Method and apparatus for locating mobile receivers using a wide area reference network for propagating ephemeris
View Patent ↗A method and apparatus for distribution and delivery of global positioning system (GPS) satellite telemetry data using a communication link between a central site and a mobile GPS receiver. The central site is coupled to a network of reference satellite receivers that send telemetry data from all satellites to the central site. The mobile GPS receiver uses the delivered telemetry data to aid its acquisition of the GPS satellite signal. The availability of the satellite telemetry data enhances the mobile receiver's signal reception sensitivity.
1. A method of improving acquisition sensitivity of a Global Positioning System (GPS) receiver, comprising:
receiving ephemeris from a reference station network;
generating, using the ephemeris, a first reduced search space for a first satellite signal of a first satellite, wherein the first reduced search space includes a reduced pseudo-range search window and a reduced pseudo-range rate search window for the first satellite signal;
increasing an integration time per search bin based on the first reduced search space to generate a first increased integration time per search bin; and
searching for the first satellite signal, within the first reduced search space, using the first increased integration time per search bin.
2. The method of claim 1 , further comprising:
deriving a pseudo-range model from the ephemeris; and
generating, using the pseudo-range model and an approximate position of the GPS receiver, pseudo-range and pseudo-range rate estimates for the first satellite signal.
3. The method of claim 2 , further comprising:
generating the first reduced search space for the first satellite signal using the pseudo-range and pseudo-range rate estimates.
4. A method of improving acquisition sensitivity of a Global Positioning System (GPS) receiver, comprising:
measuring first and second pseudo-ranges, the first and second pseudo-ranges corresponding respectively to first and second satellite signals of first and second satellites;
computing a local time offset and a correlator offset using the first and second measured pseudo-ranges;
estimating a third pseudo-range for a third satellite signal of a third satellite; and
reducing a pseudo-range search window for the third satellite signal using the estimated third pseudo-range.
5. The method of claim 1 , wherein generating, using the ephemeris, the first reduced search space is performed before acquiring any satellite signal.
6. The method of claim 1 , further comprising:
acquiring the first satellite signal; and
adjusting, using the first satellite signal, a local time offset and a correlator offset within the GPS receiver.
7. The method of claim 6 , wherein adjusting the local time offset includes adjusting an offset estimate between a local clock time of the GPS receiver and a real time.
8. The method of claim 6 , further comprising:
generating, using the ephemeris and the adjusted local time offset and correlator offset, a second reduced search space for a second satellite signal of a second satellite; and
searching for the second satellite signal within the second reduced search space.
9. The method of claim 8 , wherein searching for the second satellite signal comprises searching for the second satellite signal using a second increased integration time per search bin.
10. A method of improving acquisition sensitivity of a Global Positioning System (UPS) receiver, comprising:
generating, using a pseudo-range model, a first reduced search space for a first satellite signal of a first satellite;
increasing an integration time per search bin based on the first reduced search space to generate a first increased integration time per search bin; and
searching for the first satellite signal, within the first reduced search space, using the first increased integration time per search bin.
11. The method of claim 10 , further comprising:
receiving the pseudo-range model from a reference station network.
12. The method of claim 10 , wherein the pseudo-range model includes a pseudo-range and a pseudo-range rate for a plurality of satellites including the first satellite.
13. The method of claim 10 , wherein the first reduced search space includes a reduced pseudo-range search window and a reduced pseudo-range rate search window for the first satellite signal.
14. The method of claim 10 , wherein the integration time per search bin is equal to a total available search time divided by a determined number of search bins, and wherein the first increased integration time per search bin is equal to the total available search time.
15. The method of claim 10 , wherein searching for the first satellite signal comprises searching for a first acquired satellite signal by the GPS receiver.
16. The method of claim 10 , further comprising:
receiving ephemeris from a reference station network; and
deriving the pseudo-range model from the ephemeris.
17. The method of claim 4 , wherein computing the local time offset and the correlator offset comprises:
calculating first and second pseudo-range errors for the first and second satellite signals; and
computing the local time offset and the correlator offset using the first and second pseudo-range errors.
18. The method of claim 17 , wherein the first and second pseudo-range errors correspond respectively to first and second differences between expected first and second pseudo-ranges of the first and second satellite signals and the measured first and second pseudo-ranges of the first and second satellite signals.
19. The method of claim 4 , further comprising:
increasing an integration time per search bin for the third satellite signal based on the reduced pseudo-range search window to generate an increased integration time per search bin; and
searching for the third satellite signal, within the reduced pseudo-range search window, using the increased integration tune per search bin.
20. The method of claim 4 , wherein the first and second satellite signals represent the two highest signal strength satellite signals detected by the GPS receiver.