Performance Analysis of FSO Link under Atmospheric Turbulence and Pointing Errors

Abstract

Free space optics (FSO) has achieved prominence in extremely large bandwidth, unlicensed spectrum and low power secure transmission in the field of wireless communication. Despite the advantages, it is deeply impacted due to atmospheric turbulence and fog weather conditions. Since FSO needs line of sight (LSO) to be maintained for successful and efficient communication, but due to scintillation and other atmospheric and weather conditions misalignment between transmitter and receiver arises this will result in pointing errors. The atmospheric turbulence channel has gamma-gamma distribution throughout between transmitter and receiver. This thesis considers different modulation scheme sunder the presence of atmospheric turbulence and fog conditions and analyze the FSO link performance under different channel conditions. Throughout the analysis it can be analyzed that 16-PPM has better response among all other considered modulation techniques. The other parameter Pointing error is coming into picture when the misalignment between transmitter and receiver occurs, the combined fading channel model with both fading parameters atmospheric turbulence and pointing errors is considered for the analysis. Firstly the desired expression of bit error rate (BER) is obtained by modeling the turbulence channel with fog weather conditions and then combined effect of atmospheric turbulence with pointing errors. The final BER expression is modeled in the form of Meijer-G function, that is obtained by averaging the conditional error probability taking over the pdf of random generated atmospheric turbulence channel. The analysis done with several modulation techniques and result shows that 16-PPM has provided better performance than other schemes. This analysis can help to adopt a modulation technique according to the channel condition.