Researches On Multiple Antennas Based Low Probability Of Intercept Communication Technology

With the development of mobile communication technique,wireless communication is becoming a necessary part of transmission means.Due to the open wireless interface,the information security faces great challenges.The low probability of intercept communication(LPI)can prevent signals from being intercepted at the physical layer,thereby ensuring information security,which is a current research hotspot.Communication with low probability of interception mainly includes two aspects: low probability of information interception and low probability of signal detection.This paper focuses on low probability of information interception,which is also called covert communication.It aims to provide the reliable communication,while ensures an arbitrary small probability of being detected by the warden.Compared with other information security methods,covert communication fundamentally solves the problem of the information security.In the single-antenna covert communication system,the rate is low due to the illegitimate detection by the warden.Therefore,this paper introduces the multiantenna technology to improve the covert communication capacity by the additional degree of freedom.Firstly,this paper analyzes the imperfect channel state information(CSI)scenario under the multi-antenna system model.The beamforming is used to optimize the covert communication capacity.Secondly,the capacity decreases with the number of the channel uses under the detection constraints.This paper introduces the multi-antenna jammer to generate artificial noise,which can help transmitter realize the constant rate under the imperfect channel state information.Finally,this paper uses the random geometry method to analyze the detection performance of the randomly distributed wardens in a certain area.Then we discuss the detection performance constraints and system capacity under this scenario.Corresponding to the third,fourth and fifth chapters of the paper,the contributions of this paper are as follows.(1)This paper considers the actual covert communication scenario,there are estimation errors in the CSI from the legitimate transmitter to the illegitimate eavesdropper,which will affect the detection constraint and communication capacity.Then,we present a sufficient condition for constant rate covert communication using beamforming under the imperfect CSI channel.Based on the bounded estimation error constraint,the capacity of covert communication system is optimized under the detection performance constraint.(2)The previous results can only apply to the finite channel uses.Its capacity tends to zero as the channel uses increases.Therefore,we introduce the multi-antenna jammer to generate the artificial noise(AN),which can help the transmitter realize the constant rate in the covert communication.In this paper,we discuss the beamforming vector of the jammer under the imperfect CSI channel.The differences between the capacities under the different estimation errors are given through theoretical derivation and simulation.The gain of channel capacity with the multi-antenna jammer is compared with the single antenna jammer.The simulations show that with the multi-antenna jammer,constant rate covert communication can be realized and the capacity is significantly improved compared to the single-antenna system.(3)This paper considers another actual covert communication scenario,that is,the illegal eavesdroppers do not want to be exposed.The information of eavesdroppers is unknown to the communication nodes,including the CSI and the number of eavesdroppers.Based on the random geometric mathematical methods,we express the uncertainty for the eavesdroppers by mathematics.Also,we introduce the multi-antenna jammer to improve the system capacity.Under this scenario we discuss the optimal detection threshold.Then we derive and simulate the overall detection constraints and the capacity.The numerical results show that the area radius,number of the wardens and the distance from the transmitter to the center of the wardens will influence the capacity.The greater the change of the jammer power,the more the capacity can be improved.