# Experimental Investigation of Optimum Beam Size for FSO Uplink

## TL;DR

This study experimentally investigates how transmitter beam size affects FSO uplink performance, considering atmospheric turbulence and pointing errors, to identify an optimal beam size for minimizing bit error rate.

## Contribution

It introduces an experimental approach combined with semi-analytical methods to determine the optimal beam size considering turbulence and pointing errors in FSO systems.

## Key findings

- Optimal beam size increases with zenith angle.
- Beam size has negligible effect at low turbulence levels.
- Results aid in FSO system design and performance analysis.

## Abstract

In this paper, the effect of transmitter beam size on the performance of free space optical (FSO) communication has been determined experimentally. Irradiance profile for varying turbulence strength is obtained using optical turbulence generating (OTG) chamber inside laboratory environment. Based on the results, an optimum beam size is investigated using the semi-analytical method. Moreover, the combined effects of atmospheric scintillation and beam wander induced pointing errors are considered in order to determine the optimum beam size that minimizes the bit error rate (BER) of the system for a fixed transmitter power and link length. The results show that the optimum beam size increases with the increase in zenith angle but has negligible effect with the increase in fade threshold level at low turbulence levels and has a marginal effect at high turbulence levels. Finally, the obtained outcome is useful for FSO system design and BER performance analysis.