Patent ID: 7277050

Claim:
A positioning system that determines a position of a positioning terminal, the system including a plurality of first signal sources each emitting a respective first signal, and one or more second signal sources each emitting a respective second signal, the first signals being synchronous with a reference time and the second signals being non-synchronous with the first signals, that, based on a signal propagation time and signal propagation speed of the first signals, determines a distance from the positioning terminal, said positioning system comprising: a measurement device that receives the first signals from the first signal sources to determine a position P of the measurement device and a time of measurement when the measurement device receives the first signals and that, based on the time of measurement, measures a receiving time (TR), based on the reference time, of a predetermined event of the second signals; a control device that determines a signal propagation time (t) between the measurement device and one of the second signal sources by calculating a relative distance |P−Q| between the measurement device and the one second signal source based on the position P measured by the measurement device and a position Q of the one second signal source and by dividing the resulting distance by the signal propagation speed, and determining a time (TT), based on the reference time, at which the one second signal source originates the predetermined event by solving TR-t; the positioning terminal having a receiving device that receives the signals from the first and second signal sources; and a communication device that communicates between the control device and the positioning terminal, wherein the positioning terminal uses the time TT to limit a search for the signals from the first signal sources, and uses the signals from the first signal sources to determine the position of the positioning terminal; wherein the measurement device further comprises a mobile terminal in good condition; wherein the position P of the measurement device can be determined without accurate time information; and wherein the measurement device measures P and TR and voluntarily reports the measured P and TR to the control device.