Terminal location through measures of signal strength of a plurality of radio sources

摘要

In a satellite 10 communications system, each satellite 10 provides an array of overlapping spot beams 30 on the surface of the earth 14, the position of each spot beam 30 being known at any instant. A terminal 48, on the earth 14, listens to all audible spot beams 30 and determines which provide signals above a predetermined level. By mapping which spot beams 30 are audible above the limit, it can rapidly be determined which zone 58 the terminal 48 occupies and thus the position of the terminal 48 on the earth 14. <IMAGE>