Large-System Analysis of Joint Channel and Data Estimation for MIMO DS-CDMA Systems

This paper presents a large-system analysis of the performance of joint channel estimation, multiuser detection, and per-user decoding (CE-MUDD) for randomly spread multiple-input multiple-output (MIMO) direct-sequence code-division multiple-access (DS-CDMA) systems. A suboptimal receiver based on successive decoding in conjunction with linear minimum mean-squared error (LMMSE) channel estimation is investigated. The replica method, developed in statistical mechanics, is used to evaluate the performance in the large-system limit, where the number of users and the spreading factor tend to infinity while their ratio and the number of transmit and receive antennas are kept constant. Joint CE-MUDD based on LMMSE channel estimation is compared to several methods of one-shot channel estimation, i.e., methods that do not utilize decoded data symbols to refine the initial channel estimates, in terms of spectral efficiency. Joint CE-MUDD is found to significantly reduce the rate loss caused by transmission of pilot signals when compared to the receivers based on one-shot channel estimation. This holds particularly for multiple-antenna systems. As a result, joint CE-MUDD can provide significant performance gains compared to the receivers based on one-shot channel estimation.