Power allocation for cognitive D2D communication assisted by two-way relaying

In this paper, we propose an optimal power allocation algorithm for a cognitive radio (CR) network where a D2D pair as two secondary users (SUs) exchange their information through a relay node using network coding. Our proposed algorithm is subject to satisfying the peak transmit power constraints and the interference power constraints since the two D2D users are allowed to share the same spectrum with a primary user (PU). Applying these limitations, we provide the optimal power allocation and obtain the minimum outage probability of the D2D users in a Rayleigh block fading channel. In addition, we evaluate the performance of the direct transmission (DT) scheme without relay for comparison. Numerical results show the superiority of the proposed relay forward transmission (RFT) scheme over the DT scheme.