Mobile-assisted network based techniques for improving accuracy of wireless location system

• US 6,463,290 B1
• Filed: 10/03/2000
• Issued: 10/08/2002
• 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: Sachdev, Vineet, Anderson, Robert J., Sheehan, Joseph W., Stilp, Louis A., Rogers, Alan E. E.
• Primary Examiner(s): LE, THANH C
• Application Number:
  US09/679,228
• Time in Patent Office: 735 Days
• Field of Search: 455/403, 455/404, 455/422, 455/423, 455/424, 455/425, 455/67.1, 455/456, 455/457, 455/69, 342/450, 342/457
• US Class Current: 455/456.1
• 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 5/021 Calibration, monitoring or correction G01S5/0252 takes precedence
• CPC Class Codes: G01S 5/0273 using multipath or indirect path propagation signals in position determination
• 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

Abstract

The accuracy of the location estimate of a Wireless Location System is dependent, in part, upon both the transmitted power of the wireless transmitter and the length in time of the transmission from the wireless transmitter. In general, higher power transmissions and transmissions of greater transmission length can be located with better accuracy by the Wireless Location System than lower power and shorter transmissions. Wireless communications systems generally limit the transmit power and transmission length of wireless transmitters in order to minimize interference within the communications system and to maximize the potential capacity of the system. Several methods meet the conflicting needs of both systems by enabling the wireless communications system to minimize transmit power and length while enabling improved location accuracy for certain types of calls, such as wireless 9-1-1 (emergency) calls. Such methods include mobile-assisted techniques in which the mobile unit includes functionality to assist in improving location accuracy. The WLS locates the transmitter (mobile unit) while the latter is using a modified transmission sequence comprising a message sent from the wireless transmitter using transmission parameters different from the normal transmission parameters broadcast on the forward control channel by the base stations in the associated wireless communications system. A trigger event, such as the user dialing 9-1-1, causes the mobile unit to operate in the mode in which the modified transmission sequence is used.

Claims

1. A method for use in a Wireless Location System (WLS) in locating a mobile wireless telephone, including a wireless telephone or other type of transmitter, comprising:

a) receiving normal transmission parameters from a base station;

b) initiating a call on the wireless telephone by pressing a sequence of keys;

c) comparing the sequence of keys with a trigger event stored within the mobile wireless telephone; and

d) if the sequence of keys matches the trigger event, then employing a modified transmission sequence for completing the call with the mobile wireless telephone.

2. A method as recited in claim 1, wherein the modified transmission sequence comprises the wireless unit increasing its transmitted power by a predetermined amount over a power level setting in the normal parameters, up to a maximum power setting.

3. A method as recited in claim 2, wherein the modified transmission sequence comprises the wireless unit increasing its transmitted power to the maximum power setting.

4. A method as recited in claim 1, wherein the modified transmission sequence comprises the wireless unit transmitting an additional predetermined number of access probes even after the base station has acknowledged receipt of the access probes.

5. A method as recited in claim 1, wherein the modified transmission sequence comprises the wireless unit including additional fields in the transmitted message even if these fields are not requested in the normal parameters broadcast on forward channels by the base station.

6. A method as recited in claim 5, wherein the additional field is an Authentication field.

7. A method as recited in claim 5, wherein the additional field is a Serial Number field.

8. A method as recited in claim 5, wherein the additional field is a Mobile Assisted Channel Allocation Report field.

9. A method as recited in claim 1, wherein the modified transmission sequence comprises the wireless unit following a transmitted message with one or more repeated registration messages.

10. A method as recited in claim 9, wherein the one or more repeated registration messages are of the normal length determined from the transmission parameters broadcast on the forward channels by the base station.

11. A method as recited in claim 9, wherein the one or more repeated registration messages are modified to a longer length by including additional fields.

12. A method as recited in claim 1, wherein the modified transmission sequence comprises the wireless unit following a transmitted message transmitted on a first one of a plurality of channels with one or more repeated registration messages transmitted on a second one of the plurality of channels.

