IMPROVEMENTS TO TRACKING SYSTEMS

摘要

A spread-spectrum location and tracking system, is provided in which the vehicle (10) or object to be located emits a continual direct sequence spread spectrum radio signal (11). This transmission is received at a number of wellspaced receiving stations (12) in the coverage area and the differences in the times of arrival of the signals at these receivers are measured by determining the epoch corresponding to the correlogram peak. The carrier frequencies ƒ1, ƒ2, ƒ3 of transmitter transmissions received at a receiver site (12), are estimated and frequency errors apart from those due to relative motion between the transmitter and a particular receive site, will be seen as a common offset by all receive sites, and may thus be eliminated by suitable processing, allowing estimate of the velocity vector of a moving transmitter from a single set of measurements at (3) or more remote sites.