14 research outputs found
Fundamental Analysis for Visible Light Communication with InputâDependent Noise
Recently, visible light communication (VLC) has drawn much attention. In literature, the noise in VLC is often assumed to be independent of the input signal. This assumption neglects a fundamental issue of VLC: due to the random nature of photon emission in the lighting source, the strength of the noise depends on the signal itself. Therefore, the inputâdependent noise in VLC should be considered. Given this, the fundamental analysis for the VLC with inputâdependent noise is presented in this chapter. Based on the information theory, the theoretical expression of the mutual information is derived. However, the expression of the mutual information is not in a closed form. Furthermore, the lower bound of the mutual information is derived in a closed form. Moreover, the theoretical expression of the bit error rate is also derived. Numerical results verify the accuracy of the derived theoretical expressions in this chapter
Visible Light Communication (VLC)
Visible light communication (VLC) using light-emitting diodes (LEDs) or laser diodes (LDs) has been envisioned as one of the key enabling technologies for 6G and Internet of Things (IoT) systems, owing to its appealing advantages, including abundant and unregulated spectrum resources, no electromagnetic interference (EMI) radiation and high security. However, despite its many advantages, VLC faces several technical challenges, such as the limited bandwidth and severe nonlinearity of opto-electronic devices, link blockage and user mobility. Therefore, significant efforts are needed from the global VLC community to develop VLC technology further. This Special Issue, âVisible Light Communication (VLC)â, provides an opportunity for global researchers to share their new ideas and cutting-edge techniques to address the above-mentioned challenges. The 16 papers published in this Special Issue represent the fascinating progress of VLC in various contexts, including general indoor and underwater scenarios, and the emerging application of machine learning/artificial intelligence (ML/AI) techniques in VLC
Interference Suppression in Massive MIMO VLC Systems
The focus of this dissertation is on the development and evaluation of methods and principles to mitigate interference in multiuser visible light communication (VLC) systems using several transmitters. All components of such a massive multiple-input multiple-output (MIMO) system are considered and transformed into a communication system model, while also paying particular attention to the hardware requirements of different modulation schemes. By analyzing all steps in the communication process, the inter-channel interference between users is identified as the most critical aspect. Several methods of suppressing this kind of interference, i.e. to split the MIMO channel into parallel single channels, are discussed, and a novel active LCD-based interference suppression principle at the receiver side is introduced as main aspect of this work. This technique enables a dynamic adaption of the physical channel: compared to solely software-based or static approaches, the LCD interference suppression filter achieves adaptive channel separation without altering the characteristics of the transmitter lights. This is especially advantageous in dual-use scenarios with illumination requirements. Additionally, external interferers, like natural light or transmitter light sources of neighboring cells in a multicell setting, can also be suppressed without requiring any control over them. Each user's LCD filter is placed in front of the corresponding photodetector and configured in such a way that only light from desired transmitters can reach the detector by setting only the appropriate pixels to transparent, while light from unwanted transmitters remains blocked. The effectiveness of this method is tested and benchmarked against zero-forcing (ZF) precoding in different scenarios and applications by numerical simulations and also verified experimentally in a large MIMO VLC testbed created specifically for this purpose
Spectrum and energy efficient digital modulation techniques for practical visible light communication systems
The growth in mobile data traffic is rapidly increasing in an unsustainable direction
given the radio frequency (RF) spectrum limits. Visible light communication (VLC)
offers a lucrative solution based on an alternative license-free frequency band that is safe
to use and inexpensive to utilize. Improving the spectral and energy efficiency of intensity
modulation and direct detection (IM/DD) systems is still an on-going challenge in
VLC. The energy efficiency of inherently unipolar modulation techniques such as pulse-amplitude
modulation discrete multitone modulation (PAM-DMT) and asymmetrically
clipped optical orthogonal frequency division multiplexing (ACO-OFDM) degrades at
high spectral efficiency. Two novel superposition modulation techniques are proposed
in this thesis based on PAM-DMT and ACO-OFDM. In addition, a practical solution
based on the computationally efficient augmented spectral efficiency discrete multi-tone
(ASE-DMT) is proposed. The system performance of the proposed superposition
modulation techniques offers significant electrical and optical power savings with up
to 8 dB in the electrical signal-to-noise ratio (SNR) when compared with DC-biased
optical orthogonal frequency division multiplexing (DCO-OFDM). The theoretical bit
error ratio (BER) performance bounds for all of the proposed modulation techniques
are in agreement with the Monte-Carlo simulation results. The proposed superposition
modulation techniques are promising candidates for spectrum and energy efficient
IM/DD systems.
