Network-centric determination of node processing delay

• US 9,645,225 B2
• Filed: 11/19/2009
• Issued: 05/09/2017
• Est. Priority Date: 11/21/2008
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Aggarwal, Alok, Naguib, Ayman Fawzy, Sridhara, Vinay
• Primary Examiner(s): Hsu, Alpus H
• Assistant Examiner(s): LUO, ANTHONY L
• Application Number:
  US12/622,356
• Publication Number:
  US 20100128637A1
• Time in Patent Office: 2,728 Days
• Field of Search: 370328, 370338, 455456
• CPC Class Codes: G01S 5/021 Calibration, monitoring or correction G01S5/0252 takes precedence
• CPC Class Codes: G01S 5/0284 Relative positioning
• CPC Class Codes: G01S 5/06 Position of source determined by co-ordinating a plurality of position lines defined by path-difference measurements G01S5/12 takes precedence
• CPC Class Codes: H04L 67/52 specially adapted for the location of the user terminal
• CPC Class Codes: H04W 4/021 Services related to particular areas, e.g. point of interest [POI] services, venue services or geofences
• CPC Class Codes: H04W 64/00 Locating users or terminals or network equipment for network management purposes, e.g. mobility management

Abstract

Apparatus and methods are directed to calibrating a delay within a wireless access point for determining a position of a mobile station. One method includes receiving an initial packet at an eavesdropping device, receiving a response packet, sent by another entity, at the eavesdropping device, computing a time difference based upon the packet arrival times, and providing the time difference to a position determination entity. Another method includes providing a request to appropriate eavesdropping devices to send information, receiving, from each appropriate eavesdropping device, a time difference which represents a difference in a time of arrival of a packet transmitted by the wireless access point and a time of arrival of a packet transmitted by the mobile station, determining a processing delay estimate based upon the time differences, and determining a position of the mobile station based upon the processing delay estimate and the received time differences.

Claims

1. A method of preparing data for determining a position of a mobile station, comprising:

receiving information from a plurality of eavesdropping devices, the information from each respective one of the plurality of eavesdropping devices comprising signal strength information of a respective signal received at the respective one of the plurality of eavesdropping devices from each of the mobile station and a wireless access point;

selecting a subset of the plurality of eavesdropping devices based at least in part on the signal strength information, the subset of the plurality of eavesdropping devices comprising at least three of the plurality of eavesdropping devices;

obtaining information, from each respective eavesdropping device of the subset of the plurality of eavesdropping devices, the information comprising an indication of a time difference representing a difference in a time of arrival at the respective eavesdropping device of a respective initial packet sent by the mobile station and a time of arrival of a respective response packet sent by the wireless access point responsive to the respective initial packet;

determining a refined processing delay based upon the indications of the time differences from the subset of the plurality of eavesdropping devices by combining the information received from each of the subset of the plurality of eavesdropping devices, the information received comprises processing delay estimates computed by each of the plurality of eavesdropping devices, wherein each processing delay estimate represents an estimated amount of time that the wireless access point took to process a respective initial packet from the mobile station and to generate the respective response packet; and

determining the position of the mobile station based upon the refined processing delay and the time differences from the subset of the plurality of eavesdropping devices.

2. The method according to claim 1, further comprising:

measuring a first arrival time corresponding to the initial packet; and

measuring a second arrival time corresponding to the response packet;

wherein preparing the indication of the time difference comprises computing a difference between the second arrival time and the first arrival time.

3. The method according to claim 1, wherein the eavesdropping device comprises a wireless access point.

4. The method according to claim 1, wherein obtaining the information further comprises:

sending a request to the plurality of eavesdropping devices for the information.

5. The method according to claim 1, further comprising:

bounding the refined processing delay based upon the time differences from the subset of the plurality of eavesdropping devices.

6. The method according to claim 5, wherein the refined processing delay is bound by a triangle inequality.

7. The method of claim 1, further comprising providing the position of the mobile station to a position determination entity.

8. The method according to claim 1, further comprising:

measuring a first arrival time corresponding to the initial packet; and

measuring a second arrival time corresponding to the response packet;

wherein prepare the indication of the time difference comprises computing a difference between the second arrival time and the first arrival time; and

wherein the eavesdropping device comprises a wireless access point.

