Determination of differential forward link calibration in LTE networks for positioning

1. A method of using signal times of arrival measurements from a plurality of mobile devices, the method comprising at a location server:

receiving from each mobile device of the plurality of mobile devices an estimated location of the mobile device, wherein the estimated location is based, at least in part, upon Satellite Positioning System (SPS) signals received by the mobile device from SPS satellites;

receiving from said each mobile device of the plurality of mobile devices a determined difference between times of arrival of a first reference signal from a first base station and a second reference signal from a second base station, wherein the determined difference between times of arrival is as determined by said each mobile device, and wherein the first and second base stations are part of a Long Term Evolution (LTE) network;

determining a plurality of transmission time offsets by determining, for each of said mobile device of the plurality of mobile devices, a transmission time offset of signals from the first and second base stations based, at least in part, upon a first distance and upon a second distance and upon the determined difference between times of arrival,

wherein the first distance is a distance between an estimated location of the first base station and the estimated location of said each mobile device of the plurality of mobile devices, and

wherein the second distance is a distance between an estimated location of the second base station and the estimated location of said each mobile device of the plurality of mobile devices;

combining the plurality of transmission time offsets to determine an adjusted transmission time offset; and

determining an estimated location of a second mobile device based, at least in part, upon a second determined difference between times of arrival at the second mobile device of a third reference signal from the first base station and a fourth reference signal from the second base station and upon the adjusted transmission time offset,

wherein the second mobile device is not any one of the plurality of mobile devices.

2. The method of claim 1 , wherein the receiving of the estimated location of the mobile device and the receiving of the determined difference between times of arrival are initiated in response to receipt by said each mobile device of a message from the location server requesting the estimated location of said each mobile device and for the determined difference between times of arrival.

3. The method of claim 1 , wherein the receiving of the estimated location of the mobile device and the receiving of the determined difference between times of arrival are initiated in response to receipt of a user input selection at said each mobile device.

4. The method of claim 1 , further comprising:

receiving from said each mobile device of the plurality of mobile devices a request for positioning assistance data;

transmitting to said each mobile device of the plurality of mobile devices the positioning assistance data,

wherein the estimated location of said each mobile device of the plurality of mobile devices is based, at least in part, on the received positioning assistance data.

5. The method of claim 1 , further comprising:

transmitting to said each mobile device of the plurality of mobile devices a request for measurements by said each mobile device; and

transmitting to said each mobile device of the plurality of mobile devices positioning assistance data descriptive of aspects of at least the first and the second base stations.

6. The method of claim 5 , wherein said positioning assistance data comprises the estimated location of the first base station and the estimated location of the second base station.

7. The method of claim 1 , wherein the first reference signal comprises one of a first positioning reference signal or a first carrier reference signal, and wherein the second reference signal comprises one of a second positioning reference signal or a second carrier reference signal.

8. The method of claim 1 wherein the combining of the plurality of transmission time offsets comprises one or more of computing a mean value of the plurality of transmission time offsets, computing a median value of the plurality of transmission time offsets, computing a center of distribution of the plurality of transmission time offsets, computing a least squares fit of the plurality of transmission time offsets, or computing a weighted combination of the plurality of transmission time offsets where outliers are deweighted.

9. A location server configured for communicating with a plurality of mobile devices via a communication network, the location server comprising:

a network interface to transmit messages to and receive messages from the communication network; and

one or more processors configured to:

obtain from each mobile device of the plurality of mobile devices an estimated location of the mobile device, wherein the estimated location is based, at least in part, upon Satellite Positioning System (SPS) signals received by the mobile device from SPS satellites;

obtain from said each mobile device of the plurality of mobile devices a determined difference between times of arrival of a first reference signal from a first base station and a second reference signal from a second base station based, at least in part, on a measured time of arrival of the first reference signal and a measured time of arrival of the second reference signal, wherein the first and second base stations are part of a Long Term Evolution (LTE) network;

