Antenna selection method for a wireless location system

• US 6,400,320 B1
• Filed: 08/24/2000
• Issued: 06/04/2002
• Est. Priority Date: 01/08/1999
• Status: Expired due to Term

• Current Assignee: Skyhook Holding, Inc. (Liberty Broadband Corp.), Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology, TruePosition Incorporated
• Inventors: Anderson, Robert J., Sheehan, Joseph W., Stilp, Louis A., Rogers, Alan E. E., Harbison, Andrew F.
• Primary Examiner(s): PHAN, DAO LINDA
• Application Number:
  US09/648,404
• Time in Patent Office: 649 Days
• Field of Search: 342/357.01, 342/357.02, 342/450, 342/457, 455/277.1
• US Class Current: 342/457
• CPC Class Codes: G01S 1/026 of associated receivers
• CPC Class Codes: G01S 2205/006 for emergency situations
• CPC Class Codes: G01S 2205/008 using a mobile telephone network
• CPC Class Codes: G01S 2205/06 Emergency
• CPC Class Codes: G01S 5/021 Calibration, monitoring or correction G01S5/0252 takes precedence
• CPC Class Codes: G01S 5/0215 Interference
• CPC Class Codes: G01S 5/0218 Multipath in signal reception
• CPC Class Codes: G01S 5/02216 Timing or synchronisation of the receivers
• CPC Class Codes: G01S 5/0244 Accuracy or reliability of position solution or of measurements contributing thereto
• CPC Class Codes: G01S 5/0246 involving frequency difference of arrival or Doppler measurements G01S5/02685 takes precedence
• CPC Class Codes: G01S 5/02521 using a radio-map
• CPC Class Codes: G01S 5/0268 by deriving positions from different combinations of signals or of estimated positions in a single positioning system
• 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: H04W 4/90 Services for handling of emergency or hazardous situations, e.g. earthquake and tsunami warning systems [ETWS]
• CPC Class Codes: H04W 64/00 Locating users or terminals or network equipment for network management purposes, e.g. mobility management
• CPC Class Codes: H04W 76/50 for emergency connections
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

An antenna selection method is used in a wireless location system that determines the geographic location of a mobile wireless transmitter. The wireless location system includes signal collection systems connected to multiple antennas at a plurality of cell sites and a location processor for processing digital data provided by the signal collection systems. The antenna selection method comprises evaluating segments of data collected from a plurality of antennas at a signal collection system, selecting a subset of the segments of data, and using only the selected segments of data in location processing.

Claims

1. An antenna selection method for use in a wireless location system that determines the geographic location of a mobile wireless transmitter, the wireless location system including signal collection systems connected to multiple antennas at a plurality of cell sites and a location processor for processing digital data provided by the signal collection systems, the method comprising:

evaluating segments of data collected from a plurality of antennas at a signal collection system;

selecting a subset of the segments of data; and

using only the selected segments of data in location processing.

2. A method as recited in claim 1, wherein each antenna at a signal collection system is connected to a receiver, and each receiver converts received signals into a digital form, and then stores the digitized signals temporarily in a memory in the receiver.

3. A method as recited in claim 2, wherein the location processor directs selected signal collection systems to retrieve segments of data from the temporary memory of selected receivers, and to provide the data for use in location processing.

4. A method as recited in claim 1, wherein the subset of the segments of data is selected by evaluating the segments of data against predetermined criteria.

5. An antenna selection method for use in a wireless location system that determines the geographic location of a mobile wireless transmitter, the wireless location system including signal collection systems located within the geography of a wireless communications system and having multiple antennas, and a location processor for processing digital data provided by the signal collection systems, the method comprising:

a) receiving a transmission from the wireless transmitter at multiple antennas and at multiple signal collection systems in the wireless location system;

b) converting the transmission into a digital format in a receiver connected to each antenna;

c) storing the digital data in a memory in each signal collection system;

d) determining the channel on which the transmission occurred and a cell site and sector serving the wireless transmitter;

e) designating one signal collection system as a primary signal collection system for processing the transmission;

f) determining a timestamp associated with the received data at the primary signal collection system;

g) determining a candidate list of signal collection systems and antennas to examine for use in location processing;

h) for each candidate signal collection system/antenna, evaluating parameters of the data in the channel of the transmission and at the time of the determined timestamp;

i) rank ordering the candidate signal collection system/antennas using specified criteria and creating a subset list of signal collection system/antennas to use in the location processing; and

j) proceeding with location processing using data only from the subset list of signal collection system/antennas.

6. A method as recited in claim 5, wherein the parameters include the average SNR over the transmission interval used for location processing.

7. A method as recited in claim 6, wherein the criteria used for the average SNR parameter is higher average SNR is preferred to lower average SNR.

8. A method as recited in claim 6, wherein the criteria used for the average SNR parameter is average SNR must be greater than a predetermined threshold in order for the candidate signal collection system/antenna to be included in the subset list of signal collection system/antennas used for location processing.

9. A method as recited in claim 5, wherein the parameters include the variance in SNR over the transmission interval used for location processing.

10. A method as recited in claim 9, wherein the criteria used for the variance in SNR parameter is low variance in SNR is preferred to higher variance in SNR.

11. A method as recited in claim 9, wherein the criteria used for the variance in SNR parameter is variance in SNR must be lower than a predetermined threshold in order for the candidate signal collection system/antenna to be included in the subset list of signal collection system/antennas used for location processing.

