This paper introduces a new approach to providing secure physical-layer massive multipleinput multiple-output (MIMO) based communications that can improve the energy efficiency of the system. This is achieved by synthesizing orthogonal artificial noise (AN) that has to be constrained to lie in the null space of the legitimate users' channels while it should lie in the range space of the eavesdropper's channel. In addition, this AN reduces the peak-to-average power ratio (PAPR) of the transmit signal. Indeed, low PAPR signals are preferable and more efficient for low-cost hardware, thus improving the energy consumption of massive MIMO systems. In this paper, we propose a new PAPR-aware precoding scheme based on the use of AN to enhance the secrecy performance of massive MIMO while reducing the PAPR of the transmit signal and guaranteeing excellent transmission quality for legitimate users. The scheme is formulated as a convex optimization problem that can be resolved via steepest gradient descent (GD). Accordingly, we developed a new iterative algorithm, referred to as PAPR-Aware-Secure-mMIMO, that makes use of instantaneous information to solve the optimization problem. Simulation results show the efficiency of our proposed algorithm in terms of PAPR reduction and secrecy, which is also studied with respect to power distribution between useful signal and AN, PAPR targets and the number of BS antennas.INDEX TERMS Artificial noise (AN), massive multiple-input multiple-output (MIMO), peak-to-average power ratio (PAPR), physical layer security (PLS), power allocation, steepest gradient descent (GD), zeroforcing (ZF) precoding.

In recent years, physical layer security (PLS) has emerged as a promising concept to complement cryptography solutions. Many PLS schemes require perfect knowledge of the channel state information (CSI) at the transmitter. However, in practical cases, CSI is often imperfect due to channel estimation errors, noisy feedback channels and outdated CSI. In this paper, we study the impact of imperfect CSI on an adaptive PLS scheme that combines diversity with interleaving to provide security. Particularly, we derive the secrecy capacity expressions for the legitimate receiver and the eavesdropper's channels under imperfect CSI conditions. Numerical and theoretical simulations for secrecy capacity and bit error rate (BER) are carried out for the frequency-selective Rayleigh fading wiretap channel model. The results reveal the negative impact of imperfect CSI on the secrecy and BER performance of the single input single output (SISO) orthogonal frequency division multiplexing (OFDM) system. The analysis is done under both frequency division duplex (FDD) and time division duplex (TDD) modes.

Physical layer security (PLS) is an emerging paradigm that makes use of wireless channel characteristics to provide security. Many PLS schemes require knowledge of the channel state information (CSI). However, CSI is usually imperfect due to factors such as noisy feedback channels, channel estimation errors and outdated CSI. In this paper, we investigate the impact of imperfect CSI on the secrecy and error rate performances of a PLS scheme that combines adaptive matched-filter (MF) precoding and diversity in orthogonal frequency division multiplexing (OFDM). Particularly, we derive the secrecy capacity and error rate expressions for the legitimate and eavesdropper's channels under imperfect CSI assumption. The impact of the imperfect CSI is studied via theoretical as well as numerical techniques in frequency-selective Rayleigh fading wiretap channel. The analysis is done in both frequency division duplex (FDD) and time division duplex (TDD) modes.

In this paper, we study the secrecy energy efficiency (SEE) in an artificial noise (AN)-aided secure massive multipleinput 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.Index Terms-Artificial noise (AN), massive multiple-input multiple-output (MIMO), matched filter (MF) precoding, peakto-average power ratio (PAPR), high power amplifier (HPA), physical layer security (PLS), secrecy energy efficiency (SEE).