Hierarchically Modulated Network-Coding-Assisted Cooperation in Multiuser Relay Networks

A scheme that employs hierarchical modulation with network coding (HMNC) to minimize the number of transmission phases for information exchange among users in a multiuser relay network is developed in this paper. Specifically, for a network with multiple users and one relay, we exploit HM in all user nodes and design a joint HM and NC scheme at the relay, so that 'side-information' of a user node gained during other users' transmission phases is used efficiently to achieve a much higher system sum-rate than existing schemes while maintaining a comparative error performance. The bit error rate (BER) and the achievable sum-rate of the proposed scheme are analyzed analytically. These results can be used to optimize a network design for a proper tradeoff between reliability and effectiveness. The advantages of the proposed scheme in achievable sum- rate and BER over both AWGN and Rayleigh fading channels are verified through comparison with existing schemes that use only HM or only NC at the relay.