Joint spectrum access and transmission power management for energy harvesting cognitive radio sensor networks

In this paper, we investigate the joint optimisation of spectrum access and the transmission power for an energy harvesting cognitive sensor node, which operates in time-slotted fashion with causal knowledge of channel conditions along with the energy harvesting states. Allowing for the sensing imperfection, we formulate this joint optimisation problem as an infinite-horizon discrete time Markov decision process (MDP), in which the cognitive sensor aims at maximising the long-term expected throughput. An optimal policy which specifies the spectrum access decision as well as the power level is proposed. It is indicated that the optimal long-term expected throughput is non decreasing with the battery available energy. Moreover, we introduce a low-complexity policy and prove that the optimal low-complexity policy has a threshold structure with respect to the battery available energy. An efficient algorithm for deriving the optimal low-complexity policy is introduced. Finally, numerical results are presented to confirm the superiority of proposed policies.