9. The method of claim 1, wherein at least one of the plurality of eavesdropping devices is a mobile station operating in a peer-to-peer networking mode, and wherein the information from each respective at least one of the plurality of eavesdropping devices includes position information associated with a position of the respective at least one of the plurality of eavesdropping devices.

10. The method of claim 1, wherein determining a refined processing delay based upon the indications of the time differences from the subset of the plurality of eavesdropping devices by combining the information received from each of the subset of the plurality of eavesdropping devices comprises determining a processing delay estimate for each of the indications of the time differences by estimating an amount of time that the wireless access point took to process a respective initial packet from the mobile station and to generate the respective response packet and by combining the processing delay estimates to determine the refined processing delay.

11. A method for determining a position of a mobile station, comprising:

receiving information from a plurality of eavesdropping devices, the information from each respective one of the plurality of eavesdropping devices comprising signal strength information of a respective signal received at the respective one of the plurality of eavesdropping devices from each of the mobile station and the wireless access point;

selecting a subset of the plurality of eavesdropping devices based at least in part on the signal strength information, the subset of the plurality of eavesdropping devices comprising at least three of the plurality of eavesdropping devices;

sending a request to each eavesdropping device of the subset of the plurality of eavesdropping devices for an indication of a time difference which represents a difference in a time of arrival at the respective eavesdropping device of a response packet sent by a wireless access point and a time of arrival at the respective eavesdropping device of an initial packet sent by the mobile station;

receiving, only from each of the subset of the plurality of eavesdropping devices, the indication of the time difference;

determining a refined processing delay estimate associated with the wireless access point based upon the indications of the time differences from the subset of the plurality of eavesdropping devices by combining the information received from each of the subset of the plurality of eavesdropping devices, the information received comprises processing delay estimates computed by each of the plurality of eavesdropping devices, wherein each processing delay estimate represents an estimated amount of time that the wireless access point took to process a respective initial packet from the mobile station and to generate the respective response packet; and

determining the position of the mobile station based upon the refined processing delay estimate and the time differences from the subset of the plurality of eavesdropping devices.

12. The method according to claim 11, wherein the processing delay estimate is bound by a triangle inequality.

13. The method according to claim 11, wherein determining the processing delay estimate further comprises:

determining a relative geometry of the mobile station and the wireless access point relative to one of the subset of the plurality of eavesdropping devices;

determining a range for the processing delay estimate by using the time differences from the subset of the plurality of eavesdropping devices in a triangle inequality; and

selecting a value from the range, as a refined processing delay, based upon the relative geometry.

14. The method according to claim 13, wherein selecting the value from the range further comprises selecting the value from an upper end of the range;

wherein the relative geometry is substantially collinear; and

wherein the wireless access point is between the mobile station and the eavesdropping device, or the mobile station is between the wireless access point and the eavesdropping device.

15. The method according to claim 13, wherein selecting the value from the range further comprises selecting the value from a lower end of the range;

wherein the relative geometry is substantially collinear, and

wherein the eavesdropping device is between the mobile station and the wireless access point.

16. The method according to claim 11, wherein determining the processing delay estimate further comprises:

receiving, from each of the plurality of eavesdropping devices, a signal strength value associated with the initial packet sent by the mobile station; and

bounding a distance between each of the plurality of eavesdropping devices and the mobile station based upon the signal strength values.

17. The method according to claim 11, wherein determining the processing delay estimate further comprises:

determining a range for a distance between the mobile station and each of the subset of the plurality of eavesdropping devices based upon signal strength values from the plurality of eavesdropping devices;

setting an estimated distance between the mobile station and each of the subset of the plurality of eavesdropping devices as a midpoint of the range;

calculating the position of the mobile station using trilateration based upon the estimated distance;

calculating a first distance between the mobile station and the wireless access point, and a second distance between the mobile station and each of the subset of the plurality of eavesdropping devices, based upon the calculated position of the mobile station; and

refining the processing delay estimate based upon the calculated first and second distances and the time differences.

