A 2.4 GHz high precision local positioning system based on cooperative roundtrip time of flight ranging

In this work, a novel high precision local positioning system is presented. The system is capable of determining the two- or three-dimensional position of a localization unit relative to a set of wireless active transponders, which are mounted at defined anchor positions in a range of up to 200 meters. Operating in the 2.4 GHz ISM band at a bandwidth of approximately 60 MHz, the localization unit carries out distance measurements to the transponders and then calculates its own position in space by the use of a multilateration algorithm. The ranging measurements are based on a cooperative roundtrip time of flight estimation, using amplitude modulated pseudo-noise sequences for pulse compression and a time division multiple access scheme to support multiple transponders in a single measurement cycle. In contrast to multilateration systems based on the time difference of arrival, our roundtrip time of flight system does not need synchronization by wires or fibers between the anchor nodes. This makes setup and operation as easy as placing the transponders and their power supply at precisely known positions in the field. In this paper, the system setup and the used algorithms are described, and an evaluation of the performance is given from outdoor field tests, comparing the position estimates to those of a commercial differential GPS system with inertial sensor support. The raw, untracked positioning results show an accuracy in the decimeter region with seven anchor transponders in a field of 180 x 200 meters.