Secrecy Outage Probability in Multi-RAT Heterogeneous Networks

Practical difficulty in examining all base stations (BSs) to choose the best one providing secure transmission in heterogeneous networks (HetNets), we impose a BS association constraint in this letter that the BSs providing an average received signal power at the legitimate user greater than a predetermined receiving threshold can be candidate serving BSs. With this constraint, we derive closed-form expressions for secrecy outage probability (SOP) of both homogeneous networks and K-tier HetNets based on stochastic geometry. Our analysis reveals that security performance can be improved by deploying more low-power BSs in high path-loss environments. Besides, the SOP stays unchanged when the receiving threshold is below a critical point and increases rapidly when exceeding that point. These results depict features of SOP with practical constraint, which could provide new insights into the physical layer security in HetNets.