An Improved Tomlinson-Harashima Precoder Reducing Transmission Power

Tomlinson-Harashima precoder (THP) is an efficient interference pre-canceler, however, the transmission power is increased over the symbol power due to the modulo operation. In this paper, we propose an improved THP that reduces the transmission power of the conventional THP by tilting a group of symbols by an angle toward minimizing the transmission power. The tilted angle can be either estimated by the receiver or notified by the transmitter using a feed-forward information. Assuming a large interference, the average transmission power of the proposed THP is derived by the central limit theorem and Gumbel extreme value distribution. The symbol error rate (SER) and its asymptotic behavior is also derived and compared. The more tilted angles or the smaller size of groups are used, the more power the proposed THP saves. The transmission power can even be less than the symbol power. Accordingly, in an environment that the power gain overwhelms the other losses, the SER can be less than the SER of AWGN channel.