Research On Modulation Technology Of Visible Light Communication Based On MIMO

With the continuous development of network technology,mobile terminal equipment plays a more and more important role in human life,and with it,people have more and more requirements for the rate of information transmission and the stability of transmission network.Optical fiber communication solves the dilemma named "last mile" in the field of communication,but the wireless access spectrum resources have become increasingly tense.Therefore,a new and efficient network access mode is urgently needed in society,so the visible light communication system emerges as the times require.Visible light communication uses a LED light source to emit a visible light signal,and the receiving end uses a photodetector PD to receive and transmit information.This new network access method not only satisfies the needs of indoor lighting,but also enables high-speed information transmission.So the complicated network equipment required for traditional access methods is avoided,and it is more secure and energy-saving.Today,the spectrum resources are so precious.Therefore,the availability of visible light communication systems brings new opportunities for the development of network technology.It is precisely because of its numerous advantages and it has become a research hotspot for researchers from all over the world.In this paper,the simulation model of the visible light MIMO system is set up,The transmitter uses 4 LED transmitting arrays,and the receiver receives optical information from 4 non imaging independent concentrators.The modulation technology of the visible light communication system is simulated and analyzed under the MIMO system,including the modulation of the information transmission and the brightness.The Traditional information modulation in visible light communication can be divided into three main categories: on-off keying modulation,pulse modulation and OFDM modulation technology.And the pulse modulation is further divided into pulse amplitude modulation,pulse width modulation and pulse position modulation.Through the analysis,we can learn that the on-off keying is simple,but it has poor performance on anti-noise and low transmission rate.The pulse modulation can be more diversified to adjust the pulse to transmit information more efficiently,but the increasing demand is still not reached in the transmission rate.The OFDM modulation technology just makes up for the low modulation bandwidth of visible light communication,and can resist the multipath interference more effectively,and at the same time transmit information at high rate.In the end,the simulation proves that OFDM modulation technology has great advantages in combination with MIMO system.The brightness control modulation technology in the visible light communication system is also an important part of its research,because the indoor visible light communication has to meets the indoor lighting requirements while satisfying the information transmission.The article analyzes the existing two types of visible light communication brightness modulation methods: brightness modulation with adjustable amplitude and brightness modulation with non-adjustable amplitude techniques.In general,the brightness control is performed by adjusting the unused transmission time slots.Adjusting the time slots alone cannot improve the space very well and the detailed brightness modulation cannot be completed.After analyzing the existing brightness modulation technology,this paper proposes an improved variable multi-pulse position average modulation based on pulse amplitude,and the simulation shows that the advanced scheme greatly improves the brightness modulation fineness.Under the MIMO system model,the advanced scheme and the existing brightness modulation scheme are compared and analyzed by simulation.