Antenna array using channel estimation in an M-ary orthogonal DS/CDMA system

Various studies have shown that adaptive antenna array techniques are good one to cancel multipath and multiuser interference. However, many of them need training signals to estimate the desired signal or have heavy complexity to compute the algorithmic processing. In this paper, an antenna array receiver in a direct sequence/code division multiple access (DS/CDMA) system with M-ary orthogonal modulation is proposed. At every antenna element a channel estimation technique is used, which refers to the maximum correlator output of a RAKE receiver. The estimated channel coefficients enable the signal to be detected coherently with no need of training signals. Moreover, the antenna weights, which are determined by the estimated channel coefficients, make it possible to focus the receiver on the desired signal and to suppress the interference signal. Consequently, the proposed receiver has 2D (dimensions) RAKE structure which can exploit both spatial diversity and temporal diversity. Simulation results show that the performance of the proposed scheme improves 1.5 dB in E_b/N_o at a BER = 10^-3 over the receiver of noncoherent detection. The results also show that at a BER = 10^-2 the proposed receiver improves about 2.3 times and 3 times system capacity with 3 and 5 antenna elements, respectively.