Opportunistic half-duplex/full-duplex relaying mode selection criterion in cognitive relay networks

In this paper, adaptive transmission in a cognitive relay network where a secondary transmitter acts as cooperative relay for a primary transmitter while in return gets the opportunity to send its own data is considered. An opportunistic half-duplex (HD)/full-duplex (FD) relaying mode selection criterion which can utilize the advantages of both HD and FD is proposed. The key idea is that the cooperative relay switches between the HD mode and the FD mode according to the residual self-interference power. When the residual self-interference power is lower than a preset threshold, the FD mode is selected to get a high throughput; otherwise, the HD mode is selected to avoid the effect of self-interference. The target is to maximize the throughput of secondary system under the interference constraint of primary system and transmission power constraints. As it is difficult to solve this optimization problem directly, an alternate optimization method is used to solve it, which optimizes amplification gains in HD and FD modes in turn until convergence. Simulation results show that the proposed opportunistic mode selection criterion can select an appropriate relaying mode to achieve a higher throughput than either the FD mode or the HD mode under different residual self-interference power regimes.