Research On Intelligent Reflecting Surface Aided Short-Packet Covert Wireless Communications

Due to wireless channels without exact physical boundary,the security of wireless communication has attracted extensive attention.Covert communication serving as a high-level wireless communication security technology,it can hide the transmission(Alice)behavior of the transmitter.Aiming at the problem of low covert transmission rate in traditional covert communication schemes,this paper proposes covert transmission schemes assisted by intelligent reflecting surface(IRS)to further improve the performance of covert transmission.The main contributions are as follows:(1)For the short-packet covert communication system,an IRS assisted and artificial noise(AN)enhanced covert transmission scheme is proposed,where the legitimate receiver(Bob)works in full duplex mode and generates AN to deteriorate Willie’s detection while receiving the covert information simultaneously.The detection performance of Willie is analyzed,and the lower bound expression of the total minimum detection error probability is given.On this basis,we formulate an optimization problem that maximizing the effective throughput subject to the covert require and transmit power constraints.Firstly,the alternating iterative algorithm based on Dinkelbach is proposed to jointly design the IRS’s reflection coefficients,the transmit power of Alice and the AN transmit power of full-duplex receiver Bob.In order to reduce the computational complexity,a low complexity algorithm is further proposed.The analytical expressions of IRS reflection coefficients,Alice’s transmit power and AN transmission power are derived.Simulation results show that the covert transmission performance obtained by the proposed scheme is significantly better than that of the schemes without IRS or without AN.(2)In order to further improve the covert transmission performance,we further consider the IRS assisted covert communication that Alice is equipped with multiple antennas.The joint optimization problem of Alice transmit beamforming and IRS reflection coefficients is constructed.The optimization problem is non-convex due to the optimization variables are coupled each other,which makes it difficult to solve directly.In order to solve this problem,we first decompose the original optimization problem into two subproblems.Then,the two subproblems are transformed into semidefinite relaxation(SDR)problems.Finally,an alternating iterative algorithm is proposed to solve the two subproblems iteratively.The simulation results show that the proposed scheme can significantly improve the covert transmission performance compared with the case that Alice equip with a single antenna.