Research On Physical Layer Security Method Of Visible Light Communication Based On Achievable Secrecy Rate And Beamforming

By exploiting the optical signal intensity to transmit information,the highest rate of visible light communication(VLC)can exceed 20Gbp/s.As one of the potential key technologies of 5G/6G indoor communication,VLC has attracted extensive attention from both academia and industry.As a supplement to traditional network security encryption methods,physical layer security technology can effectively avoid eavesdroppers from eavesdropping information.However,the physical layer security of VLC network faces the following key challenges: first,unlike traditional RF communication,visible light communication signal adopts intensity modulation/direct detection,and thus the classical Shannon formula cannot be directly applied to VLC network.So far,the channel capacity and closed-form expression of VLC are still open problems.Moreover,the unknown security rate of physical layer of visible light communication restricts the design of optimal transmission mechanism of physical layer security of VLC network.Starting with the closed-form expressions of VLC channel capacity and achievable rate,this thesis presents physical layer security methods for VLC network based on achievable secrecy rate and beamforming.The specific research contents and contributions of this thesis are listed as follows:1.To overcome the challenging problem of unknown accurate channel capacity,an approximate gradient projection descent method is proposed to solve the accurate channel capacity of VLC network,which provides strong theoretical support for the physical layer security research of VLC system.Firstly,a numerical integration method is used to solve the non-integrable problem in the capacity calculation of VLC channels.Secondly,the gradient projection descent method is designed to solve the accurate channel capacity of VLC,and the optimal discrete input distribution is obtained.Moreover,the approximate gradient projection descent algorithm can converge to the optimal solution of the channel capacity problem of VLC.Finally,the closed-form expression of achievable rate for the point-to-point channel is derived and verified by simulation.2.To solve the hard problem that non-orthogonal multiple access(NOMA)transmission capacity of VLC is unknown,the inner bound and outer bound of the capacity region of VLC network are derived.Firstly,the channel capacity problem is modeled as a hybrid discrete optimization problem of discrete entropy maximization based on the NOMA VLC network based on discrete input distributions,and an approximate solution algorithm of discrete entropy maximization is proposed to obtain the inner and outer bounds of the channel capacity region.Secondly,based on the derivation of the closed-form expression of the achievable rate,the optimal beamforming design scheme of NOMA VLC is proposed for continuous input distribution.3.To deal with the problem of unknown secret rate of VLC,a physical layer secure optimal beamforming design scheme of VLC for multi-input single output(MISO)eavesdropping channel is proposed based on the derivation of closed-form expression of secret rate.Furthermore,since the estimation error of channel state information(CSI)is unavoidable in practice,a beamforming design method of minimizing transmit power is proposed under the condition of inaccurate CSI to satisfy the secrecy rate requirement of physical layer and the non-negativity constraint of transmitted signal.The non-convex NP-hard problem is relaxed into a convex problem by using positive semidefinite relaxation,and then the interior point method is used to solve the problem,and the secret rate robust beamforming design is realized.4.To handle the problem of unknown security rate in physical layer of VLC system assisted by artificial noise,the closed-form expression of security rate of VLC under artificial noise condition is derived,and the optimal beamforming design scheme of multi-LED signal and artificial noise is proposed.Finally,simulation results demonstrate the effectiveness of the proposed algorithm under the secrecy rate constraint.5.To solve the problem of unknown secure transmission rate in physical layer of NOMA VLC,the closed-form expressions of inner bound and outer bound of VLC secret rate are derived.By using positive semidefinite relaxation method,the non-convex problem of beamforming design for NOMA VLC network is transformed into a convex problem,and then the transmission power is minimized.Furthermore,the non-convex problem of minimum-secrecy rate maximization beamforming design is transformed into a series of quasi-convex problems,and the optimal beamforming design scheme for physical layer security of NOMA VLCnetwork is obtained.To deal with the problem of unknown channel capacity and physical layer security in VLC networks,this thesis studied and derved the closed-form expression of point-to-point accurate channel capacity and achievable rate of VLC and channel capacity region of NOMA network,and further deduces the closed-form expression of secret rate of communication network based on artificial noise and NOMA.The corresponding beamforming design scheme is proposed,which makes up for the lack of the basic theory of physical security strategy of VLC network,and provides theoretical support for the reliability and security problems in the development and application of VLC.