Patent ID: 6427121
Filing Date: 2002-07-30
Classification: G01C,G01S

Abstract:
A communications system for determining the position of an object using a plurality of GPS signals transmitted by a plurality of GPS sources, said system comprising:an interrogator remote from the object and responsive to the plurality of GPS signals, the interrogator adapted to transmit an RF signal comprising GPS source information and at least one of frequency information and time and code phase information of at least one of the GPS signals; and a transponder comprising a plurality of correlators positioned on the object and responsive to the RF signal and the plurality of GPS signals and adapted to track one of the plurality of GPS signals in response to the GPS source information and the at least one of frequency information and time and code phase information and generate a correlation snapshot by obtaining a noncoherent sum of a plurality of integrations using the plurality of correlators spaced one chip apart, determining the approximate signal peak from the noncoherent sum, prepositioning the correlators at a code phase predicted from the signal peak, and performing an integration with one-eighth chip correlator spacing to produce a plurality of correlator sums, the snapshot comprising a sampled coarse acquisition (C/A) code between the one of the plurality of GPS signals and a replica of the one of the plurality of GPS signals generated by the transponder at regular offsets of some fraction of a CIA code chip, and transmit the snapshot to the interrogator; wherein the interrogator is further adaptedto determine a pseudorange associated with the transponder.