Robust downlink frame synchronization schemes in CDMA wireless networks for geo-location

• US 8,331,955 B2
• Filed: 12/28/2010
• Issued: 12/11/2012
• Est. Priority Date: 12/28/2010
• Status: Active Grant

• Current Assignee: Skyhook Holding, Inc. (Liberty Broadband Corp.)
• Original Assignee: TruePosition Incorporated
• Inventors: Bull, Jeffrey F., Anderson, Robert J.
• Primary Examiner(s): Pérez-Gutiérrez, Rafael
• Assistant Examiner(s): Khan, Suhail
• Application Number:
  US12/980,098
• Publication Number:
  US 20120165037A1
• Time in Patent Office: 714 Days
• Field of Search: None
• US Class Current: 455/456.1
• CPC Class Codes: G01S 5/0205 Details
• CPC Class Codes: G01S 5/04 Position of source determined by a plurality of spaced direction-finders
• 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 24/10 Scheduling measurement reports ; Arrangements for measurement reports
• 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 72/23 in the downlink direction of a wireless link, i.e. towards a terminal

Abstract

A wireless location system is configured to operate in a CDMA-based wireless communication network. In exemplary embodiments, location measuring units (LMUs) can synchronize to sectors of base stations and store sector timing information. In response to a request to geo-locate a mobile device communicating with a sector, sector timing information for the servicing sector is sent to other LMUs and the LMUs can use the sector timing information to detect uplink signals transmitted by the mobile device. The location of the mobile device can then be estimated based on time of arrival measurements made by the LMUs.

Claims

1. A method for use by a wireless location system (WLS) associated with a CDMA-based wireless communications network (WCN), comprising:

receiving, at a first location measuring unit (LMU), a CDMA downlink signal broadcast by a sector of a base station;

determining, by the first LMU, sector timing information for the sector in response to synchronizing with the downlink signal, wherein the determination of sector timing information comprises,

determining slot timing information from a received downlink primary synchronization channel;

determining frame timing information and a scrambling code group for the sector from a received secondary synchronization channel;

determining a scrambling code for the sector from the scrambling code group for the sector and a downlink common pilot channel for the sector; and

determining a frame number and a sector identifier for the sector;

sending the sector timing information from the first LMU to a second LMU;

receiving, at the first and second LMUs, uplink signals from a mobile device communicating with the sector of the base station;

determining, at the first and second LMUs, time of arrival information for the uplink signals received at the first and second LMUs using the sector timing information; and

determining a geographic location of the mobile device using the time of arrival information.

2. The method of claim 1, wherein determining sector timing information in response to synchronizing with the downlink signal further comprises:

determining sector timing information in response to synchronizing with a downlink beacon signal.

3. The method of claim 1, wherein determining sector timing information in response to synchronizing with the downlink signal further comprises:

determining sector timing information in response to synchronizing with a downlink pilot signal.

4. The method of claim 1, wherein determining sector timing information in response to synchronizing with the downlink signal further comprises:

determining slot timing information in response to synchronizing with a downlink primary synchronization channel.

5. The method of claim 1, wherein determining sector timing information in response to synchronizing with the downlink signal further comprises:

determining frame timing information in response to synchronizing with a downlink secondary synchronization channel.

6. The method of claim 1, wherein determining sector timing information in response to synchronizing with the downlink signal further comprises:

determining a frame number and sector identifier for the sector serving the mobile device in response to synchronizing with a broadcast control channel for the sector.

7. The method of claim 1, further comprising:

selecting the first LMU from a group of LMUs in response to determining that the uplink signal received at the first LMU is stronger than the uplink signals received by other LMUs in the group of LMUs.

8. The method of claim 1, wherein receiving the CDMA downlink signal broadcast by the sector of the base station further comprises:

receiving, at the first LMU, the CDMA downlink signal broadcast by the sector, wherein the first LMU is co-located with the base station.

9. The method of claim 1, further comprising:

aiming an antenna for the first LMU at a downlink antenna of the base station, wherein the first LMU is co-located with a second base station.

10. The method of claim 1, further comprising:

determining sector timing information for the sector using a scrambling code for the sector received from the WLS.