18. The method according to claim 11, wherein determining the processing delay estimate further comprises:

calculating a first distance estimate between the mobile station and the wireless access point based upon a previous position of the mobile station;

calculating a second distance estimate between the mobile station and the subset of the plurality of eavesdropping devices based upon the previous position of the mobile station;

determining processing delay estimates based upon the first distance estimate and each second distance estimate; and

refining a processing delay estimate by combining the processing delay estimates.

19. The method according to claim 11, wherein determining the position of the mobile station further comprises:

adjusting each time difference using the processing delay estimate;

determining distance differences by subtracting a distance between the wireless access point and each of the subset of the plurality of eavesdropping device from the adjusted time differences; and

performing multilateration using the distance differences to estimate the position of the mobile station.

20. An apparatus for preparing data for determining a position of a mobile station, comprising:

a wireless transceiver;

a processor coupled to the wireless transceiver; and

a memory coupled to the processor, wherein the memory stores executable instructions and data for causing the processor to;

receive information from a plurality of eavesdropping devices, the information from each respective one of the plurality of eavesdropping devices comprising signal strength information of a respective signal received at the respective one of the plurality of eavesdropping devices from each of the mobile station and the wireless access point;

select a subset of the plurality of eavesdropping devices based at least in part on the signal strength information, the subset of the plurality of eavesdropping devices comprising at least three of the plurality of eavesdropping devices;

obtain information, from each respective eavesdropping device of the subset of the plurality of eavesdropping devices, the information comprising an indication of a time difference representing a difference in a time of arrival at the respective eavesdropping device of a respective initial packet sent by the mobile station and a time of arrival of a respective response packet sent by the wireless access point responsive to the respective initial packet;

determine a refined processing delay based upon the indications of the time differences from the subset of the plurality of eavesdropping devices by combining the information received from each of the subset of the plurality of eavesdropping devices, the information received comprises processing delay estimates computed by each of the plurality of eavesdropping devices, wherein each processing delay estimate represents an estimated amount of time that the wireless access point took to process a respective initial packet from the mobile station and to generate the respective response packet; and

determine the position of the mobile station based upon the refined processing delay and the time differences from the subset of the plurality of eavesdropping devices.

21. The apparatus according to claim 20, wherein the instructions further cause the processor to enable each of the plurality of eavesdropping devices to:

measure a first arrival time corresponding to the initial packet, and

measure a second arrival time corresponding to the response packet,

wherein the instructions for causing the processor to enable only each of the subset of the plurality of eavesdropping devices to prepare the indication of the time difference comprises instructions for causing the processor to enable only each of the plurality of eavesdropping devices to compute a difference between the second arrival time and the first arrival time.

22. The apparatus according to claim 20, wherein each of the plurality of eavesdropping devices comprises a wireless access point.

23. The apparatus according to claim 20, wherein the instructions to obtain the information further comprise instructions to cause the processor to:

send a request to the plurality of eavesdropping devices.

24. The apparatus according to claim 20, wherein the instructions further cause the processor to:

bound the refined processing delay based upon the time differences from the subset of the plurality of eavesdropping devices.

25. The apparatus according to claim 24 wherein the refined processing delay is bound by a triangle inequality.

26. The apparatus of claim 20, the instructions configured to cause the processor to determine a refined processing delay based upon the indications of the time differences from the subset of the plurality of eavesdropping devices by combining the information received from each of the subset of the plurality of eavesdropping devices further comprise instructions configured to cause the processor to determine a processing delay estimate for each of the indications of the time differences by estimating an amount of time that the wireless access point took to process a respective initial packet from the mobile station and to generate the respective response packet and by combining the processing delay estimates to determine the refined processing delay.