13. A method as recited in claim 12, wherein the one or more repeated registration messages are of the normal length determined from the transmission parameters broadcast on the forward channels by the base station.

14. A method as recited in claim 12, wherein the one or more repeated registration messages are modified to a longer length by including additional fields.

15. A method as recited in claims 11 or 14, wherein the additional field is an Authentication field.

16. A method as recited in claims 11 or 14, wherein the additional field is a Serial Number field.

17. A method as recited in claims 11 or 14, wherein the additional field is a Mobile Assisted Channel Allocation Report field.

18. A method as recited in claims 11 or 14, wherein the additional field is a Capability Report field.

19. A method as recited in claim 12, wherein the second one of a plurality of channels is selected to be one in use by a second base station within listening range of the wireless unit and for which the wireless unit can receive the forward control channel broadcast by that second base station.

20. A method as recited in claim 12, wherein the second one of a plurality of channels is selected to be one for which the wireless unit can detect no forward control channel activity by any base station.

21. A method as recited in claim 19, wherein the second base station may be the same as the first base station, another sector of the first base station, or an entirely separate base station.

22. A method as recited in claim 20, wherein the wireless unit will transmit the one or more registration messages without expecting any acknowledgement from the wireless communications system.

23. A method as recited in claim 1, wherein the trigger events are permanently stored in the wireless unit.

24. A method as recited in claim 1, wherein the trigger events are programmed by the user into the wireless unit.

25. A method as recited in claim 1, wherein the trigger events are broadcast by the wireless communications system for receipt by a plurality of wireless units.

26. A method as recited in claim 1, wherein the actions to be taken during the modified transmission sequence are permanently stored in the wireless unit.

27. A method as recited in claim 1, wherein the actions to be taken during the modified transmission sequence are programmed by the user into the wireless unit.

28. A method as recited in claim 1, wherein the actions to be taken during the modified transmission sequence are broadcast by the wireless communications system for receipt by multiple wireless units.

29. A method as recited in claim 1, wherein the trigger event includes the dialed digits “

9-1-1”

.

30. A method as recited in claim 1, wherein the wireless unit deactivates encryption when a trigger event occurs.

31. A method as recited in claim 1, wherein the wireless unit deactivates encryption for all messages transmitted as part of the modified transmission sequence.

32. A method as recited in claim 1, wherein the modified transmission sequence comprises transmission of an EDGE (Enhanced Data Rates for Global Evolution) signal by the wireless unit.

33. A method as recited in claim 32, wherein the EDGE signal is a 200 KHz EDGE signal.

34. A method as recited in claim 32, wherein the mobile unit monitors applicable PTCHs (EDGE Packet Traffic Channels) for activity, selects an idle PTCH and timeslot, and transmits a plurality of frames.

35. A method as recited in claim 34, wherein the mobile unit transmits its identity in a formatted message in the frames sent on the PTCH, and subsequently resumes normal call processing.

36. A method as recited in claim 1, wherein the modified transmission sequence comprises the generation of a new wider-band signal designed to significantly enhance location processing.

37. A method as recited in claim 36, wherein the new wider-band signal comprises an overlay wideband signal on a set of predefined channels.

38. A method as recited in claim 37, wherein the set of predefined channels comprises 30 KHz channels.

39. A method as recited in claim 37, wherein the new wider-band wideband signal is a spread spectrum transmission overlaid on 21 to 42 RF channels, 5 to 8 milliseconds in length, and repeated several times on a 24 millisecond repetition cycle.

40. A method as recited in claim 37, wherein the new wider-band signal is overlaid on existing AMPS RECC channels.

41. A method as recited in claim 37, wherein the new wider-band signal is overlaid on unoccupied spectrum in the 1900 MHz band.

42. A method as recited in claim 37, wherein the mobile unit scans a carrier spectrum and determines whether to overlay the wideband signal on existing AMPS RECC channels or on unoccupied spectrum in the 1900 MHz band;

and then transmits an RDATA L3 message indicating the intended channels to use for transmission.

