1、Rec. ITU-R S.1418 1 RECOMMENDATION ITU-R S. 141 8 METHOD FOR CALCULATING SINGLE ENTRY CARRIER-TO-INTERFERENCE RATIOS FOR LINKS IN INTER-SATELLITE SERVICE USING GEOSTATIONARY ORBIT (Question ITU-R 239/4) (1999) The ITU Radiocommunication Assembly, considering a) that Question ITU-R 23914 for the Worl
2、d Radiocommunication Conference (Geneva, 1997) (WRC-97) calls for “very urgent and priority studies” to determine sharing criteria and coordination guidelines for systems utilizing the inter-satellite service (ISS); b) cl space segments of networks; that there is extensive planned use of the ISS bet
3、ween satellites in the geostationary orbit (GSO); that GSO ISS networks typically require wide bandwidths, and typically form high data rate mnk links for the d) that high data rate trunk lines must have high availability; e) that a method is required to evaluate the level of interference between su
4、ch systems, recommends 1 that the method described in Annex 1 be used to calculate C/Z ratios for inter-satellite links in the GSO. 2 Item Rec. ITU-R S.1418 Symbol ANNEX 1 Longitude of receiver (degrees) Method for calculating single entry C/I for links of ISS using GSO Vrx 1 Inputs The required inp
5、uts for the calculation of single entry C/Z are shown in Table 1, Transmit power (dBW) Transmit gain (dBi) TABLE 1 Inputs for methodology for calculation of single entry CIZ p, G,+x Receive gain (dBi) Receive antenna diameter (m)(I) I Centre frequency (MH) I .f, I G, rx 4,rx Longitude of receiver (d
6、egrees) Longitude of transmitter (degrees) I Longitude of transmitter (degrees) I v, I Irx Transmit gain (dBi) Transmit bandwidth (MHz) I Transmit bandwidth (MHz) I B, I Gi,+x Bi Transmit antenna diameter (m)(I) I Interfering system I di, +x I Transmit power (dBW) I pi I I Receive gain (dBi) I Gi.rx
7、 I 2 Method 2.1 Carrier power To calculate carrier power, it is necessary to calculate the range loss between the satellites. The range between victim satellites is given by: R = 2rGs0 sin( I Vtx - Vrxl I /2) km where: V, : longitude of the victim transmitter V, : longitude of the victim receiver rG
8、S0 : radius of the GSO (42 164 km) R : range between satellites (km). Rec. ITU-R S.1418 The free space loss is given by: Lfs = 20 log f + 2010g R + 32.45 dB 3 where f is the carrier frequency (MHz). The carrier power is then computed: C = Pv + G,tx - Lfs + G,rx dB 2.2 Interference power To calculate
9、 interference power, it is necessary to calculate the range loss between the satellites. The range from the interfering transmitter to the victim receiver is given by: R = 2rso sin( I It, - Vrx 1/2) km where: Z, : longitude of the interfering transmitter V, : longitude of the victim receiver rGS0 :
10、radius of the GSO (42 164 km) R : range between satellites (km). The free space loss is given by: Lfs = 20 log f + 201Og R + 32.45 dB where f is the carrier frequency (MHz). To facilitate calculation of off-boresight angles, the coordinates of all satellites are transformed from polar coordinates to
11、 the rectangular coordinate system within the equatorial plane, with the origin at geocentre. The x axis component of each satellite is given by: S, = rGS0 cos(1ongitude) and the y axis component is given by: Sy = rGS0 sin(1ongitude) where S is the position of the satellite in question, and rGS0 is
12、the GSO radius (42 164 km). If A is the vector from satellite 1 to satellite 2, and B is the vector from satellite 1 to satellite 3, the angle (O) between A and B (measured at satellite 1) is given by: as illustrated in Fig. 1. IA1 and IBI are the magnitudes of A and B, and AB is the inner product o
13、f the two vectors. For example, for A and B expressed in rectangular coordinates then: AB = A,B, + AYBY + AzBz 4 Rec. ITU-R S.1418 FIGURE 1 Angle between satellites For example, if the antenna discrimination at the victim receiver is required, let A represent the vector from the victim receiver to t
14、he victim transmitter, and let B represent the vector from the victim receiver to the interfering transmitter. The resulting angle 8 is input to an appropriate antenna pattern model to compute the antenna discrimination. The bandwidth reduction factor is given by: lo otherwise The interference power
15、 is then computed: I = 9 + i,tx(etx - fi + Gv,rx(erx - LBW dB where 8, and 8, are the off-boresight angles at the interfering transmitting and victim receiving ends, respectively, and Gi,fx(8fx) and G,rx(8rx) are the off-boresight gains of the interfering transmitting and victim receiving antennas.
16、3 Sample computation of C/I for the GSO ISS The antenna pattern model used for this example is Recommendation ITU-R S.672 (Annex i), with first side lobe of 20 dB below maximum gain. The inputs for this example are shown in Table 2. It is assumed that BdB, = 1. Rec. ITU-R S.1418 Transmit gain (dBi)
17、Receive gain (dBi) TABLE 2 49 GhtX 49 G, * Inputs for example Longitude of receiver (degrees) Longitude of transmitter (degrees) Transmit power (dBW) 5 10 Irx 2 Itx 13 Pi Item Transmit gain (dBi) Receive gain (dBi) I Symbol I 55.7 Gi, tx 55.7 Gi.rx I Centre frequency (HZ) I 60x lo9 I f, I Transmit a
18、ntenna diameter (m) I Victim system I 1 di, tx I Longitude of receiver (degrees) I 12 I vrx I Receive gain (dB) Interference power (dBW) CII (dB) I Longitude of transmitter (degrees) I 0 I vtx I 29.1 G,rx (0,) -127.5 I 31.8 I Transmit power (dBW) I 13 I P, I I Receive antenna diameter (m) I 0.75 I d
19、v * I TABLE 3 C/Z calculation Symbol Carrier power Transmit power (dBW) Transmit antenna gain (dBi) 49.1 I Free space loss (dB) I -206.9 I L I I Receive antenna gain (dBi) I 49.1 I G,rx I I Carrier power (dBW) I -95.7 I c I I Inte ference power I I Transmit power (dBW) I 13.0 I Pi I I Transmit off-angle (degrees) I 1.0 I Qtx I I Transmit gain (dB) I 35.7 I Gitx (0,) I I Free space loss (dB) I -205.3 I L I I Receive off-angle (degrees) I 1.0 I e, I
