Spatial opportunity in cognitive radio networks with threshold-based opportunistic spectrum access

This paper studies the opportunistic spectrum access (OSA) of secondary users in a large-scale overlay cognitive radio network. Particularly, a threshold-based protocol is investigated, where the secondary transmitter is allowed to access the spectrum only if the maximum signal power of the received beacons transmitted by the primary receivers is lower than a certain threshold. To measure the resulting transmission opportunity for the secondary users by the proposed OSA protocol, the concept of spatial opportunity is introduced and evaluated by applying tools from stochastic geometry. Due to the dependency between the realizations of the active primary and secondary users, an exact calculation of the coverage probabilities of the primary and secondary networks is infeasible. To tackle this difficulty, approximation is made on the conditional distribution of the active secondary transmitters given a typical primary/secondary receiver activated at the origin. Based on this approximation, the coverage performance of the primary/secondary network under the proposed OSA protocol is characterized. To our best knowledge, this paper is the first attempt of using stochastic geometry to evaluate the performance of the threshold-based opportunistic spectrum access in large-scale cognitive radio networks.