Iterative decoding of coded Tomlinson-Harashima precoded signals

We present a new decoder for Tomlinson-Harashima precoded (THP) signals; it is used on a linear Gaussian channel with intersymbol interference. While the transmitter is not modified, the receiver modulo operation is replaced with an a posteriori probability (APP) module, which we term as enhanced modulo (EMOD). The EMOD accepts a priori probabilities, making it suitable for turbo operation when the THP signal is coded. The new scheme is much more complex than simple modulo operation and, in addition, induces delay. Its complexity depends exponentially on channel length. However, a large gain in performance may be obtained. The scheme performance is demonstrated for a convolutional code concatenated with THP on a few exemplary channels. Gains of up to 10 dB are demonstrated.