Moving object high-accuracy position locating method and system

Abstract

In an automated roadway system having transponders or data-stations spaced at known positions along the roadway, a vehicle mounted system determines the position of a vehicle moving along the roadway. A vehicle borne transmitter transmits a spread spectrum transmit signal which is pseudo (PN) encoded. The transmitted signal is received by the transponder which emits a reply signal back to a vehicle borne receiver. The receiver also receives a second signal which may be a reply signal from the same transponder or a reply signal from an adjacent transponder. The system then measures a time difference between transmission of the vehicle originated interrogation signal and receipt of its corresponding reply signal to determine the distance between the vehicle and the transponder or reflector. Based on the determined distances, the positions of the transponders and the distance that the vehicle has traveled during its communications, the position of a vehicle is determined using triangulation methods. The interrogation signals may be spread spectrum signals that are pseudo-random (PN) encoded. When the signal is detected by a receiver in the transponder or in the vehicle receiver, the PN code is synchronized to the incoming signal to accomplish maximum correlation. The phase delay between the transmitted PN code and received PN code is used to determine the distances between the vehicle and the transponder. The periodically located transponders produce a reply signal including a PN code and embedded data which represents the transponder identification and its position, or other data which is desirable to transmit between the transponder and the vehicle traveling the roadway.