EM estimation algorithm for TDR-IDMA systems in complex multi-path channel

In this paper, we propose a channel estimation algorithm for the interleave-division multiple access systems (IDMA) system based on time-reverse (TR) technique (named as TDR-IDMA), which can accelerate the execution of multi-user detection (MUD) algorithm for IDMA systems. In the TDR-IDMA systems, the time-reversed version of channel impulse responses (TR-CIR) is used to perfume the pre-processing for the received signal to accelerate signal to interference and noise ratio (SINR). Therefore, we need the channel state information (CSI) from channel estimator at the receiver. The complex multi-path channel estimation approach based on the expectation maximization (EM) algorithm is proposed for the TDR-IDMA system. At the first iteration we use the pilot sequences to estimate the initial channel information, and the soft estimates from the IDMA signal detector combined with the pilot information to refine the channel coefficients in the following estimation iterations. The simulation results indicate that the bit-error-rate (BER) performance of the proposed channel estimation algorithm is very close to that of ideal channel estimation.