MIMO relaying for multi-user transmission using a two stage transmit and relay pre-processing technique

The use of multiple antennas at both ends of a wireless link, known as multiple-input multiple-output (MIMO) wireless, has been shown to offer significant improvement in link reliability and spectral efficiency through space-time coding and spatial multiplexing respectively. In this contribution, a novel relaying strategy that uses MIMO relays in a two-hop wireless network is proposed to support multiuser transmission. We apply a two stage transmit and relay preprocessing technique in order to eliminate the multiple-user interference. The fixed relays process the received signal with linear operations and forward it to the multiple users i.e. the amplify-and-forward(AF) scheme. The users are partitioned into the number of groups equal to the number of relays. Each group of users communicates with its own specified relay terminal. The effective channel from transmitter to the relays and from relays to the users can be modeled as a broadcast channel and interference channel, respectively. This paper optimizes the relay amplification matrix and base station transmit power according to achievable sum rate at the users, neglecting the direct links from the base station to the users and with certain structure at the relays. Simulation results show that the sum rate achieved by the proposed system architecture is close to the sum rate achieved by the decode-and-forward relaying scheme.