We analyze the channel properties of a nonline-of-sight (NLOS) ceiling-to-device and device-to-device visible light communication systems by considering various receivers' orientation and variable fields of view (FOVs). Analyses based on the recursive indoor channel model show that for a particular transmitter configuration, the pure NLOS path can offer higher 3-dB channel bandwidth (up to 14 MHz) compared with the link with LOS and NLOS components. We also show how the receiver rotation (orientation) influences the probability of receiving signals via the NLOS path compared with the LOS and NLOS paths. Moreover, based on the experimental campaign, we demonstrate that shadowing observed at the receiver due to people’s movement results in decreased received power level (up to 1.8 dB), thus resulting in reshaping of the probability density function of received power.
Given the imminent radio frequency spectrum crunch, Visible Light Communication (VLC) is being proposed as an alternative wireless technology allowing for scalable connectivity to potentially millions of mobile and Internet-of- Things (IoT) devices. A VLC system uses a photo-detector (PD) receiver that converts the optically modulated light from a light source into a modulated electrical signal. The corresponding receiver electrical bandwidth is typically inversely proportional to the PD active area. Consequently, to construct a high-speed VLC link, the PD active area is often substantially reduced and an optical concentrator is used to enhance the receiver collection area. However, to achieve high concentrating factor, the link field-of-view (FOV) needs to be narrow due to the étendue conservation in linear passive optical systems. This paper studies a Fluorescent Concentrator (FC) that breaks this étendue conservation. The FC is not only based on reflective and refractive principles but also makes use of fluorescence process. A comparison between the FC and conventional optical concentrators, namely Compound Parabolic Concentrator (CPC) is also investigated. The trade-off between received signal strength and incoming link angle is demonstrated over 60° coverage. Experimental results show that performance degradation as the link angle increases using FC-based receivers is significantly lower than for conventional CPC.
Solid state lighting systems typically use multiple Light Emitting Diode (LED) die within a single lamp, and multiple lamps within a coverage space. This infrastructure forms the transmitters for Visible Light Communications (VLC), and the availability of low-cost detector arrays offers the possibility of building Multiple Input Multiple Output (MIMO) transmission systems. Different approaches to optical MIMO are being investigated as part of a UK government funded research programme, ‘Ultra-Parallel Visible Light Communications’ (UPVLC). In this paper we present a brief review of the area and report results from systems that use integrated subsystems developed as part of the project. The scalability of these approaches and future directions will also be discussed.
In this paper, two models for diffuse indoor cellular optical wireless communication (OWC) systems with and without a
holographic light shaping diffuser (LSD) are presented. For both models, the power distribution, the impulse response of
the channels and root mean square (RMS) delay are described and analyzed. We perform a computer simulation to
compare the channel characteristics of the typical indoor cellular OWC systems with that employing the holographic
LSD. The results show that the system with the holographic LSD provides a more uniform power distribution and a less
RMS delay spread for the same divergence angles.