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In an overlay Wireless Location System, an Abis interface is monitored to obtain information used to locate GSM phones. Signaling links of the Abis interface are passively monitored to obtain certain information, such as control and traffic channel assignment, called number, and mobile identificatio

In an overlay Wireless Location System, an Abis interface is monitored to obtain information used to locate GSM phones. Signaling links of the Abis interface are passively monitored to obtain certain information, such as control and traffic channel assignment, called number, and mobile identification, which is not available from the GSM air interface of the reverse channel. This approach also applies to IDEN and can include CDMA systems where the GSM architecture has been used and the system includes a separated BTS to BSC interface.

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What is claimed is: 1. A method for use in a wireless location system (WLS) that estimates the geographic location of a mobile station (MS), wherein the WLS overlays at least a portion of the geographic area of a wireless communications system, wherein the WLS uses radio and location processing res

What is claimed is: 1. A method for use in a wireless location system (WLS) that estimates the geographic location of a mobile station (MS), wherein the WLS overlays at least a portion of the geographic area of a wireless communications system, wherein the WLS uses radio and location processing resources to locate said MS using a process involving receiving a transmission from the MS at multiple sites and processing the received transmissions to estimate the location of the MS using time difference of arrival (TDOA) and/or angle of arrival (AOA) location processing techniques, comprising: passively monitoring communications between at least one base transceiver station (BTS) and at least one base station controller (BSC) of the wireless communications system; extracting MS information from the monitored communications, said extracted MS information including radio frequency channel information, whereby the WLS is able to receive transmissions from the MS; and using the extracted MS information to trigger location processing and to determine which radio frequency channel to use in performing location processing for said MS. 2. A method as recited in claim 1, wherein the extracted MS information further comprises at least one of: the mobile station identification (MSID), the called number dialed by the user of the MS, or the contents of messages sent to the MS or from the MS. 3. A method as recited in claim 1, wherein the extracted MS information further comprises the mobile station identification (MSID). 4. A method as recited in claim 1, wherein the extracted MS information further comprises the called number dialed by the user of the MS. 5. A method as recited in claim 1, wherein the extracted MS information further comprises the contents of messages sent to or from the MS. 6. A method as recited in claim 1, wherein the extracted MS information further comprises at least one of the following presently in use by the MS: the control channel, the traffic channel, the mobile directory number (MDN), the Electronic Serial Number (ESN), the Mobile Identity Number (MIN), the Mobile Subscriber Identification (MSI), the international mobile subscriber identity (IMSI), the temporary mobile subscriber identity (IMSI), or the mobile station international ISDN number (MSISDN). 7. A method as recited in claim 1, wherein the WLS stores the extracted MS information in a database. 8. A method as recited in claim 7, wherein the WLS removes the extracted MS information from the database after the extracted MS information is no longer valid. 9. A method as recited in claim 8, wherein the extracted MS information is determined to be no longer valid because the MS is no longer registered with the wireless communications system. 10. A method as recited in claim 8, wherein the extracted MS information is determined to be no longer valid because a predetermined period of time has expired. 11. A method as recited in claim 8, wherein the extracted MS information is determined to be no longer valid because a predetermined period of time has expired without an update to the extracted MS information. 12. A method as recited in claim 1, wherein the WLS discards the extracted MS information if the extracted MS information does not match any of a set of predetermined criteria. 13. A method as recited in claim 12, wherein the set of predetermined criteria includes at least one of the following: information about the identity of the MS or the number called by the MS. 14. A method as recited in claim 1, wherein the extracted MS information comprises an establishment cause of a channel request message indicative of an emergency call. 15. A computer readable medium comprising computer executable instructions for carrying out the method of claim 1. 16. A method for use in a wireless location system (WLS), wherein the WLS overlays at least a portion of a wireless communications system that includes base transceiver station (BTS) equipment operatively coupled to base station controller (BSC) equipment via an interface, comprising the steps of: passively monitoring communications on the interface between at least one BTS and at least one BSC; identifying certain prescribed mobile station (MS) information from the monitored communications, said information including an emergency call indication and radio frequency channel number; using the MS information to determine whether to perform location processing for said MS and to determine which radio channel to use in performing location processing for said MS; and performing location processing for said MS, whereby a location estimate is obtained for said MS. 17. A method as recited in claim 16, wherein the MS information includes one or more of the following: a mobile station identification (MSID), a called number, contents of messages sent to the MS or from the MS, and/or frequency assignment information sent to the MS. 18. A method as recited in claim 16, wherein the MS information includes one or more of the following presently in use by the MS: control channel, traffic channel, mobile directory number (MDN), Electronic Serial Number (ESN), Mobile Identity Number (MIN), Mobile Subscriber Identification (MSI), international mobile subscriber identity (IMSI), temporary mobile subscriber identity (IMSI), and/or mobile station international ISDN number (MSISDN). 19. A method as recited in claim 16, wherein the WLS stores the MS information in a database. 20. A method as recited in claim 19, wherein the WLS removes the MS information from the database after the MS information is no longer valid. 21. A method as recited in claim 20, wherein the MS information is determined to be no longer valid because the MS is no longer registered with the wireless communications system. 