RF Ranging for Location Awareness

Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, to republish, to post on servers or to redistribute to lists, requires prior specific permission. Wireless sensor networks provide an opportunity to improve performance in areas ranging from energy efficiency to industrial processes to scientific research. Many applications require awareness of sensor location, but autonomously determining device location has proven to be challenging. This localization problem can be divided into two parts: measuring relationships between nodes, and then using these relationships to estimate location. Most work on the first part has measured the RF received signal strength as a surrogate for range resulting in poor location accuracy. Several other methods have been studied with varying performance and limitations. The second part has received significant research attention resulting in several good algorithms. This work considers the first part of the localization problem and discusses RF time of flight ranging for location awareness in local area networks. A roundtrip RF time of flight ranging method for narrow-band radios is presented that successfully deals with the many error sources that cause RF based ranging methods to suffer from poor 2 accuracy and high system complexity. This method has been implemented on a custom software defined radio platform and a network of these devices has demonstrated meter level location accuracy.