Pairwise measurements for improved position determination

• US 9,213,093 B2
• Filed: 12/21/2012
• Issued: 12/15/2015
• Est. Priority Date: 12/21/2012
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Do, Ju-Yong, Venkatraman, Sai Pradeep
• Primary Examiner(s): Miah, Liton
• Application Number:
  US13/725,078
• Publication Number:
  US 20140179340A1
• Time in Patent Office: 1,089 Days
• US Class Current: 1/1
• CPC Class Codes: G01S 13/765 with exchange of information between interrogator and responder
• CPC Class Codes: G01S 5/021 Calibration, monitoring or correction G01S5/0252 takes precedence

Abstract

Approaches for enhancing range-based position determination using pairwise error detection and compensation are provided. One method for enhancing a position estimate of a first node may include performing measurements at the first node using a signal received from a second node, and receiving measurements from the second node. The received measurements may be performed at the second node using a signal provided by the first node. The method may further include determining pairwise comparisons of the performed measurements and the received measurements, and compensating the measurements performed at the first node, based on the pairwise comparisons, for estimating the position of the first node. Systems and apparatuses for performing the various position determination methods are further presented.

Claims

1. A method for enhancing a position estimate of a first node, comprising:

performing, at the first node, a first range measurement of a distance between the first node and a second node using a signal received from the second node;

receiving, from the second node, a result of a second range measurement of the distance between the first node and the second node based on a signal received from the first node at the second node;

determining a pairwise comparison by comparing the first range measurement to the result of the second range measurement;

determining a bias based on the pairwise comparison; and

generating a compensation estimate for compensating subsequent range measurements performed at the first node, based on the bias.

2. The method of claim 1, wherein:

performing the first range measurement comprises measuring a Round Trip Time (RTT) between the first node and the second node;

determining the pairwise comparison comprises comparing the RTT measured at the first node to the result of an RTT measurement determined at the second node;

determining a bias comprises determining an RTT bias; and

generating the compensation estimate comprises generating an RTT compensation estimate to remove the RTT bias.

3. The method of claim 1, wherein:

performing the first range measurement comprises measuring a Received Signal Strength Indicator (RSSI) at the first node based on the signal received from the second node;

determining the pairwise comparison comprises comparing the RSSI measured at the first node to the result of an RSSI determined at the second node for a same wireless channel;

determining a bias comprises determining an RSSI bias; and

generating the compensation estimate comprises generating an RSSI compensation estimate to remove the RSSI bias.

4. The method of claim 2, further comprising:

determining the position of the first node based on the RTT compensation estimate.

5. The method of claim 2, wherein at least one of the first node or the second node is a calibrated device.

6. The method of claim 2, wherein the first node is a first access point (AP) and the second node is a second AP.

7. The method of claim 2, wherein the first node is an access point (AP) and the second node is a mobile station.

8. The method of claim 2, wherein the first node is a first mobile station and the second node is a second mobile station.

9. The method of claim 2, further comprising:

determining a measurement error threshold;

discarding measurements that exceed the measurement error threshold; and

adjusting the RTT bias based on remaining measurements.

10. The method of claim 3, wherein the second node is calibrated and the first node is not calibrated, further comprising:

receiving calibration information from the second node; and

compensating the RTT measurement based only on the calibration information from the second node.

11. The method of claim 10, further comprising:

storing the RTT bias and/or the RSSI bias; and

using the RTT bias and/or the RSSI bias in subsequent measurement determinations with other nodes.

12. The method of claim 2, wherein the first node and second node have calibration information, further comprising:

determining a confidence level of the calibration information for each node; and

weighting the RTT bias based on the confidence level of each node.

13. A first node which determines an enhanced position estimate using pairwise measurements, 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;

perform a first range measurement of a distance between the first node and a second node using a signal received from the second node,

receive, from the second node, a result of a second range measurement of the distance between the first node and the second node based on a signal received from the first node at the second node,

determine a pairwise comparison by comparing the first range measurement to the second range measurement,

determine a bias based on the pairwise comparison, and

generate a compensation estimate for compensating subsequent range performed at the first node, based on the bias.

