Study On Wireless Optical Communication With Low Density Parity Check Encoding And Decoding Technoligy

With the continuous development of information society, the demand for high-speed data transmission is growing day by day. Wireless laser communication(FSO) is a kind of technology that uses a laser beam as a carrier to transmit information, Wireless laser communication has get the attention of the reserchers for its high bandwidth, high bit rate, high confidentiality, anti-interference advantages. Wireless laser communication has become the focus of surface-to-air and air-to-air communications in the countries now.Currently, the main problem to wireless laser communication is that the different effect of atmospheric deterioration affects the quality of carrier signal and the system performance when the light wave propagates in the atmospheric channel. We have applied the low density parity check code(LDPC) technology application in the system and studied the technology on the improvement of the system ber performance in this thesis.We have studied the description of light polarization and implementation method of circular polarization shift keying on t he wireless laser communication. Then we have expounded the related principles of the low density parity check code(LDPC) decoding technology, including the structure of the generator matrix, the method of using the generator matrix to encode and the application of related decoding algorithm to decode the optical transmission information. It has shown that the atmospheric channel attenuation coefficient decreases and the transmittance increases with increasing the visibility.And then, we have investigated the attenuation of optical carrier in atmospheric channel and the algorithm of related loss caused by a tmospheric turbulence. We have mainly analyzed the absorption of the atmospheric gas molecules or atoms and the scattering of the particles in atmospheric channel for the optical carrier. Finally, we have used the atmospheric optical transmittance of optical carrier to represent the influence of these two effects and deduced the relationship between the atmospheric optical transmittance and the visibility and the transmission distance. Then we have used the theory of turbulence of Cole Mo Grove to figure out the expression of atmospheric turbulence and discussed the influence between the refractive index structure constant of atmospheric channel and the altitude or speed.After that, we have compared the performance of the system before and after the application of LDPC decoding technology through the wireless laser communication simulation system. We have applied the LDPC decoding technology in the single way receiving FSO simulation system and dual difference receiving FSO system, and verified the improvements on the bit error rate of the system through data analysis by using the LDPC code decoding technology. And we have also verified the influence of the transmission distance and transmission power to the system. Finally, we have setted up a wireless optical communication experiment system and verified that the LDPC code decoding technology can reduce the bit error rate of wireless optical communication system, improve the performance of the system, increase the transmission distance by using this experiment system. After that, we have setted up wireless laser communication experiment platform and apply the LDPC decoding technology to the test platform. Through the data acquisition and the subsequent processing, we have analyzed the influence of the LDPC code decoding technology to the properties of the experimental system. At the same time, we have also studied the effect of the transmission power to the system bit error rate.The studies have shown that the LDPC technology can significantly reduce the system bit error rate and improve the performance of the system. At the same time, the system bit error rate decreases with the increase of transmission power decreases continuously until it reaches the minimum.