Spatial multiplexing is not always feasible in terahertz and sub-terahertz (THz) MIMO channels due to the primarily line-of-sight propagation, but recent works have explored the possibility of using orbital angular momentum (OAM) to enable multiplexing in line-of-sight scenarios. This paper explores a certain physical-layer security risk and a corresponding mitigation strategy for THz MIMO systems using orbital angular momentum (OAM). A novel successive interference cancellation eavesdropping attack is introduced for OAM-MIMO THz systems, and simulations demonstrate that the security of the link decreases in the far field. A security countermeasure is introduced and proven to be effective in physically protecting the communications link.
Spatial multiplexing is not always feasible in terahertz and sub-terahertz (THz) MIMO channels due to the primarily line-of-sight propagation, but recent works have explored the possibility of using orbital angular momentum (OAM) to enable multiplexing in line-of-sight scenarios. This paper explores a certain physical-layer security risk and a corresponding mitigation strategy for THz MIMO systems using orbital angular momentum (OAM). A novel successive interference cancellation eavesdropping attack is introduced for OAM-MIMO THz systems, and simulations demonstrate that the security of the link decreases in the far field. A security countermeasure is introduced and proven to be effective in physically protecting the communications link.
This paper presents a physically-secure wireless communication system utilizing orbital angular momentum (OAM) waves at 0.31THz. A trustworthy key distribution mechanism for symmetric key cryptography is proposed by exploiting random hopping among the orthogonal OAM-wave modes and phases. Keccak-f[400] based pseudorandom number generator provides randomness to phase distribution of OAM-wave modes for additional security. We assess the security vulnerabilities of using OAM modulation in a THz communication system under various physical-layer threat models as well as analyze the effectiveness of these threat models for varying attacker complexity levels under different conditions.
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 withMAantennas transmits using transmit antenna selection (TAS) technique and both main user and eavesdropper equipped with respectiveMMandMWantennas 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.
In this chapter, we described the fundamental system model, challenges, and technical solutions to THz physical layer security. Despite the good security performance provided by the high directivity of THz wireless communications, THz physical layer security still faces security challenges, including eavesdroppers inside beam sector, eavesdroppers in close proximity and THz covertness problem. In light of these challenges, three THz-specific security schemes were described. First, the DA-APM proposes to transmit signals at sides of molecular absorption peaks to enhance the wireless security and covertness. This scheme effectively combats eavesdroppers inside the beam sector and can even enhance the covertness of THz wireless communications. Second, the SIC-free RAN scheme takes the advantage of the distance-dependent temporal broadening effect to jam Eve in close proximity while not jamming Bob. This method handles the eavesdroppers in close proximity with a lower-complexity receiver AN mechanism. Third, we described the WSA and beamforming scheme to combat near eavesdropping without the aid of other nodes. The size rationality of practical THz WSA is justified.Despite the fruitful research progress on THz physical layer security, there are still open challenges remaining to be tackled, which are described as follows. First, since the optimal molecular absorption coefficients depend on the propagation distance, it is necessary to adjust the carrier frequency as the distance between Alice and Bob varies. How to efficiently and practically tune the carrier frequency to use proper sub-bands needs investigation. Second, the hybrid beamforming structure is usually adopted in THz communications. However, the hybrid beamformer design for the WSA is a non-convex optimization problem. It is necessary to investigate efficient and low-complexity solutions for the WSA beamformer design. Finally, active security attacks, for instance, eavesdroppers may send the jamming signal to the legitimate receiver while overhearing the secret message, need to be handled for THz physical layer security. In line with this, security mechanisms simultaneously combating active and passive eavesdropping are awaited to be explored as a future direction.
In this paper, we propose a physical layer secret key (PLSK) generation scheme for secure encrypted transmissions in orbital angular momentum (OAM) communication systems which improves the secret key capacity via taking advantage of OAM orthogonal modes. Based on the line-of-sight (LoS) quasi-static channel conditions in OAM systems, we propose a mode-based active defense phase in the PLSK scheme to invalidate keys generated by an eavesdropper when it is extremely close to the legitimate user. Our simulation results highlight that the key information generated by the eavesdropper is almost zero in the case of highly correlated legitimate and eavesdropping channels under LoS conditions. In addition, our proposed OAM PLSK scheme achieves a higher key generation rate (KGR) than existing works since mode-based active defense can disrupt the process of PLSK by the eavesdropper.
MIMO is a key enabling technology in the currently emerging 5G systems and future 6G-plus paradigms, such as heterogeneous networks, millimeter-wave networks, vehicular sensor networks, among others. The highly desired properties of MIMO such as its ability to supporting high data rates, improving energy and spectral efficiency, as well as overcoming the effects of shadowing and fading have made it increasingly attractive to the wireless communications industry. Nevertheless, a practical secure MIMO model with the required security levels to guarantee user information protection has still not been realized by the industry. In this work, we analyze and quantify the security performance of hybrid MIMO, which was originally proposed by the preceding work titled “Hybrid MIMO: A New Transmission Method For Simultaneously Achieving Spatial Multiplexing and Diversity Gains in MIMO Systems”. In the proposed method, special signal interference-canceling matrices, which are calculated based on the channel’s variations and randomness between the user and receiver, are superimposed with user data at the physical layer level before being transmitted to the receiver. The conducted performance analysis in this study indicates that the signal interference-canceling matrices provide absolute security (zero information leakage) against both internal and external eavesdroppers. Moreover, the new MIMO technique eliminates the need for any processing at the receiver, where users directly receive their intended signals, consequently lowering complexity and power consumption at the receiver. These are highly desirable properties for the future internet of things (IoT) devices as well as 6G and beyond technologies.
The future applications of terahertz (THz) wireless communication require investigations on link secrecy performance in all kinds of atmospheric conditions, including fog, snow, rain and atmospheric turbulence. Here, we present theoretical studies on physical layer security of point-to-point THz and infrared (IR) wireless links in atmospheric turbulence with a potential eavesdropper outside of the link path. Attenuations due to turbulence, gaseous absorption and beam divergence are included in the model to predict the propagation of both links. Secrecy capacity and outage probability of the THz links are calculated and compared with that of an IR (1550 nm) link. Dependences of link security on eavesdropper's position, atmospheric visibility, turbulence strength and intended data transmission rate are also presented and analyzed. We find that the THz link owns higher security at physical layer than the IR link.