Outage Analysis of Opportunistic Cooperative Multi-Antenna Multicast Based on Space-Time Coding

Two Opportunistic Multi-antenna Relay Selection (OMRS) strategies are proposed and analyzed in Decode-and-Forward (DF) relay networks for cooperative multicast using space time codes, assuming multiple antennas are available at the relay nodes. These two strategies select the best relay based on (i) maximizing the average SNR and (ii) maximizing the minimum SNR respectively. The closed-form expressions of multicast outage probability for the two strategies are studied over Rayleigh fading channel. Simulations are provided to verify the correctness of the theoretical analysis. Our multicast outage probability results reveal that OMRS based on maximizing the minimum SNR is outage-optimal among multi-antenna relay selection schemes and approaches the space time codes scheme. Moreover, it can be found that compared with previous single-antenna Opportunistic Relaying (OR) scheme, OMRS brings remarkable performance improvement obtained from maximum ratio combining (MRC) and space-time coding, which proves that multiple antennas at the relays could provide more array gain and diversity gain.