Research And Hardware Design Of Techniques Of Visible Light Communication System Based On Laser Diode

With the continuous development of wireless communication technology and the increasing number of users, the demand of bandwidth for mobile communication network is also rising, but the limited radio spectrum bandwidth restricts the pace of development of wireless communications. Under this circumstance, visible light communication comes into being. As the spectrum of visible light communication is huge and haven’t been used yet, it can be used without authorization. What’s more, visible light communication has the characteristics of high safety, great confidentiality and green energy saving etc. With so many advantages, as soon as it comes into being the visible light communication technology has attracted wide attention both at home and abroad. In this paper, key techniques of visible light communication system studied and the hardware design has been realized.At first, the characteristic of visible light communication channel has been studied. The math model of the channel considering atmospheric attenuation, atmospheric turbulence and nonzero bore sight pointing error, has been established. After that this paper obtains the closed form expression of the average bit error rate, which is verified as right after simulated with the Monte Carlo method in the Hybrid Channel mentioned above.Then, the paper studies the modulation mode which used commonly in visible light communication system. The characteristics of binary modulation technology and multi-band modulation technology have also been analyzed. Besides, the spectrum efficiency and power efficiency of binary modulation are compared including OOK, PPM and DPPM, and get the result that the spectrum of OOK modulation system better then PPM and DPPM under the same circumstances. And the binary modulation is better at the earlier time building the hardware system of visible light communication.After that, the hardware circuit of visible light communication system has been designed, during which specific problems encountered has been solved. This paper overcome the disadvantage of the slow modulation speed which deseeded by the manufacturing technique of the semiconductor light source using the improved circuit scheme. Overcome the nonlinearity with the method of linear equalization, and solve the problem of weak drive ability by enlarger the current with the buffer. The designed circuit has been tested by the eye diagram.Finally, the hardware driver module of the designed system base on FPGA has been designed also, including A/D and D/A converter and tri-speed Ethernet. Except that the influence of A/D converter’s selection to the hardware system performance are researched also. Besides, paper also studies the function of MAC in Internet protocol and the construction of the data frame in MAC. Through the hardware simulation we get the result that the designed drivers can function well and the data can get through the hardware reliably.