Multipath rejection using cooperative GPS receivers

1. A computer program product comprising a non-transitory machine-readable medium storing instructions that, when executed by at least one programmable processor of a reference-receiver that includes a beacon-signal receiver and a transceiver, cause the at least one programmable processor to perform operations comprising:

receiving, at the transceiver of the reference-receiver, receiver-distance information from one or more unknown-location receivers using at least one inter-receiver communication link, the receiver-distance information including an indication of the distance between the reference-receiver and the one or more unknown-location receivers, and distances between the unknown-location receivers determined using at least one inter-receiver communication link, wherein the unknown-location receivers and the reference-receiver form an ad hoc antenna system;

receiving at the transceiver of the reference-receiver, beacon-distance information from the one or more unknown-location receivers, the beacon-distance information including an indication of the distance between one or more beacons and the one or more unknown-location-receivers;

receiving, at the beacon-signal receiver the reference-receiver, one or more signals from the one or more beacons;

determining, using the at least one programmable processor, based on one or more positions of the one or more beacons, one or more expected delays of a receipt of one or more beacon-to-receiver signals at each receiver, including each unknown-location receiver and the reference-receiver;

generating, using the at least one programmable processor, based on the one or more determined expected delays, a correlation function representative of cross-correlations between known beacon-to-receiver distances and received beacon-to-receiver distances;

identifying, using the at least one programmable processor, based on the generating, a maximum value of the correlation function; and

searching, using the at least one programmable processor, locations of the unknown-location receivers and selecting locations for the one or more unknown-location receivers based on the identified maximum value of the correlation function; and

determining, using the at least one programmable processor of the reference-receiver, based on the selecting, the locations of the one or more unknown-location receivers relative to the reference-receiver based on the received receiver-distance information from the one or more unknown-location receivers, and the received beacon-distance information from the one or more unknown-location receivers.

2. The computer program product as in claim 1 , wherein the operations further comprise:

computing a local-coordinate system for the reference-receiver and the one or more unknown-location-receivers centered on the reference-receiver.

3. The computer program product as in claim 2 , wherein the operations further comprise:

defining a sphere having a surface area on which individual ones of the one or more unknown-location receivers are positioned, the radius of the sphere based on the receiver-distance information received by the reference-receiver from individual ones of the one or more unknown-location receivers and the center of the sphere based on the local-coordinate system.

4. The computer program product as in claim 3 , wherein the operations further comprise:

determining a plane on which the reference-receiver and at least some of the one or more unknown-location receivers reside to provide the radius of a circle on which the one or more unknown-location receivers are positioned relative to the reference-receiver.

5. The computer program product as in claim 4 , wherein the operations further comprise:

determining a range of beacon-to-unknown-location-receiver distances based on the beacon-distance information received from the unknown-location receivers and constrained by the circle.

6. The computer program product method as in claim 1 , wherein the operations further comprise:

computing, at the one or more unknown-location-receivers, the one or more correlation coefficients based on the ranges of beacon-to-unknown-location-receiver distances for the one or more unknown-location receivers; and,

receiving, at the reference-receiver, the one or more correlation coefficients from the one or more unknown-location-receivers.

7. The computer program product as in claim 5 , wherein the operations further comprise:

computing, at the one or more unknown-location-receivers, the one or more correlation coefficients based on the ranges of beacon-to-unknown-location-receiver distances for the one or more unknown-location receivers; and,

receiving, at the reference-receiver, the one or more correlation coefficients from the one or more unknown-location-receivers.

8. The computer program product as in claim 7 , wherein the operations further comprise:

filtering, at the reference-receiver, the one or more correlation coefficients based on constraints provided by the determined radii of the circles on which the one or more unknown-location-receivers are located to provide filtered correlation coefficients; and,

computing, at the reference-receiver, the likely locations of the one or more unknown-location-receivers relative to the reference-receiver based on the filtered correlation coefficients.

9. The computer program product as in claim 8 , wherein computing the likely location of the one or more unknown-location receivers relative to the reference-receiver includes applying each of the filtered correlation coefficients to a location algorithm to converge to a solution.

10. The computer program product as in claim 1 , wherein the receiver-distance information is based on one or more wireless communications between the reference-receiver and the one or more unknown-location receivers.

11. The computer program product of claim 1 , wherein the received beacon-distance information from the one or more unknown-location receivers comprises one or more correlation coefficients for individual ones of the one or more beacons based on the one or more signals received at the unknown-location-receivers from the one or more beacons, each beacon emitting a signal containing a code specific to that beacon.

12. The computer program product as in claim 1 , wherein the operations further comprise:

receiving geographic location information at one of the reference-receiver or the one or more unknown-location-receivers; and,

determining the geographic location of the reference-receiver and/or the one or more unknown-location-receivers based on the received geographic location information and the relative location of the reference-receiver to the one or more unknown-location receivers.