14. The first node of claim 13, wherein the memory comprises further instructions which cause the processor to:

perform the first range measurement by measuring a Round Trip Time (RTT) between the first node and the second node,

determine the pairwise comparison by comparing the RTT measured at the first node to the result of an RTT measurement determined at the second node,

determine the bias by determining an RTT bias, and

generate a compensation estimate by generating an RTT compensation estimate to remove the RTT bias.

15. The first node of claim 14, wherein the memory comprises further instructions which cause the processor to:

perform the first range measurement by measuring a Received Signal Strength Indicator (RSSI) at the first node based on the signal received from the second node;

determine the pairwise comparison by comparing the RSSI measured at the first node to an RSSI determined at the second node for a same wireless channel;

determine the bias by determining an RSSI bias; and

generate a compensation estimate by generating an RSSI compensation estimate to remove the RSSI bias.

16. The first node of claim 14, wherein the memory comprises further instructions which cause the processor to:

determine the position of the first node based on the RTT compensation estimate.

17. The first node of claim 14, wherein at least one of the first node or the second node is a calibrated device.

18. The first node of claim 14, wherein the first node is a first access point (AP) and the second node is a second AP.

19. The first node of claim 14, wherein the first node is an access point (AP) and the second node is a mobile station.

20. The first node of claim 14, wherein the first node is a first mobile station and the second node is a second mobile station.

21. The first node of claim 14, wherein the memory comprises further instructions which cause the processor to:

determine a measurement error threshold,

discard RTT measurements that exceed the measurement error threshold, and

adjust the RTT bias based on remaining measurements.

22. The first node of claim 15, wherein the second node is calibrated and the first node is not calibrated, and further wherein the memory comprises further instructions which cause the processor to:

receive calibration information from the second node, and

compensate the RTT measurement based only on the information from the second node.

23. The first node of claim 22, wherein the memory comprises further instructions which cause the processor to:

store the RTT bias and/or the RSSI bias, and

use the RTT bias and/or the RSSI bias in subsequent measurement determinations with other nodes.

24. The first node of claim 14, wherein the first node and second node have calibration information, further wherein the memory comprises further instructions which cause the processor to:

determine a confidence level of the calibration information for each node, and

weight the RTT bias based on the confidence level of each node.

25. An apparatus for enhancing a position estimate, comprising:

means for performing, at a first node, a first range measurement of a distance between the first node and a second node using a signal received from the second node;

means for receiving, from the second node, a result of a second range measurement of the distance between the first node and the second node based on a signal received from the first node at the second node;

means for determining a pairwise comparison by comparing the first range measurement to the second range measurement;

means for determining a bias based on the pairwise comparison; and

means for generating a compensation estimate for compensating subsequent range measurements performed at the first node, based on the bias.

26. The apparatus of claim 25, wherein:

means for performing a first range measurement comprises means for measuring a Round Trip Time (RTT) between the first node and the second node; and

means for determining a pairwise comparison comprises means for comparing the RTT measured at the first node to an RTT measurement determined at the second node;

means for determining a bias comprises means for determining an RTT bias; and

means for generating the compensation estimate comprises means for generating an RTT compensation estimate to remove the RTT bias.

27. The apparatus of claim 26, further comprising:

means for determining a measurement error threshold;

means for discarding measurements that exceed the measurement error threshold; and

means for adjusting the RTT bias based on remaining measurements.

28. The apparatus of claim 26, wherein the second node is calibrated and the first node is not calibrated, further comprising:

means for receiving calibration information from the second node; and

means for compensating the RTT measurement based only on the information from the second node.

29. A non-transitory computer-readable medium comprising instructions, which, when executed by a processor, cause the computer to perform operations, the instructions comprising:

instructions to perform a first range measurement of a distance between a first node and a second node using a signal received from the second node;

instructions to receive, from the second node, a second range measurement of the distance between the first node and the second node based on a signal received from the first node at the second node;

instructions to determine a pairwise comparison by comparing the first range measurement to the second range measurement;

instructions to determine a bias based on the pairwise comparison; and

instructions to generate a compensation estimate for compensating subsequent range measurements performed at the first node, based on the bias.

30. The non-transitory computer-readable medium of claim 29, further comprising:

instructions to perform the first range measurement by measuring a Round Trip Time (RTT) between the first node and the second node;

instructions to determine the pairwise comparison by comparing the RTT measured at the first node to an RTT measurement determined at the second node;

instructions to determine the bias by determining an RTT bias; and

instructions to generate a compensation estimate by generating an RTT compensation estimate to remove the RTT bias.

