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IEEE Internet of Things Journal

Physical Layer Security for MIMO THz Communication System

Shubha Sharma, Ankush Vashistha, A. S. Madhukumar

Published Aug 5, 2026• 0 citations
Publisher

Abstract

In this work, the secrecy performance of a multiple-input–multiple-output (MIMO) terahertz (THz) communication system is investigated. To enhance physical layer security (PLS), a novel transmission protocol is proposed, which dynamically tunes the carrier frequency to align with the centers of molecular absorption loss (MAL) lines. This frequency-selection strategy increases atmospheric attenuation, thereby limiting the signal’s effective range and making it significantly more difficult for a distant eavesdropper (Eve) to intercept the transmission. To assess the secrecy performance, the exact statistical characteristics of the signal-to-noise ratios (SNRs) at both the legitimate user and Eve are derived. Using these statistical characteristics, a unified analytical framework is developed, which yields closed-form expressions for key secrecy metrics, such as the average secrecy capacity (ASC), the lower bound on the secrecy outage probability (SOP), and the probability of strictly positive secrecy capacity (SPSC). Asymptotic analyses in the high-SNR regime further reveal the secrecy diversity order and secrecy coding gain, providing deeper insight into the system’s robustness. Numerical results show that the proposed MAL-aligned frequency tuning can improve ASC by up to 25% and achieves nearly a twofold reduction in insecure area compared to conventional fixed-frequency transmission. These gains are achieved while imposing only a marginal reduction in the legitimate user’s capacity, thereby maintaining an efficient balance between security and communication performance.

