Improved Tomlinson-Harashima precoding with interference optimization

This paper investigates a novel strategy for reducing the power loss in Tomlinson-Harashima precoding (THP) based on optimising the interference to be canceled. The proposed scheme is motivated by the fact that, since both the desired and interfering signals originate from the base station (BS) of the downlink system, the resulting interference can be influenced to reduce the transmission power required to cancel it, without altering the information content of the downlink message. This optimization aims at bringing the interference closer to the replica of the desired symbol in the modulo-extended constellation. By doing so, the quantized distance between the useful signal and interference is reduced and therefore the power required to pre-subtract interference is decreased. Here, the above concept is applied to a practical THP design for multiple input multiple output systems (MIMO-THP). The results show a considerable transmit power reduction compared to conventional THP.