Automatic Tracking of Li-Fi Links for Wireless Industrial Ethernet

The proceeding digitalization of our environment leads to continuously increasing data traffic. Especially in industrial environments, automation is an omnipresent trend. Autonomous systems incorporate a rising amount of sensors as well as continuous Machine-to-machine (M2M) communication. The resulting enormous data volumes are often transmitted using wired interconnections. Nonetheless, wireless communication approaches can simplify the integration into complex systems and enable the connection to dynamic parts like vibrating or rotating components. Because of the open communication channel engineers have to face a number of challenges like security issues, interferences and regulation of irradiated power. Radio frequency (RF) technologies are used in manifold applications, but in certain scenarios they are still cumbersome. For instance, wireless hard real-time operations require a careful analysis of the channel and its environment to avoid interferences. An easier handling by using exactly defined communication spots is possible by using light transmission. These so-called Li-Fi technologies are ideal for autonomous systems in Industry 4.0 since optical communication offers reliable and high data rate communication links with low-latency characteristics. However, there is always a trade-off between communication range and coverage. The latter is determined by the systems field-of-view (FOV) which describes the defined light spot where the link is established. Unfortunately, a large FOV reduces the received power and the related maximum communication range. This contradiction can be overcome by forming a small, dynamic steerable spot. In this paper we present a compact Li-Fi tracking system based on a steerable optical wireless link, which enables full-duplex bi-directional data communication with a data rate of 1.25 Gb/s. This approach shows the feasibility and handling of an energy efficient wireless link thanks to its 12-bit-precise beam alignment by using a MEMS mirror. The optical setup and the interaction of a dynamic communication link with the corresponding software is described. Moreover, we introduce a tracking algorithm which enables a fully autonomous link establishment and thus a simple installation. Data rate measurements underline the high performance of the wireless link whereas the systems mobility is characterized by measurements of the settle time for the steered beam.