Performance of a TDOA-AOA hybrid mobile location system

A time difference of arrival (TDOA) technique has been proposed for providing location services in future UMTS networks. The performance of such a system is limited by errors in the time difference (TD) measurements primarily cause by non-line of sight (NLOS) propagation conditions. In future systems angle of arrival (AOA) measurements at the serving base station (BS) may be available, primarily as a requirement to increase downlink capacity via beamforming. These measurements may also be useful far location purposes, though they will also be subject to errors caused by NLOS propagation conditions between the mobile (MS) and the serving BS. In this paper the performance improvement of a TDOA location system utilising the AOA measurement from the serving BS, over a TDOA only system is evaluated. Simulation results are presented which show that location accuracy improvement is possible even in highly NLOS conditions. Furthermore location estimation is now possible when only two BSs are detectable, rather than the three BSs required in the TDOA only system, thus increasing the coverage of the system.