13. The computer program product as in claim 1 , wherein the reference-receiver is a GPS receiver.

14. A method for determining the positions of one or more unknown-location-receivers at a reference-receiver that includes a beacon-signal receiver and a transceiver and configured to receive signals from one or more beacons, the method implemented by at least one programmable processor forming at least one computing device, the method comprising:

receiving, at the transceiver of the reference-receiver, receiver-distance information from one or more unknown-location receivers using at least one inter-receiver communication link, the receiver-distance information including an indication of the distance between the reference-receiver and the one or more unknown-location receivers, and distances between the unknown-location receivers determined using at least one inter-receiver communication link, wherein the unknown-location receivers and the reference-receiver form an ad hoc antenna system;

receiving, at the transceiver of the reference-receiver, beacon-distance information from the one or more unknown-location receivers, the beacon-distance information including an indication of the distance between one or more beacons and the one or more unknown-location-receivers;

receiving, at the beacon-signal receiver of the reference-receiver, one or more signals from the one or more beacons;

determining, by at least one programmable processor, based on one or more positions of the one or more beacons, one or more expected delays of a receipt of one or more beacon-to-receiver signals at each receiver, including each unknown-location receiver and the reference-receiver;

generating, by at least one programmable processor, based on the one or more determined expected delays, a correlation function representative of cross-correlations between known beacon-to-receiver distances and received beacon-to-receiver distances;

identifying, by at least one programmable processor, based on the generating, a maximum value of the correlation function;

searching, by at least one programmable processor, locations of the unknown-location receivers and selecting locations for the one or more unknown-location receivers based on the identified maximum value of the correlation function; and

determining, by at least one programmable processor, based on the selecting, the locations of the one or more unknown-location receivers relative to the reference-receiver based on the received receiver-distance information from the one or more unknown-location receivers, and the received beacon-distance information from the one or more unknown-location receivers.

15. The method as in claim 14 , further comprising:

computing a local-coordinate system for the reference-receiver and the one or more unknown-location-receivers centered on the reference-receiver;

defining a sphere having a surface area on which individual ones of the one or more unknown-location receivers are positioned, the radius of the sphere based on the receiver-distance information received by the reference-receiver from individual ones of the one or more unknown-location receivers and the center of the sphere based on the local-coordinate system;

determining a plane on which the reference-receiver and at least some of the one or more unknown-location receivers reside to provide the radius of a circle on which the one or more unknown-location receivers are positioned relative to the reference-receiver; and,

determining a range of beacon-to-unknown-location-receiver distances based on the beacon-distance information received from the unknown-location receivers and constrained by the circle.

16. The method as in claim 14 , further comprising:

computing, at the one or more unknown-location-receivers, the one or more correlation coefficients based on the ranges of beacon-to-unknown-location-receiver distances for the one or more unknown-location receivers; and, receiving, at the reference-receiver, the one or more correlation coefficients from the one or more unknown-location-receivers.

17. The method as in claim 16 , further comprising:

filtering, at the reference-receiver, the one or more correlation coefficients based on constraints provided by the determined radii of the circles on which the one or more unknown-location-receivers are located to provide filtered correlation coefficients;

computing, at the reference-receiver, the likely locations of the one or more unknown-location-receivers relative to the reference-receiver based on the filtered correlation coefficients.

18. A system comprising:

a beacon-signal receiver configured to receive and decode signals received from one or more beacons having a known location, the signals from the one or more beacons comprising beacon-identifying information and a time at which the signals were emitted;

a transceiver configured to transmit and/or receive signals from one or more unknown-location receivers, the signals from the one or more unknown location receivers including:

beacon-distance information, the beacon-distance information including an indication of the distance between one or more beacons;

distances between the unknown-location receivers, the information determined using at least one inter-receiver communication link; and,

receiver-distance information, the receiver-distance information including an indication of the distance between a reference-receiver and the one or more unknown-location receivers received using at least one inter-receiver communication link, wherein the unknown-location receivers and the reference-receiver form an ad hoc antenna system; and,

at least one programmable processor of the reference-receiver, configured to perform the following operations:

determine, based on one or more positions of the one or more beacons, one or more expected delays of a receipt of one or more beacon-to-receiver signals at each receiver, including each unknown-location receiver and the reference-receiver;

generate, based on the one or more determined expected delays, a correlation function representative of cross-correlations between known beacon-to-receiver distances and received beacon-to-receiver distances;

identify, based on the generating, a maximum value of the correlation function;

search locations of the unknown-location receivers and select locations for the one or more unknown-location receivers based on the identified maximum value of the correlation function; and

determine, based on the selecting, the locations of the one or more unknown-location receivers relative to the reference-receiver based on the received receiver-distance information from the one or more unknown-location receivers, and the received beacon-distance information from the one or more unknown-location receivers.

19. The system as in claim 18 , wherein:

the one or more unknown-location receivers are configured to compute the one or more correlation coefficients based on the ranges of beacon-to-unknown-location-receiver distances for the one or more unknown-location receivers;

the transceiver is configured to receive the one or more correlation coefficients from the one or more unknown-location-receivers; and,

the at least one programmable processor is configured to:

filter the one or more correlation coefficients based on constraints provided by the determined radii of the circles on which the one or more unknown-location-receivers are located to provide filtered correlation coefficients; and,

compute the likely locations of the one or more unknown-location-receivers relative to the reference-receiver based on the filtered correlation coefficients.