Adaptive Energy-Efficient Power Allocation under Imperfect Channel Sensing in OFDM-Based Cognitive Opportunistic Relaying Links

This paper investigates energy efficient power allocation scheme for OFDM-based cognitive opportunistic relaying links (CORL), where secondary users (SUs) may incorrectly sense the unlicensed spectrum and hence transmit data in collision. We aim to maximize the energy efficiency (EE) by optimal and low complexity power allocation design. At first, an energy efficient power allocation optimization problem with imperfect sense is formulated, under the individual power budget and peak primary user’s (PU’s) interference constraints. Then, we focus on the analysis of the optimal non-convex power allocation problem, which is of great concern for the EE in CORL. At last, with the aid of the fractional programming method, an EE-oriented power allocation policy with low complexity is proposed which used the bisection method to speed up the search of the optimum. Numerical results are provided to corroborate our theoretical analysis and to demonstrate the effectiveness of the proposed schemes. Key-Words: Cognitive Opportunistic Relay, OFDMA, Energy Efficiency, Power Allocation, Spectrum Sensing Errors, Low Complexity.