Atmospheric Turbulence Of Ldpc Code In The Application Of Wireless Optical Communication Research

Wireless optical communication is a technology of high-speed two-way transmission of voice, data, images and other information through the space or the atmosphere directly using lasers. We can establish a complete network of three-dimensional communications such as sky-to-sky, sky-to-ground, satellite-to-sky, satellite-to-ground and ground-to-ground using this technology. It combines the characteristics of the optical fiber communication and other wireless communication, with advantages such as low cost, high bandwidth, convenient installation, flexibility and strong capability of anti-jamming. In addition, it has broad application prospects in the fields of "last mile" access, LAN/MAN extension and the communication of satellite-to-satellite, satellite-to-ground and sky-to-ground.The transmission channel for wireless optical communication systems is the atmospheric channel which has random nature. There is light absorption and scattering due to the variety of gas molecules, suspended particles and other particles in the atmosphere. The optical signal is severely interference particularly in the case of strong turbulence, which expressed as the effects of beam drift, beam extension, intensity flashing. These effects have a negative impact on the bit error rate, communication range and the bandwidth of the system.The serious impact produced during the laser transmission in the atmospheric channel will degrade the performance of the communication system. Channel coding techniques can greatly improve the atmospheric channel, in particular, the bit error performance of the laser communication when the effect of the light intensity flashing exists, which has far-reaching significance on the development and practical application of wireless optical communication technology. The low density parity check code (LDPC) is one of channel codes with excellent performance. Its performance can gradually approach the channel capacity in the channel with high-speed data transmission and high-capacity storage, at the same time the code achieves decoding, which can effectively ensure the reliability of data transmission and access. The LDPC codes with excellent performance, simple forms are widely used in the systems of optical communication, deep space communication, satellite communication, personal communication, the fourth generation mobile communication, light and magnetic recording.This paper mainly introduced the characteristics and related technologies of wireless optical communication, including its basic concepts, principles etc. Then we analyzed the impact factors of wireless optical communication, and described the formation and various effects of the atmospheric turbulence. We introduced and analyzed the basic principles of LDPC codes and the techniques of coding and decoding in detail. Also we applied the LDPC code in the wireless optical communication system, built the model of the system, simulated and analyzed the application, and proved the improvement of the performance of wireless optical communication finally. In the case of weak turbulence, the coding gain of LDPC with5iterations is3dB higher than uncoded system’s when the bit error rate is2×10-3. In the case of strong turbulence, the bit error rate of system with5iterations LDPC is2orders of magnitude lower than uncoded one. And with the number of iterations increased, the improvement of the system will become more apparent.