Joint Optimization Scheme for the Reconfigurable Intelligent Surface-Assisted Untrusted Relay Networks

To further improve the secrecy rate,a joint optimization scheme for the reconfigurable intelligent surface(RIS)phase shift and the power allocation is proposed in the untrusted relay(UR)networks assisted by the RIS.The eavesdropping on the UR is interfered by a source-based jamming strategy.Under the constraints of unit modulus and total power,the RIS phase shift,the power allocation between the confidential signal and the jamming signal,and the power allocation between the source node and the UR are jointly optimized to maximize the secrecy rate.The complex multivariable coupling problem is decomposed into three sub-problems,and the non-convexity of the objective function and the constraints is solved with semi-definite relaxation.Simulation results indicate that the secrecy rate is remarkably enhanced with the proposed scheme compared with the equal power allocation scheme,the random phase shift scheme,and the no-RIS scheme.

Physical Layer Security for Wireless and Quantum Communications

This special issue is dedicated to security problems in wireless and quantum communications.Papers for this issue were invited,and after peer review,eight were selected for publication.The first part of this issue comprises four papers on recent advances in physical layer security for wireless networks.The second part comprises another four papers on

Novel self-embedding holographic watermarking image encryption protection scheme

For digital image transmission security and information copyright,a new holographic image self-embedding watermarking encryption scheme is proposed.Firstly,the plaintext is converted to the RGB three-color channel,the corresponding phase hologram is obtained by holographic technology and the watermark is self-embedded in the frequency domain.Secondly,by applying the Hilbert transform principle and genetic center law,a complete set of image encryption algorithms is constructed to realize the encryption of image information.Finally,simulation results and security analysis indicate that the scheme can effectively encrypt and decrypt image information and realize the copyright protection of information.The introduced scheme can provide some support for relevant theoretical research,and has practical significance.

Tunable optical second-order sideband effects in a parity-time symmetric optomechanical system

We theoretically investigate the optical second-order sideband generation(OSSG)in an optical parity-time(PT)symmetric system,which consists of a passive cavity trapping the atomic ensemble and an active cavity.Compared with the double-passive system,it is found that near the exceptional point(EP),the efficiency of the OSSG increases sharply not only for the blue probepump detuning resonant case but also for the red one.Using experimentally achievable parameters,we study the effect of the atomic ensemble on the efficiency of the OSSG in the PT-symmetric system.The numerical results show that the efficiency of the OSSG is 30%higher than that of the first-order sideband,which is realized easily by simultaneously modulating the atom-cavity coupling strength and detuning.Moreover,the efficiency of the OSSG can also be tuned effectively by the pump power,and the efficiency is robust when the pump power is strong enough.This study may have some guidance for modulating the nonlinear optical properties and controlling light propagation,which may stimulate further applications in optical communications.