A computationally efficient decorrelator for multibeam antennas using an iterative method with fast correlation in DS-CDMA systems

We present a fast method of reducing the computational complexity of a decorrelator, which is one of the suboptimal methods for eliminating multiple access interference (MAI) in direct sequence-code division multiple access (DS-CDMA) systems. The proposed approach rests upon the following: (1) incorporating a multibeam antenna to partially suppress the MAI, (2) an iterative method to obtain decorrelated signals rather than direct inversion of a correlation matrix of user codes, and (3) the FFT-based fast correlation for the multiplication of the correlation matrix and signal vector, exploiting the structural properties of the correlation matrix. The proposed decorrelator has a lower computational complexity than the conventional ones. Furthermore, the simulation results show that the proposed decorrelator achieves the same performance as the conventional decorrelators in terms of the bit error rate