In this paper, we consider a modulation scheme for a network-coded bi-directional relaying (CBR) scheme in which two different signals from mutually communicating nodes are network-coded in the relay node. It employs dual constellations as a useful means of dealing with its performance degradation in the CBR over asymmetric channel (i.e., the different signal-to-noise ratio in each link), which provide not only a diversity gain from the symbol repetition but also a coding gain from the constellation rearrangement to protect the network-coded symbols. We study the channel utilization and bit error rate performance of the different CBR schemes to show that the proposed diversity-enhanced CBR system always outperforms other existing systems as long as traffic load is properly balanced along the bi-directional links.
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