Channel estimation and demodulation of asynchronous CDMA signals in frequency-selection fading channels

In this paper, we propose an iterative scheme for joint tracking of fading channels and demodulation of multiuser CDMA signals operating asynchronously over multipath fading channels. We use the expectation maximization algorithm to track the time-varying channel and as a by-product we also achieve estimates of the input signals. We show that the maximum a posteriori estimates of the fading channels is iteratively computed by the Kalman smoother. The input signals are demodulated using a hidden Markov model smoother. Our scheme has computational complexity and memory requirement that grow linearly with the data length. Computer simulations illustrate the performance of our proposed detection and estimation method.