Moderate-to-Strong Turbulence Generation in a Laboratory Indoor Free Space Optics Link and Error Mitigation via RaptorQ Codes

Abstract

Free Space Optics (FSO) is rapidly gaining interest as a line-of sight communication technology that offers capabilities similar – in terms of bandwidth and transfer rates – to optical fibre, also possessing several advantages compared with traditional radio frequency links. However, FSO link quality can be strongly affected by unfavourable weather conditions and also by the phenomenon of optical turbulence, even in clear sky. In this work, we have implemented an indoor FSO link and generated moderate-to-strong turbulence conditions along the optical path by using heaters and a mechanical ventilation system. In this way, we have been able to investigate the effects of the generated turbulence on the link quality: both erasure errors and packet losses occur during transmission. In order to reduce packet losses, we have used an appositely developed data recovery software integrating the most recent rateless codes (i.e., RaptorQ codes). The results demonstrate that, when properly setting the coding parameters, the link quality can be strongly improved using RaptorQ codes, thanks to the drastic reduction of the Packet Error Rate.