Aimed at the problem that system energy consumption of the traditional cooperative multicast is large with increase of the number of users, four energy-efficient relay selection schemes are proposed to reduce system energy consumption. By using exhaustive search method, the optimal relay selection algorithm selects relays from all the possible combinations of relays, the scheme could reduce energy consumption and improve energy efficiency effectively at high computational complexity. According to the thought of iteration, greedy algorithm chooses relays using the selected relays, though the scheme doesn't achieve the energy efficiency of the optimal relay selection algorithm, it reduces computational complexity. Besides, relay selection based on multicast rate of users selects relays using the multicast rate of each user by which the rest users with bad channel condition could decode data correctly, and relay selection based on channel state information (CSI) among users chooses relays according to the whole CSI between each user decoded data correctly and all users failed to decode data, these two schemes further reduce complexity compared to greedy algorithm. Results show that all the proposed energy-efficient relay selection approaches could improve energy efficiency while meeting the requirement of fairness.
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