ STD-ITU-R RECMN S-125b-ENGL 1797 4855232 0530358 403 3 Rec. ITU-R S.1256 FIGURE 2 GSO/non-GSO constellation geometry to c
19、alculate pfd: AC2 it Oo Equatorial plane (,y Aries STD-ITU-R RECMN S-125b-ENGL 1997 4855222 0530359 348 4 Rec. ITU-R S.1256 FIGURE 3 Methodology flow chart Input non-GSO system and GSO test location parameters Initialize simulation parameters and variables: = Oo Mpfd = - 9999.0 dB Start simulation t
20、=O pfd,(An = - 9999.0 dB For each non-GSO satellite calculate d(t), and Cp(t), as in , Steps 1,2 and 3 of 8 2 Calculate the aggregate pfd(t) as in Steps 4 and 5 of 8 2 time step No A NextGSO I An = AR i- 6R I 1 I I Li END - STDSITU-R RECMN S.125b-ENGL 1777 L1855212 05303bU UbT Rec. ITU-R S.1256 5 2
21、Basic simulation steps Step I: Orbital position of the non-GSO satellites FIGURE 4 Non-GSO orbit and reference systems Figure 4 indicates the various parameters that are needed to fully assess at any instant the position of any non-GSO satellite on its orbit. These parameters are referenced in 5 A.3
22、 vii) of Annex 1 to Resolution 46 (Rev.WRC-95): a : semi-major axis, in case of a circular orbit the semi-major axis is constant and equal to the orbit radius; I: inclination of the orbit relative to the equatorial plane Ri : right ascension of the ascending node for the j-th orbital plane, measured
23、 counter-clockwise in the equatorial plane from the direction of the vernal equinox to the point where the satellite makes its south-to-north crossing of the equatorial plane (O“ I sZj 360“) wp : argument of perigee, for a circular orbit, the perigee is equal to the apogee and thus op can be put to
24、O“ mi: initial phase angle of the i-th satellite in its orbital plane at reference time t=O, measured from the point of ascending node (O“ I ai 360“) 8 : true anomaly of the satellite. For a constellation of non- GSO satellites using circular orbits, a and I will be constant and op will be equal to
25、zero, then the variation of the position of each satellite will be defined by R and 8. STD-ITU-R RECMN S.125b-ENGL 1997 m Y855212 05303b13 TTb m 6 Rec. ITU-R S.1256 For a circular orbit, the angular velocity of a satellite is constant, the angular position of a satellite is then equal to its true an
26、omaly and is given by: r + Oi,J e(t), = - 360 T for i = 1 to Ns andj = 1 to Np where N, is the number of satellites in each orbital plane, N, is the number of orbital planes and Tis the orbital period in seconds given by: T=2% Ja3/p where p is the geocentric gravitational constant and is equal to 3.
27、986 E14(m3r2). The various values of LIj will depend on the geometry of the constellation and will be given in the set of elements found in 8 A.3 vii) of Annex 1 to Resolution 46 (Rev.WRC-95). The same principal applies to the values of wi,. Knowing for each satellite its true anomaly e&) and the ri
28、ght ascension of its ascending node Q, its geocentric coordinates are given by: y(t)i, = +cos R cos e(r). . + cos I sin 2 sin e(+, j 1,J +). . = alsin I sin qt). . 1,J LJ (4) (5) The position of the GSO test location with respect to the line of nodes of the non-GSO constellation is determined by AC!
29、 (see 5 1). Hence, in equations (3), (4) and (5) LIj = Rj, 0 + AR, where AC! ranges from O to AC!, (see 8 1) and ni, 0 = for AC! = O. Srep 2: Distance between the non-GSO satellite and the test location at the GSO XGSO, YGSO and ZGSO are the geocentric coordinates of the GSO test location given by:
30、xGSO = aGSO cos IGSO YGSO = o zGSO = aGSO . sin IGSO where: UGSO : semi-major axis of the geostationary orbit (42 164 km) 10 : inclination of the geostationary orbit (-5“ S IGSO I So). These equations remain constant during the simulation since it is simpler to vary Qj in equations (3), (4) and (5)
31、by incrementing the offset AQ. The distance between a non-GSO satellite and the GSO test location can then be calculated using Pythagoras theorem: STD-ITU-R RECMN S-125b-ENGL 1997 4855232 05303b2 932 Rec. ITU-R S.1256 7 Step 3: Calculation of the non-GSO antenna off-axis angle to the test location a
32、t the GSO Fig. 5 shows the geometry, represented in a two-dimensional diagram, of the non-GSO satellite off-axis angle relative to the test location at the GSO. FIGURE 5 Calculation of Pi The non-GSO antenna off-axis angle can be determined using Camots theorem (known also as the “cosine theorem): S
33、tep 4: Calculation of the non-GSO off-axis antenna gain toward the test location at the GSO Taken the off-axis angle calculated in equation (lo), for each visible satellite it is possible to calculate the off-axis antenna gain G(c(t),). However, as seen in Fig. 5, this is only necessary if p(t), is
34、higher than a minimum value of qmin given by: qmin = arc sin (/cr) (1 1) Step 5: The aggregate pfd level can be expressed as: Calculation of the aggregate pfd level towards the GSO test location where: PPak 4& : peak power in the worst 4 kHz band at the input of the non-GSO satellite antenna, assume
35、d constant and equal for all the non-GSO satellites N(0Y : number of visible non-GSO satellites from the GSO test location at the time t. 8 Rec. ITU-R S.1256 3 Two simulation steps are needed to perform the calculation of the maximum aggregate pfd toward the GSO from a non-GSO network, the time step
36、 At and the right ascension step 6Q. Since there is no direct in-line interference from the non-GSO satellites (either they use isoflux low gain antenna or interference comes from the side lobes of the transmitting antenna), various simulations (for LEO-D and LEO-F) have shown that an angular step o
37、f no more than 0.5 is sufficient to get valid results. The calculation steps will then be: Total number of simulation steps and simulation step increments T(s) x 05“ 3 60“ At= 5i2 = 0.5“ The total simulation time for each GSO test location and the total number of GSO test locations are given in 4 1.
