Photonics 2022, 9, 446. https://doi.org/10.3390/photonics9070446 www.mdpi.com/journal/photonics Article Analysis of Scintillation Effects on Free Space Optical Communication Links in South Africa Olabamidele O. Kolawole 1, *, Thomas J. O. Afullo 1 and Modisa Mosalaosi 2 1 School of Electrical, Electronic, and Computer Engineering, University of KwaZulu-Natal, Durban 4001, South Africa; afullot@ukzn.ac.za 2 Department of Electrical, Computer and Telecommunication Engineering, Botswana International University of Science and Technology, Private Bag 16, Palapye 10071, Botswana; mosalaosim@biust.ac.bw * Correspondence: kolawole.olabamidele@gmail.com; Tel.: +27-835854063 Abstract: The performance of free space optical communication (FSOC) systems is severely de- graded by certain atmospheric conditions prevalent in places where they are deployed, in spite of their numerous advantages. In clear weather conditions, the random fluctuation in the atmosphere’s refractive index causes substantial scintillation losses to transmitted optical signals. It is therefore imperative to estimate the potential losses due to atmospheric turbulence in locations where FSOC links are to be deployed. This will provide the necessary fade margin for FSOC systems so that designed links withstand such atmospheric disturbances. In this paper, statistical analysis of wind speed data collected for various cities of South Africa is used for calculating the corresponding re- fractive index structure parameter ( 2 n C ). These 2 n C values, as well as the zero inner scale and infi- nite outer scale model and finite inner and finite outer scale model, are used in computing the scin- tillation indices not exceeding 50%, 99%, 99.9%, and 99.99% of the time for the investigated locations. The Lognormal and Gamma–gamma distribution models are then employed for the computational analysis of the irradiance fluctuations and channel characteristics while considering the effect of pointing errors for weak and moderate to strong turbulence regimes. Finally, derived mathematical expressions for outage probabilities and bit error rate (BER) performances for FSOC links, employ- ing various intensity modulation and direct detection (IM/DD) schemes, are presented. Keywords: free space optical communication; wind speed; refractive index structure parameter; scintillation index; atmospheric turbulence; pointing errors 1. Introduction The International Mobile Telecommunications 2020 (IMT-2020) specifications, devel- oped by the third generation partnership project (3GPP) for new radio (NR) operations in the fifth generation (5G) spectrum, is expected to accomplish the following performance requirements: ultra-reliable and low latency communications (URLLC) in the user plane as low as 1 ms; massive machine type communications (mMTC) that support up to 1 mil- lion devices per square km; and enhanced mobile broadband (eMBB) with uplink and downlink speeds of up to 10 and 20 Gbits/s [1,2]. These technical requirements are needed for the high bandwidth demands of augmented reality (AR), virtual reality (VR), and mixed reality (MR) applications, as well as the seamless and optimal functionality of Mas- sive Internet of Things (MIoT) and Vehicle-to-Everything (V2X) connections for the smooth running of emerging smart cities [3–5]. Free space optical communication (FSOC), whether as a standalone or hybrid tech- nology, is a promising complementary solution platform for 5G backhaul networks [6]. FSOC systems convey bidirectional information at high data rates through the atmos- phere between line-of-sight (LOS) optical transceivers. Their numerous advantages in- clude: very high throughput, highly secure transmission, relatively low cost, and ease of Citation: Kolawole, O.O.; Afullo, T.J.O.; Mosalaosi, M. Analysis of Scintillation Effects on Free Space Optical Communication Links in South Africa. Photonics 2022, 9, 446. https://doi.org/10.3390/ photonics9070446 Received: 31 December 2021 Accepted: 22 June 2022 Published: 25 June 2022 Publisher’s Note: MDPI stays neu- tral with regard to jurisdictional claims in published maps and institu- tional affiliations. Copyright: © 2022 by the authors. Li- censee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and con- ditions of the Creative Commons At- tribution (CC BY) license (https://cre- ativecommons.org/licenses/by/4.0/).