PERFORMANCE INVESTIGATION OF FSO COMMUNICATION SYSTEM UNDER SUB-TROPICAL WEATHER CONDITION OF BANGLADESH

Abstract

Performance Investigation of FSO Communication System Under Sub Tropical Weather Condition of Bangladesh Use of optical signal for primitive communication is very historic. Signaling communication by means of fire beacons and smoke dates back to 800 -150 BC. However, FSO communication system had seen its mature application since 1960s. Today FSO communication competes with radio due to its high bandwidth, easy installation, low initial cost, versatile applications, etc. However, its signal degradation due to environment is inherent and higher than that associated with radio signal. This paper has defined FSO channel models based on MPSK and LPPM modulation schemes while analyzing their performances under the variation of modulation order and environmental factors including the local rain condition. Meijer G function based close-form expressions and MATLAB-based simulation for performance evaluation have been used. The study analysis has confirmed that FSO links degrade heavily under turbulence, misalignment and local rain condition. The study finds that the SNR degradation due to change of turbulence condition is 20 dB for MPSK and 20-27 dB LPPM links at BER value of 10-4. The strong misalignment causes a degradation of 20 dB for MPSK and 18 dB for LPPM schemes. Lastly, the heavy rain conditions of Bangladesh cause a loss of 15-20 dB for MPSK and 14-25 dB for LPPM schemes. The higher order FSO links provide better spectral efficiency with disadvantage of SNR penalty for MPSK, but with the advantage of SNR gain for LPPM schemes. The penalty of MPSK schemes becomes as high as 13 dB when switched from BPSK to 16-PSK link. Conversely, the gain of LPPM schemes becomes 15 dB when switched from 2-PPM to 16-PPM link. Both MPSK-SIM and LPPM based FSO links have their merits and demerits relative to each other. Higer order MPSK is more beneficial for band-width efficiency and high data-rate applications. But it is more sensitive to phase noise and atmospheric turbulence. Besides, its system is more complex due to the need of phase tracking. On the other hand, higher order LPPM is better power efficient and more advantageous in turbulent environment due to its strong resilience against amplitude jitters, although it has sensitivities to timing jitters. Its system has some complexities due to slot and timing synchronization requirement. Considering Bangladesh environment with unfavorable conditions, both schemes are subject to link degradation and even link break due to extreme conditions. The high-speed high-order FSO link with either modulation scheme fits better for short distance application in Bangladesh environment. Even mitigation techniques can be applied to improve SNR performance. The link needs to be adaptive with switching features from high order to low order for maintaining the link continuity.