Cooperative transmission is an emerging communication technique that takesadvantage of the broadcast nature of wireless channels. However, due to lowspectral efficiency and the requirement of orthogonal channels, its potentialfor use in future wireless networks is limited. In this paper, by making use ofmultiuser detection (MUD) and network coding, cooperative transmissionprotocols with high spectral efficiency, diversity order, and coding gain aredeveloped. Compared with the traditional cooperative transmission protocolswith single-user detection, in which the diversity gain is only for one sourceuser, the proposed MUD cooperative transmission protocols have the merit thatthe improvement of one user's link can also benefit the other users. Inaddition, using MUD at the relay provides an environment in which networkcoding can be employed. The coding gain and high diversity order can beobtained by fully utilizing the link between the relay and the destination. From the analysis and simulation results, it is seen that the proposedprotocols achieve higher diversity gain, better asymptotic efficiency, andlower bit error rate, compared to traditional MUD schemes and to existingcooperative transmission protocols. From the simulation results, theperformance of the proposed scheme is near optimal as the performance gap is0.12dB for average bit error rate (BER) 10^{-6} and 1.04dB for average BER10^(-3), compared to two performance upper bounds.
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