22. A method as recited in claim 20, wherein the MS information is determined to be no longer valid because a predetermined period of time has expired. 23. A method as recited in claim 20, wherein the MS information is determined to be no longer valid because a predetermined period of time has expired without an update to the MS information. 24. A method as recited in claim 16, wherein the WLS discards the MS information if the MS information does not match any of a set of predetermined criteria. 25. A method as recited in claim 24, wherein the set of predetermined criteria includes information about the identity of the MS or the number called by the user of the MS. 26. A method as recited in claim 16, wherein the extracted MS information comprises an establishment cause of a channel request message indicative of an emergency call. 27. A computer readable medium comprising computer executable instructions for carrying out the method of claim 16. 28. A wireless location system (WLS) that overlays at least a portion of a wireless communications system that includes base transceiver station (BTS) equipment operatively coupled to base station controller (BSC) equipment via an interface, comprising: a first mechanism for passively monitoring communications on the interface between at least one BTS and at least one BSC, and for identifying certain prescribed mobile station (MS) information from the monitored communications, said information including an emergency call indication and radio frequency channel number; and a second mechanism for using the MS information to determine whether to perform location processing for said MS and to determine which radio channel to use in performing location processing for said MS. 29. A system as recited in claim 28, wherein the MS information includes one or more of the following: a mobile station identification (MSID), a called number, contents of messages sent to the MS or from the MS, and/or frequency assignment information sent to the MS. 30. A system as recited in claim 28, wherein the MS information includes one or more of the following presently in use by the MS: control channel, traffic channel, mobile directory number (MDN), Electronic Serial Number (ESN), Mobile Identity Number (MIN), Mobile Subscriber Identification (MSI, international mobile subscriber identity (IMSI), temporary mobile subscriber identity (IMSI), and/or mobile station international ISDN number (MSISDN). 31. A system as recited in claim 28, further comprising a database, wherein the WLS stores the MS information in said database. 32. A system as recited in claim 31, wherein the WLS removes the MS information from the database after the MS information is no longer valid. 33. A system as recited in claim 32, wherein the MS information is determined to be no longer valid because the MS is no longer registered with the wireless communications system. 34. A system as recited in claim 32, wherein the MS information is determined to be no longer valid because a predetermined period of time has expired. 35. A system as recited in claim 32, wherein the MS information is determined to be no longer valid because a predetermined period of time has expired without an update to the MS information. 36. A system as recited in claim 28, wherein the WLS discards the MS information if the MS information does not match any of a set of predetermined criteria. 37. A system as recited in claim 36, wherein the set of predetermined criteria includes information about the identity of the MS or the number called by the user of the MS. 38. A system as recited in claim 28, wherein the extracted MS information comprises an establishment cause of a channel request message indicative of an emergency call. 39. A method for use in a wireless location system (WLS) that estimates the geographic location of a mobile station (MS), wherein the WLS overlays at least a portion of the geographic area of a wireless communications system, wherein the WLS includes radio resources and location processing resources and uses said resources to locate said MS using a process involving receiving a transmission from the MS at multiple signal collection sites and processing the received transmissions to estimate the location of the MS using time difference of arrival (TDOA) and/or angle of arrival (AOA) location processing techniques, wherein the wireless communications system includes base transceiver station (BTS) equipment connected to base station controller (BSC) equipment, and wherein said radio resources of the WLS may be at least partially co-located with said BTS equipment of the wireless communications system but are different from said BTS equipment, comprising the steps of: passively monitoring the communications between at least one BTS and at least one BSC, and extracting MS information from the monitored communications, and using the extracted MS information to trigger location processing and to determine channel assignment information for said MS to enable the WLS to receive transmissions from the MS for location purposes; wherein the extracted MS information comprises at least one of: the mobile station identification (MSID), the called number dialed by the user of the MS, the contents of messages sent to the MS or from the MS, or frequency assignment information sent to the MS. 40. A computer readable medium comprising computer executable instructions for carrying out the method of claim 39. 41. A method for use in a wireless location system (WLS) that estimates the geographic location of a mobile station (MS), wherein the WLS overlays at least a portion of the geographic area of a wireless communications system, wherein the WLS includes radio resources and location processing resources and uses said resources to locate said MS using a process involving receiving a transmission from the MS at multiple signal collection sites and processing the received transmissions to estimate the location of the MS using time difference of arrival (TDOA) and/or angle of arrival (AOA) location processing techniques, wherein the wireless communications system includes base transceiver station (BTS) equipment connected to base station controller (BSC) equipment, and wherein said radio resources of the WLS may be at least partially co-located with said BTS equipment of the wireless communications system but are different from said BTS equipment, comprising the steps of: passively monitoring the communications between at least one BTS and at least one BSC, and extracting MS information from the monitored communications, and using the extracted MS information to trigger location processing and to determine channel assignment information for said MS to enable the WLS to receive transmissions from the MS for location purposes; wherein the extracted MS information comprises at least one of the following presently in use by the MS: the control channel, the traffic channel, the mobile directory number (MDN), the Electronic Serial Number (ESN), the Mobile Identity Number (MIN), the Mobile Subscriber Identification (MSI), the international mobile subscriber identity (IMSI), the temporary mobile subscriber identity (IMSI), or the mobile station international ISDN number (MSISDN). 