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DF equalizer synthesis for ST-based MIMO OFDM transceiver exploiting ARQ retransmissions

In this paper, we address the synthesis of the receiver for a multiple input/multiple output (MIMO) communication system based on Automatic Repeat Request (ARQ) retransmission. More specifically, at the transmitter, we employ the orthogonal frequency division multiplexing (OFDM) on each transmit antenna in order to counteract the multipath degradations and, at the receiver, we propose to resort to a minimum-mean-square-error (MMSE) decision-feedback (DF) MIMO equalizer that can process the received signals over multiple OFDM symbol periods in order to exploit the time redundancy of the ARQ retransmissions at the data-link-layer. Moreover, we propose a transmitter architecture that space-time codes the OFDM signals on the transmit antennas when the ARQ retransmission occurs: such a strategy allows the MIMO transceiver to better exploit the space redundancy between multiple transmissions. The performance analysis has been carried out in terms of the packet delivery ratio and of the normalized throughput. The results show that both the uncoded and the coded systems can achieve important advantages with respect to the standard transceiver that does not exploit the time redundancy of the ARQ retransmissions. Moreover, by means of the computer simulations we show that the coded system is more robust to the channel state information errors with respect to the uncoded and the standard ones.