E911 overlay solution for GSM, for use in a wireless location system

• US 20040203429A1
• Filed: 09/03/2002
• Published: 10/14/2004
• Est. Priority Date: 09/03/2002
• Status: Active Grant

• Current Assignee: Skyhook Holding, Inc. (Liberty Broadband Corp.)
• Original Assignee: TruePosition Incorporated
• Inventors: Anderson, Robert J., Sheehan, Joseph W.
• Granted Patent: US 6,996,392 B2
• Time in Patent Office: Days
• US Class Current: 455/67.11
• CPC Class Codes: H04W 24/00 Supervisory, monitoring or testing arrangements
• 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 72/20 Control channels or signalling for resource management
• CPC Class Codes: H04W 74/0833 Random access procedures, e.g. with 4-step access
• CPC Class Codes: H04W 76/50 for emergency connections

Abstract

In a network overlay Location Services solution for a GSM communications network, the LMU monitors the uplink and/or downlink control channels and determines which call originations are for E911 emergencies and which call setup (Stand-alone Dedicated Control Channel, or SDCCH), assigned traffic (TCH) and associated (Slow Associated Control Channel, or SACCH) channels are subsequently assigned. Capturing the energy on the call setup channel, SDCCH, and its associated SACCH will typically provide a sub-100 meter level of accuracy. If not, the SMLC can redirect the LMU to the assigned traffic channel, TCH, to capture additional RF energy and improve the location accuracy as required. This approach takes advantage of the fact that Channel Request messages on the RACH include an information element that indicates the purpose for the access request. One of the values of this information element identifies that the Channel Request is for an emergency call. By monitoring the Access Grant channels (downlink), e.g., the AGCH, the primary (serving) LMU (LMU 200A in FIG. 1) can capture the Immediate Assignment Message (IMM ASS) for emergency calls. The Immediate Assignment Message contains the Channel Request message (with the emergency call indication) and the SDCCH channel to be used by the MS for subsequent call setup messaging. The primary LMU will forward the Immediate Assignment Message to the SMLC, which will task the cooperating LMUs to collect the RF energy from the associated SDCCH, SACCH and TCH channels and provide TDOA, AoA, and FDOA determinations.

Claims

1. A wireless location system comprising:

first and second LMUs for collection of a mobile transmitter'"'"'s radio emissions;

a sensor for monitoring of control channel messages for emergency call detection and channel allocation; and

a central processor for the tasking of LMUs and computation of the mobile transmitter'"'"'s position and delivery of computed position.

2. A system as recited in claim 1 comprising the step of monitoring uplink control channels.

3. A system as recited in claim 1 comprising the step of monitoring downlink control channels.

4. A system as recited in claim 1 comprising the step of monitoring both uplink and downlink control channels.

5. A system as recited in claim 1 wherein the sensor is co-located with an LMU.

6. A system as recited in claim 1 wherein the sensor is located independently of an LMU.

7. A system as recited in claim 1 comprising the step of detecting the emergency call from the Channel Request message on an uplink Random Access Channel with an establishment cause field set to indicate an emergency call.

8. A system as recited in claim 1 comprising the step of detecting the emergency call from an Immediate Assignment message on a downlink Access Grant Channel, where the enclosed establishment cause field is set to indicate an emergency call.

9. A system as recited in claim 1 comprising the step of detecting the emergency call from a CM Service Request on an uplink Standalone Dedicated Control Channel with an establishment cause field set to indicate an emergency call.

10. A system as recited in claim 1 comprising the step of detecting the emergency call from a CM Service Request on a downlink Standalone Dedicated Control Channel with an establishment cause field set to indicate an emergency call.

11. A system as recited in claim 1 comprising the step of detecting the emergency call from a SETUP message on a Standalone Dedicated Control Channel where dialed digits correspond to an emergency services call.

12. A system as recited in claim 1 comprising the step of detecting the emergency call from the use of the Emergency SETUP message on a Standalone Dedicated Control Channel.

13. A system as recited in claim 1, comprising a mechanism to effect disabling of ciphering for emergency calls so that an assigned Traffic Channel can be determined by monitoring a downlink Standalone Dedicated Control Channel.

14. A system as recited in claim 1 wherein a Standalone Dedicated Control Channel assignment is obtained from an Immediate Assignment message on a downlink Access Grant Channel.

15. A system as recited in claim 1 wherein a Standalone Dedicated Control Channel assignment is obtained by monitoring uplink Standalone Dedicated Control Channels for a CM Service Request message with an establishment cause field set to indicate an emergency call.

16. A system as recited in claim 1 wherein a Standalone Dedicated Control Channel assignment is obtained by monitoring downlink Standalone Dedicated Control Channels for a CM Service Request message with an establishment cause field set to indicate an emergency call.

