We present a concept for networked optical wireless communications, also denoted as LiFi, to meet the requirements of industrial wireless applications. These are primarily mobility support with moderate data rates per device, reliable real-time communication, and integrated positioning. We describe a distributed multiuser multiple-input multiple-output architecture, serving mobile devices via an optical wireless infrastructure. The system consists of a central unit, being connected to a number of distributed optical frontends covering a larger area. Our main contribution is a medium access control protocol based on space division multiple access. Evaluation results demonstrate the advantages of joint transmission from adjacent optical frontends and the dynamic switching between spatial diversity and multiplexing. The relevance of spatial multiplexing becomes obvious through channel measurements in an indoor scenario. Moreover, we highlight a low-power physical layer based on on-off-keying for battery-powered mobile devices. Our architecture can easily integrate positioning by simultaneously measuring the time-of-flight between multiple optical frontends and the mobile device. We highlight the use of plastic optical fiber as an analog fronthaul technology and discuss the integration with other networks. The main functions described in this paper will be supported by the upcoming IEEE Std 802.15.13.

In this paper, artificial intelligence tools are implemented in order to predict trajectory positions, as well as channel performance of an optical wireless communications link. Case studies for industrial scenarios are considered to this aim. In a first stage, system parameters are optimized using a hybrid multi-objective optimization (HMO) procedure based on the grey wolf optimizer and the non-sorting genetic algorithm III with the goal of simultaneously maximizing power and spectral efficiency. In a second stage, we demonstrate that a long short-term memory neural network (LSTM) is able to predict positions, as well as channel gain. In this way, the VLC links can be configured with the optimal parameters provided by the HMO. The success of the proposed LSTM architectures was validated by training and test root-mean square error evaluations below 1%.

Energy consumption is one of the critical issues in optical wireless communications transmitter design and a limiting factor to miniaturization and deployment in mobile devices. In order to reduce energy requirements, we assess a physical layer based on high-bandwidth on-off keying modulation. The use of on-off keying allows for highly efficient transmitter frontend designs that avoid operation of amplifier stages in a resistive mode, which has the potential of reducing their energy usage by an order of magnitude. Link-level simulations show that this physical layer can deal with typical frontend limitations and can operate in challenging non-line-of-sight channels. For these reasons, we believe that the solution evaluated here can deliver a significant contribution to optical wireless communications technology in a wide range of use cases.

We present a new, accurate, low complexity channel modelling methodology for LiFi in realistic indoor scenarios. A LIDAR scanner is used to capture the 3D environment in which the LiFi system is to be deployed. Next, the generated 3D point cloud data is pre-processed to determine the reflectance parameters of the walls and objects in the room. This is easier and more realistic than the manual definition of the environment, which is the current state of the art. As an additional innovation, the complexity of the channel modelling is reduced by: 1) modelling the line-of-sight and initial reflections precisely in the frequency-domain; 2) using a well-established analytical model based on the integrating sphere for all higher-order diffuse reflections. All steps together yield a substantially simplified channel modelling approach and model the links between multiple optical frontends and multiple mobile devices realistically. As a validation of our new approach, we compare measurements and simulations in two indoor scenarios: an empty room and a conference room with furniture. Simulations and measurements show excellent agreement with a mean square error below 3 percent. Moreover, we evaluate the performance of a distributed multiuser multiple-input multiple-output (MIMO) link and found excellent agreement between the model and measurements. Finally, we discuss the fundamental trade-off between complexity and model error, which depends on the scenario.

Due to its better power efficiency, pulsed modulation such as on-off keying (OOK) has the potential of maximizing reach and minimizing energy consumption for future high data rate optical wireless communication (OWC), especially LiFi systems. In this paper, we introduce enhancements of the OOKbased Pulsed Modulation Physical Layer (PM-PHY) defined in IEEE Std. 802.15.13-2023. Namely, we evaluate robust linecoding and equalization techniques with reduced overhead and complexity, and increase bandwidth by using a vertical-cavity surface-emitting laser (VCSEL) array as transmitter. With these enhancements, we demonstrate data rates up to 4.25 Gbit/s using large VCSEL arrays with a combined optical power of 350mW. These VCSEL arrays can cover an area of 4.32 m$^{2}$ at a distance of 2.5m. Our results show that the large bandwidth, high power and low energy consumption of low-cost VCSEL arrays, when combined with pulsed modulation, can reach Multi-Gbit/s data rates and enable user mobility in large areas.

We propose an energy efficient physical layer (PHY) employing pulsed modulation and simultaneous transmission enabling reliable Li-Fi networks for industrial applications. Essential PHY components are laid out and tested in a simulated manufacturing cell.