Design And Implementation Of Optical Communication System Based On LED And APD

Visible light communication technology has broad application prospects. But the realization of this communication system is complicated and the cost is high. At present, there is not a large scale application, still need a lot of research.The data modulation method has important influence on the realization of the visible light communication system. In this paper, digital pulse interval modulation(DPIM) and orthogonal frequency division multiplexing(OFDM) modulation for visible light communication are studied. The relationship between the protective time slot, no protection time slot, different order of positive modulation and negative modulation under various DPIM modulation symbol structure, average transmit power and bandwidth requirements are studied. The realization principle of OFDM modulation method is studied, and the selection basis of important parameters of OFDM modulation is given.Using light emitting diode(LED) and avalanche photodiode(APD) to realize visible light communication system is the main method at present. This paper analyzes and studies the modulation characteristics of LED to guide the design of LED drive circuit. Based on the study of the temperature characteristics of APD, a practical APD power supply circuit is designed to ensure the stability of the signal gain. Amplifier circuit generally has a fixed bandwidth gain product, so narrow band pass amplifier circuit can simplify the system, improve the signal gain, also can better filter power supply noise and high frequency noise, improve signal to noise ratio. In this work, we use a few components constitute a narrow band pass amplifier circuit to produce a unidirectional visible light communication system.It is found that the spectral characteristic of the DPIM can be achieved by employing relatively narrow bandwidth data transmission.In this paper, the design of the unidirectional visible light communication system uses LED as a data carrier, and APD is used as a photosensitive device, STC series microcontroller as a microprocessor(MCU). The visible light communication is realized by combining the DPIM modulation and the narrow band pass amplifier circuit. The experimental results show that the visible light communication system can realize the unidirectional data transmission with the transmission rate of about 45.8Kb/s in the m direct sight distance. The design of the visible light communication system balanced consideration of performance and cost and has good stability, low cost, and good application prospect.OFDM modulation can achieve high-speed optical data communication, it is the focus of the current research. Based on the design experience of one-way visible light communication system, design the circuit principle diagram of some important modules of the OFDM visible light communication system, which has important reference significance for the realization of OFDM visible light communication system.