HARQ Throughput Performance of OFDM / TDM Using MMSE-FDE in a Frequency-selective Fading Channel
Throughput is an important performance measure for data communications over a wireless channel. Orthogonal frequency division multiplexing (OFDM) with hybrid automatic repeat request (HARQ) achieves a good throughput performance over a frequency-selective fading channel. In OFDM with HARQ, however, during the first transmission uncoded information packet is transmitted. Consequently, the channel frequencyselectivity cannot be exploited since frequency-domain equalization (FDE) is not designed to take the channel advantages. In particular, the HARQ throughput performance of OFDM cannot be improved even for a high signal-to-noise power ratio (SNR). In this paper, to increase the HARQ throughput of conventional OFDM, we present the use of OFDM combined with time division multiplexing (OFDM/TDM) using minimum mean square error FDE (MMSE-FDE) designed to exploit the channel frequency-selectivity. It was shown, by computer simulation, that OFDM/TDM using MMSE-FDE with HARQ achieves a higher throughput than the conventional OFDM due to frequency diversity gain during the first transmission. It was also shown that OFDM/TDM using MMSE-FDE performs better in a stronger frequency-selective fading channel.