31. A method for enhancing a position determination performed by a server, comprising:

receiving from a first node a first range measurement of a distance between the first node and a second node;

receiving from a second node a second range measurement of the distance between the first node and the second node based on a signal received from the first node at the second node;

determining a pairwise comparison by comparing the first range measurement to the second range measurement;

determining a bias of the first node based on the pairwise comparison; and

generating a compensation estimate for compensating subsequent range measurements received from the first node based on the bias.

32. The method of claim 31, wherein:

receiving the first range measurement comprises receiving a first Round Trip Time (RTT) measurement from the first node, wherein the first RTT measurement is measured on a common wireless channel that is common to the first node and the second node;

receiving the second range measurement comprises receiving a second RTT measurement from the second node, wherein the second RTT measurement is measured on the common wireless channel that is common to the first node and the second node; and

determining the pairwise comparison comprises subtracting the second RTT measurement received from the second node from the first RTT measurement received from the first node.

33. The method of claim 31, wherein:

receiving the first range measurement comprises receiving a first Received Signal Strength Indicator (RSSI) measurement from the first node, wherein the first RSSI measurement is measured on a common wireless channel that is common to the first node and the second node;

receiving the second range measurement comprises receiving a second RSSI measurement from the second node, wherein the second RSSI measurement is measured on the common wireless channel that is common to the first node and the second node; and

determining the pairwise comparison comprises subtracting the RSSI measurement received from the second node from the RSSI measurement received from the first node.

34. The method of claim 33, wherein the pairwise comparison further comprises:

calculating statistics of the first range measurement;

determining uncertainties for the common wireless channel based on the statistics of the first range measurement; and

removing outliers of the pairwise comparisons based upon uncertainties of the common wireless channel associated with the pairwise comparisons.

35. The method of claim 33, wherein:

determining the bias of the first node comprises determining RSSI bias values based on a weighted average of the pairwise RSSI differences having the outliers removed; and

generating a compensation estimate comprises generating compensated RSSI measurements by removing RSSI bias values from the RSSI measurements.

36. The method of claim 32, wherein:

determining the bias of the first node comprises determining RTT bias values based on a weighted average of the pairwise RTT differences having the outliers removed; and

generating a compensation estimate comprises generating compensated RTT measurements by removing RTT bias values from the RTT measurements.

37. The method of claim 36, further comprising determining a position estimate of the first node further using the compensated RTT measurements, the compensated RSSI measurements, and uncertainties of the wireless channel.

38. A server which enhances a position determination of a node using pairwise measurements, 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 from a first node a first range measurement of a distance between the first node and a second node,

receive from a second node a second range measurement of the distance between the first node and the second node based on a signal received from the first node at the second node,

determine a pairwise comparison by comparing the first range measurement to the second range measurement,

determine a bias of the first node based on the pairwise comparison, and

generate a compensation estimate for compensating subsequent range measurements received from the first node based on the bias.

39. The server of claim 38, wherein the memory comprises further instructions which cause the processor to:

receive the first range measurement by receiving a first Round Trip Time (RTT) measurement from the first node, wherein the first RTT measurement is measured on a common wireless channel that is common to the first node and the second node,

receive the second range measurement by receiving a second RTT measurement from the second node, wherein the second RTT measurement is measured on the common wireless channel that is common to the first node and the second node, and

determine the pairwise comparison by subtracting the RTT measurement received from the second node from the RTT measurement received from the first node.

40. The server of claim 38, wherein the memory comprises further instructions which cause the processor to:

receive the first range measurement by receiving a first Received Signal Strength Indicator (RSSI) measurement from the first node, wherein the first RSSI measurement is measured on a common wireless channel that is common to the first node and the second node,

receive the second range measurement by receiving a second RSSI measurement from the second node, wherein the second RSSI measurement is measured on the common wireless channel that is common to the first node and the second node, and

determine the pairwise comparison by subtracting the RSSI measurement received from the second node from the RSSI measurement received from the first node.

