Performance Analysis And Optimization Methods Of Free Space Optical Communication

Free space optical communication technology has received much attention because of its high security, unrestricted frequency and high flexibility. It can meet the increasing demand of internet in current life.However, the space optical communication system will suffer disturbance when transmitting in atmospheric channel. The communication performance of the free space optical communication system will be severely reduced because of the random uncertainties of the atmospheric channel, which limits the wide application of free space optical communication system in daily life. The adaptive transmission and MIMO spatial diversity technique can suppress effect of atmospheric on the laser.The adaptive transmission and spatial diversity techniques are complementary to each other and can be used to improve the communication performance of free space optical communication systems.What's more, it's an important research topic to improve the performance of free space optical communication system.This paper study the communication performance of free space optical communication such as bit error rate and outage probability, and analyze the performance of free space optical communication with adaptive transmission MIMO-FSO system. The main work and research results are as follows:Firstly, this paper analyzed the influence of different atmospheric effects on the spatial transmission of the laser. In most cases, atmospheric attenuation effect will reduce the power of the laser beam in the transmission. The effect of atmospheric turbulence on space transmission is not only the attenuation of power but also the distortion of phase. The influence of atmospheric turbulence is more serious than the atmospheric attenuation. Therefore, the atmospheric channel is modeled by the main influencing factors - atmospheric turbulence.Secondly, based on the atmospheric attenuation coefficient and atmospheric turbulence model, this paper studied the effect of atmospheric on the intensity of laser light. And establish the mathematical model. On the basis of it, analyzed the differences of performance parameters such as OOK, PPM and BPSK, studied the error rate, outage probability and channel capacity of the three different modulation formats. From the simulation results, it show that the BPSK modulation method can significantly suppress the interference of the atmospheric channel and reduce the bit error rate of the system, therefor effectively improving the performance of the system. The simulation results also show that turbulence intensity, transmission distance and modulation format are the main factors that affect the performance of free space optical communication.Finally, this paper presents an adaptive MIMO-FSO optimization method based on spatial diversity, which is based on the analysis of the influence of atmospheric channel on the performance of free-space optical communication. Three different adaptive transmission strategies can be used in the optimization method, such as adaptive modulation, adaptive coding and adaptive modulation coding, respectively. The optimization method of spatial diversity adaptive transmission based on the above three transmission schemes under the atmospheric channel is analyzed , The bit error rate (BER), outage probability and channel capacity of the MIMO-FSO system using adaptive transmission are simulated and analyzed. The results show that the proposed method can effectively improve the system spectral efficiency, reduce the system error rate and interrupt probability, and then increasing the reliability of free space optical communication system.