In this paper, a novel concept for visible light positioning is introduced, which employs a liquid crystal display as a dynamic optical filter in front of a photodetector. By electronically switching dedicated pixel areas in transparent or blocking mode, respectively, the angle of arrival is estimated. The measurement principle is supported by a mathematical model. Finally, an experimental setup is presented and measurement results are compared to the theoretical findings.

Underwater swarm robotics is an emerging topic. Compared to individual autonomous vehicles, high-capacity communication links are required between the mobile agents. In this tutorial, suitable communication technologies are studied, with emphasis on LED-based underwater optical wireless communications. A comprehensive overview about challenges, advances, and practical aspects of underwater swarm robotics employing optical wireless communications is provided. The tutorial includes the following topics: (1) Channel modeling fundamentals; (2) Physical layer transmission techniques for underwater optical wireless communications; (3) Data link layer aspects and hybrid transmission schemes; (4) Ambient light and interference suppression; and (5) Realization aspects. Finally, suggestions regarding future work are given. The tutorial is intended for readers with a background or interest in electrical and information engineering.Index Terms-Autonomous underwater vehicles, channel models, free-space optical communication, light emitting diodes, physical layer, swarm robotics, underwater communication, unmanned underwater vehicles, vehicular ad hoc networks, visible light communication.

We consider error-rate prediction for dual-use lighting systems with visible light communication (VLC) functionality. Since light planning rather than communications engineering is usually the driving discipline for practical dual-use settings, we extract VLC channel parameters as a by-product from advanced 3-dimensional (3D) light-planning models. By this means, we attain realistic signal-to-noise ratios for exemplary positions of a VLC receiver, which allows us to predict corresponding end-to-end bit error rates (BERs). Specifically, our procedure accounts for important aspects of state-of-art lighting systems, such as realistic light distribution curves of employed luminaires, possible presence unmodulated light sources, and, particularly, adaptive dimming operations in response to prevalent sunlight. In this paper, we (i) devise a methodology for VLC systems with optical receive filtering to convert photometric quantities into radiometric quantities, (ii) present examples of BER predictions for selected modulation schemes within some basic office environments, and (iii) conduct an analysis of the resulting simulation accuracy for a particular 3D light-planning tool. Simulation results show that our approach is indeed suited to predict realistic end-to-end BERs for dual-use lighting/VLC systems. Moreover, our procedure is fairly general and may be tailored to specific practical office settings and particular light plans of interest.

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In visible light communication systems, the ability to suppress interference caused by other light sources is a major benefit towards performance improvements. Especially for large transmitter arrays or even multi-cell arrangements, the interference problem needs to be handled. In previous work, we have presented a liquid crystal display (LCD) used as an adaptive interference-suppression filter mounted in front of each photodetector. The display elements are switched on and off in such a way that light emitted by unwanted light sources ideally is blocked, but light emitted by desired light sources reaches the detector. The pattern generated by the LC display has strong impact on the system performance. In this paper, we propose combined precoding in conjunction with LCD-based interference suppression in order to increase the signal-to-interference-plusnoise ratio and to ensure user fairness in massive MIMO scenarios. The suggested precoding strategy uses a new heuristic optimization approach based on the Santa Claus problem on unrelated machines known from computer sciences, and employs only binary entries in the weighting matrix. Corresponding results are compared with a genetic evolutionary optimization strategy and with conventional zero-forcing precoding. Regarding performance evaluation, we perform numerical ray-tracing simulations and present a room-scale VLC testbed for experimental verification.