1、ITU-R RECMN*SA* I1018 79 4855232 052317L 757 74 Rec. ITU-R SA.1018 RECOMMENDATION ITU-R SA. 101 8 HYPOTHETICAL REFERENCE SYSTEM FOR SYSTEMS COMPRISING DATA RELAY SATELLITES IN THE GEOSTATIONARY ORBIT AND USER SPACECRAFT IN LOW-EARTH ORBITS (Question ITU-R 117/7) (1994) The ITU-R Radiocommunication A
2、ssembly, considering a) research, Earth exploration and other purposes is essential; that communications between the ground and low-orbiting spacecraft and launch vehicles used for space b) that such communications may be required to be continuous or near continuous; cl surface; that such communicat
3、ions may be required while the spacecraft are passing over specific points on the Earths d) that a land-based station has only limited visibility of a low-orbiting spacecraft; e) that available land-based stations are only able to cover limited portions of any low orbit; 0 more complete coverage; th
4、at it is not economically or practically feasible to extend networks of land-based stations to provide full or 8) station and a low-orbiting spacecraft for more than one-half of its orbit; that a data relay satellite (DRS) in geostationary orbit can provide communications between a single earth h) t
5、hat two such DRSs, suitably located in geostationary orbit, with a wide separation angle, can provide communications between two co-located earth stations and a low-orbiting spacecraft almost continuously, with the exception only of a zone of exclusion (ZOE), above the part of the Earth opposite to
6、these earth stations; j) separate earth stations and a low-orbiting spacecraft; that two such DRSs, suitably placed in geostationary orbit, can provide fully-continuous coverage between two k) user spacecraft by means of time-sharing; that a DRS system comprising two DRSs can serve several user spac
7、ecraft simultaneously, and many more 1) receiving signals from user spacecraft; that a DRS system can also serve additional earth stations, either both transmitting and receiving or only m) that a DRS must be capable of supporting at least four distinct links: - an Earth-to-space link in the forward
8、 direction, from the earth station to the data relay satellite (known as the uplink or the forward feeder link); a space-to-space link in the forward direction, from the data relay satellite to the low orbit spacecraft (known as the forward inter-orbit link); a space-to-space link in the return dire
9、ction, from the low orbit spacecraft to the data relay satellite (known as the return inter-orbit link); and a space-to-Earth link in the return direction, from the data relay satellite to the earth station (known as the downlink or the return feeder link); - - - n) transmitted from and those receiv
10、ed by the data relay satellite, that, for these four links, four separate frequency bands are required, with a guard band between the signals COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling Services ITU-R RECMN*SA. 3038 94 4855232 0523372 893
11、Rec. ITU-R SA.1018 75 recommends 1. 1.1 feeder link); 1.2 forward inter-orbit link); that a hypothetical reference system for data relay satellite systems (as shown in Fig. i) should consist of: an Earth-to-space link in the forward direction, from the earth station to the data relay satellite (the
12、forward a space-to-space link in the forward direction, from the data relay satellite to the low-orbiting spacecraft (the 1.3 inter-orbit link); and a space-to-space link in the return direction, from low-orbiting spacecraft to the data relay satellite (the return 1.4 link); a space-to-Earth link in
13、 the return direction, from the data relay satellite to the earth station (the return feeder HGRE 1 Hypothetical reference system for data relay Satellite systems A: Data Relay Satellite (DRS) B: DRS earth station C: DRS user spacecraft D: forward feeder link E: forward inter-orbit link (IOL) F: ret
14、urn inter-orbit link (IOL) G: return feeder fink COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling Services ITU-R RECMN*SA* 3038 94 m 4855232 0523373 72T m 76 Rec. ITU-R SA.1018 2. carrying out the translation from the baseband to the radio freq
15、uency carrier and the output should: 2. I demodulator on board the user satellite, or in the forward direction, the input to the circuit should correspond to the input of the earth station modulator for the case of a demodulating receiver on board the user spacecraft, correspond to the output of the
16、 2.2 demodulator receiving the return feeder-link signal; for the case of a repeater on board the user spacecraft, correspond to the output of the earth station 3. in the return direction, the input to the circuit should correspond to the input of the user spacecraft modulator carrying out the trans
17、lation from the baseband to the radio-frequency carrier and the output should correspond to the output of the earth station demodulator carrying out the reverse operation; 4. included in this hypothetical reference system. that links between earth stations and the operations, data processing or other earth-based centres should not be COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling Services
