Abstract: A navigation system in which an uncoordinated beacon positioning system (UBS) is used in conjunction with an absolute positioning system (APS) is described herein. The UBS employs a multiplicity of transmitters, at known locations, each of which transmits a beacon signal having a phase that is at least partially un-synchronized with the phases of the beacon signals of the other transmitters. Within a mobile unit, separate receivers are provided for receiving these beacon signals and for receiving APS signals. The absolute positioning system (APS) receiver is disposed to receive the APS signals, and to estimate an initial position of the mobile unit therefrom. The mobile unit processor is disposed to modify the estimated mobile unit position on the basis of the detected beacon signal phases. The mobile unit processor may also be programmed to determine the uncertainty of location information provided by the beacon signal receiver and by the APS receiver.

Abstract: A positioning system uses a multiplicity of commercial broadcast stereo FM radio signal transmitters, at known fixed locations, each of which transmits a beacon signal having a phase that is un-synchronized with the phases of the beacon signals of the other transmitters. All the beacon signals have a frequency approximately equal to a 19 KHz. A fixed position observer unit, positioned at a known location, receives the beacon signals from all the transmitters in the vicinity, determines their relative phases, and broadcasts data representing these relative phases. Mobile units, at unknown locations, receive these broadcast values, as well as beacon signals from at least three radio transmitters. Each mobile unit includes phase detection circuitry that detects the phases of the beacon signals at the mobile receivers current position. This is accomplished using a single radio signal receiver. A digital phase-locked loop, coupled to the radio signal receiver, generates a phase error signal for each beacon signal.