Two-way relaying with distributed role selection

It is well known that for classical analog network coding (ANC) protocol, the maximum achievable diversity gain is one according to previous investigations. Nonetheless, the pursuit of higher diversity gain, as an eternal topic in the field of cooperative diversity, calls for cooperative strategies with a higher diversity order. In this paper, we attempt to break this durance by designing cooperative strategies with an improved diversity gain. Specifically, assuming a two-way relaying scenario, we incorporate an opportunistic role decision mechanism into ANC protocol and propose a distributed role selection (ROSE) strategy (a.k.a. d-ROSE) to designate the cooperative role of each node in a fully dynamic manner. It is proved that the proposed d-ROSE strategy can make exactly the same role decision with the counterpart of the optimal ROSE strategy, achieving therefore the outage-optimal transmission robustness. In particular, both theoretical analysis and numerical results demonstrate that besides maintaining a low signaling overhead to make role decision, the d-ROSE strategy can achieve a diversity order of two, i.e., one order higher than that of classical ANC protocol.