Wide-Band Collaborative Spectrum Search Strategy for Cognitive Radio Networks

We consider a scenario where
n
collaborating cognitive radios (CRs) try to jointly detect spectrum opportunities in a wide-band spectrum within a predefined spectrum sensing interval
T
_S
. We assume that each CR is equipped with a tunable bandpass filter (BPF) and is able to sense one frequency band (channel) at a time. The sensing interval consists of
L
sensing slots of length
T
. During each sensing slot, each of the collaborating CRs is assigned to sense one of the channels and report its observation to the other CRs. The occupancy of each channels is decided after
L
sensing slots based on a fusion rule that is fitted to a regulatory constraint or a coarse sensing task. We aim to maximize the expected number of identified idle channels by optimally choosing the index of the channel to be sensed by each collaborating CR at each sensing slot. We model this problem in its most general form as a finite horizon Markov decision process. We derive closed-form solutions for an optimal spectrum sensing policy and the associated value functions for the case of two collaborating CRs where individual sensing decisions are fused together according to the OR-rule. We show that the gain due to the optimal sensing policy is more significant when the spectrum utilization is high.