Array Antenna Beamforming Based On Estimation Of Arrival Angles Using DFT On Spatial Domain

Abstract

Fading which is caused by multipath distortion due to wave reflection from an obstacle such as a building is a major problem in personal, indoor and mobile radio communications. As strategies for the fading, an error-correcting code, an automatic equalizer, and a diversity technique have been studied and developed. An adaptive array antenna, which is a kind of a diversity technique, is useful to suppress indirect or delayed signal waves due to multipath because it can adaptively direct its nulls at them[l][2]. Adaptive algorithm for controlling complex weights of antenna elements is required to achieve appropriate beamforming for direct and indirect signals with unknown arrival angles. In LMS (least mean square) algorithm, weights of antenna elements are adaptively updated so as to minimize mean square errors between antenna output and reference signals. In CMA (constant modulus algorithm), constant envelope of received constant modulus signals is used as a criterion to update the weights. These algorithms originate in the updating coefficients of adaptive digital filters and take a long time for convergence of weights because weights are updated sample by sample. Errors in the reference signals aff'ect the convergence of weights. If arrival angles of the received signals are varied quickly like in mobile communications, their adaptability will not be guaranteed.