Two experimental studies are presented for a VLC system based on DCO-OFDM with
adaptive bit and energy loading. Micrometer-sized Gallium Nitride light emitting
diode (m-LED) and light amplification by stimulated emission of radiation diode (LD)
are used in these studies due to their high modulation bandwidth. Record data rates are
achieved with a BER below the forward error correction (FEC) threshold at 7.91 Gb/s
using the violet m-LED and at 15 Gb/s using the blue LD. These results highlight
the potential of VLC systems in practical high speed communication solutions. An
additional experimental study is demonstrated for the proposed superposition modulation
techniques based on ASE-DMT. The experimentally achieved results confirm the
theoretical and simulation based performance predictions of ASE-DMT. A significant
gain of up to 17.33 dB in SNR is demonstrated at a low direct current (DC) bias.
Finally, the perception that VLC systems cannot work under the presence of sunlight is
addressed in this thesis. A complete framework is presented to evaluate the performance
of VLC systems in the presence of solar irradiance at any given location and time. The
effect of sunlight is investigated in terms of the degradations in SNR, data rate and
BER. A reliable high speed communication system is achieved under the sunlight
effect. An optical bandpass blue filter is shown to compensate for half of the reduced
data rate in the presence of sunlight. This thesis demonstrates data rates above 1 Gb/s
for a practical VLC link under strong solar illuminance measured at 50350 lux in clear
weather conditions
Indoor Visible Light Communication:A Tutorial and Survey
Abstract
With the advancement of solid-state devices for lighting, illumination is on the verge of being completely restructured. This revolution comes with numerous advantages and viable opportunities that can transform the world of wireless communications for the better. Solid-state LEDs are rapidly replacing the contemporary incandescent and fluorescent lamps. In addition to their high energy efficiency, LEDs are desirable for their low heat generation, long lifespan, and their capability to switch on and off at an extremely high rate. The ability of switching between different levels of luminous intensity at such a rate has enabled the inception of a new communication technology referred to as visible light communication (VLC). With this technology, the LED lamps are additionally being used for data transmission. This paper provides a tutorial and a survey of VLC in terms of the design, development, and evaluation techniques as well as current challenges and their envisioned solutions. The focus of this paper is mainly directed towards an indoor setup. An overview of VLC, theory of illumination, system receivers, system architecture, and ongoing developments are provided. We further provide some baseline simulation results to give a technical background on the performance of VLC systems. Moreover, we provide the potential of incorporating VLC techniques in the current and upcoming technologies such as fifth-generation (5G), beyond fifth-generation (B5G) wireless communication trends including sixth-generation (6G), and intelligent reflective surfaces (IRSs) among others
A review of communication-oriented optical wireless systems
This article presents an overview of optical wireless (OW) communication systems that operate both in the short-
(personal and indoor systems) and the long-range (outdoor and hybrid) regimes. Each of these areas is discussed
in terms of (a) key requirements, (b) their application framework, (c) major impairments and applicable mitigation
techniques, and (d) current and/or future trends. Personal communication systems are discussed within the context
of point-to-point ultra-high speed data transfer. The most relevant application framework and related standards are
presented, including the next generation Giga-IR standard that extends personal communication speeds to over 1
Gb/s. As far as indoor systems are concerned, emphasis is given on modeling the dispersive nature of indoor OW
channels, on the limitations that dispersion imposes on user mobility and dispersion mitigation techniques. Visible
light communication systems, which provide both illumination and communication over visible or hybrid visible/
infrared LEDs, are presented as the most important representative of future indoor OW systems. The discussion on
outdoor systems focuses on the impact of atmospheric effects on the optical channel and associated mitigation
techniques that extend the realizable link lengths and transfer rates. Currently, outdoor OW is commercially
available at 10 Gb/s Ethernet speeds for Metro networks and Local-Area-Network interconnections and speeds are
expected to increase as faster and more reliable optical components become available. This article concludes with
hybrid optical wireless/radio-frequency (OW/RF) systems that employ an additional RF link to improve the overall
system reliability. Emphasis is given on cooperation techniques between the reliable RF subsystem and the
broadband OW system