43. A method as recited in claim 42, wherein, if AMPS RECC is selected, the mobile unit transmits an invalid AMPS RECC burst followed by the new wider-band signal.

44. A method as recited in claim 42, wherein, if unoccupied spectrum is selected, the mobile unit still transmits an invalid AMPS RECC burst in the unoccupied spectrum followed by the new wider-band signal.

45. A method as recited in claim 36, wherein the new wider-band signal is characterized by energy placed complementary to the energy in either AMPS or TDMA signals.

46. A method as recited in claim 45, wherein the new wider-band signal is transmitted in bandwidth gaps between channels of an IS-136B signal comprising symbols having a 3 dB bandwidth of 24.3 kHz and bandwidth gaps between adjacent channels.

47. A method as recited in claim 45, wherein the new wider-band signal is a “

comb”

signal.

48. A method as recited in claim 47, wherein the mobile unit transmits an RDATA L3 message that identifies the mobile unit, followed by the comb signal, wherein the comb signal comprises a series of narrowband transmissions of less than about 1 KHz centered on RF channel boundaries of an AMPS RECC or TDMA DTC frequency plan.

49. A method as recited in claim 47, wherein the comb signal comprises transmissions in a fixed frequency pattern.

50. A method as recited in claim 47, wherein the comb signal comprises transmissions in a frequency pattern downloaded from a cell site.

51. A method as recited in claim 36, wherein the new wider-band signal comprises transmissions on both a CDMA Access Channel and an AMPS RECC.

52. A method as recited in claim 51, wherein the use of both the CDMA Access Channel and AMPS RECC provides a frequency separation of about 5 to 10 MHz.

53. A method as recited in claim 52, wherein the mobile unit transmits an L3 message on the CDMA Access Channel, followed with a second message on the AMPS RECC.

54. A method as recited in claim 53, wherein the mobile unit uses the AMPS RECC assigned to the same cell site and sector as the CDMA Access Channel used for an initial burst.

55. A method as recited in claim 54, wherein the message sent on the AMPS RECC is an invalid message, thereby avoiding causing the base station to assign an analog voice channel.

56. A method as recited in claim 55, wherein the message is made invalid by using an illegal digital color code.

57. A method as recited in claim 55, wherein the message is made invalid by transmitting a message with an invalid check sum.

58. A method as recited in claim 36, wherein the new wider-band signal comprises transmissions on an unoccupied PCS CDMA carrier.

59. A method as recited in claim 58, wherein the mobile unit searches a designated PCS frequency band to determine the presence of unoccupied spectrum.

60. A method as recited in claim 59, wherein the unoccupied spectrum is identified as spectrum within the designated frequency band of a particular carrier for which the mobile unit can detect no CDMA Pilot Channels.

61. A method as recited in claim 60, wherein, once the mobile unit has selected the RF channel on which to transmit, the mobile unit transmits an L3 message on a valid Access Channel on a CDMA RF carrier.

62. A method as recited in claim 61, wherein the L3 message is followed with one or more high power Access Channel transmissions in the chosen unoccupied spectrum.

63. A method as recited in claim 36, wherein the new wider-band signal comprises transmissions in an unoccupied 850 MHz spectrum.

64. A method as recited in claim 63, wherein the transmissions of the new wider-band signal occupy a guard band between CDMA carriers and AMPS channels.

65. A method as recited in claim 63, wherein the transmissions of the new wider-band signal occupy spectrum remaining after AMPS channels have been removed.

66. A method as recited in claim 63, wherein the mobile unit searches the 850 MHz frequency band to determine the presence of unoccupied spectrum, identified as spectrum within the designated frequency band of a particular carrier for which the mobile phone can detect no CDMA Pilot Channels or AMPS channels.

67. A method as recited in claim 66, comprising an algorithm whereby the mobile unit searches in a particular default sequence beginning with the portion of the band that will be last assigned to a CDMA RF carrier.

