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.
An indoor VLC network has multiple attocells to provide full wireless communication coverage. Inter-cell-interference (ICI) becomes an issue in such networks due to the overlapping of optical transmission beams. Different approaches have been proposed to mitigate ICI, for example, frequency division based carrier allocation @cite_7 , a dynamic interference-constrained sub-carrier reuse algorithm @cite_36 , and using angle diversity receivers (ADRs). In @cite_11 , an ADR was proposed with a hemispherical base where the PDs were placed in one or two layers. In @cite_2 @cite_19 , different ADR designs were presented where the PDs are placed at a given inclination angle on the same horizontal plane. Such ADRs can help maintain a VLC link in stationary scenario or during yaw movement but not in the presence of roll and or pitch movement of the receiver. In this paper, we present a multi-detector VR-headset design that can provide connectivity for any orientation of the VR-user's head, such as, roll, pitch, and yaw (Fig. ).
@cite_7 @cite_36 @cite_19 @cite_2 @cite_11
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Due to severe inter-cell interference (ICI), the signal-to- interference-and-noise ratio (SINR) suffers from very significant fluctuation in indoor multi-cell visible light communication (VLC) systems, which greatly limits the overall system performance. In this paper, we propose and evaluate a generalized angle diversity receiver (ADR) structure to reduce SINR fluctuation in indoor multi-cell VLC systems. The generalized ADR consists of one top detector and multiple inclined side detectors. In an indoor multi-cell VLC system using the generalized ADR, the inclination angle of the side detectors is optimized in order to minimize the SINR fluctuation over the receiving plane, where the impact of receiver random rotation is considered. An optimized ADR with different numbers of detectors is analyzed with different LED layouts and diversity combining techniques in a typical indoor environment. Analytical results show that the SINR fluctuation is gradually reduced when more detectors are equipped in the optimized ADR. In an indoor two-cell VLC system, much more significant SINR fluctuation reduction is achieved by using select-best combining (SBC). However, nearly the same SINR fluctuations are obtained in an indoor four-cell VLC system when using SBC and maximal-ratio combining (MRC). By applying the optimized ADR, up to 15.9 and 32.4-dB SINR fluctuation reductions can be achieved in comparison to a conventional single-element receiver (SER) in indoor two-cell and four-cell VLC systems, respectively. 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. The enormous success of advanced wireless devices is pushing the demand for higher wireless data rates. Denser spectrum reuse through the deployment of more access points (APs) per square mile has the potential to successfully meet such demand. In principle, distributed multiuser multiple-input-multiple-output (MU-MIMO) provides the best approach to infrastructure density increase since several access points are connected to a central server and operate as a large distributed multiantenna access point. This ensures that all transmitted signal power serves the purpose of data transmission, rather than creating interference. In practice, however, a number of implementation difficulties must be addressed, the most significant of which is aligning the phases of all jointly coordinated APs. In this paper, we propose AirSync, a novel scheme that provides timing and phase synchronization accurate enough to enable distributed MU-MIMO. AirSync detects the slot boundary such that all APs are time-synchronous within a cyclic prefix (CP) of the orthogonal frequency-division multiplexing (OFDM) modulation and predicts the instantaneous carrier phase correction along the transmit slot such that all transmitters maintain their coherence, which is necessary for multiuser beamforming. We have implemented AirSync as a digital circuit in the field programmable gate array (FPGA) of the WARP radio platform. Our experimental testbed, comprising four APs and four clients, shows that AirSync is able to achieve timing synchronization within the OFDM CP and carrier phase coherence within a few degrees. For the purpose of demonstration, we have implemented two MU-MIMO precoding schemes, Zero-Forcing Beamforming (ZFBF) and Tomlinson-Harashima Precoding (THP). In both cases, our system approaches the theoretical optimal multiplexing gains. We also discuss aspects related to the MAC and multiuser scheduling design, in relation to the distributed MU-MIMO architecture. To the best of our knowledge, AirSync offers the first realization of the full distributed MU-MIMO multiplexing gain, namely the ability to increase the number of active wireless clients per time-frequency slot linearly with the number of jointly coordinated APs, without reducing the per client rate. 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.