In this paper we experimentally demonstrate a multiband carrier-less amplitude and phase modulation format for the first time in VLC. We split a conventional carrierless amplitude and phase modulated signal into m subcarriers in order to protect from the attenuation experienced at high frequencies in low-pass VLC systems. We investigate the relationship between throughput/spectral efficiency and m, where m = {10, 8, 6, 4, 2, 1} subcarriers over a fixed total signal bandwidth of 6.5 MHz. We show that transmission speeds (spectral efficiencies) of 31.53 (4.85), 30.88 (4.75), 25.40 (3.90), 23.65 (3.60), 15.78 (2.40), 9.04 (1.40) Mb/s (b/s/Hz) can be achieved for the listed values of m, respectively.
Visible light communications (VLC) is a new emerging technology, which provides both data transmission and illumination by utilizing the visible range (370 780 nm) of the electromagnetic spectrum. In order to maximize the available data rate and enhance the users mobility within an indoor environment, it is essential to characterize the communication channel. In this paper we present both analytical and experimental results for a VLC system affected by movement of people for different indoor conditions (i.e. furnished office room, empty hall and corridor). VLC systems utilize multiple light-emitting diodes mounted in the ceiling and the configuration is based on the non-directed line of sight. We consider random movement of people within the room, focusing on the impacts of shadowing and blocking on mobility and link system performance by investigating changes in the channel characteristics using the cumulative distribution function of the received power distribution and the delay profile. We demonstrate the behaviour of communication channels for different scenarios from corridor, the most robust against people movement induced fading, to the office rooms and halls, the most vulnerable to the received power fluctuation.
In general, visible light communication (VLC) systems, which utilise white light-emitting diodes (LEDs), only offer a bandwidth limited to the lower MHz region. Therefore, providing VLC-based high data rate communications systems becomes a challenging task. To address this challenge, we propose a solution based on multiplexing in both the frequency and space domains. We experimentally demonstrate a 4 × 4 imaging multiple-input multiple-output (MIMO) VLC system (i.e., space multiplexing) utilising multi-band carrier-less amplitude and phase (m-CAP) modulation (i.e., frequency multiplexing). Independently, both MIMO and m-CAP have shown the remarkable ability to improve transmission speeds in VLC systems, and hence, here we combine them to further improve the net data rate. We investigate link performance by varying the number of subcarriers m, link distance L, and signal bandwidth Bsig. From all the values tested, we show a data rate of ~249 Mb/s can be maximally achieved for for m = 20, Bsig = 20 MHz, and L = 1 m, at a bit error rate of 3.2×10-3 using LEDs with ~4 MHz bandwidth. Index Terms-Modulation bandwidth, multi-band carrier-less amplitude and phase modulation, multiple-input multiple-output, visible light communications.
Abstract-Widespread use of white light-emitting diodes and ubiquitous smart devices offer the opportunity to establish visible light communications (VLC) which has become a hot research topic based on the growing number of publications over the last decade. Camera-based VLC, namely optical camera communications (OCC), provide many unique features when compared with a single photodiode-based system, such as the ability to separate incident light in spatial and color domains. OCC technology represents a promising approach to utilize the benefits of VLC in beyond-5G scenarios and is one of the key technologies of the Internet of Things. Establishing a long communication channel in OCC, as well as non-flickering illumination in using low-frame-rate camera detectors, requires special modulation schemes. This article provides an overview of the principles of three categories of modulation schemes for OCC systems using a low-frame-rate camera detector. In addition, a series of undersampled modulation schemes are proposed and discussed to achieve flicker-free OCC with higher spectral efficiency. In addition, framing structures are designed to solve problems occurring in OCC systems using particular modulation schemes. To evaluate the performance of these modulation schemes, measured bit error rate values are shown. Finally, challenges in the implementation of OCC systems are also outlined.Index Terms -optical camera communications, non-flickering illumination, undersampled phase shift ON-OFF keying, undersampled quadrature-amplitude-modulation, visible light communications, optical wireless communications
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