Combination of spectrum allocation and multi-relay selection in overlay cognitive radio network

In overlay cognitive radio network, the available spectrum for secondary users are dynamically grabbed from a wideband of hundreds megahertz by spectrum sensing, which leads to remarkably differential path loss among different frequencies according to propagation theory. Adjusting the global path loss of cognitive relay system through spectrum allocation can serve nontrivial increment to the performance of multi-relay selection. In this paper, we propose a novel scheme combining multi-relay selection with spectrum allocation in the cognitive radio relay system to obtain maximum signal to noise ratio (SNR) at the receiver, called SAMS (spectrum allocation and multi-relay selection). Given the available frequencies, we first search all the possible resolutions for spectrum allocation, then make multi-relay selection under each possible spectrum allocation resolution to optimize the SNR value at the receiver. Finally, we choose the largest SNR, achieve the corresponding spectrum allocation resolution and also figure out the selected relays. Compared with conventional multi-relay selection scheme (CMS), simulation results demonstrate that our proposed scheme has a 4dB-increment of SNR value at the receiver.