27. An apparatus for determining a position of a mobile station, comprising:

a network interface;

a processor coupled to the network interface; and

a memory coupled to the processor, wherein the memory stores executable instructions and data for causing the processor to;

receive information from a plurality of eavesdropping devices, the information from each respective one of the plurality of eavesdropping devices comprising signal strength information of a respective signal received at the respective one of the plurality of eavesdropping devices from each of the mobile station and a wireless access point;

select a subset of the plurality of eavesdropping devices based at least in part on the signal strength information, the subset of the plurality of eavesdropping devices comprising at least three of the plurality of eavesdropping devices;

send a request to each eavesdropping device of the subset of the plurality of eavesdropping devices for an indication of a time difference which represents a difference in a time of arrival at the respective eavesdropping device of a response packet sent by a wireless access point and a time of arrival at the respective eavesdropping device of an initial packet sent by the mobile station;

receive, from only each of the subset of the plurality of eavesdropping devices, the indication of the time difference;

determine a refined processing delay estimate associated with the wireless access point based upon the indications of the time differences from the subset of the plurality of eavesdropping devices by combining the information received from each of the subset of the plurality of eavesdropping devices, the information received comprises processing delay estimates computed by each of the plurality of eavesdropping devices, wherein each processing delay estimate represents an estimated amount of time that the wireless access point took to process a respective initial packet from the mobile station and to generate the respective response packet; and

determine the position of the mobile station based upon the refined processing delay estimate and the time differences from the subset of the plurality of eavesdropping devices.

28. The apparatus according to claim 27, wherein processing delay estimate is bound by a triangle inequality.

29. The apparatus according to claim 27, wherein the instructions to determining the processing delay estimate comprises instructions to:

determine a relative geometry of the mobile station and the wireless access point relative to one of the subset of the plurality of eavesdropping devices,

determine a range for the processing delay estimate by using the time differences from the plurality of eavesdropping devices in a triangle inequality, and

select a value from the range, as a refined processing delay, based upon the relative geometry.

30. The apparatus according to claim 29, the instructions to select the value from the range further comprises instructions to select the value from an upper end of the range;

wherein the relative geometry is substantially collinear; and

wherein the wireless access point is between the mobile station and an eavesdropping device of the plurality of eavesdropping devices, or the mobile station is between the wireless access point and an eavesdropping device of the subset of the plurality of eavesdropping devices.

31. The apparatus according to claim 29, the instructions to select the value from the range further comprises instructions to select the value from a lower end of the range;

wherein the relative geometry is substantially collinear, and

wherein an eavesdropping device of the subset of the plurality of eavesdropping devices is between the mobile station and the wireless access point.

32. The apparatus according to claim 27, wherein the instructions to determine the processing delay estimate causes the processor to:

receive, from each of the subset of the plurality of eavesdropping devices, a signal strength value associated with the initial packet sent by the mobile station; and

bound a distance between each of the subset of the plurality of eavesdropping devices and the mobile station based upon the signal strength values.

33. The apparatus according to claim 27, wherein the instructions to determine the processing delay estimate causes the processor to:

determine a range for a distance between the mobile station and each of the subset of the plurality of eavesdropping devices based upon signal strength values from the plurality of eavesdropping devices,

set an estimated distance between the mobile station and each of the subset of the plurality of eavesdropping devices as a midpoint of the range,

calculate the position of the mobile station using trilateration based upon the estimated distance,

calculate a first distance between the mobile station and the wireless access point, and a second distance between the mobile station and each of the subset of the plurality of eavesdropping devices, based upon the calculated position of the mobile station, and

refine the processing delay estimate based upon the calculated first and second distances and the time differences.

34. The apparatus according to claim 27, wherein the instructions to determine the processing delay estimate causes the processor to:

calculate a first distance estimate between the mobile station and the wireless access point based upon a previous position of the mobile station,

calculate a second distance estimate between the mobile station and the subset of the plurality of eavesdropping devices based upon the previous position of the mobile station,

determine processing delay estimates based upon the first distance estimate and each second distance estimate, and

refine a processing delay estimate by combining the processing delay estimates.

35. The apparatus according to claim 27, wherein the instructions to determine the position of the mobile station causes the processor to:

adjust each time difference using the processing delay estimate,

determine distance differences by subtracting a distance between the wireless access point and each eavesdropping device of the subset of the plurality of eavesdropping devices from the adjusted time differences, and

perform multilateration using the distance differences to estimate the position of the mobile station.

