Joint data detection and estimation of time‐varying multipath rayleigh fading channels in asynchronous DS‐CDMA systems with long spreading sequences

Abstract

Abstract. In this paper, we present a joint approach to data detection and channel estimation for the asynchronous direct-sequence code-division multiple access (DS-CDMA) systems employing orthogonal signaling formats and long scrambling codes. Our emphasis is placed on different channel estimation algorithms since the performance of a communication system depends largely on its ability to retrieve an accurate measurement of the underlying channel. We investigate channel estimation algorithms under different conditions. The estimated channel information is used to enable coherent data detection to combat the detrimental effect of the multiuser interference and the multipath propagation of the transmitted signal. In the considered multiuser detector, we mainly use interference cancellation techniques, which are suitable for long-code CDMA systems. Interference cancellation and channel estimation using soft estimates of the transmitted signal is also proposed in this paper. Different channel estimation schemes are evaluated and compared in terms of mean square error (MSE) of channel estimation and bit error rate (BER) performance. Based on our analysis and numerical results, some recommendations are made on how to choose appropriate channel estimators in practical systems.

Iterative Multiuser Detection and Decoding for DS-CDMA System With Space-Time Linear Dispersion

“…To prevent error propagation from the decision feedback, soft interference cancellation was proposed, e.g., in [27], for uncoded Q-ary DS-CDMA systems. The rationale is that the cancellation with hard decisions tends to propagate errors and increase the interference with incorrect decision feedback, while with soft cancellation, an erroneously estimated symbol usually has a small LLR and does not make much contribution to the feedback, and therefore, the error propagation problem is alleviated.…”