Adaptive Coded Cooperation in Wireless Networks

User cooperation enables single antenna terminals to benefit from spatial diversity by partnering with other users to create a virtual transmit antenna array. A promising form of cooperation is called coded cooperation which integrates cooperation with channel coding, showing great performance gains. However, the optimal degree of cooperation between the users changes with the channel conditions and furthermore, there is no known expressions indicating the required degree of cooperation for given channel conditions. This paper proposes an adaptive protocol based on incremental redundancy using an ARQ/FEC scheme with rate-compatible punctured convolutional codes (RCPC). By employing a ACK/NACK feedback channel from the partner, each user incrementally decreases its coding rate in the first cooperation phase in order to increase its chances of being correctly decoded by the partner and thus benefit from spatial diversity, while preserving as much resources as possible to provide relaying diversity for the other user. Simulation results illustrate the gains and flexibility of our protocol for both reciprocal and non-reciprocal channels. The results show that our adaptive protocol outperforms for all channel conditions coded cooperation with a fixed degree of cooperation with gains on the order of 2 to 4 dB.