DOI
10.1109/jiot.2026.3720657

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In this work, the secrecy performance of a multiple-input–multiple-output (MIMO) terahertz (THz) communication system is investigated. To enhance physical layer security (PLS), a novel transmission protocol is proposed, which dynamically tunes the carrier frequency to align with the centers of molecular absorption loss (MAL) lines. This frequency-selection strategy increases atmospheric attenuation, thereby limiting the signal’s effective range and making it significantly more difficult for a distant eavesdropper (Eve) to intercept the transmission. To assess the secrecy performance, the exact statistical characteristics of the signal-to-noise ratios (SNRs) at both the legitimate user and Eve are derived. Using these statistical characteristics, a unified analytical framework is developed, which yields closed-form expressions for key secrecy metrics, such as the average secrecy capacity (ASC), the lower bound on the secrecy outage probability (SOP), and the probability of strictly positive secrecy capacity (SPSC). Asymptotic analyses in the high-SNR regime further reveal the secrecy diversity order and secrecy coding gain, providing deeper insight into the system’s robustness. Numerical results show that the proposed MAL-aligned frequency tuning can improve ASC by up to 25% and achieves nearly a twofold reduction in insecure area compared to conventional fixed-frequency transmission. These gains are achieved while imposing only a marginal reduction in the legitimate user’s capacity, thereby maintaining an efficient balance between security and communication performance.
Terahertz (THz) band offers large accessible band-width and spatially confined beams for the realization of secure and high data rate communication. The paper aims to achieve security at THz band by considering a multiple-input-multiple-output (MIMO) wiretap channel. Source withMAM_{A}MA​antennas transmits using transmit antenna selection (TAS) technique and both main user and eavesdropper equipped with respectiveMMM_{M}MM​andMWM_{W}MW​antennas receive using maximal ratio combining (MRC) technique. In order to assess the secrecy performance, statistical characteristics are derived for the proposed system. Based on the derived statistical characteristics, the exact closed-form expressions for lower bounds for secrecy outage probability and probability of strictly positive secrecy capacity are derived. Results show that the improvement is oserved in the secrecy performance, which is primarily attributed to the utilization of transmit diversity techniques. It is demonstrated that non-linearity of the channel and multi-paths can also be exploited to enhance the physical layer security.
The inherent openness of wireless networks exposes them to eavesdropping threats. In dense urban environments, signal propagation is frequently characterized by the keyhole effect, which causes channel rank deficiency and cascaded fading, challenging the assumptions of conventional multiple-input multiple-output (MIMO) physical layer security. This paper investigates the secrecy performance of MIMO multiple-antenna-eavesdropper (MIMOME) systems over keyhole channels with independent legitimate and eavesdropper links. We analyze the secrecy performance under three progressive scenarios: perfect CSI without artificial noise (AN), perfect CSI with AN-aided transmission, and practical imperfect CSI with AN. Specifically, we derive closed-form asymptotic expressions for the secrecy outage probability (SOP) and average secrecy rate (ASR) in the high signal-to-noise ratio (SNR) regime using Meijer G-functions and Gauss hypergeometric functions, from which the secrecy diversity order and secrecy array gain are explicitly extracted. The analytical results reveal that AN injection successfully restores the secrecy diversity order from zero to one, while imperfect CSI causes AN leakage that leads to ASR saturation and an SOP floor. The derived asymptotic expressions are verified by Monte Carlo simulations. Our findings provide theoretical guidelines by quantifying the trade-off between AN suppression capabilities and self-interference in cascaded fading environments.
Physical layer security is an important method to improve the secrecy performance of wireless communication systems. In this paper, we analyze the effect of employing channel correlation to improve security performance in multiple-input multiple-output (MIMO) scenario with antenna selection (AS) scheme. We first derive the analytical expressions of average secrecy capacity (ASC) and secrecy outage probability (SOP) by the first order Marcum Q function. Then, the asymptotic expressions of ASC and SOP in two specific scenarios are further derived. The correctness of analytical and asymptotic expressions is verified by Monte Carlo simulations. The conclusions suggest that the analytical expressions of ASC and SOP are related to the product of transmitting and receiving antennas; increasing the number of antennas is beneficial to ASC and SOP. Besides, when the target rate is set at a low level, strong channel correlation is bad for ASC, but is beneficial to SOP.
Massive Multiple-Input Multiple-Output (MIMO) has become a crucial enabling technology for 5G and beyond, providing previously unheard-of increases in energy and spectrum efficiency. It is still difficult to guarantee secure communication in these systems, particularly when it comes to passive eavesdroppers whose base station is unaware of their channel state information. By taking advantage of the inherent randomness of wireless channels, Physical Layer Security (PLS) offers a promising paradigm; however, its efficacy in massive MIMO is heavily reliant on resource allocation and transmission strategies. In this work, the performance of secure transmission schemes, such as Maximum Ratio Transmission (MRT), Zero-Forcing (ZF), and Artificial Noise (AN)-aided beamforming, is examined when passive eavesdroppers are present. This work will use extensive Monte Carlo simulations to assess important performance metrics such as energy efficiency, secrecy outage probability, and secrecy sum rate under different system parameters (e.g., number of antennas, Signal-to-Noise Ratio (SNR), power allocation). The results aim to provide comparative insight into the strengths and limitations of different PLS strategies and to highlight open research directions to design scalable, energy-efficient, and robust secure transmission techniques in future 6G networks.
In this paper, the secrecy performance of the physical layer security (PLS) of the hybrid free-space optical/radio frequency (FSO/RF) communication system is analyzed. The transmission protocol of the considered system is performed under the eavesdropper's attempt to overhear the RF link between the transmitter and legitimate receiver of the hybrid system. The FSO link is characterized by Málaga-M distribution while the RF links are modeled by Nakagami-m distribution. The two practical eavesdropping modes considered in this paper include: colluding and non-colluding. Exact closed-form expressions for the system's secrecy outage probability (SOP), the asymptotic of the SOP (SOP∞), the probability of strictly positive secrecy capacity (SPSC), the average secrecy capacity (ASC), and the asymptotic of the ASC (ASC∞), are specifically derived under the influence of both eavesdropper modes. Our derived analytical expressions present an efficient tool to investigate the impact of some channel parameters on the secrecy performance, namely the fading severity of the RF links, atmospheric turbulence severity, pointing error of the FSO link, number of eavesdroppers, and the power of the eavesdropper links. The results show that the increase of the eavesdroppers' number under both modes profoundly degrades the considered system secrecy performance. The accuracy of the numerical results obtained is validated by Monte-Carlo simulations.
Physical Layer Security of MRC in Fisher–Snedecor FFF Fading Channels
The physical layer security (PLS) is explored in quasi-static Fisher-Snedecor F Fading Channels with maximal ratio combining (MRC), which have been used to model the conventional and emerging realistic wireless communication channels. We consider the secure transmission of privileged information from a single antenna legitimate transmitter to L-antenna legitimate receiver are wiretapped by L-antenna eavesdropper. The receiver maximizes the probability of secure transmission by adopting MRC, whereas eavesdropper maximizes the probability of eavesdropping by adopting MRC. We derive PLS secrecy metrics for a system setup where the transmitter is having no channel state information (CSI) of both the receiver and eavesdropper. Specifically, we derive a novel closed-form expressions for secure outage probability (SOP) and strictly positive secrecy capacity (SPSC). Furthermore, to obtain important insight into the effect of channel parameters on the secrecy performance, an asymptotic analysis is conducted for SOP at high signal-to-noise ratio (SNR) regime.