68. A method as recited in claim 67, wherein the algorithm is fixed in the mobile unit.

69. A method as recited in claim 67, wherein the algorithm is downloaded under carrier control.

70. A method as recited in claim 67, wherein, once the mobile unit has selected the spectrum and bandwidth of the spectrum on which it intends to transmit, it then communicates the intended spectrum and bandwidth of the spectrum in an L3 message on a valid Access Channel on a CDMA RF carrier monitored by the wireless location system.

71. A method as recited in claim 70, wherein the L3 message is immediately followed with one or more high power transmissions in the chosen unoccupied spectrum.

72. A wireless telephone, adapted for use in connection with a mobile-assisted network based wireless location technique, comprising:

means for receiving normal transmission parameters from a base station of a wireless communications system;

means for initiating a call on the wireless telephone when a user presses a sequence of keys;

means for comparing the sequence of keys with a trigger event stored with the wireless telephone; and

means for employing a modified transmission sequence for completing the call if the sequence of keys matches the trigger event.

73. A wireless telephone as recited in claim 72, wherein the modified transmission sequence comprises the wireless telephone increasing its transmitted power by a predetermined amount over a power level setting in the normal parameters, up to a maximum power setting.

74. A wireless telephone as recited in claim 73, wherein the modified transmission sequence comprises the wireless telephone increasing its transmitted power to the maximum power setting.

75. A wireless telephone as recited in claim 72, wherein the modified transmission sequence comprises the wireless telephone transmitting an additional predetermined number of access probes even after the base station has acknowledged receipt of the access probes.

76. A wireless telephone as recited in claim 72, wherein the modified transmission sequence comprises the wireless telephone including additional fields in the transmitted message even if these fields are not requested in the normal parameters broadcast on forward channels by the base station.

77. A wireless telephone as recited in claim 76, wherein the additional fields comprise an Authentication field.

78. A wireless telephone as recited in claim 76, wherein the additional fields comprise a Serial Number field.

79. A wireless telephone as recited in claim 76, wherein the additional fields comprise a Mobile Assisted Channel Allocation Report field.

80. A wireless telephone as recited in claim 72, wherein the modified transmission sequence comprises the wireless telephone following a transmitted message with one or more repeated registration messages.

81. A wireless telephone as recited in claim 80, wherein the one or more repeated registration messages are of the normal length determined from the transmission parameters broadcast on the forward channels by the base station.

82. A wireless telephone as recited in claim 80, wherein the one or more repeated registration messages are modified to a longer lend by including additional fields.

83. A wireless telephone as recited in claim 72, wherein the modified transmission sequence comprises the wireless telephone following a transmitted message transmitted on a first one of a plurality of channels with one or more repeated registration messages transmitted on a second one of the plurality of channels.

84. A wireless telephone as recited in claim 83, wherein the one or more repeated registration messages are of the normal length determined from the transmission parameters broadcast on the forward channels by the base station.

85. A wireless telephone as recited in claim 83, wherein the one or more repeated registration messages are modified to a longer length by including additional fields.

86. A wireless telephone as recited in claim 82 or 85, wherein the additional fields comprise an Authentication field.

87. A wireless telephone as recited in claim 82 or 85, wherein the additional fields comprise a Serial Number field.

88. A wireless telephone as recited in claim 82 or 85, wherein the additional fields comprise a Mobile Assisted Channel Allocation Report field.

89. A wireless telephone as recited in claim 82 or 85, wherein the additional fields comprise a Capability Report field.

90. A wireless telephone as recited in claim 83, wherein the second one of a plurality of channels is selected to be one in use by a second base station within listening range of the wireless telephone and for which the wireless telephone can receive the forward control channel broadcast by that second base station.

91. A wireless telephone as recited in claim 83, wherein the second one of a plurality of channels is selected to be one for which the wireless telephone can detect no forward control channel activity by any base station.

92. A wireless telephone as recited in claim 90, wherein the second base station may be the same as the first base station another sector of the first base station, or an entirely separate base station.

