Distributed Cognitive Sensing for Time Varying Channels: Exploration and Exploitation

Spectrum under-utilization calls for the open and dynamic spectrum access mechanism, which allows the unlicensed user equipped with cognitive radios to opportunistically sense and access the spectrum that not occupied by primary users. In practice due to the hardware limitations, each cognitive radio user may be only able to sense a portion of the interested wide span spectrum. Hence, a hardware-constrained cognitive MAC to conduct efficient and intelligent spectrum sense decision is desired. In this paper, we formulate the cognitive radio spectrum sensing problem under time-varying channels as an adversarial bandit problem without any assumption of the channel statistics. A fully distributed strategy is proposed to address the fundamental tradeoff between spectrum exploration and spectrum exploitation during the sensing periods. Simulation results demonstrate that significant performance gain can be achieved by the proposed algorithm when the channels are time-varying on small time-scales. A coordination scheme for the multi-user case is also presented and the effectiveness is also demonstrated by the simulation results.