| With the development of various types of multimedia terminal access services,people have put forward more comprehensive requirements for the speed,bandwidth and flexible access applications of indoor communication systems.At present,light-emitting diode(LED)has been widely used due to its low cost,high reliability and long life,and LED can support highspeed data modulation while taking into account indoor lighting,making visible light communication(VLC)technology one of the potential indoor access technologies for 6G communication.Compared with other traditional indoor communication systems,the process of sending and receiving signals in VLC system has many application advantages such as high speed,large bandwidth,low energy consumption,easy implementation,and no need to apply for frequency permission,which has attracted much attention from the industry.At present,in many environments such as stations,airports and offices in modern cities,the flow of users is very dense,and there will be interference between adjacent users and conflict channels when using channels for signal transmission.Therefore,in order to meet the demand of multi-users in the above high-density application scenarios,multi-color multiplexing technology and orthogonal frequency division multiplexing multiple access(OFDMA)access technology are adopted in the visible light communication system to improve the transmission capacity and efficiency of VLC technology and realize the access of multiple users.This paper expounds the transceiver structure and basic principle of VLC communication system;the principle and application advantages of multi-color multiplexing and OFDMA technology are analyzed,and the parameters of visible light communication channel are optimized and configured.On the basis of the above research work,the combination of multi-color multiplexing and OFDMA technology with other modulation techniques is simulated.The specific research work is as follows:The paper designs and proves the feasibility of using return-to-zero(RZ)and quaternary pulse amplitude modulation(PAM4)hybrid modulation scheme in visible light communication system.A multi-user multi-color multiplexing VLC system using red,green,blue and yellow LED(RGBY-LED)as the emitting light source is designed and studied.The transmission performance of RZ-PAM4 signals with three duty cycles(33%,50% and 67%)is analyzed and compared.The results show that although the bit error rate performance is slightly worse than that of the alternating signal inversion(AMI)code,the RZ-PAM4 signal has higher spectral efficiency and has potential application value in future broadband access systems.An eight-color multiplexed visible light communication system model is designed,which successfully realizes the transmission of eight signals at1.5 Gbit/s,3 Gbit/s,and 5 Gbit/s transmission rates,making full use of the visible light band.A hybrid scheme of multi-color multiplexing and OFDMA technology is designed to verify the feasibility of OFDMA technology in visible light communication system.The multi-band phase shift keying(MPSK)technology is also used in the multi-color multiplexing OFDMA-VLC system.The results show that when different order modulation techniques are used,the MPSK-OFDMA signal exhibits different transmission performance in the red,green and blue three visible light signals.At the same time,the constellation diagrams of different users are concentrated and clear in the two-dimensional space,and the constellation points are not overlapped.The research on the visible light signal in the 6 GHz band is carried out,and the signal transmission performance under different rates,different transmission distances and different low-pass filter parameters is analyzed.The results show that the signal transmission in the 6 GHz band can alleviate the current 2.4 GHz band and 5 GHz band.The spectrum bandwidth resource shortage problem. |
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