Cooperative Spectrum Sharing in OFDM Two-Way Relay Systems With Bidirectional Transmissions

In this letter, we propose a cooperative spectrum sharing protocol, where both primary users (PUs) and secondary users (SUs) achieve bidirectional transmission. In particular, the SUs help PUs to achieve their bidirectional target rates through orthogonal frequency division multiplexing two-way relaying. In return, the PUs allow SUs to communicate bidirectionally on a subset of subcarriers. Subcarrier and power allocation are jointly optimized for both directions to maximize the SU data rate, given that the PUs' target rate is satisfied. Simulation results demonstrate a significant enhancement in spectrum efficiency compared with several benchmark schemes.