Abstract
Physical layer security is a cross research hotspot of information security and wireless communications. Recently, orbital angular momentum (OAM) technology has attracted widespread attention due to its potential of improving capacity and spectrum efficiency. However, there are few researches on system security based on OAM technology. In this work, we studied the security of the proposed OAM wiretap system by applying physical layer security theory to OAM communications. Firstly, we proposed a uniform circular array-based multi-mode OAM system and derived the secrecy capacity. Secondly, the phase profiles, channel capacity and received power of OAM beams are analyzed in terms of various system parameters in oblique scenarios at 30GHz. Thirdly, we discussed the security of the proposed OAM wiretap system. The results show that the system using vortex waves is superior to conventional communication systems using planar electromagnetic waves in terms of system security due to the inherent divergence and spiral phase structure of OAM beams. Moreover, we found that the distortion of OAM beams during transmission and the center shift at receiving end will occur and that system is more stable for high-mode OAM propagation in oblique scenarios. This work can provide an effective guidance for the research and application of OAM communications.
Highlights
Orbital angular momentum (OAM), a physical property of electromagnetic waves discovered recently, has attracted widespread attention due to its potential of improving capacity and spectrum efficiency [1]–[3] and could be used as an alternative key technology of the 6th generation mobile networks
The crucial difference between vortex waves and plane electromagnetic waves is that the former carries a spiral phase factor exp(ilφ), where l is an unbounded integer termed as OAM mode index satisfying l ∈ {0, 1, . . . , L - 1} with physical degree of freedom L equal to min(Nr, Nt), and φ is the azimuthal angle [4]
We study the performance of OAM system in oblique scenarios and analyze the security of OAM wiretap system
Summary
Orbital angular momentum (OAM), a physical property of electromagnetic waves discovered recently, has attracted widespread attention due to its potential of improving capacity and spectrum efficiency [1]–[3] and could be used as an alternative key technology of the 6th generation mobile networks. From the perspective of transmission, the combination of OAM technology and mmwave is expected to further improve the energy efficiency and increase the communication distance, and makes it easy to achieve a large-scale antenna array for improving higher channel capacity [15]–[17]. Sun et al studied the physical-layer security of a line-of-sight (LoS) free-space optical (FSO) link using OAM multiplexing and demonstrated the OAM multiplexing technique provides higher security over a single-mode transmission channel in terms of the total secrecy capacity and the probability of achieving a secure communication under certain conditions [22]. Djordjevic et al proposed using the hybrid FSO-THz technologies employing OAM modes can significantly improve the spectral efficiency and physical-layer security of both FSO and radio communications [23].
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