Processing a satellite navigation signal whilst reducing the prospect of erroneous position readings being determined

摘要

A system for determining a geo-location comprises a satellite constellation 30 operable to transmit first and second signals; a receiver 40 operable to receive the first and second signal, the receiver further comprising: a signal detector detecting the first signal, but incapable of detecting the second signal; a local timing means generating a local timing signal; means for determining a geo-location from the first signal, the geo-location information describing a locus of possible locations of the receiver; and means for transmitting the geo-location information, at least a sample of the first and second signal, and the local timing information. A remote location fixer 80 receives a signal from the receiver 40, detects one or more of the second signals from the samples, and determines a location fix from the second signals by correlation with knowledge of the second signals, the correlation being focussed on the local timing information. Other embodiments include: a computer network comprising a plurality of communications broadcasters, and a receiver operable to detect signals transmitted from the communications broadcasters; an apparatus for verifying locally determined geo-locations; and an apparatus for determining if a geo-location device has been subject to an attack.