Physical Layer Security On Millimeter-wave Using Beamforming

In order to meet the bandwidth requirements of the 5G system,millimeter wave communication is proposed to be used.Meanwhile,as one of the key technology of 5G system,Massive MIMO has more accurate beam-control capability.When combined with millimeter wave,the problem of short propagation path of millimeter wave can be overcome.Besides,beamforming can concentrate the energy of the signal to desired direction,thus improving the spectral efficiency.This paper focuses on the millimeter-wave Cluster-Ray communication model and studies the communication security in practical applications.It includes the following three parts:1.A RF beamforming method based on iterative minimum outage is proposed.The aim of this method is to minimize the secrecy outage probability.At the same time,in order to realize spatial diversity,we formulate the problem as maximizing the geometric mean of the projections of the RF precoder on the transmit steering vectors and the geometric mean of the projections of the RF combiner on the receive steering vectors.And the beamformer is initialized by the superposition of the transmit steering vectors and receive steering vectors.Based on this,the optimal RF precoder andcombiner can be calculated iteratively,which can avoid the problem of local maximum value.The proposed algorithm converges in a small number of iterations and has better roubtness than other spatial diversity schemes.2.A spatially controllable noise injection hybrid beamforming method is proposed.The beamforming vector and noise vector are initialized to maximize the beamforming gain of the receiver.On this basis,the hybrid precoders are designed to beamform information symbols towards the receiver and simultaneously inject artificial noise in directions of interest.To reduce the computational complexity,we randomly group antennas,and on/off switching is applied to each group instead of individual antenna.The simulation results show that the proposed method can significantly improve the secrecy rate.3.A power allocation strategy based on artificial noise is proposed under the condition of partial channel state information feedback.Secrecy is defined based on satisfying QoS constraints both at the receiver and at the eavesdroppers.The aim is to offer a given probability of secrecy by enforcing a minimum SNR at Bob and ensuring that the SNR at each eavesdropper is appropriately upper bounded by a given value.Thus we propose an optimal power allocation strategy that minimizes the transmitted power subject to guaranteeing a given probability of secrecy satisfying given QoS constraints.The simulation results show that the proposed method can effectively meet the QoS constraints and achieve secure transmission.