Importance

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Abstract

Methods and apparatus are disclosed which allow many satellites (A1-M, B1-N) in a plurality of Systems (A, B) to use the same radio frequencies (f1-n) so long as there is no interference between radio signals. The methods compute times (t) when satellite radio signals (32, 36) have overlapping reception areas or 'footprints' (30, 35) on the Earth's surface (E) whereby a user's reception or transmission of a message would be interfered unless different frequencies (f1-n) are used for the 'competing' signals. The methods use a timing algorithm that does not allow two satellites (Ai, Bi) which are 'visible' at the same point on the Earth (E) to transmit on the same frequency (fi). In one preferred embodiment, a timing algorithm (48) produces a radio frequency use schedule (49) computed on the Earth from orbital data maintained in an ephemeris (46) of satellite communications systems (A, B) which communicate on frequencies (f1-n) giving rise to interfering radio signals. The radio frequency use schedule (49) is updated frequently, and is transmitted to and stored on board each satellite in System A (A1-M). System A satellites (A1-M) are then operated in accordance with the radio frequency use schedule (49).

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First Claim