Joint Precoder and Decoder for MIMO Dual-Hop Relay Systems in Delay Spread Channels

Multiple input multiple output (MIMO) dual-hop relay systems in delay spread channels are analyzed in this work. The delay spread channel caused by multipath phenomenon in radio propagation is a major reason of intersymbol interference (ISI), increasing bit error ratio (BER) significantly at large enough delay time. To solve this problem, a joint of linear precoder and decoder is designed using unweighted minimum mean-squared error (MMSE) criterion for the system in two proposed schemes. The relay in Scheme 1 has none of the precoder and the decoder whereas that in Scheme 2 has both of them. System performance is evaluated in both perfect and imperfect channel state information (CSI) conditions. With the perfect CSI, the system is analyzed under effects of parameters such as modulation order, data block size, and delay tap numbers to form the basis for selecting their values. With the imperfect CSI, factors including correlation coefficients and estimation error variances are considered to evaluate their effects on the system performance. Simulation results show that BER of Scheme 1 is better with the perfect CSI but more sensitive to CSI errors than that of Scheme 2 is. Which scheme is suitable for a practical system it depends on a trade-off between complexity of the system and accuracy of the channel estimation.