Secure resource allocations for polarization-enabled cooperative cognitive radio networks with energy harvesting capability

We address secure communications over energy-harvesting based OFDMA cooperative cognitive radio networks, where one primary user (PU) cooperates with several secondary users (SUs) in terms of both information transmission and energy harvesting. To improve spectrum utilization and ensure that SU transmitters can harvest as much energy as possible, we suppose that SUs are equipped with orthogonally dual-polarized antennas. Based on these setting-ups, we propose the polarization-enabled two-phase cooperative framework, where SU transmitters first apply power splitting technique to harvest energy from radio frequency signals radiated by the PU transmitter, and then use the harvested energy to concurrently transmit their own and the PU's data. Under the proposed framework, we develop the secure resource allocation schemes for the scenarios when SU receivers are untrusted users, implying that each SU receiver may overhear the PU's and the other SUs' confidential information. For this scenario, which has hardly been studied, we investigate the joint allocation of relays, subcarriers, power splitting ratios, and powers, with the objective to maximize the total secrecy rate of all SUs while guaranteeing the PU's minimum secrecy rate. Finally, we validate and evaluate our proposed cooperative framework and resource allocation schemes through numerical analyses.