Spectrum sharing in cognitive two-way relay networks

Spectrum sharing between primary and secondary systems in cognitive two-way relay networks is discussed in this paper. A two-phase spectrum sharing protocol is proposed, in which a secondary (cognitive) user acts as the relay to assist the bidirectional primary transmission. Analog network coding (ANC) is employed for two-way relaying between the two primary users, and spectrum sharing is achieved by superimposing the secondary signal on the network-coded primary signals at the secondary relay. We analytically derive the outage probability of the primary users under our proposed two-phase protocol, and identify the spectrum sharing regions within which the spectrum sharing protocol can achieve higher (or at least equal) outage performance for the primary users than direct transmission without spectrum sharing. Results show that our proposed two-phase spectrum sharing protocol can outperform another recently proposed three-phase protocol which is based on decode-and-forward (DF) network coding operation.