Relay selection for multiuser MIMO amplify-and-forward relaying systems

Abstract

A variety of results to date have expressed the advantageous of relay nodes assisting transmissions in a wireless network. In a multi-user system, not all users may wish or be able to be involved in every transmission. However, idle users can be used as a relay node in each transmission when the system requires them. In this paper we propose a new multi-user MIMO cooperative communication protocol which combines block diagonalization (BD) with an amplify-and-forward cooperative Protocol. Comparing with related works we consider that each mobile station (MS) experiences co-channel interference (CCI) from other unassociated relay nodes. So the major concept behind the proposed scheme is to transform each MIMO relay channels into an equivalent block diagonal channel using BD, which removes CCI. First, Base station (BS) performs a selection phase and selects relays among idle users using the available channel state information in the mobile users and BS nodes. Next, BS at the first hop transmits a linear combination of the intended users' data to related relay nodes. Finally, at the second hop relays and BS transmit their own data to designated MS simultaneously. In order to achieve better diversity gain we utilize Space-Time Block codes in two transmission links, and each MS Combines the received signal of the two transmitters using maximal ratio combining (MRC). We compare our schemes' performance with direct noncooperative transmission.