Research On Physical Layer Security Of Mobile User In Visible Light Communication Systems

Visible Light Communication(VLC),with ultra-high speed transmission rate,immunity to electromagnetic interference and license-free spectrum,has been received extensive attention and study by scientific researchers.Due to the characteristic of openness for optical wireless channel,the information may be intercepted or even eavesdropped.Physical Layer Security(PLS)makes full use of the randomness and difference of the channel to ensure the transmission of information safely.At present,the research on the physical layer security of indoor VLC systems mainly focuses on stationary user,without considering the scene of user's mobility.However,user mobility is a significant feature of VLC.With the rapid growth of the mobile Internet,secure communication under mobile user is a key requirement for future communications.Therefore,it is of great significance to study the PLS under mobile user in VLC systems.The main research contents and innovations of this paper are summarized as follows:Firstly,the PLS performance of the direct transmission VLC system under typical mobility models such as Random Waypoint(RWP)and Random Direction(RD)model for mobile user is analyzed.At first,for the scenario of a single legitimate user and a single eavesdropper,a security protected zone is proposed to improve the secrecy performance of mobile user.Then,based on the analysis of the statistical characteristics of the signal-tonoise for mobile users and eavesdropper,the closed-form expressions of non-zero security capacity probability and secrecy throughput are obtained.Finally,the secrecy outage probability of the VLC system when the pause time is not zero during the user's movement is analyzed.Simulation results show that setting the security protected zone could increase the secrecy performance of the VLC systems by about 18%,and the secrecy performance of mobile user under RWP model is always better than RD model.In addition,extending the pause time of mobile user will deteriorate the secrecy performance of the VLC system.Secondly,in view of the situation that user's movement may cause the Line-of-Sight(LOS)link of VLC system to be interrupted,combined with the ubiquitous coverage characteristics of Radio Frequency(RF)communication,the PLS of two-hop hybrid VLC/RF system is analyzed.At first,by deploying a relay node with photoelectric conversion and light energy harvesting,the harvested light energy is used to retransmit the data so as to realize the two-hop transmission of the VLC/RF link.Then the statistical characteristics of the signal-to-noise ratio of mobile users under RWP model are analyzed,and the secrecy outage probability of the two-hop hybrid VLC/RF system is derived.The simulation results show that enlarging the radius of the security protected zone,reducing the semi-angle at half illuminance of LED,and configuring an appropriate lightwave energy collection coefficient can reduce the secrecy outage probability and improve the secrecy performance of two-hop hybrid VLC/RF system under random mobile user.