Iterative MAP channel estimation and multiuser detection for DS-CDMA in frequency-selective fading channels

A joint channel estimation and symbol detection scheme is proposed for asynchronous code-division multiple-access systems over multipath fading channels. A low-complexity Kalman-like filter is developed for blind channel tracking using the recursive expectation maximization (EM) algorithm and the maximum a posteriori probability (MAP) symbol detection method. The recursive EM algorithm yields channel estimates with discrete valued phase ambiguities. By exploiting the statistical properties of the EM-based blind estimators as well as the robustness of noncoherent MAP detection to phase errors, a method to resolve the phase ambiguity problem even in the presence of a deep fading environment is proposed. Based on the proposed blind channel estimator and phase corrector, an iterative structure is introduced for joint channel estimation, symbol detection and soft multiple access interference cancellation.