Remote radio frequency unit selection of self-sustaining distributed base-station system based on downlink physical layer secure transmission

In the energy harvesting self-sustaining distributed base-station system (SS-DBS), the problem of optimal resource allocation for secure transmission at the downlink physical layer is studied, including the energy sharing mode, the power allocation, and the remote radio frequency unit (RRFU) selection. First, considering the existence of the eavesdropping user, an SS-DBS model, consisting of a baseband processing subsystem, an energy subsystem, and a radio frequency subsystem, is established for downlink secure transmission at the physical layer. Among the model, the remote radio frequency units are divided into secure remote radio frequency units that transmit secure information to the legitimate user and friendly cooperative remote radio frequency units that transmit artificial noise to interfere with the eavesdropping user. On this basis, a joint optimization problem of energy sharing, power allocation, and RRFU selection with the objective of maximizing the secure information rate of system is formulated. To solve this optimization problem, the problem is decomposed into an energy scheduling optimization subproblem and a RRFU selection optimization subproblem to solve separately. Through mathematical analysis and solution, the condition for the SS-DBS to adopt the partial energy sharing mode or the full energy sharing mode, the optimal power allocation of the RRFUs, and the RRFU selection algorithm for secure transmission at the physical layer of the SS-DBS downlink are obtained. Finally, Monte Carlo simulation is carried out and the simulation results verify the validity of the model and also show that the proposed algorithm has superior performance in terms of secure information rate and secure energy efficiency.