Joint Tomlinson-Harashima Precoding and Transmit Equalization in Time-Domain for Single-Carrier MU-MIMO Block Transmission

This paper is concerned with cyclic prefix (CP) inserted broadband single-carrier (SC) multi-user multi-input multi-output (SC-MU-MIMO). The use of Tomlinson-Harashima precoding (THP) is effective to remove the inter-user interference (IUI). To remove the inter-symbol interference (ISI) caused by the channel frequency-selectivity, transmit equalization (TE) can be introduced. In the Degen and Rrühl´s SC-MU-MIMO scheme (called as FD-SC-TETHP in this paper), THP and TE are performed separately in the frequency-domain. The modulo operation in THP suppresses the power increase caused by the IUI removal. TE can remove the ISI and the amplitude variation in the signals of a block received at each user, though it increases the signal power after equalization. This degrades significantly the received signal-to-noise power ratio (SNR). In this paper, we propose a time-domain SC-TETHP (TD-SC-TETHP), in which the ISI subtraction is performed together with IUI subtraction both in the time-domain. The modulo operation suppresses the power increase caused by both IUI and ISI removal. To prevent the amplitude variation, pre-removal of the received signal amplitude variation is inserted between the modulo operation and the precoding matrix multiplication. Uncoded average bit error rate (BER) performance achievable by our proposed TD-SC-TETHP is evaluated by computer simulation to confirm its superiority to the FD-SC-TETHP. Computational complexity is also discussed.