Modulo loss reduction for Tomlinson-Harashima precoding in a multi-beam satellite forward link

Full frequency reuse in multi-beam satellite communication systems allows to achieve a high capacity, provided that the inter-beam co-channel interference (CCI) can be properly dealt with. Tomlinson-Harashima precoding (THP) is a popular technique applied at the basestation transmitter to cancel the interference in the forward link. However, the conventional detection of THP, involving a modulo operation at the receiver terminals, is known to suffer from modulo loss, which becomes considerable at low SNR. This contribution explores alternative detection techniques to reduce the modulo loss. We point out that by applying proper signal rotations at the basestation transmitter, these alternative detectors almost completely recover the modulo loss for 2-PAM, achieving a higher mutual information (MI) than 4-QAM at low SNR.