Optimal power allocation scheme for the two-way relay channel using ANC in cognitive radio

In this paper, we study the optimal power allocation (OPA) for the two-way relay channel employing the analogue network coding (ANC) protocol in cognitive radio (CR) network. The OPA scheme is proposed by minimizing the weaker link´s individual outage probability under the sum-power constraint and interference power threshold (IPT) constraints to the primary user (PU) in a Rayleigh fading channel environment. Particularly, for the purpose of accomplishing the power allocation more realistically, the interference to each other between PU and secondary user (SU) and relay is taken into consideration. And the closed-form solution for the optimum power allocation scheme of each case is derived. Numerical Results confirm that the system with the proposed scheme for the two-way relaying with ANC has a gain of 3dB over the equal power allocation (EPA) scheme no matter with or without IPT. When introduced IPT constraints into the optimization scheme, the outage probability of SU communication cannot be reduced after a certain level of total power, even though the total power is sufficient. Meanwhile, the best location for the relay is near by the middle point of the two end nodes regardless of the power allocation scheme.