| In recent years,mobile communication technology has developed rapidly.The 5th Generation(5G)mobile communication.system has officially entered commercial use.Technical discussions on the 6th Generation(6G)mobile communication system are also being actively carried out.Visible Light Communication(VLC)is considered to be an important direction for the development of 6G technology.Visible light communication mainly uses light emitting diodes(LED)to transmit data,uses photodiodes(PD)for detection,and uses light in the visible light band as an information carrier.It has the advantages of ultra-high bandwidth,no electromagnetic pollution,and environmental protection.It can be widely used in indoor communication and other scenarios.This paper focuses on indoor visible light communication systems.Due to the limited coverage of LED lighting and its strong directionality,system structure design and deployment schemes are critical to system performance.First of all,in this paper,the structure design and performance of the visible light communication system receiver are studied under different indoor visible light communication system models.In the indoor multiple input multiple output(MIMO)visible light communication system,because of the high channel correlation,an angular diversity receiver(ADR)using PDs with different field of view(FOV)angles is designed.It is called 2FOV-ADR.2FOV-ADR can improve the MIMO channel and get a good channel matrix.Compared with traditional receivers,it has a higher signal to noise ratio(SNR)and a lower bit error rate(BER).In the indoor multi-cell visible light communication system,in order to reduce the inter-cell interference,a 2FOV-ADR is designed to reduce the inter-cell interference,and its structure is optimized to determine its optimal elevation angle and the best combination method.Simulation results show that compared with traditional receivers,2FOV-ADR has higher signal to interference and noise ratio(SINR)and higher area spectral efficiency(ASE).After that,considering the horizontal rotation of the receiver,an angular diversity receiver with optimized field of view is designed,it is called OFOV-ADR.By optimizing the PD's field of view,it can receive signals from LED without interference.It improves the SINR performance of receiver and reduces the impact of horizontal rotation on SINR performance.Then,this paper studies the structure and application of the multi-LED angle diversity transmitter(ADT),and based on this,the space division multiple access(SDMA)indoor visible light communication system is studied.Compared with the TDMA system using the single LED transmitter,SDMA system has higher area spectral efficiency,and the larger the number of transmitter's LED units is,the better its area spectral efficiency performance is,but it is more sensitive to the user's position error.After that,the physical layer security performance of SDMA system is further studied.Simulation results show that it has higher security throughput than TDMA system,and the larger the number of transmitter's LED units is,the better the security performance is.Finally,this paper studies the system design method to improve the physical layer security performance of the indoor visible light communication system.For the typical legitimate user at the center of the room,the analytical expressions of secrecy outage probability,ergodic secrecy rate and their upper and lower limits are derived through the use of mathematical tools of random geometry,and simulation verification is carried out.Then,it compares the system security performance of two layouts of communication access points(APs),namely poisson point processes(PPP)layout and square layout.And then it simulates and analyzes the ergodic secrecy rate distribution when the legitimate user is at different indoor locations.The results show that increasing the number of APs,using LEDs with smaller half-power intensity angle,implementing secrecy protected zone,and regular AP layout can improve the physical layer security performance of the system. |
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