Impact of hardware impairments on the physical layer security of cell-free massive MIMO

Abstract

The development of new technologies and applications such as virtual reality, ultra-highdefinition video conferencing, and Internet of Things (IoT) has caused a substantial increase in the demand for higher data rate in cellular systems. Massive Multiple-Input MultipleOutput (MaMIMO) is a reliable solution to fulfill this demand, not only providing higher data rates, but also offering enhanced coverage and network capacity. These aspects are essential to accommodate the rapidly increasing number of mobile subscribers with each passing year. However, the swift progression of wireless communication technologies, including fifth-generation (5G) networks and beyond raises a critical concern: ensuring the security of these systems. This thesis focuses on enhancing the security of Cell-Free Massive Multiple-Input Multiple-Output (CF-MaMIMO), an advanced extension of MaMIMO. It uses a Physical Layer Security (PLS) technique which involves beamforming artificial noise (AN) in the null of the users. Previous studies have demonstrated that implementing PLS techniques always enhance the security performance of wireless communication systems. However, these studies often overlook a crucial aspect: the impact of hardware impairments (HWIs). They assume ideal transceivers in their research, neglecting the practical implications where hardware non-idealities can significantly impact system security. Therefore, this thesis analyzes the impact of HWIs on security performance based on broadcasting AN as a PLS technique in CF-MaMIMO systems For this purpose, the Signal-to-interference-plus-noise ratio (SINR) of the legitimate users and Signal-to-noise ratio (SNR) of the eavesdroppers is derived considering HWIs in the implementation of AN broadcasting. Contrary to existing literature, it is demonstrated in this thesis that in certain instances, the AN leads to degradation in the security performance of the system due to HWIs. The findings of this study reveal that fluctuations in the hardware quality of users, eavesdroppers and access points (APs) directly affect the system’s security. Furthermore, these findings emphasize the significance of considering hardware quality when applying PLS techniques by broadcasting AN to maximize security performance.