Power Allocation and Opportunistic User Scheduling for Secrecy Rate Enhancement in Downlink Network with Potential Eavesdroppers

Abstract

Due to the broadcast nature of the wireless medium, the wireless networks are more vulnerable to the security threats than the wired networks. For this reason, the concerns on the security of private information are rapidly growing as the wireless communications make its way into everyday life with the realization of internet of things (IoT) concept. As a promising tool for mitigating the security problems in wireless communication, the physical layer security has been receiving a great attention by exploiting the physical properties of the wireless channel. In this thesis, we discuss physical layer security techniques in downlink networks. We consider user scheduling and power allocation techniques for a downlink network where transmitted message must be kept confidential from all other unintended users and the number of users is much larger than that of BS antennas. In order to maximize network secrecy rate with a limited number of antennas, the base station schedules the user who can achieve the largest secrecy rate and exploits multiple antennas for transmitting artificial noise to the unintended users. We derive the closed-form expressions of the optimal power allocation for the artificial noise and the average network secrecy rate through asymptotic analysis. The analysis results provide the insightful information on the behaviors of the user scheduling and the effect of system parameters on the network secrecy rate performance. The simulations confirm the validity of the analysis results and provide additional information on the network performance in general cases. Moreover, the simulation results also show that the proposed system outperforms the existing work based on RCI in terms of network secrecy rate if there are a limited number of BS antennas.