Direction finding methods for CDMA systems

This paper examines the problem of estimating the angle of arrival (AOA) of a signal transmitted by a mobile user in a CDMA wireless network. This problem is of interest because AOA information can be used for geolocation services. If the power of the desired signal is high relative to the multiple access interference: conventional DF methods can be used. However, techniques which exploit a known sequence in the signal yield better performance at low power. The possibility of replacing the known sequence with an estimated sequence is investigated. It is shown that a simple demodulation does not provide adequate signal estimates for this purpose. Finally a modified ML method which is able to determine the AOA of each separate path in a coherent multipath environment is proposed.