Abstract: In order to improve the energy efficiency and reliability of wireless communication system, based on the underlying spectrum sharing mechanism, the selection strategy of the cognitive radio-internet of things (CR-IoT) users and the user transmission distance optimization problem are studied for the system where the energy-constrained CR-IoT users assist remote users to upload the information and their data. In this model, the CR-IoT cooperative users adopt the power splitting protocol for energy harvesting (EH). Considering the nonlinear characteristics of the actual energy harvesting process, a selection strategy of active opportunistic cognitive users under limited transmission power is proposed. The outage probability (OP) of the proposed user selection strategy is analyzed. The closed-form result of OP is obtained by using the Gauss-Chebyshev approximate integral formula, and the approximate result of OP under high signal-to-noise ratio (SNR) is further derived. To minimize the OP and maximize the transmission distance of cooperative cognitive users, a joint optimal allocation scheme of power splitting factor and signal power allocation factor is proposed. Finally, the accuracy of the theoretical derivation and the performance advantages of the proposed strategy are verified by Monte Carlo simulation.

Key words: nonlinear energy harvesting, user selection strategy, internet of things, cognitive radio