Relay-assisted MIMO transmission with three-phase scheduling in cognitive radio networks

In this paper, we investigate a joint scheduling and transmitting scheme in cognitive radio networks. Three phases are considered in the proposed scheme(named scheme 1): l)in the first phase, N_t primary users(PUs) in the high-rate region are chosen to implement communication with primary base station (PBS); 2)in the second phase, PBS will support simultaneously the fixed relay station(RS) and the selected PUs in the high-rate region based on certain beamforming(BF); 3)in the third phase, selected PUs in the low-rate region and selected cognitive users(CUs) in the cognitive region are supported by RS. In particular, during the phases above, all selected users send back their channel covariance matrices to PBS or RS on the purpose of lowering the feedback and implementing certain BE Furthermore, a frame structure used for the joint scheduling and transmitting scheme is presented and the performance of scheme 1 with imperfect channel covariance matrix feedback is evaluated to compare with that of scheme 1 with perfect feedback. From the simulation results, the proposed scheme(scheme 1) can significantly improve the throughput of the network over the basic system(named scheme 2) without spectral sharing.