93. A wireless telephone as recited in claim 83, wherein the wireless telephone will transmit the one or more registration messages without expecting any acknowledgement from the wireless communications system.

94. A wireless telephone as recited in claim 72, wherein the trigger events are permanently stored in the wireless telephone.

95. A wireless telephone as recited in claim 72, wherein the trigger events are programmed by the user into the wireless telephone.

96. A wireless telephone as recited in claim 72, wherein the trigger events are broadcast by the wireless communications system for receipt by a plurality of wireless telephones.

97. A wireless telephone as recited in claim 72, wherein the actions to be taken during the modified transmission sequence are permanently stored in the wireless telephone.

98. A wireless telephone as recited in claim 72, wherein the actions to be taken during the modified transmission sequence are programmed by the user into the wireless telephone.

99. A wireless telephone as recited in claim 72, wherein the actions to be taken during the modified transmission sequence are received from the wireless communications system.

100. A wireless telephone as recited in claim 72, wherein the trigger event includes the dialed digits “

9-1-1”

.

101. A wireless telephone as recited in claim 72, wherein the wireless telephone deactivates encryption when a trigger event occurs.

102. A wireless telephone as recited in claim 72, wherein the wireless telephone deactivates encryption for all messages transmitted as part of the modified transmission sequence.

103. A wireless telephone as recited in claim 72, wherein the modified transmission sequence comprises transmission of an EDGE (Enhanced Data Rates for Global Evolution) signal by the wireless telephone.

104. A wireless telephone as recited in claim 103, wherein the EDGE signal is a 200 KHz EDGE signal.

105. A wireless telephone as recited in claim 103, wherein the wireless telephone monitors applicable PTCHs (EDGE Packet Traffic Channels) for activity, selects an idle PTCH and timeslot, and transmits a plurality of frames.

106. A wireless telephone as recited in claim 105, wherein the wireless telephone transmits its identity in a formatted message in the frames sent on the PTCH, and subsequently resumes normal call processing.

107. A wireless telephone as recited in claim 72, wherein the modified transmission sequence comprises the generation of a new wider-band signal designed to significantly enhance location processing.

108. A wireless telephone as recited in claim 107, wherein the new wider-band signal comprises an overlay wideband signal on a set of predefined channels.

109. A wireless telephone as recited in claim 108, wherein the set of predefined channels comprises 30 KHz channels.

110. A wireless telephone as recited in claim 108, wherein the new wider-band wideband signal is a spread spectrum transmission overlaid on 21 to 42 RF channels, 5 to 8 milliseconds in length, and repeated several times on a 24 millisecond repetition cycle.

111. A wireless telephone as recited in claim 108, wherein the new wider-band signal is overlaid on existing AMPS RECC channels.

112. A wireless telephone as recited in claim 108, wherein the new wider-band signal is overlaid on unoccupied spectrum in the 1900 MHz band.

113. A wireless telephone as recited in claim 108, wherein the wireless telephone scans a carrier spectrum and determines whether to overlay the wideband signal on existing AMPS RECC channels or on unoccupied spectrum in the 1900 MHz band;

and then transmits an RDATA L3 message indicating the intended channels to use for transmission.

114. A wireless telephone as recited in claim 113, wherein, if AMPS RECC is selected, the wireless telephone transmits an invalid AMPS RECC burst followed by the new wider-band signal.

115. A wireless telephone as recited in claim 113, wherein, if unoccupied spectrum is selected, the wireless telephone still transmits an invalid AMPS RECC burst in the unoccupied spectrum followed by the new wider-band signal.

116. A wireless telephone as recited in claim 107, wherein the new wider-band signal is characterized by energy placed complementary to the energy in either AMPS or TDMA signals.

117. A wireless telephone as recited in claim 116, wherein the new wider-band signal is transmitted in bandwidth gaps between channels of an IS-136B signal comprising symbols having a 3 dB bandwidth of 24.3 kHz and bandwidth gaps between adjacent channels.

118. A wireless telephone as recited in claim 116, wherein the new wider-band signal is a “

comb”

signal.

