Virtual and augmented reality (VR AR) systems are emerging technologies requiring data rates of multiple Gbps. Existing high quality VR headsets require connections through HDMI cables to a computer rendering rich graphic contents to meet the extremely high data transfer rate requirement. Such a cable connection limits the VR user's mobility and interferes with the VR experience. Current wireless technologies such as WiFi cannot support the multi-Gbps graphics data transfer. Instead, we propose to use visible light communication (VLC) for establishing high speed wireless links between a rendering computer and a VR headset. But, VLC transceivers are highly directional with narrow beams and require constant maintenance of line-of-sight (LOS) alignment between the transmitter and the receiver. Thus, we present a novel multi-detector hemispherical VR headset design to tackle the beam misalignment problem caused by the VR user's random head orientation. We provide detailed analysis on how the number of detectors on the headset can be minimized while maintaining the required beam alignment and providing high quality VR experience.
VLC systems typically use white LEDs as transmitters. The modulation bandwidth of such LEDs is a few MHz which limits the transmission rate of a VLC system @cite_25 . To achieve the desired high speed data rate, different methods have been proposed, such as, frequency domain equalization @cite_35 , using optical filters, modulation techniques like orthogonal frequency division multiplexing @cite_22 @cite_15 , multiple-input multiple output (MIMO) @cite_30 @cite_17 , and using red-green-blue (RGB) LEDs @cite_33 . In @cite_27 , a data rate of 3.4 Gbps was reported which was achieved using wavelength division multiplexing (WDM) and RGB LEDs. In @cite_18 @cite_9 , RGB laser diodes (RGB-LDs) were used instead of LEDs, since LDs can provide the high modulation bandwidth of multiple GHz. It has been shown in @cite_4 @cite_12 that a combination of visible RGB lasers along with a diffuser can generate white light that has comparable properties with white LED sources. @cite_9 has shown that data rates of as high as 25Gbps can be achieved using RGB-LDs.
@cite_30 @cite_35 @cite_18 @cite_4 @cite_22 @cite_33 @cite_9 @cite_27 @cite_15 @cite_25 @cite_12 @cite_17
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Solid-state lighting is a rapidly growing area of research and applications, due to the reliability and predicted high efficiency of these devices. The white LED sources that are typically used for general illumination can also be used for data transmission, and Visible Light Communications (VLC) is a rapidly growing area of research. One of the key challenges is the limited modulation bandwidth of sources, typically several MHz. However, as a room or coverage space would typically be illuminated by an array of LEDs there is the potential for parallel data transmission, and using optical MIMO techniques is potentially attractive for achieving high data rates. In this paper we investigate non-imaging and imaging MIMO approaches: a non-imaging optical MIMO system does not perform properly at all receiver positions due to symmetry, but an imaging based system can operate under all foreseeable circumstances. Simulations show such systems can operate at several hundred Mbit s, and up to Gbit s in many circumstances. This letter describes a high-speed visible light communications link that uses a white-light light-emitting diode (LED). Such devices have bandwidths of few megahertz, severely limiting the data rates of any communication system. Here, we demonstrate that by detecting only the blue component of the LED, and using a simple first-order analogue equalizer, a data rate of 100 Mb s can be achieved using on-off keying nonreturn-to-zero modulation. Over the past decade, visible light communication (VLC) systems have typically operated between 50 Mbps and 3.4 Gbps. In this paper, we propose and evaluate mobile VLC systems that operate at 10 Gbps. The enhancements in channel bandwidth and data rate are achieved by the introduction of laser diodes (LDs), angle diversity receivers (ADR), imaging receivers, relay nodes, and delay adaptation techniques. We propose three mobile VLC systems: an ADR relay assisted LD-VLC, an imaging relay assisted LD-VLC (IMGR-LD), and select-the-best imaging relay assisted LD-VLC. The ADR and imaging receiver are proposed for the VLC system to mitigate the intersymbol interference, maximize the signal-to-noise ratio (SNR), and reduce the impact of multipath dispersion due to mobility. The combination of IMGR-LD with a delay adaptation technique adds a degree of freedom to the link design, which results in a VLC system that has the ability to provide high data rates under mobility. The proposed IMGR-LD system achieves significant improvements in the SNR over other systems in the worst case scenario in the considered real indoor environment. Solid-state lighting is currently based on light-emitting diodes (LEDs) and phosphors. Solid-state lighting based on lasers would offer significant advantages including high potential efficiencies at high current densities. Light emitted from lasers, however, has a much narrower spectral linewidth than light emitted from LEDs or phosphors. Therefore it is a common belief that white light produced by a set of lasers of different colors would not be of high enough quality for general illumination. We tested this belief experimentally, and found the opposite to be true. This result paves the way for the use of lasers in solid-state lighting. Visible light LEDs are being used for indoor optical wireless systems as well as room lighting. In indoor diffuse optical wireless links multipath dispersion limits the maximum transmission data rates. In this paper we investigate OFDM system where multipath induced intersymbol interference (ISI) is reduced, enabling higher data rates. Pilot signals are uniformly inserted into data symbols (subcarriers) and are extracted at the receiver for channel estimation. Predicted and simulated results for the symbol error rate (SER) for an OFDM employing BPSK, QPSK and M-QAM for line of sight (LOS) and diffuse links are presented for a range of pilot signal. We report the first Gigabit-range visible light link based on off-the-shelf RGB-type white LEDs. By application of WDM and DMT modulation an aggregate rate of 1.25 Gbit s within the FEC 2·10-3 limit has been reached at illumination levels recommended by the lighting standard for the working environment. Visible light communication (VLC) systems have typically operated at data rates below 20 Gbps and operation at this data rate was shown to be feasible by using laser diodes (LDs), beam steering, imaging receivers and delay adaptation techniques. However, an increase in the computational cost is incurred. In this paper, we introduce fast computer generated holograms (FCGHs) to speed up the adaptation process. The new, fast and efficient fully adaptive VLC system can improve the receiver signal to noise ratio (SNR) and reduce the required time to estimate the position of the VLC receiver. In addition, an imaging receiver and a delay adaptation technique are used to reduce the effect of inter symbol interference (ISI) and multipath dispersion. Significant enhancements in the SNR, with VLC channel bandwidths of more than 36 GHz are obtained resulting in a compact impulse response and a VLC system that is able to achieve higher data rates (25 Gbps) with full mobility in the considered indoor environment. In this paper, we experimentally realized a gigabit-class indoor visible light communication system using commercially available RGB White LED and exploiting an optimized DMT modulation. We achieved data rate of 1.5 Gbit s with single channel and 3.4 Gbit s by implementing WDM transmission at standard illumination levels. In both experiments, the resulting bit error ratios were below the FEC limit. To the best of our knowledge, these values are the highest ever achieved in VLC systems. Multiple-input multiple-output (MIMO) is a natural and effective way to increase the capacity of white light-emitting diode (LED) based visible light communication (VLC) systems. Orthogonal frequency division multiplexing (OFDM) using high-order modulation is another widely used technique in VLC systems. Due to the intensity modulation and direct detection nature of VLC systems, Hermitian symmetry is usually imposed in OFDM so as to obtain a real-valued signal. In this paper, we investigate a non-Hermitian symmetry OFDM (NHS-OFDM) scheme for MIMO-VLC systems. By transmitting the real and imaginary parts of a complex-valued OFDM signal via a pair of white LEDs, NHS-OFDM circumvents the constraint of Hermitian symmetry. We evaluate the performance of an indoor 2×2 MIMO-VLC system using conventional Hermitian symmetry-based OFDM (HS-OFDM) and NHS-OFDM, where both a non-imaging receiver and an imaging receiver are considered. Analytical results show that the system using NHS-OFDM achieves superior bit error rate (BER) performance to that using HS-OFDM, with lower or nearly the same computational complexity. The superior BER performance of NHS-OFDM-based MIMO-VLC is further verified by experiments. The experimental results demonstrate that, in a 400 Mb s2×2 MIMO-VLC system with an imaging receiver, NHS-OFDM improves the communication coverage by about 30 compared with conventional HS-OFDM for a target BER of 3.8×10−3. Detailing a systems approach, Optical Wireless Communications: System and Channel Modelling with MATLAB, is a self-contained volume that concisely and comprehensively covers the theory and technology of optical wireless communications systems (OWC) in a way that is suitable for undergraduate and graduate-level students, as well as researchers and professional engineers. Incorporating MATLAB throughout, the authors highlight past and current research activities to illustrate optical sources, transmitters, detectors, receivers, and other devices used in optical wireless communications. They also discuss both indoor and outdoor environments, discussing how different factorsincluding various channel modelsaffect system performance and mitigation techniques. In addition, this book broadly covers crucial aspects of OWC systems: Fundamental principles of OWC Devices and systems Modulation techniques and schemes (including polarization shift keying) Channel models and system performance analysis Emerging visible light communications Terrestrial free space optics communication Use of infrared in indoor OWC One entire chapter explores the emerging field of visible light communications, and others describe techniques for using theoretical analysis and simulation to mitigate channel impact on system performance. Additional topics include wavelet denoising, artificial neural networks, and spatial diversity. Content also covers different challenges encountered in OWC, as well as outlining possible solutions and current research trends. A major attraction of the book is the presentation of MATLAB simulations and codes, which enable readers to execute extensive simulations and better understand OWC in general. Laser-based white lighting offers a viable option as an efficient and color-stable high-power solid-state white light source. We show that white light generation is possible using blue or near-UV laser diodes in combination with yellow-emitting cerium-substituted yttrium aluminum garnet (YAG:Ce) or a mixture of red-, green-, and blue-emitting phosphors. A variety of correlated color temperatures (CCT) are achieved, ranging from cool white light with a CCT of 4400 K using a blue laser diode to a warm white light with a CCT of 2700 K using a near-UV laser diode, with respective color rendering indices of 57 and 95. The luminous flux of these devices are measured to be 252 lm and 53 lm with luminous efficacies of 76 lm W and 19 lm W, respectively. An estimation of the maximum efficacy of a device comprising a blue laser diode in combination with YAG:Ce is calculated and the results are used to optimize the device. Multiple-input multiple-output (MIMO) systems using multiple light emitting diode (LED) sources and photodiode (PD) detectors are attractive for visible light communication (VLC) as they offer a capacity gain proportional to the number of parallel single-input single-output (SISO) channels. MIMO VLC systems exploit the high signal-to-noise ratio (SNR) of a SISO channel offered due to typical illumination requirements to overcome the capacity constraints due to limited modulation bandwidth of LEDs. In this work, a modified singular value decomposition VLC (SVD-VLC) MIMO system is proposed. This system maximizes the data rate while maintaining the target illumination and allowing the channel matrix to vary in order to support mobility in a practical indoor VLC deployment. The upper bound on capacity of the proposed SVD-VLC MIMO system is calculated assuming an imaging receiver. The relationship between the proposed system performance and system parameters total power constraint, lens aperture and random receiver locations are described.