Patent ID: 8253628

Claim:
A method of calibrating un-calibrated time information within a mobile terminal having one or more receivers, a first receiver capable of receiving signals from which calibrated time information carried by a calibrated system can be extracted, and the first or second receiver being capable of receiving signals from multiple transmitters of an un-calibrated stable communications system, said transmitters having offsets in their signal transmission times, from which signals un-calibrated time information carried by said un-calibrated stable communications system may be extracted together with the transmission time offsets, the method comprising: determining said transmission time offsets using only the signals transmitted by the transmitters of the un-calibrated stable communication system and without requiring the mobile terminal to register on the un-calibrated stable communications system; at a first terminal position where the signals from a first set of said transmitters of said un-calibrated stable communications system are available and the signals from the calibrated system are available, determining, within the terminal, first travel times of the signals from said first set of said transmitters and the transmission times offsets of said first set of said transmitters, and the time offset between said calibrated time information extracted from the calibrated system and said un-calibrated time information extracted from the un-calibrated stable communications system; and at a second terminal position, where calibrated time information is not available but where the signals from a second set of said transmitters and one of said first set of said transmitters of said un-calibrated stable communications system are available, determining, within the terminal, second travel times of the signals from the transmission time offsets of said second set of said transmitters and said one of said first set of said transmitters, and calibrating said un-calibrated time information, extracted from signals of the un-calibrated stable communications system using said first and second travel times, said transmission time offsets, and said time offset determined at the first terminal position.