The Performance And Apllication Study Of Spatial Diversity Technology In Free Space Optical Communication

Free Space Optical (FSO) Communication which is also called atmospheric optical communication is an attractive solution for wireless optical communication and catches widely attention recently for its potential high-data-rate, good security, high cost-efficiency, and particularly wide bandwidth on unregulated spectra. FSO channel has a wider bandwidth to support more users. And FSO can cover further place through using relaying technology. Now, FSO is already the key technology of broadband communication in developed country. However, atmospheric optical communication is easily affected by atmospheric condition. Laser beam may be influenced by many atmospheric factor when pass the atmosphere. The particulate matter and air molecules will lead absorption and scattering of laser. The atmosphere turbulence caused by atmosphere motion can produce random fluctuation of the atmospheric refractive index. This will lead intensity scintillation, phase fluctuation, beam wander and beam spread. These will cause fading and distortion of signal and damage the performance of FSO links.There are lots of methods that can mitigate the influence of atmosphere. Spatial diversity is an effective technology to reduce the turbulence affect. It uses multiple transmitters or receivers to make independent channel fading for lower overall fading. This paper uses the phase screen numerical simulation to study the performance of spatial diversity in FSO system. We propose a parallel receive scheme and use phase screen method to compare its performance with a classical single aperture receive scheme. Besides, we propose a new simulation method based on the "frozen turbulence" hypothesis and study the BER performance of a correlation reception system. Results show that spatial diversity can dramatically reduce the scintillation index, and the parallel receive scheme is better than the single aperture scheme. In addition, the BER will decrease with the decrease of the correlation coefficient. So, the FSO spatial diversity system performance will be promoted when the channel correlation is reduced by proper means.