Energy and throughput tradeoff in hybrid cognitive radio networks based on POMDP

This paper considers energy-constrained cognitive radios (CR) which can access a time-slotted licensed spectrum band in hybrid mode. At the beginning of each time slot, CR decides whether to be idle or to transmit. If transmission, CR has to determine which access mode to operate in. If the underlay mode is selected, CR shares spectrum with licensed systems by transmitting with a low power to ensure interference constraints. If the hybrid mode is selected, CR has to carry out spectrum sensing to detect spectrum occupancy. If the sensing outcome indicates idle, CR operates in overlay access mode; otherwise, CR operates in underlay access mode. The objective is to investigate the tradeoff between energy consumption and throughput gain. To this end, CR dynamically determines its operation mode for each time slot, e.g., to be idle or to transmit, and determines the sensing time and access mode if it is to transmit. We formulate this problem as a partially observable Markov decision process (POMDP) and prove important properties of the optimal policy. Simulation results validate our analysis and performance of the proposed dynamic control approach.