Self interference in non geostationary satellite systems

By early 2000, several non geostationary satellite mobile communication systems will be in operation. The frequency bands allocated by the ITU-R to the Mobile Satellite Service (MSS) being scarce, such systems will be allowed to operate only in narrow frequency bands, not large enough to allow them, in the absence of frequency reuse, to cope with the traffic generated by the total number customers. Therefore, the implementation of frequency reuse will be mandatory. The implementation strategy will have to consider reducing as much as possible the system self-noise generated by the interference between spot beams reusing a common frequency band. The important parameter is the ratio C/I between the useful received carrier power on a mobile-to-satellite or satellite-to-mobile link and the overall contribution at the receiver input of interference power generated by other links. This ratio depends on the system characteristics, such as type of orbits, number of satellites in the constellation, antenna radiation patterns, etc. The paper presents a method for calculating the ratio C/I, and the results obtained for two types of constellations. One is a 48 Low Earth Orbit (LEO) constellation, the other is a 12 Intermediate Circular Orbit (ICO) constellation. The results are displayed in the form of maps with C/I areas about the geographical location of a mobile within which a given value of C/I is guaranteed for a given percentage of time for the uplink or the downlink. These results are of paramount importance for designing subsequently a frequency reuse policy.<
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