36. An apparatus for preparing data for determining a position of a mobile station, comprising:

means for receiving information from a plurality of eavesdropping devices, the information from each respective one of the plurality of eavesdropping devices comprising signal strength information of a respective signal received at the respective one of the plurality of eavesdropping devices from each of the mobile station and a wireless access point;

means for selecting a subset of the plurality of eavesdropping devices based at least in part on the signal strength information, the subset of the plurality of eavesdropping devices comprising at least three of the plurality of eavesdropping devices;

means for obtaining information, from each respective eavesdropping device of the subset of the plurality of eavesdropping devices, the information comprising an indication of time difference representing a difference in a time of arrival at the respective eavesdropping device of a respective initial packet sent by the mobile station and a time of arrival of a respective response packet sent by the wireless access point responsive to the respective initial packet;

means for determining a refined processing delay based upon the indications of the time differences from the subset of the plurality of eavesdropping devices by combining the information received from each of the subset of the plurality of eavesdropping devices, the information received comprises processing delay estimates computed by each of the plurality of eavesdropping devices, wherein each processing delay estimate represents an estimated amount of time that the wireless access point took to process a respective initial packet from the mobile station and to generate the respective response packet; and

means for determining the position of the mobile station based upon the refined processing delay and the time differences from the subset of the plurality of eavesdropping devices.

37. The apparatus according to claim 36, further comprising:

means for measuring a first arrival time corresponding to the initial packet; and

means for measuring a second arrival time corresponding to the response packet;

wherein the means for preparing the indication of the time difference comprises means for determining a difference between the second arrival time and the first arrival time.

38. The apparatus of claim 36, wherein the means for determining a refined processing delay based upon the indications of the time differences from the subset of the plurality of eavesdropping devices by combining the information received from each of the subset of the plurality of eavesdropping devices comprise means for determining a processing delay estimate for each of the indications of the time differences by estimating an amount of time that the wireless access point took to process a respective initial packet from the mobile station and to generate the respective response packet and by combining the processing delay estimates to determine the refined processing delay.

39. An apparatus for determining a position of a mobile station, comprising:

means for receiving information from a plurality of eavesdropping devices, the information from each respective one of the plurality of eavesdropping devices comprising signal strength information of a respective signal received at the respective one of the plurality of eavesdropping devices from each of the mobile station and a wireless access point;

means for selecting a subset of the plurality of eavesdropping devices based at least in part on the signal strength information, the subset of the plurality of eavesdropping devices comprising at least three of the plurality of eavesdropping devices;

means for sending a request to each eavesdropping device of the subset of the plurality of eavesdropping devices for an indication of a time difference which represents a difference in a time of arrival at the respective eavesdropping device of a response packet sent by a wireless access point and a time of arrival at the respective eavesdropping device of an initial packet sent by the mobile station;

means for receiving, from only each of the subset of the plurality of eavesdropping devices, the indication of a time difference;

means for determining a refined processing delay estimate associated with the wireless access point based upon the indications of the time differences from the subset of the plurality of eavesdropping devices by combining the information received from each of the subset of the plurality of eavesdropping devices, the information received comprises processing delay estimates computed by each of the plurality of eavesdropping devices, wherein each processing delay estimate represents an estimated amount of time that the wireless access point took to process a respective initial packet from the mobile station and to generate the respective response packet; and

means for determining the position of the mobile station based upon the refined processing delay estimate and the time differences from the subset of the plurality of eavesdropping devices.

40. The apparatus according to claim 39, wherein the means for determining the processing delay estimate further comprises:

means for determining a relative geometry of the mobile station and the wireless access point relative to one of the subset of the plurality of eavesdropping devices;

means for determining a range for the processing delay estimate by using the time differences from the subset of the plurality of eavesdropping devices in a triangle inequality; and

means for selecting a value from the range, as a refined processing delay, based upon the relative geometry.

41. The apparatus according to claim 40, wherein the means for selecting the value from the range comprises selecting the value from an upper end of the range;

wherein the relative geometry is substantially collinear, and

wherein the wireless access point is between the mobile station and the eavesdropping device, or the mobile station is between the wireless access point and the eavesdropping device.

