Iterative Joint Data Detection and Channel Estimation for DS-CDMA Systems in the Presence of Time-Varying Channels

In this paper, we present an efficient iterative receiver structure of computationally tractable complexity for joint multiuser detection and multichannel estimation (JDE) of directsequence code-division multiple-access (DS-CDMA) systems operating in the presence of time-varying flat fading channel. The time-varying channel is assumed to be modeled according to a piece-wise constant channel model at the receiver. The scheme results from an application of the expectation-maximization (EM) algorithm. The resulting EM-JDE receiver updates the data bit sequences in parallel while the channel parameters are also updated in parallel. The EM algorithm provides a set of free parameters, called weight coefficients, which can be selected to optimize its performance. An optimality criterion is defined and analytical expressions for the corresponding optimized weight coefficients are given. Monte-Carlo simulations of a synchronous scenario show that the proposed JDE receiver have excellent multiuser efficiency and are robust against errors in the estimation of the channel parameters. Moreover, very short training sequences are required for the JDE schemes to converge.