electronics Article Flickering-Free Distance-Independent Modulation Scheme for OCC Patricia Chavez-Burbano 1, * , Jose Rabadan 2, * , Victor Guerra 2, * and Rafael Perez-Jimenez 2, *   Citation: Chavez-Burbano, P.; Rabadan, J.; Guerra, V.; Perez-Jimenez, R. Flickering-Free Distance-Independent Modulation Scheme for OCC. Electronics 2021, 10, 1103. https://doi.org/10.3390/ electronics10091103 Academic Editors: Martin Reisslein and Kiat Seng Yeo Received: 23 February 2021 Accepted: 3 May 2021 Published: 8 May 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Escuela Superior Politécnica del Litoral, ESPOL, Facultad de Ingeniería en Electricidad y Computación, Campus Gustavo Galindo Km 30.5 Vía Perimetral, P.O. Box 09-01-5863, Guayaquil 090112, Ecuador 2 Institute for Technological Development and Innovation in Communications (IDeTIC), Universidad de Las Palmas de Gran Canaria, 35001 Las Palmas, Spain * Correspondence: pchavez@idetic.eu (P.C.-B.); jose.rabadan@ulpgc.es (J.R.); vguerra@idetic.eu (V.G.); rafael.perez@ulpgc.es (R.P.-J.) Abstract: Communications for IoT sensor networks in Smart City applications are demanding new technologies to avoid the radio frequency spectrum saturation and support the massive nodes situation required in this kind of network. Visible Light Communications are gaining interest as an alternative scheme for solving this problem. In particular, Optical Camera Communication (OCC) takes advantage of the presence of cameras in a wide range of devices (smartphones, surveillance systems). Several transmission and modulation schemes, specifically developed for OCC, have been proposed but they present different problems as the communication range, the flickering effects in the transmitted signal, or the system complexity. In this work, an Optical Camera Communication modulation scheme that addresses the considerable variability of the transmitter–receiver distance is proposed. As will be shown, the modulation scheme works properly independently of this separation for a wide range of distances. Additionally, it performs a flickering free transmission to avoid undesired blinking effects for humans and uses a simplified transmission and reception scheme, reducing the system complexity and cost. Results of the modulation’s performance for short (<20 m), medium (20–60 m), and long (>60 m) ranges are presented in the paper, showing a 16 bps transmission rate with Bit Error Rate below the Forward Error Correction (FEC) limit (3.8 · 10 −3 ). Keywords: visible light communications; optical camera communications; modulation scheme; flickering free; distance independence 1. Introduction A Smart City is usually defined as an urban area that employs devices (general- purpose sensors) to collect data and manage assets, resources, and services by applying data analytic tools in several applications such as governance, environmental impact, security, or emergency management. These different sensors gathering information can be considered Internet of Things (IoT) elements that generally connect and communicate with other devices over short, medium, and long distances using wired or wireless networks. Due to the number of sensor devices that a Smart City would require for making accurate decisions, traditional wireless communication links, based on Radio Frequency (RF), may be insufficient. This type of communication presents issues related to the current spectrum saturation and the inter-systems interference based on the extensive use of RF links, so other complementary wireless communication techniques are needed. On account of the advantages of the Light Emitting Diodes (LED), such as energy efficiency, extended life span, cost-efficiency, and high available bandwidth, there is a trend in the use of LED-based devices for illumination, advertising, and decoration in both indoor and outdoor environments. This massive utilization of LED-based devices impulses the development and implementation of Visible Light Communications (VLC) systems [1], Electronics 2021, 10, 1103. https://doi.org/10.3390/electronics10091103 https://www.mdpi.com/journal/electronics