Method and apparatus for determining whether a wireless station is operating within a prescribed geographic region

A method for determining whether a mobile station is operating within a prescribed geographic region comprising the steps of:

• during an initialization session wherein said mobile station is operating within said prescribed geographic region:
• receiving pilot signals from a plurality of base stations;
• computing time delays between an expected time of receipt and actual time of receipt of said pilot signals from at least two of said base stations at said mobile station;
• storing said computed time delays in a memory of said mobile station;
• and
• during a check session subsequent to said initialization session:
• receiving pilot signals from a plurality of base stations;
• computing time delays between an expected time of receipt and actual time of receipt of said pilot signals from at least two of said base stations at said mobile station;
• comparing:
• a) the differences between the time delays of pilot signals of pairs of base stations computed during the check session;
• with
• b) the differences between the stored time delays of pilot signals of pairs of base stations computed during the initialization session;
• and
• determining that said mobile station is operating within a prescribed geographic region if results of said comparing step are within a predetermined tolerance.

A mobile station comprising:

• a receiver for receiving pilot signals from a plurality of base stations;
• means for computing time delays between an expected time of receipt and actual time of receipt of said pilot signals from at least two of said base stations at said mobile station;
• a memory for storing reference time delays;
• means for comparing said computed time delays with said stored reference time delays;
• and
• means for determining that said mobile station is operating within a prescribed geographic region if said computed time delays are within a predetermined tolerance of said stored reference time delays.