Rateless codes mitigation technique in a turbulent indoor Free Space Optics link

Abstract

Free Space Optics (FSO) links are affected by several impairments and, among them, optical turbulence is the most important factor that can degrade the link quality. Due to the presence of this phenomenon, the signal irradiance detected by the receiver fluctuates, thus causing erasure errors and fading events. In this work, we present an indoor Free Space Optics link, in which several turbulence conditions are generated by using two heating elements. We show that the generated turbulence causes erasure errors and packet losses during the data transmission, and we also compare the statistical distribution of the samples with the theoretical models. Moreover, we demonstrate how the application of the most recent rateless codes, i.e., RaptorQ codes, can strongly improve the link quality. In particular, results show that the Packet Error Rate strongly decreases when employing RaptorQ codes. Finally, we conclude that, by properly setting the encoding/decoding parameters, we can correctly receive the whole transmitted data without any errors

Error mitigation using RaptorQ codes in an experimental indoor free space optical link under the influence of turbulence

“…To create a thermal gradient and hence to generate the turbulence we have used two 25 cm-long heating elements along the optical beam propagation path (OBPP) [10,11]. In [29,33,34] it has been experimentally demonstrated that turbulence can be generated over a short FSO link. A fan placed close to the collimator is used to generate the air flux towards the heating elements, in order to create more controlled and repeatable turbulence conditions.…”

“…The rateless codes (RC) are the most recent software based solution [20][21][22][23][24][25][26][27][28][29], specifically designed for the erasure channels because of ease of operation and no rate mismatch as a result of imprecise channel estimation. RC have high potential for increasing the capacity of wireless systems in which the information is transmitted at a very high R and at the receiver it is accumulated in a form of graph, trellis, or matrix structure.…”

“…However, the evaluation of the codes was carried out offline using the recorded measured data. In this paper, we experimentally investigate the use of most recent and powerful RC (i.e., RaptorQ codes (RQC) [25][26][27][28][29]) for an FSO system and compare the link performance under both weak and moderate turbulence regimes using an indoor experimental set up.…”

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