Research On Modulation And Demodulation Technology In Visible Light Communication System

With the fast development of communication technology and the diversified demands for communication methods,visible light communication(VLC)technology has attracted more and more attentions from people.Its advantages include free spectrum,no electromagnetic pollution,safe and reliable,etc.VLC technology is a new type of communication technology which developed rapidly with the wide application of LED.In this thesis,the modulation and demodulation technology for VLC system were intensively studied.The purpose of the thesis is to explore and verify the modulation and demodulation scheme that is suitable for the VLC transmission channel.The main works of this thesis includes:Firstly,the principle of two kinds of modulation and demodulation methods named OOK and PPM were investigated.The optical properties of the light source and photoelectric detector were discussed.The channel model named directional line of sight channel was chosen as the optical channel for VLC system.Secondly,the hardware circuits for the point to point VLC system was designed and implemented.It was included the transmitter circuit,the receiver circuit and the serial communication circuit.The transmitter circuit included modulation circuit,LED drive circuit and LED light source.The receiver circuit included the photoelectric conversion circuit,amplifying circuit,filtering circuit and the demodulation circuit.The STM32F103C8T6 chip was chosen as the processing chip.Finally,the designed point to point VLC system was tested experimentally.The computer sent the character information to the transmitting terminal of the VLC system through the serial communication module,and the receiving terminal transmitted the demodulated information to the computer through the serial communication module.Experimental results showed that characters can be successfully transmitted via the designed VLC system and the maximum transmission distance was 60cm.