Patent ID: 6611757
Filing Date: 2003-08-26
Classification: G01C,G01S

Abstract:
A communication system for determining the position of an object, said system comprising:an interrogator remote from the object and adapted to receive GPS signals from GPS satellites; transmit pre-positioning data for each of the received GPS signals including a pseudorandom noise (PRN) code number a Doppler frequency offset and code offset, and a tracking signal including reference time and frequency information; transmit a wake-up signal prior to transmitting the pre-positioning data and the tracking signal, wherein the wake-up signal comprises an unmodulated carrier transmitted at a higher power than the pre-positioning data and the tracking signal; and determine the pseudorange associated with at least one of the GPS signals using a subsequently received correlation snapshot; and a transponder comprising processing circuitry, a two bit sampler, and a power subsystem, wherein the power subsystem comprises, a switch connected to a receiver adapted to receive the wake-up signal; a passive standby circuit normally connected to the receiver through the switch; and a power supply control adapted to provide power to the processing circuitry and to be switched on and off by the passive standby circuit, wherein the transponder is positioned on the object and is adapted to, receive the pre-positioning data and tracking signal; collect RF samples of at least one of the GPS signals associated with one of the PRN code numbers; correlate the RF samples of the GPS signal against code replicas of the GPS signal based on the Doppler frequency offset, code phase offset and reference time and frequency information for that GPS signal to produce the correlation snapshot; and transmit the correlation snapshot to the interrogator.