Equalization and Precoding in Multi-User MIMO Relaying Systems and Their Diversity Bottleneck

In this paper, equalization and precoding in multiuser multiple-input/multiple-output (MIMO) relaying systems are considered. In particular, the user devices are connected to relays or small base stations which only cover small areas, socalled small cells. Via wireless backhaul, the relays are in turn connected to a central base station, forming a two-hop multiuser relaying system. It is shown how a naive realization of these relaying systems provokes a diversity bottleneck in the small cells, degrading the overall system performance. A strategy to prevent this bottleneck is proposed in combination with an antenna selection strategy for backhaul communication. Results obtained from numerical simulations are provided to complement the theoretical considerations. To this end, lattice-reduction-aided schemes are used to enable a full-diversity channel equalization.