17. A system as recited in claim 1 wherein the Standalone Dedicated Control Channel assignment is obtained by monitoring uplink Standalone Dedicated Control Channels for a SETUP message with dialed digits indicating an emergency call.

18. A system as recited in claim 1 wherein a Standalone Dedicated Control Channel assignment is obtained by monitoring all uplink Standalone Dedicated Control Channels for an Emergency SETUP message.

19. A system as recited in claim 1 wherein a Standalone Dedicated Control Channel assignment is obtained by monitoring all uplink Standalone Dedicated Control Channels for an Emergency SETUP message.

20. A system as recited in claim 1 wherein the sensor communicates a Standalone Dedicated Control Channel assignment to the central processor so that LMUs may be tasked to collect signaling on that channel.

21. A system as recited in claim 1 wherein a Traffic Channel assignment for an emergency services call is obtained from an Assignment Command message on a downlink Standalone Dedicated Control Channel.

22. A system as recited in claim 1 wherein the sensor communicates a Traffic Channel assignment to the central processor so that LMUs may be tasked to collect signals on that channel

23. A system as recited in claim 1 wherein the method of position estimation includes Angle of Arrival algorithms.

24. A system as recited in claim 1 wherein the method of position estimation includes Time Difference of Arrival algorithms.

25. A system as recited in claim 23 wherein the computation of position estimation includes Frequency Difference of Arrival algorithms.

26. A system as recited in claim 24 wherein the computation of position estimation includes Frequency Difference of Arrival algorithms.

27. A system as recited in claim 1 wherein the computation of position estimation includes both Angle of Arrival and Time Difference of Arrival algorithms.

28. A system as recited in claim 27 wherein the computation of position estimation includes Frequency Difference of Arrival algorithms.

29. A method for use in a wireless location system, comprising:

employing first and second LMUs to collect a mobile transmitter'"'"'s radio emissions;

monitoring control channel messages for emergency call detection and channel allocation; and

computing the mobile transmitter'"'"'s position.

30. A method as recited in claim 29 comprising the step of monitoring uplink control channels.

31. A method as recited in claim 29 comprising the step of monitoring downlink control channels.

32. A method as recited in claim 29 comprising the step of monitoring both uplink and downlink control channels.

33. A method as recited in claim 29 comprising use of a sensor that is co-located with an LMU.

34. A method as recited in claim 29 comprising use of a sensor that is located independently of an LMU.

35. A method as recited in claim 29 comprising the step of detecting the emergency call from the Channel Request message on an uplink Random Access Channel with an establishment cause field set to indicate an emergency call.

36. A method as recited in claim 29 comprising the step of detecting the emergency call from an Immediate Assignment message on a downlink Access Grant Channel, where the enclosed establishment cause field is set to indicate an emergency call.

37. A method as recited in claim 29 comprising the step of detecting the emergency call from a CM Service Request on an uplink Standalone Dedicated Control Channel with an establishment cause field set to indicate an emergency call.

38. A method as recited in claim 29 comprising the step of detecting the emergency call from a CM Service Request on a downlink Standalone Dedicated Control Channel with an establishment cause field set to indicate an emergency call.

39. A method as recited in claim 29 comprising the step of detecting the emergency call from a SETUP message on a Standalone Dedicated Control Channel where dialed digits correspond to an emergency services call.

40. A method as recited in claim 29 comprising the step of detecting the emergency call from the use of an Emergency SETUP message on a Standalone Dedicated Control Channel.

41. A method as recited in claim 29 comprising the step of disabling of ciphering for emergency calls so that an assigned Traffic Channel can be determined by monitoring a downlink Standalone Dedicated Control Channel.

42. A method as recited in claim 29 wherein a Standalone Dedicated Control Channel assignment is obtained from an Immediate Assignment message on a downlink Access Grant Channel.

43. A method as recited in claim 29 wherein a Standalone Dedicated Control Channel assignment is obtained by monitoring uplink Standalone Dedicated Control Channels for a CM Service Request message with an establishment cause field set to indicate an emergency call.

44. A method as recited in claim 29 wherein a Standalone Dedicated Control Channel assignment is obtained by monitoring downlink Standalone Dedicated Control Channels for a CM Service Request message with an establishment cause field set to indicate an emergency call.

45. A method as recited in claim 29 wherein the Standalone Dedicated Control Channel assignment is obtained by monitoring uplink Standalone Dedicated Control Channels for a SETUP message with dialed digits indicating an emergency call.

46. A method as recited in claim 29 wherein a Standalone Dedicated Control Channel assignment is obtained by monitoring all uplink Standalone Dedicated Control Channels for an Emergency SETUP message.

