In multiuser multiple-input multiple-output (MUMIMO) systems for beyond-5G, many user groups are served by the same transmitter in a time-based scheduling. Considering all unscheduled users as eavesdroppers puts a high complexity on algorithms to achieve physical layer security (PLS). Moreover, due to the Line-of-Sight channel properties, PLS is even more challenging to achieve in satellite communication (SATCOM) downlinks. In multibeam MU-MIMO satellite systems, which will be part of beyond-5G networks, the spatial degrees of freedom can be used for both throughput and secrecy improvements. We extend a user-fairness zero-forcing algorithm with artificial noise to achieve secure precoding even if the channel state information of the eavesdroppers is unknown. We define the secrecy outage probability for Line-of-Sight MU-MIMO SATCOM channels and analyze how it can be reduced by the aforementioned algorithm. Moreover, we introduce a trade-off between a high system throughput and a low secrecy outage probability for the cost-effectiveness considerations of PLS.
In multiuser multiple-input multiple-output (MUMIMO) systems for beyond-5G, many user groups are served by the same transmitter in a time-based scheduling. Considering all unscheduled users as eavesdroppers puts a high complexity on algorithms to achieve physical layer security (PLS). Moreover, due to the Line-of-Sight channel properties, PLS is even more challenging to achieve in satellite communication (SATCOM) downlinks. In multibeam MU-MIMO satellite systems, which will be part of beyond-5G networks, the spatial degrees of freedom can be used for both throughput and secrecy improvements. We extend a user-fairness zero-forcing algorithm with artificial noise to achieve secure precoding even if the channel state information of the eavesdroppers is unknown. We define the secrecy outage probability for Line-of-Sight MU-MIMO SATCOM channels and analyze how it can be reduced by the aforementioned algorithm. Moreover, we introduce a trade-off between a high system throughput and a low secrecy outage probability for the cost-effectiveness considerations of PLS.
In satellite communication downlinks, physical layer security is challenging to achieve due to their broadcasting nature and Line-of-Sight channel characteristics. This paper provides a precoding algorithm to secure the downlinks of multiple users against multiple eavesdroppers with optimization of the minimum secrecy capacity. By the use of artificial noise, a positive secrecy capacity is achievable even if the number of eavesdroppers is higher than the number of beams. We demonstrate that a multiple-reflector antenna design provides a significantly higher secrecy and throughput performance when compared to a single-reflector design due to additional degrees of freedom, exhibited by the signal phases. The total vulnerability region is introduced as a new figure of merit with respect to unidentified eavesdroppers.
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.
We consider secure downlink multiple-input–multiple-output (MIMO) communications between a transmitter and multiple users when there exists a passive eavesdropper. A downlink main channel between the transmitter and a user is estimated through uplink pilot symbols in a time-division duplex mode. On the other hand, to hinder an eavesdropper from estimating the eavesdropper channel between the transmitter and the eavesdropper, the transmitter does not send any pilot symbols. The main channel is hence available at the transmitter only, while the eavesdropper channel is unavailable at any node. Assuming these channel state information (CSI) conditions, we propose a MIMO transmission method using space–time line code (STLC) with artificial noise (AN) for enhancing the physical layer security. The STLC enables noncoherent detection at the receiver, i.e., a user, without CSI and achieves full spatial diversity. We derive the lower bound of the secrecy sum rate for the proposed STLC transmission method without AN, with AN, and with AN and imperfect CSI. Moreover, numerical results verify that the proposed STLC scheme outperforms the conventional eigen-beamforming and the precoding space-time block code in terms of secrecy sum rate regardless of the signal-to-noise ratio, the number of transmit antennas, and the CSI uncertainty.
In satellite communications physical layer security is rather challenging to achieve due to the broadcasting nature of satellite downlinks. We investigate how the advances in multiuser multiple-input multiple-output satellite communications can protect downlinks from eavesdropping. The additional degrees of freedom in multi-antenna systems can not only be utilized for higher spectral efficiency but also to improve the security of the links. Our analysis shows that the area where a hostile interceptor is able to capture the signal is small due to the interference of other user signals. Moreover, the area can be tuned by applying a modified precoding matrix.
Physical layer security (PLS) has grown in popularity as it guarantees secure and reliable communication between wireless devices without restricting the ability of data analysts to eavesdrop. PLS benefits from the randomization property of the wireless channel, which improves immunity and protects against many dangers of information breaches from eavesdroppers. MIMO and Massive MIMO, which use numerous antennas at the transmitter and receiver ends, are fundamental technologies for improving efficiency in 5G and future network systems. The PLS still requires a significant amount of work before it can be employed in practical systems. The interception of eavesdroppers can be made difficult by adding artificial noise. This paper focuses on the physical layer security considering maximal ratio combining, and artificial noise with beamforming techniques to further enhance the secrecy rate. The proposed work demonstrates that the use of transmitter beamforming with artificial noise can significantly improve the degree of confidentiality of information being transmitted between a transmitter and an intended receiver while making it more difficult for eavesdroppers to intercept. The simulation results in terms of bit error rate show that the proposed method has a significant impact on the error rate performance of the eavesdropper.
Recently, wireless security has been highlighted as one of the most important techniques for 6G mobile communication systems. Many researchers have tried to improve the Physical-Layer Security (PLS) performance such as Secrecy Outage Probability (SOP) and Secrecy Energy-Efficiency (SEE). The SOP indicates the outage probability that the data transmission between legitimate devices does not guarantee a certain reliability level, and the SEE is defined as the ratio between the achievable secrecy-rate and the consumed transmit power. In this paper, we consider a Multi-User Multi-Input Single-Output (MU-MISO) downlink cellular network where a legitimate Base Station (BS) equipped with multiple transmit antennas sends secure information to multiple legitimate Mobile Stations (MSs), and multiple potential eavesdroppers (EVEs) equipped with a single receive antenna try to eavesdrop on this information. Each potential EVE tries to intercept the secure information, i.e., the private message, from the legitimate BS to legitimate MSs with a certain eavesdropping probability. To securely receive the private information, each legitimate MS feeds back its effective channel gain to the legitimate BS only when the effective channel gain is higher than a certain threshold, i.e., the legitimate MSs adopt an Opportunistic Feedback (OF) strategy. In such eavesdropping channels, both SOP and SEE are analyzed as performance measures of PLS and their closed-form expressions are derived mathematically. Based on the analytical results, it is shown that the SOP of the OF strategy approaches that of a Full Feedback (FF) strategy as the number of legitimate MSs or the number of antennas at the BS increases. Furthermore, the trade-off between SOP and SEE as a function of the channel feedback threshold in the OF strategy is investigated. The analytical results and related observations are verified by numerical simulations.