Research On Visible Light Communication Transmission Technology Combining Dimming Control

With the increasing scarcity of radio frequency spectrum resources,people's demand for high-speed transmission rates is also becoming more and more urgent.People gradually turned their attention to Visible Light Communication(VLC).VLC does not occupy radio frequency spectrum resources and does not require spectrum license,which has many advantages such as low cost,good confidentiality and high transmission rate.By using widely existing Light Emitting Diode for information transmission,both lighting and communication needs can be met.Orthogonal Frequency Division Multiplexing(OFDM)can effectively resist multipath fading and inter-symbol interference in the wireless transmission process,and its transmission rate is high,so the application of OFDM technology in visible light communication system can improve the communication ability of the system.As a key problem in VLC,dimming control is a hot topic in the field of visible light communication.Based on this,the main contents of this paper are as follows:(1)We have a comprehensive overview of the VLC system and dimming technology.This paper introduces the VLC,OFDM technology and the typical scheme based on OFDM-VLC.We summarize the two current research statuses of dimming technology,and emphasize that digital dimming technology can better meet the requirements of dimmable communication systems.It is the current research hotspot,laying the foundation for subsequent research.(2)A hybrid visible light modulation scheme compatible with dimming control is proposed.In view of the problem of low spectrum utilization of single carrier modulation technology in VLC,firstly,a hybrid visible light OFDM scheme based on Variable On-Off Keying(VOOK)and Variable Pulse Position Modulation(VPPM)is conceived.It is simple to implement and suitable for high-speed VLC links.Then we not only calculate the dimming degree of the proposed scheme in detail,but also prove that the OFDM signal and the dimming signal at the receiving end can receive signals independently without interference with each other,and the complexity is low.Finally,the simulation results show that the scheme can support a wider dimming level and has higher spectral efficiency.(3)An adaptive bias dimmable OFDM scheme based on Pulse Width Modulation(PWM)is proposed.First,for the Layered Asymmetrically Clipped Optical Orthogonal Frequency-Division Multiplexing(LACO-OFDM)scheme,which each layer of ACO-OFDM performs clipping operation,it will produce a higher layer.For the problem of interference,a low-complexity adaptive offset layered optical OFDM modulation scheme is proposed.Through signal reconstruction,superimposed adaptive offset to ensure that the transmission signal is non-negative,etc.,reduce the complexity and reduce the time delay to a certain extent.Then on this basis,the PWM technology is superimposed to support the dimming compatible VLC link.Finally,the simulation results show that the scheme can support a wider dimming level and at the same time has a higher spectral efficiency.(4)An adaptive biasing optical OFDM scheme based on VOOK is proposed.Compared with PWM,VOOK is the preferred solution in the industry because of its own nature,its information potential can transmit more information while dimming,and it is more safe and reliable.According to the VOOK in two different states of high level and low level,different adaptive bias is superimposed respectively to ensure that the dimming signal sent is within the linear range of LED.Simulation results show that the proposed scheme can support a wider dimming range and has a good ability to suppress nonlinear distortion,and the proposed scheme has a lower bit error rate in nonlinear environment compared with LACO-OFDM.