47. A method as recited in claim 29 wherein a Standalone Dedicated Control Channel assignment is obtained by monitoring all uplink Standalone Dedicated Control Channels for an Emergency SETUP message.

48. A method as recited in claim 29 wherein a Standalone Dedicated Control Channel assignment is communicated to a processor so that LMUs may be tasked to collect signaling on that channel.

49. A method as recited in claim 29 wherein a Traffic Channel assignment for an emergency services call is obtained from an Assignment Command message on a downlink Standalone Dedicated Control Channel.

50. A method as recited in claim 29 wherein a Traffic Channel assignment is communicated to a central processor so that LMUs may be tasked to collect signals on that channel

51. A method as recited in claim 29 wherein the step of position estimation includes Angle of Arrival algorithms.

52. A method as recited in claim 29 wherein the step of position estimation includes Time Difference of Arrival algorithms.

53. A method as recited in claim 52 wherein the computation of position estimation includes Frequency Difference of Arrival algorithms.

54. A method as recited in claim 29 wherein the computation of position estimation includes both Angle of Arrival and Time Difference of Arrival algorithms.

55. A wireless location system (WLS) overlaid on a GSM or UMTS wireless communications system, comprising:

a first Location Measuring Unit (LMU), which in use is operable as a primary LMU for monitoring a downlink control channel carrying signals from a Base Transceiver Station (BTS) to a first Mobile Station (MS), and from said downlink control channel identifying an E911 call origination from the first MS and identifying call setup (SDCCH), assigned traffic (TCH) and associated channels subsequently assigned to said first MS;

at least one additional LMU, which in use is operable as a cooperating LMU; and

a Serving Mobile Location Center (SMLC) for receiving data from the primary and cooperating LMUs and calculating the geographic location of the first MS;

wherein the primary and cooperating LMUs are operable to capture energy on the uplink call setup channel, SDCCH, and its associated channels, and provide information to the SMLC sufficient to enable the SMLS to calculate the geographic location of the first MS.

56. A WLS as recited in claim 55 where the control channel monitor is separate from the primary LMU.

57. A WLS as recited in claim 55, wherein the primary LMU is further operable to monitor Channel Request messages on a Reverse Access Channel (RACH) to obtain an information element that indicates that the Channel Request message is for an emergency E911 call.

58. A WLS as recited in claim 55, wherein the associated channel includes a Slow Associated Control Channel (SACCH).

59. A WLS as recited in claim 55, wherein the associated channel includes a Fast Associated Control Channel (FACCH).

60. A WLS as recited in claim 55, wherein the SMLC is operable to redirect one or more LMUs to an assigned traffic channel (TCH) to capture additional RF energy.

61. A WLS as recited in claim 60, wherein the SMLC is operable to redirect said one or more LMUs to the assigned traffic channel only when necessary to improve location accuracy.

62. A WLS as recited in claim 55, wherein the primary LMU is further operable to monitor a downlink Access Grant channel (AGCH) and to capture an Immediate Assignment Message (IMM ASS) for emergency calls.

63. A WLS as recited in claim 62, wherein the Immediate Assignment Message contains the Channel Request message with the emergency call indication and the identifying call setup channel (SDCCH) to be used by the first MS for subsequent call setup messaging.

64. A WLS as recited in claim 62, wherein the primary LMU is further operable to forward the Immediate Assignment Message to the SMLC, and the SMLC is operable to task the cooperating LMUs to collect RF energy from one or more of the call setup (SDCCH), associated (SACCH and/or FACCH) to provide TDOA and FDOA data to the SMLC.

65. A WLS as recited in claim 55, wherein the WLS is overlaid on the GSM wireless communications system in that each of said LMUs is co-located with a Base Transceiver Station (BTS) and shares an RF antenna of the BTS.

66. A WLS as recited in claim 65, wherein:

the primary LMU is further operable to monitor Channel Request messages on a Reverse Access Channel (RACH) to obtain an information element that indicates that the Channel Request message is for an emergency E911 call;

the SMLC is operable to redirect one or more LMUs to an assigned traffic channel (TCH) to capture additional RF energy; and

wherein the primary LMU is further operable to forward the Immediate Assignment Message to the SMLC, and the SMLC is operable to task the cooperating LMUs to collect RF energy from one or more of the call setup (SDCCH), associated (SACCH and/or FACCH) and assigned traffic (TCH) channels and to provide TDOA and FDOA data to the SMLC.

67. A WLS as recited in claim 66, wherein the primary LMU is further operable to monitor a downlink Access Grant channel (AGCH) and to capture an Immediate Assignment Message (IMM ASS) for emergency calls, wherein the Immediate Assignment Message contains the Channel Request message with the emergency call indication and the identifying call setup channel (SDCCH) to be used by the first MS for subsequent call setup messaging.