Spatial opportunity in cognitive radio networks with primary transmitter assisted opportunistic spectrum access

This paper studies the opportunistic spectrum access (OSA) of secondary users in a large-scale overlay cognitive radio (CR) 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 pilots sent from the primary transmitters 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 interaction between the primary and secondary users under the proposed OSA protocol, an exact calculation of the coverage probabilities of the primary and secondary networks is infeasible. To tackle this difficulty, approximation is made on the distribution of the active secondary transmitters. Based on this approximation, the coverage performance of the overlay CR network under the proposed OSA protocol is characterized. Simulation results are provided to validate our analysis.