Synchronizing ranging signals in an asynchronous ranging or position system

Abstract

In a local positioning system, the land-based transmitters include free running oscillators or oscillators free of clock synchronization with any remote oscillator. A reference receiver receives the ranging signals from different transmitters and generates timing offset information, such as code phase measurements. The timing offset information is then communicated back to transmitters. The temporal offset information indicates relative timing or phasing of the different transmitted ranging signals to the reference receiver. The transmitters then transmit the temporal offset information with the ranging signals, such as modulating the transmitted code by the timing offset information. A mobile receiver is operable to receive the ranging signals and timing offset information in a same communications path, such as on a same carrier. Position is determined with the temporal offset information and the ranging signals. The temporal offset information for the various transmitters allows the mobile receiver to more accurately determine position than in an unsynchronized system.