Tomlinson–Harashima precoding for transmitter‐side inter‐symbol interference cancellation in PSK modulation

Dirty paper coding (DPC) is a non-linear transmit scheme in presence of known interference, which is capacity achieving. Unfortunately, the implementation complexity of DPC is usually prohibitive. A sub-optimal yet practical method to implement DPC in inter-symbol interference channels is Tomlinson-Harashima precoding (THP). However, THP is not applicable to the constant-envelope phase shift keying (PSK) modulation. In this study, a modified Tomlinson-Harashima precoder is proposed to implement DPC for PSK modulation. The technique involves design of decision region at the receiver side and an algorithm to select the phase of transmitted symbol optimally at the transmitter side accordingly. Various patterns, namely, striped, checked, hexagonal, and radial are proposed and examined. Simulation results show that by using the proposed equaliser, the error floor is eliminated and significantly smaller bit-error rate is achieved. Numerical and simulation results show that the striped pattern outperforms other decision region designs. Moreover, its implementation and computational complexities is almost the same as the Tomlinson-Harashima precoder.