42. The apparatus according to claim 39, wherein the means for determining the processing delay estimate further comprises:

means for receiving, from each of the subset of the plurality of eavesdropping devices, a signal strength value associated with the initial packet sent by the mobile station; and

means for bounding a distance between each of the plurality of eavesdropping devices and the mobile station based upon the signal strength values.

43. The apparatus according to claim 39, wherein the means for determining the processing delay estimate further comprises:

means for determining a range for a distance between the mobile station and each of the subset of the plurality of eavesdropping devices based upon received signal strength values from the plurality of eavesdropping devices;

means for setting an estimated distance between the mobile station and each of the subset of the plurality of eavesdropping devices as a midpoint of the range;

means for calculating the position of the mobile station using trilateration based upon the estimated distance;

means for calculating a first distance between the mobile station and the wireless access point, and a second distance between the mobile station and each of the subset of the plurality of eavesdropping devices, based upon the calculated position of the mobile station; and

means for refining the processing delay estimate based upon the calculated first and second distances and the time differences.

44. The apparatus according to claim 39, wherein the means for determining the processing delay estimate further comprises:

means for calculating a first distance estimate between the mobile station and the wireless access point based upon a previous position of the mobile station;

means for calculating a second distance estimate between the mobile station and the subset of the plurality of eavesdropping devices based upon the previous position of the mobile station;

means for determining processing delay estimates based upon the first distance estimate and each second distance estimate; and

means for refining a processing delay estimate by combining the processing delay estimates.

45. The apparatus according to claim 39, wherein the means for determining the position of the mobile station further comprises:

means for adjusting each time difference using the processing delay estimate;

means for determining distance differences by subtracting a distance between the wireless access point and each eavesdropping device from the adjusted time differences; and

means for performing multilateration using the distance differences to estimate the position of the mobile station.

46. A non-transitory machine-readable medium for preparing data for determining a position of a mobile station, comprising instructions, which, when executed by a machine, cause the machine to perform operations, the instructions comprising:

instructions to receive information from a plurality of eavesdropping devices, the information from each respective one of the plurality of eavesdropping devices comprising signal strength information of a respective signal received at the respective one of the plurality of eavesdropping devices from each of the mobile station and a wireless access point;

instructions to select a subset of the plurality of eavesdropping devices based at least in part on the signal strength information, the subset of the plurality of eavesdropping devices comprising at least three of the plurality of eavesdropping devices;

instructions to obtain information from each respective eavesdropping device of the subset of the plurality of eavesdropping devices, the information comprising an indication of time difference representing a difference in a time of arrival at the respective eavesdropping device of a respective initial packet sent by the mobile station and a time of arrival of a respective response packet sent by the wireless access point responsive to the respective initial packet;

instructions to determine a refined processing delay based upon the indications of the time differences from the plurality of eavesdropping device, the instructions configured to cause the machine to determine the refined processing delay comprising instructions configured to cause the machine to combine the information received from each of the subset of the plurality of eavesdropping devices, the information received comprises processing delay estimates computed by each of the plurality of eavesdropping devices, wherein each processing delay estimate represents an estimated amount of time that the wireless access point took to process a respective initial packet from the mobile station and to generate the respective response packet; and

instructions to determine the position of the mobile station based upon the refined processing delay and the time differences from the plurality of eavesdropping devices.

47. The non-transitory machine-readable medium of claim 46, wherein the instructions to determine a refined processing delay based upon the indications of the time differences from the plurality of eavesdropping device, the instructions configured to cause the machine to determine the refined processing delay comprise instructions configured to cause the machine to combine the information received from each of the subset of the plurality of eavesdropping devices further comprise instructions to determine a processing delay estimate for each of the indications of the time differences by estimating an amount of time that the wireless access point took to process a respective initial packet from the mobile station and to generate the respective response packet and instructions configured to cause the machine to combine the processing delay estimates to determine the refined processing delay.