119. A wireless telephone as recited in claim 118, wherein the wireless telephone transmits an RDATA L3 message that identifies the wireless telephone, followed by the comb signal, wherein the comb signal comprises a series of narrowband transmissions of less than about 1 KHz centered on RF channel boundaries of an AMPS RECC or TDMA DTC frequency plan.

120. A wireless telephone as recited in claim 118, wherein the comb signal comprises transmissions in a fixed frequency pattern.

121. A wireless telephone as recited in claim 118, wherein the comb signal comprises transmissions in a frequency pattern downloaded from a cell site.

122. A wireless telephone as recited in claim 107, wherein the new wider-band signal comprises transmissions on both a CDMA Access Channel and an AMPS RECC.

123. A wireless telephone as recited in claim 122, wherein the use of both the CDMA Access Channel and AMPS RECC provides a frequency separation of about 5 to 10 MHz.

124. A wireless telephone as recited in claim 123, wherein the wireless telephone transmits an L3 message on the CDMA Access Channel, followed with a second message on the AMPS RECC.

125. A wireless telephone as recited in claim 124, wherein the wireless telephone uses the AMPS RECC assigned to the same cell site and sector as the CDMA Access Channel used for an initial burst.

126. A wireless telephone as recited in claim 125, wherein the message sent on the AMPS RECC is an invalid message, thereby avoiding causing the base station to assign an analog voice channel.

127. A wireless telephone as recited in claim 126, wherein the message is made invalid by using an illegal digital color code.

128. A wireless telephone as recited in claim 126, wherein the message is made invalid by transmitting a message with an invalid check sum.

129. A wireless telephone as recited in claim 107, wherein the new wider-band signal comprises transmissions on an unoccupied PCS CDMA carrier.

130. A wireless telephone as recited in claim 129, wherein the wireless telephone searches a designated PCS frequency band to determine the presence of unoccupied spectrum.

131. A wireless telephone as recited in claim 130, wherein the unoccupied spectrum is identified as spectrum within the designated frequency band of a particular carrier for which the wireless telephone can detect no CDMA Pilot Channels.

132. A wireless telephone as recited in claim 131, wherein, once the wireless telephone has selected the RF channel on which to transmit, the wireless telephone transmits an L3 message on a valid Access Channel on a CDMA RF carrier.

133. A wireless telephone as recited in claim 132, wherein the L3 message is followed with one or more high power Access Channel transmissions in the chosen unoccupied spectrum.

134. A wireless telephone as recited in claim 107, wherein the new wider-band signal comprises transmissions in an unoccupied 850 MHz spectrum.

135. A wireless telephone as recited in claim 134, wherein the transmissions of the new wider-hand signal occupy a guard band between CDMA carriers and AMPS channels.

136. A wireless telephone as recited in claim 134, wherein the transmissions of the new wider-band signal occupy spectrum remaining after AMPS channels have been removed.

137. A wireless telephone as recited in claim 134, wherein the wireless telephone searches the 950 MHz frequency band to determine the presence of unoccupied spectrum, identified as spectrum within the designated frequency band of a particular carrier for which the mobile phone can detect no CDMA Pilot Channels or AMPS channels.

138. A wireless telephone as recited in claim 137, comprising an algorithm whereby the wireless telephone searches in a particular default sequence beginning with the portion of the band that will be last assigned to a CDMA RF carrier.

139. A wireless telephone as recited in claim 138, wherein the algorithm is fixed in the wireless telephone.

140. A wireless telephone as recited in claim 138, wherein the algorithm is downloaded under carrier control.

141. A wireless telephone as recited in claim 138, wherein, once the wireless telephone has selected the spectrum and bandwidth of the spectrum on which it intends to transmit, it then communicates the intended spectrum and bandwidth of the spectrum in an L3 message on a valid Access Channel on a CDMA RF carrier.

142. A wireless telephone as recited in claim 141, wherein the L3 message is followed with one or more high power transmissions in the chosen unoccupied spectrum.