Visible light communication (VLC) is an emerging technology that enables broadband data rates using the visible spectrum. In this paper, considering slow beam steering where VLC beam directions are assumed to be fixed during a transmission frame, we find the steering angles that simultaneously serve multiple users within the frame duration and maximize the data rates. This is achieved by solving a non-convex optimization problem using a grid-based search and majorization-minimization (MM) procedure. Subsequently, we consider multiple steerable beams with a larger number of users in the network and propose an algorithm to cluster users and serve each cluster with a separate beam. We optimize the transmit power of each beam to maximize the data rates. Finally, we propose a non-orthogonal multiple access (NOMA) scheme for the beam steering and user clustering scenario, to further increase the data rates of the users. The simulation results show that the proposed beam steering method can efficiently serve a high number of users, and with power optimization, a sum rate gain up to thirteen times is possible. The simulation results for NOMA suggests an additional 10 Mbps sum rate gain for each NOMA user pair.

Visible light communications (VLCs) are a promising technology to address the spectrum crunch problem in radio frequency networks. A major advantage of VLC networks is that they can use the existing lighting infrastructure in indoor environments, which may have large number of LEDs for illumination. While LEDs used for lighting typically have limited bandwidth, presence of many LEDs can be exploited for indoor VLC networks, to serve each user by multiple LEDs for improving link quality and throughput. In this paper, LEDs are grouped and assigned to the users based on received signal strength from each LED, for which different solutions are proposed to achieve maximum throughput, proportional fairness, and quality of service. Additionally, power optimization of LEDs for a given assignment is investigated, and the Jacobian and Hessian matrices of the corresponding optimization problem are derived. Moreover, for multi-element receivers with LED grouping at the transmitter, an improved optimal combining method is proposed. This method suppresses interference caused by simultaneous data transfer of LEDs and improves the overall signal-to-interference-plus-noise-ratio by 2-5 dB. Lastly, an efficient calculation of channel response is presented to simulate multipath VLC channel with low computational complexity.

In this study, we investigate angle-of-arrival (AOA) and received signal strength (RSS) based localization methods for visible light communication (VLC) systems. We show that while AOA-based localization allows the receiver to locate itself via a least squares estimator by exploiting the directionality of light-emitting diodes (LEDs), RSS-based approach takes Lambertian pattern of LEDs into account and better deals with further improving the localization accuracy via a nonlinear least squares (NLS) estimator. In order to reduce the complexity of the NLS estimator, we develop an analytical learning rule based on the Newton-Raphson method and use the result of AOA-based localization as an initial point for the learning rule. As a benchmark, we also derive generic analytical expressions of the Cramer-Rao lower bound (CRLB) for RSS-based localization.

Wireless networking has conventionally been realized via radio frequency (RF) based communication technologies. However, the capacity of these networks are limited by the availability of the RF spectrum. Free-Space-Optical (FSO) communication has the potential to deliver wireless communication links at optical-level speeds. Although it has the advantage of high-speed modulation, maintenance of line-of-sight (LOS) between transceivers during an on-going transmission is an important issue since FSO transmitters are highly directional. In this paper, we present a prototype implementation of such multi-transceiver electronically-steered communication structures. Our prototype uses a simple LOS detection and establishment protocol and assigns logical data streams to appropriate physical links.We show that by using multiple directional transceivers we can maintain optical wireless links with minimal disruptions that are caused by relative mobility of communicating nodes.