determine a plurality of transmission time offsets by determining, for each of said mobile device of the plurality of mobile devices, a transmission time offset of signals from the first and second base stations based, at least in part, upon a first distance and upon a second distance and upon the determined difference between times of arrival,

wherein the first distance is a distance between an estimated location of the first base station and the estimated location of said each mobile device of the plurality of mobile devices, and

wherein the second distance is a distance between an estimated location of the second base station and the estimated location of said each mobile device of the plurality of mobile devices;

combine the plurality of transmission time offsets to determine an adjusted transmission time offset, and

determine an estimated location of a second mobile device based, at least in part, upon a second determined difference between times of arrival at the second mobile device of a third reference signal from the first base station and a fourth reference signal from the second base station and upon the adjusted transmission time offset,

wherein the second mobile device is not any one of the plurality of mobile devices.

10. The location server of claim 9 , wherein the one or more processors are further configured to:

initiate transmission to said each mobile device of the plurality of mobile devices a request for measurements by the mobile device; and

initiate transmission to said each mobile device of the plurality of mobile devices positioning assistance data descriptive of aspects of at least the first and the second base stations.

11. The location server of claim 10 , wherein said positioning assistance data comprises the estimated locations of the first and the second base stations.

12. The location server of claim 9 , wherein the first reference signal comprises one of a first positioning reference signal or a first carrier reference signal, and wherein the second reference signal comprises one of a second positioning reference signal or a second carrier reference signal.

13. The location server of claim 9 wherein the one or more processors are configured to combine the plurality of transmission time offsets by one or more of computing a mean value of the plurality of transmission time offsets, computing a median value of the plurality of transmission time offsets, computing a center of distribution of the plurality of transmission time offsets, computing a least squares fit of the plurality of transmission time offsets, or computing a weighted combination of the plurality of transmission time offsets where outliers are deweighted.

14. A non-transitory storage medium comprising machine-readable code stored thereon which is executable by a location server configured for communicating with a plurality of mobile devices via a communication network, the code comprising:

code to obtain from each mobile device of the plurality of mobile devices an estimated location of the mobile device, wherein the estimated location is based, at least in part, upon Satellite Positioning System (SPS) signals received by the mobile device from SPS satellites;

code to obtain from said each mobile device of the plurality of mobile devices a determined difference between times of arrival of a first reference signal from a first base station and a second reference signal from a second base station based, at least in part, on a measured time of arrival of the first reference signal and a measured time of arrival of the second reference signal, wherein the first and second base stations are part of a Long Term Evolution (LTE) network;

code to determine a plurality of transmission time offsets by determining, for each of said mobile device of the plurality of mobile devices, a transmission time offset of signals from the first and second base stations based, at least in part, upon a first distance and upon a second distance and upon the determined difference between times of arrival,

wherein the first distance is a distance between an estimated location of the first base station and the estimated location of said each mobile device of the plurality of mobile devices, and

wherein the second distance is a distance between an estimated location of the second base station and the estimated location of said each mobile device of the plurality of mobile devices;

code to combine the plurality of transmission time offsets to determine an adjusted transmission time offset; and

code to determine an estimated location of a second mobile device based, at least in part, upon a second determined difference between times of arrival at the second mobile device of a third reference signal from the first base station and a fourth reference signal from the second base station and upon the adjusted transmission time offset,

wherein the second mobile device is not any one of the plurality of mobile devices.

15. The non-transitory storage medium of claim 14 , wherein said instructions are further executable to:

code to initiate transmission to said each mobile device of the plurality of mobile devices a request for measurements by the mobile device; and

code to initiate transmission to said each mobile device of the plurality of mobile devices positioning assistance data descriptive of aspects of at least the first and the second base stations.

16. The non-transitory storage medium of claim 15 , wherein said positioning assistance data comprises the estimated locations of the first and second base stations.

17. The non-transitory storage medium of claim 14 , wherein the first reference signal comprises one of a first positioning reference signal or a first carrier reference signal, and wherein the second reference signal comprises one of a second positioning reference signal or a second carrier reference signal.

