Bearing estimation with uniform resolution in broadband environments

High rate and highly reliable mobile communication systems require methods for acting against fading. One of the measures to cope with fading is spatial division multiple access (SDMA) which distinguishes radio signals in a space or angular domain by using antenna directivity or beamforming according to the direction of arrival (DOA) of signals. Conventional bearing angle estimators suffer from the different precision associated with different angles. The method presented in this paper employs a set of digital two-dimensional filters associated with different angles of arrival. Each filter is a fan filter and performs a broadband characteristic. It is shown that the precision of the bearing estimation is highly dependent upon the angle itself and is maximum in the broadside and minimum in the endfire. The set of filters is then designed according to the criteria obtained by theory, so that the precision at different angles is kept uniform. It is demonstrated by computer simulations that in the presence of noisy broadband incoming signals, the estimation of the arriving angle for different angles is accomplished with the same resolution and hence with this method complex and separately sectored antennas are not required.