Collaborative spectrum sensing: Optimising the number of collaborating users

In the IEEE 802.22 standard, the spectrum sensing mechanism is identified as a key functionality of a cognitive radio. Due to the channel uncertainty, a single cognitive user, in most cases, can not make a reliable decision and hence collaboration or cooperation of and among multiple users is required. However, when large number of cognitive users are collaborating with each other, the bandwidth requirements for sending their result to the fusion centre tends to be very large. In this paper, a metric for spectrum efficiency is defined and used for the optimisation of collaborative spectrum sensing. An optimisation algorithm is presented to calculate the optimal number of collaborating cognitive users with the aim to maximise overall spectrum efficiency by satisfying certain constraints in terms of global probability of detection and probability of false alarm. Numerical results show that for maximum spectrum efficiency collaboration of only a subset of the available cognitive users is required.