Patent ID: 6898197

Claim:
A method for geographically locating a mobile terminal within a wireless CDMA communication system having base stations with fixed locations, the method comprising: transmitting from a plurality of base stations a first spread spectrum signal having an associated code; receiving of the first spread spectrum signals transmitted by said plurality of base stations at the mobile terminal; for each received first spread spectrum signal, transmitting a second spread spectrum signal having an associated code time synchronized with that received first spread spectrum signal from the mobile terminal to said plurality of base stations, wherein the synchronizing of the associated code of the second spread spectrum signal with that received first spread spectrum signal is by despreading that received first spread spectrum signal using the associated code of the first spread spectrum signal, processing that despread received first spread spectrum signal by a delay lock loop, and adjusting a timing of the associated code of the first spread spectrum signal used for despreading and a clock pulse in response to the delay lock loop, and adjusting a timing of the associated code of the second spread spectrum signal in response to the adjusted timing of the clock pulse and the associated code of the first spread spectrum signal; receiving the second spread spectrum signals at the plurality of base stations; determining a delay between each base station and the mobile terminal based on in part a received timing of the second signals, wherein the determining a delay between each base station and the mobile terminal is by despreading that received second spread spectrum signal using the associated code of the second spread spectrum signal, processing that despread received second spread spectrum signal by a delay lock loop, and adjusting a timing of the associated code of the second spread spectrum signal used for despreading in response to the delay lock loop, and comparing a timing of the time adjusted associated code of the second spread spectrum signal and the associated code of the first spread spectrum signal; and determining the mobile terminal's geographic location based on in part round trip delay information between the mobile terminal and each base station of signals transmitted between the mobile terminal and the respective base stations.