41. The server of claim 40, wherein the memory comprises further instructions which cause the processor to:

calculate statistics of the first range measurement,

determine uncertainties for the common wireless channel based on the statistics of the first range measurement, and

remove outliers of the pairwise comparisons based upon uncertainties of the common wireless channel associated with the pairwise comparisons.

42. The server of claim 40, wherein the memory comprises further instructions which cause the processor to:

determine the bias of the first node by determining RSSI bias values based on a weighted average of the pairwise RSSI differences having the outliers removed, and

generate a compensation estimate by generating compensated RSSI measurements by removing RSSI bias values from the RSSI measurements.

43. The server of claim 39, wherein the memory comprises further instructions which cause the processor to:

determine the bias of the first node by determining RTT bias values based on a weighted average of the pairwise RTT differences having the outliers removed, and

generate a compensation estimate by generating compensated RTT measurements by removing RTT bias values from the RTT measurements.

44. The server of claim 43, wherein the memory comprises further instructions which cause the processor to:

determine a position of the first node using the compensated RTT measurements, the compensated RSSI measurements, and uncertainties of the wireless channel.

45. A server which enhances a position determination of a node using pairwise measurements, comprising:

means for receiving from a first node a first range measurement of a distance between the first node and a second node;

means for receiving from a second node a second range measurement of the distance between the first node and the second node based on a signal received from the first node at the second node;

means for determining a pairwise comparison by comparing the first range measurement to the second range measurement;

means for determining a bias of the first node based on the pairwise comparison; and

means for generating a compensation estimate for compensating subsequent range measurements received from the first node based on the bias.

46. The server of claim 45, further comprising:

means for receiving the first range measurement comprises means for receiving a first Round Trip Time (RTT) measurement from the first node, wherein the first RTT measurement is measured on a common wireless channel that is common to the first node and the second node;

means for receiving the second range measurement comprises means for receiving a second RTT measurement from the second node, wherein the second RTT measurement is measured on the common wireless channel that is common to the first node and the second node; and

means for determining the pairwise comparison comprises means for subtracting the second RTT measurement received from the second node from the first RTT measurement received from the first node.

47. The server of claim 45, further comprising:

means for receiving the first range measurement comprises means for receiving a first Received Signal Strength Indicator (RSSI) measurement from the first node, wherein the first RSSI measurement is measured on a common wireless channel that is common to the first node and the second node;

means for receiving the second range measurement comprises means for receiving a second RSSI measurement from the second node, wherein the second RSSI measurement is measured on the common wireless channel that is common to the first node and the second node; and

means for determining the pairwise comparison comprises means for subtracting the second RSSI measurement received from the second node from the first RSSI measurement received from the first node.

48. A non-transitory computer-readable medium comprising instructions, which, when executed by a processor, cause the computer to perform operations, the instructions comprising:

instructions to receive from a first node a first range measurement of a distance between the first node and a second node;

instructions to receive from a second node a second range measurement of the distance between the first node and the second node based on a signal received from the first node at the second node;

instructions to determine a pairwise comparison by comparing the first range measurement to the second range measurement;

instructions to determine a bias of the first node based on the pairwise comparison; and

instructions to generate a compensation estimate for compensating subsequent range measurements received from the first node based on the bias.

49. The non-transitory computer-readable medium of claim 48, further comprising:

instructions to receive the first range measurement by receiving a first Round Trip Time (RTT) measurement from the first node, wherein the first RTT measurement is measured on a common wireless channel that is common to the first node and the second node;

instructions to receive the second range measurement by receiving a second RTT measurement from the second node, wherein the second RTT measurement is measured on the common wireless channel that is common to the first node and the second node; and

instructions to determine the pairwise comparison by subtracting the RTT measurement received from the second node from the RTT measurement received from the first node.

50. The non-transitory computer-readable medium of claim 49, further comprising:

instructions to receive the first range measurement by receiving a first Received Signal Strength Indicator (RSSI) measurement from the first node, wherein the first RSSI measurement is measured on a common wireless channel that is common to the first node and the second node;

instructions to receive the second range measurement by receiving a second RSSI measurement from the second node, wherein the second RSSI measurement is measured on the common wireless channel that is common to the first node and the second node; and

instructions to determine the pairwise comparison by subtracting the RSSI measurement received from the second node from the RSSI measurement received from the first node.