18. The non-transitory storage medium of claim 14 wherein the code to combine the plurality of transmission time offsets comprises one or more of code to compute a mean value of the plurality of transmission time offsets, code to compute a median value of the plurality of transmission time offsets, code to compute a center of distribution of the plurality of transmission time offsets, code to compute a least squares fit of the plurality of transmission time offsets, or code to compute a weighted combination of the plurality of transmission time offsets where outliers are deweighted.

19. An apparatus at a location server configured for communicating with a plurality of mobile devices via a communication network, the apparatus, comprising:

means for receiving from each mobile device of the plurality of mobile devices an estimated location of the mobile device, wherein the estimated location is based, at least in part, upon Satellite Positioning System (SPS) signals received by the mobile device from SPS satellites;

means for receiving from said each mobile device of the plurality of mobile devices a determined difference between times of arrival of a first reference signal from a first base station and a second reference signal from a second base station, wherein the determined difference between times of arrival is as determined by said each mobile device, and wherein the first and second base stations are part of a Long Term Evolution (LTE) network;

means for determining a plurality of transmission time offsets by determining, for each of said mobile device of the plurality of mobile devices, a transmission time offset of signals from the first and second base stations based, at least in part, upon a first distance and upon a second distance and upon the determined difference between times of arrival,

wherein the first distance is a distance between an estimated location of the first base station and the estimated location of said each mobile device of the plurality of mobile devices, and

wherein the second distance is a distance between an estimated location of the second base station and the estimated location of said each mobile device of the plurality of mobile devices;

means for combining the plurality of transmission time offsets to determine an adjusted transmission time offset; and

means for determining an estimated location of a second mobile device based, at least in part, upon a second determined difference between times of arrival at the second mobile device of a third reference signal from the first base station and a fourth reference signal from the second base station and upon the adjusted transmission time offset,

wherein the second mobile device is not any one of the plurality of mobile devices.

20. The apparatus of claim 19 , wherein the means for receiving the estimated location of the mobile device and the means for receiving the determined difference between times of arrival include means for initiating the receiving of the estimated location of the mobile device and for initiating the receiving of the determined difference between times of arrival in response to receipt by said each mobile device of a message from the location server requesting the estimated location of said each mobile device and for the determined difference between times of arrival.

21. The apparatus of claim 19 , wherein the means for receiving the estimated location of the mobile device and the means for receiving the determined difference between times of arrival include means for initiating the receiving of the estimated location of the mobile device and for initiating the receiving of the determined difference between times of arrival in response to receipt of a user input selection at said each mobile device.

22. The apparatus of claim 19 , further comprising:

means for receiving from said each mobile device of the plurality of mobile devices a request for positioning assistance data; and

means for transmitting to said each mobile device of the plurality of mobile devices the positioning assistance data,

wherein the estimated location of said each mobile device of the plurality of mobile devices is based, at least in part, on the received positioning assistance data.

23. The apparatus of claim 19 , further comprising:

means for transmitting to said each mobile device of the plurality of mobile devices a request for measurements by said each mobile device; and

means for transmitting to said each mobile device of the plurality of mobile devices positioning assistance data descriptive of aspects of at least the first and the second base stations.

24. The apparatus of claim 23 , wherein said positioning assistance data comprises the estimated location of the first base station and the estimated location of the second base station.

25. The apparatus of claim 19 , wherein the first reference signal comprises one of a first positioning reference signal or a first carrier reference signal, and wherein the second reference signal comprises one of a second positioning reference signal or a second carrier reference signal.

26. The apparatus of claim 19 wherein the means for combining the plurality of transmission time offsets comprises one or more of means for computing a mean value of the plurality of transmission time offsets, means for computing a median value of the plurality of transmission time offsets, means for computing a center of distribution of the plurality of transmission time offsets, means for computing a least squares fit of the plurality of transmission time offsets, or means for computing a weighted combination of the plurality of transmission time offsets where outliers are deweighted.