Joint Iterative Channel Estimation and Multiuser Detection for Overloaded MIMO OFDM Systems

In this paper, a joint iterative channel estimation (CE) and multiuser detection (MUD) technique is proposed for overloaded multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems. In the first iteration, a pilot based channel estimator is employed, which can provide estimated channel impulse responses (CIRs) for the detector. At the detection part, the CIRs are used to calculate the reliable log-likelihood ratio (LLR) for the decoder. The calculated soft signals from decoder output can be used to improve the accuracy of CE. Low complexity RAKE reception and parallel interference cancellation (PIC)-based approach is also used to reconstruct the interference, which can obtain more reliable LLRs, and therefore more accurate soft signals. The simulation results show that the proposed joint method can make full use of CIRs to obtain the channel gain, and the performance of detection is affected by CE, but not much.