Energy-Spectrum Efficiency Trade-Off in Energy Harvesting Cooperative Cognitive Radio Networks

This paper addresses energy efficiency (EE)-spectrum efficiency (SE) trade-off in an energy harvesting (EH) cooperative cognitive radio network operated in a frame structure comprising of spectrum sensing (SS) and cooperation-transmission mode. The secondary users (SUs) are clustered into two groups and function in a way that when the SUs in Group I participate in cooperative SS, the SU nodes in Group II harvest energy from the radio frequency signal of primary user (PU). If PU is detected to be in transmit mode, the SU nodes in Group II cooperate in PUs transmission while the SUs in Group I perform EH. All the SU nodes transmit data when PU is detected idle. The objective is to maximize EE and SE via joint optimization of SS time, final decision threshold, self and cooperative transmission power gains. Mathematical analysis is done to solve the problem of EE-SE trade-off under the constraints of SS reliability, SU power budget, PU cooperative SE and fairness in SE for each SU. Numerical results highlight about 19% and 14% gain in normalized EE and SE values, respectively, compared to the existing work and the issue of EE-SE trade-off is clearly investigated.