Iterative Channel Estimation for MIMO MC-CDMA

In this paper, we investigate the performance of a downlink multiple-input multiple-output (MIMO) multi-carrier code division multiple access (MC-CDMA) system employing a receiver with iterative channel estimation (ICE). The MC-CDMA system transmits several data symbols per user and per orthogonal frequency division multiplexing (OFDM) symbol in parallel, with each data symbol being spread with a Walsh-Hadamard code. Due to the superposition of spread data signals, (chips), zero-valued subcarriers can occur, which cannot be used to compute least-squares (LS) channel estimates in ICE. Further, the transmitted data signals coincide non-orthogonal at each receive antenna. Hence, we propose the modified LS (MLS) MIMO channel estimation method to overcome these problems and avoid noise enhancement in ICE. We further investigate the robustness of ICE with the MLS MIMO method if the channel statistics are not perfectly known.