Iterative Demodulation and Channel Estimation for Asynchronous Joint Multiple Access Reception

Iterative demodulation with integrated channel estimation is investigated for multiple access systems as alternative to separate estimation/demodulation, which is the current state-of-the-art method. While basic theoretical system performance is well understood, practical aspects such as those arising from estimating the time-varying channels due to parameter drifts or inherent channel dynamics are not so well explored. The integration of adaptive estimators for these time-varying channels into the iterative receiver is studied, and it is shown that simple correlation-based estimators are sufficient to allow adequate tracking even for time-varying channels in a multiple access environment, and that near-ideal performance of the receiver is achievable. The requirements of the estimators and their performance in the demodulation loops are investigated via system convergence functions. Quantitative analytical results are verified with selected simulation examples. Spread-spectrum access is used to illustrate the principles of iterative demodulation and other potential areas for application are identified and discussed.