Patent ID: 7363043

Claim:
A passive self locating device that uses GSM common channel signals (containing FCCH, SCH, and BCCH data) transmitted by GSM base transceiver stations (BTS's) associated with a GSM network to determine its geographic location, comprising: a receiver to locate a most local BTS by scanning GSM common channel signals and identifying a common channel signal having the highest power level, thereby identifying the common channel frequency of the most local BTS; the receiver further to monitor the common channel frequency of the most local BTS, obtain the SCH data and interpret the BCCH data from the most local BTS to identify the most local BTS, and obtain common channel frequencies of at least two additional BTS's; the receiver further to tune to the additional BTS's, to obtain their identities, and to receive SCH data from the additional BTS's; an observed time difference measurement unit to use the SCH data to measure the observed time differences between transmissions from the most local BTS and the additional BTS's; a database memory that stores data representing geographic locations of BTS's near the device; and a processing unit to receive observed time difference data from the measurement unit and geographic location data from the database memory, and to use that data and time offset data to determine device location data representing the current location of the device; wherein the device determines its location from only GSM common channel signals and the data contained therein, without additional data transmitted from the GSM network, and without authorization from the GSM network and without communication of any nonbroadcast messages within the GSM network.