Search

As industrial communication continues to evolve to increase flexibility through wireless communication, networked optical wireless communication (OWC), also known as LiFi, has emerged as a promising candidate technology due to its unlicensed spectrum and relatively deterministic propagation. The inherent containment of light improves security, enables dense cellular networks with spatial reuse, and results in reduced sporadic interference while providing high-capacity short range communication links to mobile end devices. This paper outlines the features of the new IEEE Std 802.15.13-2013, suitable for industrial OWC, and presents details of our prototype implementation along with initial experiments. The standard specifies deterministic medium access control (MAC), based on dynamic time division multiple access (TDMA), as well as two physical layers (PHYs) for extended range and robustness, and for spectral efficiency, respectively. Our prototype includes a central coordinator, implemented entirely in software, running on commodity server hardware. It connects to distributed ceiling-mounted optical wireless frontends via a packet-switched network (Ethernet) and is capable of forming them into adaptive virtual cells on a per-user basis. This approach enhances reliability through multiple-input multiple-output (MIMO) transmission and allows for smooth mobility. We implemented the Pulsed Modulation PHY (PM-PHY) on a commercially available field programmable gate array (FPGA) evaluation board. Initial test results indicate that the PM-PHY supports typical distances of up to 6 m between the ceiling and the mobile device. The MAC achieves deterministic latency values below 4 ms.

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.

LiFi or networked optical wireless communication is likely to play an important role in offloading mobile data traffic from radio into the optical spectrum. As the number of Internet of Things (IoT) devices is growing, the RF spectrum becomes a rare resource. Imaging IoT sensors like cameras, ultrasonic devices, and Lidars have real-time requirements, need a high-capacity uplink, and operate in environments that cause or are sensitive against electromagnetic interference. In this paper, for the first time, we present realtime communication over an all-optical fixed-wireless LiFi link based on the distributed multiple-input multiple-output concept. For distributing the wireless signals, plastic optical fibers are used as an analog front-haul. We study the operation of the distributed multiple-input multiple-output link in two modes, i.e., spatial diversity and spatial multiplexing. For the diversity mode, a new combiner is presented, which can support equal gain as well as selection combining. We demonstrate that selection combining is highly effective and enables a similar LiFi performance in up- and downlink, as it is desirable for industrial applications. For the spatial multiplexing mode, we observe that the channel rank and the achievable throughput depend strongly on the user location. As effective solutions, we study the benefits of angular diversity and multiple-input multiple-output mode switching together with multi-user multiplexing and conclude that a dynamic switching between spatial diversity and spatial multiplexing is a practical approach.

The wireless information carrier shift from the radio frequencies to optical frequencies has been studied in increasing detail since the invention of the laser in the 1960s [...]