Multistage decision-directed channel estimation scheme for DS-CDMA system with M-ary orthogonal signaling

In this paper, a multistage decision-directed channel estimation scheme is proposed for a coherent direct-sequence code-division multiple-access (DS-C DMA) system with M-ary orthogonal signaling, The receiver with multistage d ecision-directed channel estimator makes alternate use of symbol detection and channel estimation in an iterative manner, resulting in a multistage st ructure where each stage consists of an estimator and a detector. The estim ator obtains the estimates of the channel by using the decisions from the d etector in the previous stage, and the detector uses these estimates for co herent detection of the transmitted symbols. Modifications to the process o f generating the channel estimates and the decision variables are made to m itigate the error propagation in successive stages. It is shown that the pe rformance of the proposed estimation scheme is better than the conventional scheme, especially for channels with high diversity order. The gain is mos tly achieved by two stages for channels with low diversity order and by fiv e stages for channels with high diversity order, The proposed scheme can be used to increase the capacity of DS-CDMA systems currently operating in su ch environments.