We describe a new type of radio navigation and tracking system which, unlike conventional systems, does not depend on a costly infrastructure of coherent radio transmitters. This new system measures positions using spatial, rather than temporal, coherence and can therefore use any existing radio transmitters set up for any purpose. We describe the principles of operation, applications and present results obtained with a demonstration unit (in Cambridge) which can measure the position of a motor vehicle to a precision of about 5 m using local medium-wave public broadcast transmitters.