48. A non-transitory machine-readable medium for preparing data for determining a position of a mobile station, comprising instructions, which, when executed by a machine, cause the machine to perform operations, the instructions comprising:

instructions to receive information from a plurality of eavesdropping devices, the information from each respective one of the plurality of eavesdropping devices comprising signal strength information of a respective signal received at the respective one of the plurality of eavesdropping devices from each of the mobile station and a wireless access point;

instructions to select a subset of the plurality of eavesdropping devices based at least in part on the signal strength information, the subset of the plurality of eavesdropping devices comprising at least three of the plurality of eavesdropping devices;

instructions to send a request to each eavesdropping device of the subset of the plurality of eavesdropping devices for an indication of a time difference which represents a difference in a time of arrival at the respective eavesdropping device of a response packet sent by a wireless access point and a time of arrival at the respective eavesdropping device of an initial packet sent by the mobile station;

instructions to receive, only from each of the subset of the plurality of eavesdropping devices, the indication of the time difference;

instructions to determine a refined processing delay estimate associated with the wireless access point based upon the indications of the time differences from the subset of the plurality of eavesdropping devices, the instructions configured to cause the machine to determine the refined processing delay comprising instructions configured to cause the machine to combine the information received from each of the subset of the plurality of eavesdropping devices, the information received comprises processing delay estimates computed by each of the plurality of eavesdropping devices, wherein each processing delay estimate represents an estimated amount of time that the wireless access point took to process a respective initial packet from the mobile station and to generate the respective response packet; and

instructions to determine the position of the mobile station based upon the processing delay estimate and the time differences from the subset of the plurality of eavesdropping devices.

49. The non-transitory machine-readable medium according to claim 48, wherein the instructions to determine the processing delay estimate further comprise:

instructions to determine a relative geometry of the mobile station and the wireless access point relative to one of the subset of the plurality of eavesdropping devices;

instructions to determine a range for the processing delay estimate by using the time differences from the subset of the plurality of eavesdropping devices in a triangle inequality; and

instructions to select a value from the range, as the refined processing delay, based upon the relative geometry.

50. The non-transitory machine-readable medium according to claim 49, wherein the instructions to select the value from the range further comprises:

selecting the value from an upper end of the range;

wherein the relative geometry is substantially collinear, and

wherein the wireless access point is between the mobile station and the eavesdropping device, or the mobile station is between the wireless access point and the eavesdropping device.

51. The non-transitory machine-readable medium according to claim 48, wherein the instructions to determine the processing delay estimate further comprise:

instructions to receive, from each of the subset of the plurality of eavesdropping devices, a signal strength value associated with the initial packet sent by the mobile station; and

instructions to bound a distance between each of the subset of the plurality of eavesdropping devices and the mobile station based upon the signal strength values.

52. The non-transitory machine-readable medium according to claim 48, wherein the instructions to determine the processing delay estimate further comprise:

instructions to determine a range for a distance between the mobile station and each of the subset of the plurality of eavesdropping devices based upon received signal strength values from the plurality of eavesdropping devices;

instructions to set an estimated distance between the mobile station and each of the subset of the plurality of eavesdropping devices as a midpoint of the range;

instructions to calculate the position of the mobile station using trilateration based upon the estimated distances;

instructions to calculate a first distance between the mobile station and the wireless access point, and a second distance between the mobile station and each of the subset of the plurality of eavesdropping devices, based upon the calculated position of the mobile station; and

instructions to refine the processing delay estimate based upon the calculated first and second distances and the time differences.

53. The non-transitory machine-readable medium according to claim 48, wherein the instructions to determine the processing delay estimate further comprise:

instructions to calculate a first distance estimate between the mobile station and the wireless access point based upon a previous position of the mobile station;

instructions to calculate a second distance estimate between the mobile station and the subset of the plurality of eavesdropping devices based upon the previous position of the mobile station;

instructions to determine processing delay estimates based upon the first distance estimate and each second distance estimate; and

instructions to refine a processing delay estimate by combining the processing delay estimates.

54. The non-transitory machine-readable medium according to claim 48, wherein the instructions to determine the position of the mobile station further comprise:

instructions to adjust each time difference using the processing delay estimate;

instructions to determine distance differences by subtracting a distance between the wireless access point and each eavesdropping device from the adjusted time differences; and

instructions to perform multilateration using the distance differences to estimate the position of the mobile station.