Global positioning system tag system

A method of determining the position of an object comprising:

• receiving, at a location remote from the object, GPS signals from GPS satellites;
• transmitting, at the location remote from the object, pre-positioning data for each of the received GPS signals including a pseudorandom noise (PRN) code number, a Doppler frequency offset and code phase offset, and a tracking signal including reference time and frequency information;
• receiving, at the object, the pre-positioning data and tracking signal;
• collecting at the object, using a two bit sampler, RF samples of at least one of the GPS signals associated with one of the PRN code numbers;
• correlating, using a plurality of correlators located at the object, 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 a correlation snapshot, wherein correlating comprises,
• obtaining a noncoherent sum of a plurality of integrations using the plurality of correlators spaced one chip apart;
• determining an approximate signal peak from the noncoherent sum;
• prepositioning the correlators at a code phase predicted from the signal peak;
• and
• performing an integration to produce a plurality of correlator sums;
• transmitting, at the object, the correlation snapshot;
• receiving, at the location remote from the object, the correlation snapshot;
• and
• determining, at the location remote from the object, a pseudorange associated with at least one of the GPS signals using the correlation snapshot.

A transponder adapted to be associated with an object for use in providing data to an interrogator remote form the object, the data for use in determining the location of the object, said transponder comprising:

• a transceiver adapted to receive signals from the interrogator, the signals including a wake-up signal, pre-positioning data for GPS signals received by the interrogator including a pseudorandom noise (PRN) code number, a Doppler frequency offset and code phase offset, and a tracking signal including reference time and frequency information;
• a plurality of correlators comprising at least one two bit sampler, wherein the plurality of correlators is adapted to collect RF samples of at least one of the GPS signals associated with one of the PRN code numbers and correlate the RF sample 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 a correlation snapshot;
• processing circuitry;
• a power subsystem adapted to maintain the processing circuitry in a power-off mode prior to receipt of the wake-up signal, the power subsystem comprising,
• 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 interrogator is further adapted to transmit a wake-up signal prior to transmitting the pre-positioning data and the tracking signal, and the transceiver is further adapted to transmit the correlation snapshot to the interrogator.