An efficient iterative frequency domain equalization for relay-assisted ARQ single carrier transmissions

This paper proposed an efficient iterative frequency domain equalization (FDE) for cooperative multi-relay-assisted automatic repeat request (ARQ) single carrier systems operating over multiple-input-multiple-output (MIMO) channel. The receiver employs each retransmission as an additional set of virtual receive antennas to exploit the space diversity. At each iteration, soft inter-symbol interference (ISI) cancellation and inter-antenna interference (IAI) cancellation followed by minimum-mean-square-error (MMSE) based frequency domain filtering are carried out. The estimated symbols are demapped into bit extrinsic log likelihood ratio (LLR) using an equivalent Gaussian channel assumption as the input of the soft-in-soft-out (SISO) decoder. Both implementation for decode-and-forward (DF) and amplify-and-forward (AF) are investigated. Simulation results demonstrate the effectiveness of the proposed algorithm compared to conventional LLR-based combining scheme.