Global positioning system tag system
First Claim
1. 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.
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Accused Products
Abstract
A system for determining the location of an object includes an interrogator remote from the object and a transponder located at the object. The interrogator receives GPS signals and transmits pre-positioning data and a tracking signal to the transponder. The pre-positioning data includes pseudorandom noise (PRN) code number, Doppler frequency offset and code phase offset while the tracking signal includes reference time and frequency information. The transponder collects RF samples of at least one of the GPS signals associated with one of the PRN code numbers and correlates 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. The transponder transmits the correlation snapshot to the interrogator and the interrogator determines the pseudorange associated with the GPS signal using the correlation snapshot.
212 Citations
10 Claims
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1. A communication system for determining the position of an object, said system comprising:
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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. - View Dependent Claims (2, 3, 4, 5)
a low pass filter connected to the receiver and adapted to output a voltage, the voltage increasing as a function of time in response to receipt of an RF signal at the resonant frequency of the low pass filter by the receiver; and
a comparator adapted to compare the output voltage to a threshold voltage and trigger the power supply control on when the output voltage is greater than the threshold voltage.
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3. The system of claim 1 wherein the passive standby circuit comprises:
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three passive tuned filters, each connected to the receiver, two receivers adapted to detect continuous wave tone signals and one adapted to measure noise and interference in a band of interest, each further adapted to output a corresponding voltage; and
a pair of comparators adapted to combine the three output voltages, compare the combination to a threshold voltage, and trigger the power supply control on when the result is greater than the threshold voltage.
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4. The system of claim 1 wherein the code replicas are generated by the transponder at regular offsets of some fraction of a C/A code chip.
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5. The system of claim 1 wherein the correlation snapshot comprises a set of fixed-point correlator sums and a range offset in chips.
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6. A method of determining the position of an object comprising:
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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. - View Dependent Claims (7)
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8. 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:
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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. - View Dependent Claims (9, 10)
a low pass filter connected to the receiver and adapted to output a voltage, the voltage increasing as a function of time in response to receipt of an RF signal at a resonant frequency of the low pass filter by the receiver; and
a comparator adapted to compare the output voltage and trigger the power supply control on when the output voltage is greater than the threshold voltage.
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10. The transponder of claim 8 wherein the passive standby circuit comprises:
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three passive tuned filters, each connected to the receiver, two receivers adapted to detect continuous wave tone signals and one adapted to measure noise and interference in a band of interest, each further adapted to output a corresponding voltage; and
a pair of comparators adapted to combine the three output voltages, compare the combination to a threshold voltages, and trigger the power supply control on when the result is greater than the threshold voltage.
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Specification