Coverage probability in cognitive radio networks powered by renewable energy with primary transmitter assisted protocol

This paper studies the opportunistic spectrum access (OSA) of the secondary users in a large-scale overlay cognitive radio (CR) network powered by renewable energy to improve both the energy and spectral efficiency of data transmission. Particularly, with energy harvesting module and energy storage module, the primary transmitters (PTs) and secondary transmitters (STs) are assumed to be able to collect ambient renewables and store them in batteries for future use. Upon harvesting sufficient energy, the corresponding PTs and STs (denoted by eligible PTs and STs) are then allowed to access the spectrum according to their respective medium access control (MAC) protocols. For the primary network, an Aloha type of MAC protocol is considered, under which the eligible PTs make independent decisions to access the spectrum with probability ρp. For the secondary network, a threshold-based Opportunistic spectrum access (OSA) scheme, namely the primary transmitter assisted (PTA) protocol, is investigated, under which an eligible ST is allowed to access the spectrum only if the maximum signal power of the received pilots sent from the active primary transmitters (PTs) is lower than a certain threshold Nta. By applying tools from random walk theory and stochastic geometry, and assuming infinite battery capacity for energy storage module, we characterize the transmission probabilities of PTs and STs, respectively. With the obtained results of transmission probability, we then evaluate the coverage (transmission non-outage) performance of the overlay CR network powered by renewable energy. Simulations are provided to validate our analysis.