Research And Implementation Of Modulation And Demodulation Technology In Long-Distance Visible Light Communication System

As a new type of wireless communication technology,visible light communication has the advantages of rich spectrum,safety,and energy-saving.The emergence of this technology has attracted great attention.As an important part of the transmission system,the performance of the modulator and demodulator will directly affect the overall performance of the transmission system.In this paper,the relevant knowledge of digital modulation and demodulation technology is used,and the appropriate modulation and demodulation scheme is selected in combination with the actual application scenarios of long-distance visible light communication.With the help of MATLAB and ModelSim simulation software,the modem is analyzed theoretically and verified to be feasible.Finally,the scheme is implemented on the FPGA platform.The following work has been done during the implementation of this topic:1.The structure of the visible light communication system is analyzed in detail.Through the performance analysis of several alternative modulation and demodulation schemes,the modulation and demodulation scheme with the best comprehensive performance is selected and applied to the modem design of this subject.At the same time,in order to achieve a higher system transmission rate under the same hardware conditions,DQPSK is selected as another modulation and demodulation scheme applied to the system based on DPSK modulation and demodulation scheme.2.Complete the overall architecture design of the DPSK modem system.The modulator mainly discusses the principle of single-bit differential encoding and decoding module,shaping filter module,carrier generator module,and FPGA-based design and implementation.Demodulator mainly discusses the principle of carrier synchronization module and bit synchronization module and the design and implementation based on FPGA.The correctness of the modem system design scheme is verified by simulation experiments.3.Completed the overall architecture design of the DQPSK modem system.The modulator part mainly discusses the principle of the double-bit differential encoding and decoding module and the design and implementation based on FPGA.Demodulator mainly discusses the principle of carrier synchronization module in multi-system demodulation and the design and implementation based on FPGA.The correctness of the modem system design scheme is verified by simulation experiments.4.The structure of the real-time long-distance visible light communication system and the design of the test scheme are completed.And a platform was built for experimental verification.In the back-to-back connection test between the receiver and the transmitter of the system,the system realized effective transmission with a bit error rate of 0.When we use the corridor full of background light as the experimental site,we use a red LED with an optical power of 0.5W as the signal source,carry out photoelectric conversion with APD and send it to FPGA demodulation terminal for demodulation.Finally,a real-time visible light communication system with a speed of 10Mbps,a communication distance of 66m and a bit error rate of 1E-5 is realized.