Cognitive radio technique improves spectrum utilization by allowing secondary users (SUs) to opportunistically exploit the authorized spectrum of primary users (PUs) to transmit their data. In order to avoid colliding with PU, SUs often sense the channel before transmission. As many secondary users are mobile devices, how to preserve energy consumption of the secondary users is considered in this paper. According to a defined utility function, SU dynamically schedules its actions, i.e., sensing, transmission or sleeping. the utility function is optimized based on the reward and penalty of sleeping actions. Those sleeping actions obeying the rule will be rewarded and those opposite actions will be penalized. SU schedules its action of sensing and sleeping so as to reach a tradeoff between the minimum energy consumption and PU's protection. By maximizing the mean benefit, the proposed strategy exhibits a simple threshold-based structure. Simulation results show that the proposed scheme can greatly reduce energy cost and achieve similar PU collision rate as previous works, with only negligible throughput reduction.
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