Local area radio navigation - A tool for GPS-denied geolocation

Ranger is a local area radio frequency ranging system implemented in the 2.4 GHz Industrial, Scientific and Medical band. Roundtrip time-of-flight measurements are made in a two-stage process: a coarse measurement provides +/- 3.4 m accuracy, followed by a fine measurement correction that reduces error to below 20 cm. This innovative approach can be implemented in other parts of the radio frequency spectrum; the 2.4 GHz band was chosen both for regulatory acceptance and availability of commercial components. The Ranger system consists of fixed and mobile radios. Fixed location radios provide the reference from which distances are measured to the mobile radio. A single distance measurement requires approximately 50 ins, therefore with a network of four fixed radios, the position of the mobile can be updated five times per second. Additionally, the digital communications link that is used for distance measurement is also used for concurrent high-bandwidth data communication.