1、Rec. ITU-R SA. 1022-1 15 RECOMMENDATION ITU-R SA. 1022-1 METHODOLOGY FOR DETERMINING INTERFERENCE CRITERIA FOR SYSTEMS IN THE EARTH EXPLORATION-SATELLITE AND METEOROLOGICAL-SATELLITE SERVICES (Question ITU-R 138/7) (1 994- 1999) The ITU Radiocommunication Assembly, considering that system designers
2、require guidance on the levels of radio-frequency interference that their systems should a) tolerate; b) meteorological-satellite services should be based on performance objectives for those services; cl that, although specific systems may have performance objectives that differ from those recommend
3、ed for the service, all systems operating in the Earth exploration-satellite and meteorological-satellite services should accommodate interference thresholds greater than or equal to the permissible levels of interference that are recommended for the service; that permissible total levels of interfe
4、rence for systems operating in the Earth exploration-satellite and d) that the methodology used to develop interference criteria for the Earth exploration-satellite and meteorological-satellite services may be applied to a specific system in order to determine the extent to which the permissible tot
5、al levels of interference may be exceeded while meeting performance specifications for the system, recommends 1 exploration-satellite and meteorological-satellite services; 2 that the methodology of Annex 1 be used for the determination of interference thresholds for specific systems, with the provi
6、sion that these thresholds must be greater than or equal to the permissible levels established for the services according to 5 1 above and specified in the relevant Recommendations. that the methodology of Annex 1 be used for the development of interference criteria for the Earth Previous page is bi
7、ank COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling Services16 - 4855212 053b545 Ob9 Rec. ITU-R SA.1022-1 ANNEX I Methodology for determining interference criteria The interference-free margin for the victim system can be defined as: CINO (CIN
8、O )required M= where C/NO is the carrier-to-noise density ratio at the victim receiver, and C C/ NO),.,. is the minimum carrier-to-noise density ratio needed to achieve the required system performance. A4 is conventionally expressed in dB, but in the equations that follow it is convenient not to do
9、so. Defining i, as the interference spectral density at the victim receiver, the system margin in the presence of interference can be written: If the interference is allowed to consume a fraction q of the interference-free margin expressed in dB (Le. “O + Io) and the permissible interference qMd = C
10、/(No + I,),33 - (C/NO)B), then y = M- = spectral density becomes Io = No (M - I). This expression for the permissible interference spectral density is not helpful when the victim system has little margin (MG I) because 10 becomes unrealistically small. Furthermore, it has no meaning when M Mmin Inte
11、rference criteria for specific systems can be calculated from this equation after selecting suitable values for the parameters q and Mmin. a) Single-link communication systems Application of the above methodology to single-link systems (e.g. earth stations receiving sensor data from meteorological s
12、atellites) is straightforward. NO represents the system noise density of the destination receiver, and IO represents the interference density entering that receiver. b Two-link communication systems Application of the above methodology to two-link systems (e.g. earth stations receiving processed dat
13、a from another earth station via a meteorological satellite transponder) is somewhat more complicated. No and Io now represent the composite noise and interference densities at the destination receiver. Therefore they include not only the receive system noise and the interference that enters the rec
14、eiver directly, but also the noise and interference received via the satellite. Determination of interference criteria must include an allocation for sharing the composite permissible interference by each link of the system. Typically it may be assumed that half of the interference is received via the satellite, and half enters the receiver directly, though this allocation may change in some situations. COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling Services