42. A computer readable medium comprising computer executable instructions for carrying out the method of claim 41. 43. A method for use in a wireless location system (WLS) that estimates the geographic location of a mobile station (MS), wherein the WLS overlays at least a portion of the geographic area of a wireless communications system, wherein the WLS uses radio resources and location processing resources to locate said MS using a process involving receiving a transmission from the MS at multiple signal collection sites and processing the received transmissions to estimate the location of the MS using time difference of arrival (TDOA) and/or angle of arrival (AOA) location processing techniques, wherein the wireless communications system includes base transceiver station (BTS) equipment connected to base station controller (BSC) equipment, comprising the steps of: passively monitoring communications between at least one BTS and at least one BSC, wherein the monitored communications contain indications of a call origination or call termination; and using the monitored information to trigger location processing for said MS and to determine which radio resources to use in performing location processing for said MS. 44. A method as recited in claim 43, wherein the step of monitoring communications includes monitoring messages containing radio frequency channel information, and wherein the radio frequency channel information is used to identify a radio channel to which receivers of the WLS are tuned. 45. A method as recited in claim 44, wherein said radio frequency channel information includes Standalone Digital Control Channel Information. 46. A method as recited in claim 44, wherein said radio frequency channel information includes Digital Control Channel Information. 47. A method as recited in claim 44, wherein said radio frequency channel information includes Traffic Channel Information. 48. A method as recited in claim 44, wherein the radio frequency channel information includes an Absolute Radio Frequency Channel Number, Timeslot number, Subchannel number, and Training Sequence Code. 49. A method as recited in claim 44, wherein the radio frequency channel information includes a Hopping Sequence number, Mobile Allocation Index Offset, Hopping Flag, Mobile Allocation, and Cell Allocation. 50. A method as recited in claim 43, wherein the step of monitoring communications includes monitoring messages containing the identity of the mobile station. 51. A method as recited in claim 50, wherein the identify of the MS is compared to a table of mobile stations of interest. 52. A method as recited in claim 43, wherein the step of monitoring comprises monitoring communications containing indications of an emergency call origination. 53. A method as recited in claim 52, wherein the emergency call indication is contained in a Channel Request message as an Establishment cause value of binary 10100000 to 10111111. 54. A method as in claim 53, wherein a Request Reference is used to link A-bis messages to location events. 55. A method as recited in claim 52, wherein the said emergency call indication is determined from monitoring use of an Emergency Setup message. 56. A method as in claim 43, wherein the step of monitoring communications includes monitoring for an Immediate Assignment Command. 57. A computer readable medium comprising computer executable instructions for carrying out the method of claim 43. 58. A system for use in a wireless location system (WLS) that estimates the geographic location of a mobile station (MS), wherein the WLS overlays at least a portion of the geographic area of a wireless communications system, wherein the WLS uses radio resources and location processing resources to locate said MS using a process involving receiving a transmission from the MS at multiple signal collection sites and processing the received transmissions to estimate the location of the MS using time difference of arrival (TDOA) and/or angle of arrival (AOA) location processing techniques, wherein the wireless communications system includes base transceiver station (BTS) equipment connected to base station controller (BSC) equipment, comprising: means for passively monitoring communications between at least one BTS and at least one BSC, wherein the monitored communications contain indications of a call origination or call termination; and means for using the extracted MS information to trigger location processing for said MS and to determine which radio resources to use in performing location processing for said MS. 59. A system as recited in claim 58, wherein the means for monitoring communications monitors messages containing radio frequency channel information. 60. A system as recited in claim 59, wherein said radio frequency channel information includes Standalone Digital Control Channel Information. 61. A system as recited in claim 59, wherein said radio frequency channel information includes Digital Control Channel Information. 62. A system as recited in claim 59, wherein said radio frequency channel information includes Traffic Channel Information. 63. A system as recited in claim 59, wherein the radio frequency channel information includes an Absolute Radio Frequency Channel Number, the Timeslot number, Subchannel number, and Training Sequence Code. 64. A system as recited in claim 59, wherein the radio frequency channel information includes Hopping Sequence number, Mobile Allocation Index Offset, Hopping Flag, Mobile Allocation, and Cell Allocation. 65. A system as recited in claim 58, wherein the means for monitoring communications monitors messages containing the identity of the mobile station. 66. A system as recited in claim 65, further comprising means for comparing the identify of the mobile station to a table of mobile stations of interest. 67. A system as recited in claim 58, wherein the means for monitoring monitors communications containing indications of an emergency call origination. 68. A system as recited in claim 67, wherein the emergency call indication is contained in a Channel Request message as an Establishment cause value of binary 10100000 to 10111111. 69. A system as in claim 68, wherein a Request Reference is used to link A-bis messages to location events. 70. A system as recited in claim 67, wherein the emergency call indication is determined from monitoring of use of an Emergency Setup message. 71. A system as in claim 58, wherein the monitored communications includes an Immediate Assignment Command.