Localization in Optical Wireless Sensor Networks for IoT Applications

Abstract

Optical wireless communications (OWC) and the internet of things (IoT) are two recent paradigms that are expected to be ubiquitous in the near future. In this paper, we introduce an early concept of how OWC can play a critical role in IoT applications in the context of real-time location-based services. OWC systems such as visible light communications (VLC) use light-emitting diodes (LED), already present in most user electronics as data transmission nodes. Studies on indoor OWC positioning generally assume that the location of the nodes, the LEDs that are connected to the backbone communications network, is provided to the user equipment (UE). In this paper, we consider a scenario where no a priori knowledge of the LED and UE locations is available, and the UE uses a single photodetector to measure the received optical intensity. We use these measurements to extract the distance between the UE and LEDs, and form geometric relations to find their locations. Once the LED locations have been found, we can track the UE using an extended Kalman filter. The joint source LED localization and UE tracking process is enhanced by using measurements that are collected by other members of the OWC-IoT network. Results show that the root mean square error of the LED localization can be decreased to 10 centimeters, and this leads to a user tracking accuracy better than 20 centimeters using the proposed method.