Opportunistic Stable Two-Way Relaying: With or Without Direct Link

In this paper, we investigate a three-node two-way relaying network over fading channels. The stability of this system is first discussed. Three protocols are then investigated in this work in terms of throughput, including the opportunistic digital network coding (ODNC) scheduling protocol, the physical network coding (PNC) protocol, and the cooperation protocol of DNC with direct link (CDNC-DL). For the first two protocols, we assume that the direct link is not available. For the third protocol, the direct link is available and can support data rates. The problems of maximizing the long-term totally fair optimal throughput with the three protocols, with respect to the stability constraints, are formulated and solved by allocating power resources with respect to channel fluctuations. To complement this work, optimal time resource allocation for each phase of the three protocols as well as the associated end-to-end throughput are investigated. In the end, it is shown in simulation that ODNC performs better than the conventional DNC and that CDNC-DL outperforms the other two proposed protocols as long as the direct link is in relatively good condition.