Joint Filter Design of Alternate MIMO AF Relaying Networks with Interference Alignment

We study in this paper a two-hop relaying network consisting of one source, one destination, and three amplify-and-forward (AF) relays operating in a half-duplex mode. In order to compensate for the inherent loss of capacity pre-log factor 12 in a half-duplex mode, we consider alternate transmission protocol among three relays where two relays and the other relay alternately forward messages from source to destination. We consider a multiple-antenna environment where all nodes have M antennas. Aligning the inter-relay interference due to the alternate transmission is utilized to make additional degrees of freedom (DOFs) and recover the pre-log factor loss. It is shown that the proposed relaying scheme can achieve 3M4 DOFs compared with the M 2 DOFs of conventional AF relaying. In addition, suboptimal linear filter designs for a source and three relays are proposed to maximize the system achievable sum-rate for different fading scenarios when the destination utilizes a linear minimum mean-square error filter for decoding. We verify from our selected numerical results that the proposed filter designs give significant improvement over a naive filter or conventional relaying schemes. Index Terms Relaying network, amplify-and-forward, half-duplex, alternate relaying, interference alignment, linear filter design. K.-H. Park and M.-S. Alouini are with the Electrical Engineering Program, Physical Science and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal, Makkah Province, Kingdom of Saudi Arabia (Email: {kihong.park; slim.alouini}@kaust.edu.sa). This paper is an extended version of work accepted for presentation at the IEEE International Conference on Communications (ICC’12), Ottawa, Canada, June 2012.