Secrecy Energy Efficiency in PAPR-Aware Artificial Noise Scheme for Secure Massive MIMO

In this paper, we study the secrecy energy efficiency (SEE) in an artificial noise (AN)-aided secure massive multiple-input multiple-output (MIMO) scheme. The scheme uses instantaneous information to design a peak-to-average power (PAPR)-aware AN that simultaneously improves secrecy and reduces PAPR. High PAPR leads to non-linear in-band signal distortion and out-of-band radiation causing adjacent channel interference. To ensure optimal secrecy performance, high power amplifiers (HPAs) at the base station (BS) are backed off to operate in the linear region only. The amount of back-off needed to ensure linearity of the HPA has a direct impact on the energy efficiency of the system and by extension the SEE. For our scheme, the magnitude of this back-off is determined by the power allocation ratio between the data and AN. Hence, we propose an optimal power allocation ratio for the scheme. This is to ensure a good trade-off between the energy efficiency, security, and reliability of the system. Simulation results show a better SEE performance for our scheme compared to legacy massive MIMO schemes with or without random AN injection. Finally, we study the impact of spatially correlated Rayleigh fading on the proposed scheme.