Research On Physical Layer Security Based On Jamming And OFDM For Visible Light Communications

The mobile communication network has developed from the first generation to the fifth generation.With the rapid change of wireless communication technologies,the demand for high-speed communication becomes higher.Visible light communication(VLC)is a burgeoning field in wireless communications as it has rich and license-free spectrum resources.The broadcast nature of VLC makes it vulnerable to eavesdropping by illegal users,so the security issues cannot be ignored.Physical layer security(PLS)enhances the security performance by using channel randomness or artificial interference to weaken the ability of eavesdroppers.PLS provides a basic guarantee for upper-layer secure transmission.Unlike radio frequency(RF)systems,VLC relies on intensity modulation/direct detection(IM/DD)method.The input signal is required to be non-negative real number,and restricted by the average power and peak power.This paper introduces the advantages and potential application scenarios of VLC technologies,outlines the VLC systems,and describes the typical VLC modulation technologies briefly.The classic Wyner wiretap Gaussian channel model and secrecy capacity for VLC are introduced in details.In this paper,an indoor VLC secure system using jamming is studied.The lower bound of the secrecy capacity of the system is derived.The system includes one message sender,one legitimate user and multiple eavesdroppers.And the number and location of eavesdroppers are unknown.In the simulation,three kinds of distribution are set for the input signal:truncated generalized Gaussian(TGN)distribution,uniform distribution,and exponential distribution.These three kinds of distribution can achieve maximum entropy power under three conditions respectively:limited average power,limited peak power,and limited mean.This paper simulates the performance of three distributions under two conditions:fixed power and fixed mean.The results show that jamming can improve the secrecy performance efficiently.The average secrecy rate can be maximized when the numbers of light-emitting diodes(LEDs)transmitting information-bearing signal and jamming signal are equal.A novel secure transmission method for orthogonal frequency division multiplexing(OFDM)VLC system is proposed in this paper.The VLC secure system combines chaotic sequence,discrete Hartley transform(DHT)and spatial modulation.The original condition of the chaotic sequence is formed based on the main channel matrix.Through the simulation results,it is found that chaotic sequence can greatly improve the bit error rate(BER)of eavesdropper,and improve the secrecy performance of the system.This secure transmission method is a low-complexity and high-flexibility scheme.