11. A method for use by a wireless location system (WLS) associated with a CDMA-based wireless communications network (WCN), comprising:

receiving, at a first location measuring unit (LMU), a CDMA downlink signal broadcast by a sector of a base station;

determining, by the first LMU, sector timing information for the sector, wherein the determination of sector timing information for the sector comprises determining slot timing information from a downlink primary synchronization channel;

determining frame timing information from a secondary synchronization channel;

determining a scrambling code for the sector; and

determining a frame number for the sector;

sending the sector timing information from the first LMU to a second LMU;

receiving, at the first and second LMUs, uplink signals from a mobile device communicating with the sector of the base station; and

determining, at the first and second LMUs, time of arrival information for the uplink signals received at the first and second LMUs using the sector timing information;

wherein receiving a CDMA downlink signal broadcast by a sector of a base station comprises;

generating a plurality of weight value sets;

sequentially configuring an adaptive antenna array in accordance with each weight value set and sampling the downlink signal;

determining, for each weight value set, signal strength information for samples of the downlink signal;

selecting a weight value set from the group based on the signal strength information determined for each sample of the downlink signal; and

storing the selected weight value set for the sector.

12. The method of claim 11, further comprising:

determining, from a received downlink primary synchronization channel, slot timing information for the sector;

determining, from a received secondary synchronization channel, frame timing information and a scrambling code group for the sector; and

determining, using the scrambling code group for the sector and a downlink common pilot channel for the sector, the scrambling code for the sector.

13. The method of claim 11, further comprising:

selecting the adaptive antenna array from a group of geographically dispersed adaptive antenna arrays to receive the CDMA downlink signal based on the strength of the sampled downlink signal at the adaptive antenna array.

14. A wireless location system, comprising:

a first antenna array;

a weight control system configured to adjust weight values for the first antenna array to cause a downlink signal associated with a sector of a base station to be detected;

a first location measuring unit (LMU) configured to synchronize with the detected downlink signal, thereby obtaining sector timing information for the sector, wherein the first LMU is configured to obtain sector timing information by,

determining, from a received downlink primary synchronization channel, slot timing information;

determining, from a received secondary synchronization channel, frame timing information and a scrambling code group for the sector;

determining, from the scrambling code group for the sector and a downlink common pilot channel for the sector, a scrambling code for the sector; and

determining, using the scrambling code for the sector, a frame number and a sector identifier for the sector; and

a second LMU configured to receive the determined sector timing information for the detected downlink signal from the first LMU;

wherein the first and second LMUs are configured to use the sector timing information to determine time of arrival information for uplink signals from a mobile device communicating with the sector; and

a servicing mobile location center configured to determine a geographic location of the mobile device using the time of arrival information determined by the first and second LMUs.

15. The wireless location system of claim 14, wherein the downlink signal is a common pilot channel for the sector.

16. The wireless location system of claim 14, wherein the sector timing information comprises slot timing information obtained from a primary synchronization channel for the sector.

17. The wireless location system of claim 14, wherein the sector timing information comprises frame timing information obtained from a secondary synchronization channel for the sector.

18. The wireless location system of claim 14, wherein the sector timing information comprises frame number information obtained from a broadcast control channel for the sector.

19. The wireless location system of claim 14, further comprising:

a switch configured to select the first antenna array from a group of antenna arrays, wherein each antenna array in the group is positioned at a different location relative to the first LMU.

20. The wireless location system of claim 14, wherein the weight control system is configured to:

adjust sets of weight values;

sample the downlink signal;

determine the ratio of Energy per Bit (Eb) to the Spectral Noise Density (No) (Eb/No) for each sample of the downlink signal; and

select the set of weight values that is associated with a sample of the downlink signal that has an Eb/No ratio greater than a threshold.

21. The wireless location system of claim 14 wherein the first antenna array is a directional array aimed at a downlink transmission antenna of the base station, wherein the first antenna array is co-located with a second base station.

22. A wireless location system including a servicing mobile location center configured to determine a geographic location of a mobile device using time of arrival information determined by a first location measuring unit and a second location measuring unit, wherein the first location measuring unit and the second location measuring unit are configured to determine the time of arrival information from uplink CDMA signals transmitted by the mobile device and sector timing information for the sector serving the mobile device, the first location measuring unit comprising:

means for determining sector timing information for a sector of a base station in response to synchronizing with a downlink signal transmitted by the sector, wherein the means for determining sector timing information comprises means for determining slot timing information, means for determining frame timing information, means for determining a scrambling code for the sector, and means for determining a frame number for the sector;

means for receiving a signal indicating that the mobile device is communicating with the sector; and

means for sending the sector timing information to the second location measuring unit.

23. The first location measuring unit of claim 22, further comprising:

means for selecting a downlink receiver subsystem from a group of downlink receiver subsystems positioned at different locations relative to the first location measuring unit, wherein the downlink receiver subsystem is configured to receive the downlink signal transmitted by the sector.

24. The first location measuring unit of claim 22, further comprising:

means for selecting a weight value set for a downlink receiver subsystem from a group of weight value sets that maximizes the ratio of Energy per Bit (Eb) to the Spectral Noise Density (No) (Eb/No) for the downlink signal.

