Efficient ARQ Protocols for a Two-Way Amplify-and-Forward Relaying System

In this paper, we investigate automatic repeat request (ARQ) protocols for a two-way amplify-and-forward relaying system. We first propose an outage-efficient ARQ protocol which exploits two-way retransmission for failure of reception at both terminals and one-way retransmission for failure of reception at only one terminal. This scheme significantly reduces the outage probability of the system at a cost of spectral efficiency loss due to the use of one-way retransmission. To fully utilize the channel resources, we also propose a spectral-efficient ARQ protocol that adopts two-way partial retransmission, instead of one-way retransmission, when reception failure occurs at only one terminal, where the corresponding source performs retransmission and the other source continues to transmit new data. Through an outage probability analysis, it is proved that both of the proposed ARQ protocols achieve full temporal diversity. Simulation results of them also show that the outage-efficient approach attains a lower outage probability, while the spectral-efficient approach achieves a higher effective throughput.