Turbo Equalization based Iterative Channel Estimation in SDMA SC-FDE Systems

In this paper, we propose an LDPC-based Frequency Domain (FD) turbo receiver to improve the channel estimates iteratively in a Single Carrier Frequency Domain Equalization (SC-FDE)1 uplink system in the presence of intra and inter-cell interference. Upper layer co-ordination is necessary to keep the average received power of the co-channel Out of Cell Interferers (OCIs) low. Such control can be achieved by appropriate frequency reuse strategy. It is shown that in an interference-prone system, a combination of orthogonal pilots, spatial processing and Iterative Channel Estimation (ICE) with Turbo Equalization (TE) is effective. Low-Density Parity-Check (LDPC) code-based adaptive FDTE is employed to improve the decisions. An attempt is made to suppress the effect of OCIs using a sub-space technique by estimating the correlation matrices of the OCIs. It is shown that a combination of Parallel Interference Cancellation (PIC) with the turbo processing is a promising way to improve the channel estimation and to suppress inter-user effects caused by inter-cellular and intra-cellular interference.