ARQ Protocols for Two-User Cooperative Diversity Systems

Automatic repeat-request (ARQ) protocols for two-user cooperative diversity system employing Alamouti space-time coding are investigated in this paper. A whole cooperative transmit frame of the original cooperative system consists of three sub-frames. According to different feedback schedules in a transmit frame at the destination, two basic ARQ protocols, namely post-cooperating and pre-cooperating, are proposed and analyzed. We show that both proposed ARQ protocols can improve the throughput in two-user cooperative system. Pre- cooperating protocol yields 50% gains in users' throughput than post-cooperating protocol if both users have high user-destination average received signal-to-noise ratio (SNR) at the destination. Nevertheless, if both of user-destination average received SNRs are low, post-cooperating protocol is more effective than pre-cooperating protocol. Proposed protocols provide useful basic tools for designing more complicated ARQ protocols. Finally, simulation results verify our analysis.