Hybrid ARQ for modulo loss reduction in multi-user MIMO THP systems

Multi-user MIMO (MU-MIMO) using Tomlinson-Harashima precoding (THP) has great potential to achieve high system capacity in wireless systems. On the other hand, hybrid ARQ (HARQ) is essential to realize the reliable wireless packet transmission and therefore, the combination of THP with HARQ can be seen as a promising approach to achieve reliable high-capacity wireless transmissions. However, this combination has a problem of severe performance degradation due to the accumulation of modulo loss which is the inherent drawback of THP. In this paper, we propose the HARQ scheme to cancel the accumulation of modulo loss in Multi-user MIMO THP systems. The main feature of the proposed approach is to add the same perturbation vector as the initial transmit packet to the retransmit packets in order to prevent the accumulation of modulo loss. The effectiveness of the proposed scheme is demonstrated in comparison with the conventional packet combining scheme by means of computer simulations.