25. The first location measuring unit of claim 22, wherein the means for determining sector timing information for the sector of the base station in response to synchronizing with the downlink signal transmitted by the sector further comprise:

means for determining sector timing information in response to synchronizing with a downlink beacon signal.

26. The first location measuring unit of claim 22, wherein the means for determining sector timing information further comprise:

means for determining sector timing information in response to synchronizing with a downlink pilot signal.

27. The first location measuring unit of claim 22, wherein the means for determining sector timing information further comprise:

means for determining slot timing information in response to synchronizing with a downlink primary synchronization channel.

28. The first location measuring unit of claim 22, wherein the means for determining sector timing information further comprise:

means for determining frame timing information in response to synchronizing with a downlink secondary synchronization channel.

29. The first location measuring unit of claim 22, wherein the means for determining sector timing information further comprise:

means for determining a frame number and sector identifier for the sector in response to synchronizing with a broadcast control channel for the sector.

30. A method for use by a first location measuring unit configured to operate within a wireless location system, the wireless location system including a servicing mobile location center configured to determine a geographic location of a mobile device using time of arrival information received from the first location measuring unit and a second location measuring unit, the method comprising:

aiming an antenna of a downlink receiver subsystem at a downlink antenna for a sector of a base station, the base station co-located with the second location measuring unit;

detecting a downlink signal transmitted by the sector;

synchronizing with the downlink signal, thereby obtaining sector timing information for the sector, wherein obtaining sector timing information comprises,

determining, from a received downlink primary synchronization channel, slot timing information;

determining, from a received secondary synchronization channel, frame timing information and a scrambling code group for the sector;

determining, from the scrambling code group for the sector and a downlink common pilot channel for the sector, a scrambling code for the sector; and

determining, using the scrambling code for the sector, a frame number and a sector identifier for the sector;

sending the sector timing information to the second location measuring unit;

determining, using the sector timing information, time of arrival information for the uplink signals; and

sending the determined time of arrival information to the servicing mobile location center.

31. The method of claim 30, further comprising:

generating a plurality of weight value sets;

sequentially configuring antennas of the downlink receiver subsystem in accordance with each weight value set and sampling the downlink signal;

determining, for each weight value set, signal strength information for samples of the downlink signal;

selecting a weight value set from the plurality based on the signal strength information for the samples determined for each weight value set; and

storing the selected weight value set for the sector.

32. The method of claim 30, further comprising:

selecting the downlink receiver subsystem from a group of geographically dispersed downlink receiver subsystems based on the strength of a sampled downlink signal at the downlink receiver subsystem.

33. A non-transitory computer-readable storage medium for use in a wireless location system that includes a servicing mobile location center configured to determine the geographic location of a mobile device from time of arrival information generated by at least a first location measuring unit (LMU) and a second LMU, wherein the group of LMUs is configured to generate the time of arrival information from uplink CDMA signals transmitted by the mobile device and sector timing information for a sector servicing the mobile device, the computer-readable storage medium comprising instructions that upon execution cause the first LMU to:

direct a plurality of geographically dispersed downlink receiver subsystems to measure signal strength of a downlink signal of a sector;

select a downlink receiver subsystem from the plurality based on the signal strength of the downlink signal at each of the geographically dispersed downlink receiver subsystems;

determine sector timing information for the sector in response to synchronizing with the downlink signal detected by the selected downlink receiver subsystem, wherein the determination of sector timing information comprises,

determining, from a received downlink primary synchronization channel, slot timing information;

determining, from a received downlink secondary synchronization channel, frame timing information and a scrambling code group for the sector;

determining, from the scrambling code group for the sector and a downlink common pilot channel for the sector, a scrambling code for the sector; and

determining, using the scrambling code for the sector, a frame number and a sector identifier for the sector;

send the sector timing information to the second LMU; and

send time of arrival information determined from an uplink signal transmitted by the mobile device and the sector timing information to the servicing mobile location center.

34. The non-transitory computer-readable storage medium of claim 33, wherein the instructions that upon execution cause the first LMU to determine sector timing information further comprise instructions that upon execution cause the first LMU to:

determine slot timing information in response to synchronizing with a downlink primary synchronization channel.

35. The non-transitory computer-readable storage medium of claim 33, wherein the instructions that upon execution cause the first LMU to determine sector timing information further comprise instructions that upon execution cause the first LMU to:

determine frame timing information in response to synchronizing with a downlink secondary synchronization channel.

36. The non-transitory computer-readable storage medium of claim 33, wherein the instructions that upon execution cause the first LMU to determine sector timing information further comprise instructions that upon execution cause the first LMU to:

determine a frame number and sector identifier for the sector serving the mobile device in response to synchronizing with a broadcast control channel for the sector.