Performance of Retransmission Partner Selection Scheme for Cooperative HARQ

User cooperation is employed to explore the inherent distributed spatial diversity priority of wireless network. Nodes based rather than linked based protocol is employed and the broadcast nature of radio network is considered by user cooperation. However cooperative partner selection might be difficult especially for nomadic cooperative networks as it requires partner's additional power consumption and it's generally quite limited due to battery size. Therefore partner selection metric should be carefully designed to meet high system power efficiency (SPE) that takes both source and partners power consumption into account. As the transmission power of the source is supposed to be fixed, high SPE requires minimal partner's forwarding power for certain reception performance. In this paper a novel retransmission partner selection method for cooperative HARQ is proposed to meet high SPE, which requires the forwarding power consumption for certain received SNR as small as possible. After the reception of 1st transmission fails, a SNR based region selection method is employed to choose the proper forwarding partner. Partners with different distance from destination would use different transmission power to ensure the reliable reception at the destination and the one with minimal forwarding power will be selected to improve SPE. As the partner moves towards the destination the required forwarding power for certain FER performance could be reduced. However, if it were too far from the source the received SNR would be less than the sensitivity and the partner isn't able to recognize the message needs forwarding. The tradeoff between system performance and forwarding power is studied and the preferred partner is suggested by simulation for high SPE.