12. A method as recited in claim 5, wherein the parameters include the number of bit errors in a demodulated form of the data.

13. A method as recited in claim 12, wherein the criteria used for the number of bit errors parameter is lower number of bit errors is preferred to higher number of bit errors.

14. A method as recited in claim 12, wherein the criteria used for the number of bit errors parameter is the number of bit errors must be lower than a predetermined threshold in order for the candidate signal collection system/antenna to be included in the subset list of signal collection system/antennas used for location processing.

15. A method as recited in claim 5, wherein the parameters include a measure of the correlation of the beginning of the received transmission against a predetermined pre-cursor.

16. A method as recited in claim 15, wherein the predetermined pre-cursor includes an AMPS dotting and barker code.

17. A method as recited in claim 15, wherein the predetermined pre-cursor includes a sync word.

18. A method as recited in claim 5, wherein the parameters include the magnitude and rate of change of SNR from just before the onset of the transmission to the onset of the transmission.

19. A method as recited in claim 18, wherein the criteria used for the magnitude and rate of change of SNR from just before the onset of the transmission to the onset of the transmission parameter is higher magnitude and faster rate of change of SNR is preferred to lower magnitude and slower rate of change of SNR.

20. A method as recited in claim 5, wherein the parameters include comparing a demodulated form of the data at each candidate against a demodulated form of the data at the primary.

21. A method as recited in claim 5, wherein the signal collection system/antenna with the highest rank ordering is designated as the reference signal collection system/antenna.

22. A method as recited in claim 5, wherein the transmission is received and demodulated at a plurality of signal collection systems, and then a group of prescribed parameters is examined to determine which signal collection system/antenna to designate as the reference signal collection system/antenna.

23. A method as recited in claim 22, wherein the prescribed parameters include an average SNR over a transmission interval.

24. A method as recited in claim 23, wherein the criteria used for the average SNR parameter is the highest average SNR.

25. A method as recited in claim 22, wherein the prescribed parameters include a variance in SNR over the transmission interval.

26. A method as recited in claim 25, wherein the criteria used for the variance in SNR parameter is lowest variance in SNR.

27. A method as recited in claim 22, wherein the prescribed parameters include a correlation of the beginning of the received transmission against a predetermined pre-cursor.

28. A method as recited in claim 22, wherein the prescribed parameters include the number of bit errors in the demodulated data.

29. A method as recited in claim 22, wherein the prescribed parameters include the magnitude and rate of change of SNR from just before the onset of the transmission to the onset of the transmission.

30. A method as recited in claim 24, wherein the average SNR is determined over an interval shorter than the transmission length.

31. A method as recited in claim 5, further comprising the step of ordering the signal collection system/antennas using the following criteria:

signal collection system/antennas with a lower number of bit errors are preferred to signal collection system/antenna with a higher number of bit errors;

average SNR for a given signal collection system/antenna must be greater than a predetermined threshold to be designated as the primary;

signal collection system/antennas with higher average SNR are preferred over those with lower average SNR;

signal collection system/antennas with lower SNR variance are preferred to those with higher SNR variance; and

signal collection system/antennas with a faster SNR rate of change at the on-set of the transmission are preferred to those with a slower rate of change.

32. A method as recited in claim 5, wherein the candidate list of signal collection systems and antennas is determined using a predetermined set of criteria based upon knowledge of the types of cell sites, types of antennas at the cell sites, geometry of the antennas.

33. A method as recited in claim 32, wherein a weighting factor is applied that weights certain antennas more than other antennas.

34. A method as recited in claim 33, wherein the weighting factor takes into account knowledge of the terrain in which the wireless location system is operating.

35. A method as recited in claim 33, wherein the weighting factor takes into account past empirical data on the contribution of each antenna has made to good location estimates.

36. A method as recited in claim 5, wherein the candidate list includes all signal collection systems up to a maximum number of signal collection systems that are closer than a predefined maximum radius from the primary signal collection systems.

37. A method as recited in claim 5, wherein the wireless location system dynamically determines the candidate list of signal collection systems and antennas based upon the predetermined set of criteria.

38. A method as recited in claim 5, wherein a fixed list is used to determine the candidate list of signal collection systems and antennas.

39. A method as recited in claim 38, wherein the fixed list is read directly from a table when location processing is initiated.

40. An antenna port selection method for use in a wireless location system that determines the geographic location of a mobile wireless transmitter, the wireless location system including signal collection systems having multiple antennas and a location processor for processing digital data provided by the signal collection systems, the method comprising:

selecting segments of data collected from a plurality of antenna ports at a candidate signal collection system, wherein the candidate signal collection system receives transmissions from multiple antennas via corresponding antenna ports;

selecting one of said antenna ports as a best port; and

using the segments of data from the best antenna port in location processing.

41. A method as recited in claim 40, wherein, in selecting the best port, the candidate signal collection system divides the received transmission into segments, measures the SNR separately in each segment, and then selects the best port on the basis of the highest SNR.

42. A method as recited in claim 41, wherein the highest SNR is determined by using the antenna port with the most segments with the highest SNR.

43. A method as recited in claim 41, wherein the highest SNR is determined by averaging the SNR in all segments and using the antenna port with the highest average SNR.

44. A method as recited in claim 41, wherein the highest SNR is determined by using the antenna port with the highest SNR in any one segment.

45. A method as recited in claim 40, wherein, in selecting the best port, the candidate signal collection system selects the port with the lowest variance in SNR over the transmission interval used for location processing.