Block diagonalization for interference mitigation in Ka-band backhaul networks

This paper considers the design of precoding and decoding techniques for backhaul networks at Ka band. In this frequency band, large antenna arrays must be employed with appropriate beamforming and precoding techniques to combat the high path loss. Traditional multi-antenna systems use digital baseband beamforming and precoding that is not economical for large antenna arrays due to its cost and power consumption. Recently, hybrid analog-digital solutions were suggested for millimeter wave multiple-input-multiple-output systems. They rely on two steps. The first step consists of an analog only beamforming which aims at the exploitation of the high antenna gain offered by the large-scale antenna array. The second step mitigates the multiuser interference by means of digital precoding. In this paper, we focus on the second step of the hybrid precoding. We propose a solution for interference mitigation in multi-base station scenarios. Our solution is based on a block diagonalization technique and requires full channel state information at each base station of a backhaul network. The performance of the algorithm is compared to a partial block diagonalization which was originally proposed for the single base station downlink scenario.