Optimization of Visible-Light Optical Wireless Systems: Network-Centric Versus User-Centric Designs

Visible light communication (VLC) may be expected to become a new member in the small-cell family of the next-generation heterogeneous network landscape for complementing the overloaded radio frequency band. In order to further improve the performance of our user-centric (UC) cluster formation design proposed in our previous work, the quality-of-service (QOS) metric in terms of statical delay requirements is considered, when constructing the UC clusters. Inspired by the concept of effective capacity (EC), we formulate the proportional-fairness-based utility function of each optical link, while satisfying the statistical delay requirement. Upon maximizing the sum utility of the system, the joint cluster formation and user association problem is solved by our proposed greedy algorithm, which is capable of providing an average user EC of about 90% of the optimal value found via exhaustive search. Furthermore, the performance of the UC cluster formation is superior than the traditional cellular designs in all scenarios considered.

Wireless communications refer to data transmissions in unguided propagation media through the use of wireless carriers such as radio frequency (RF) and visible light (VL) waves. The rising demand for high data rates, especially, in indoor scenarios, overloads conventional RF technologies. Therefore, technologies such as millimeter waves (mmWave) and cognitive radios have been adopted as possible solutions to overcome the spectrum scarcity and capacity limitations of the conventional RF systems. In parallel, visible light communication (VLC) has been proposed as an alternative solution, where a light source is used for both illumination and data transmission. In comparison to RF links, VLC links present a very high bandwidth that allows much higher data rates. VLC exhibits also immunity to interference from electromagnetic sources, has unlicensed channels, is a very low power consumption system, and has no health hazard. VLC is appealing for a wide range of applications including reliable communications with low latency such as vehicle safety communication. Despite the major advantages of VLC technology and a variety of its applications, its use has been hampered by its cons such as its dependence on a line of sight connectivity. Recently, hybrid RF/VLC systems were proposed to take advantage of the high capacity of VLC links and better connectivity of RF links. Thus, hybrid RF/VLC systems are envisioned as a key enabler to improve the user rates and mobility on the one hand and to optimize the capacity, interference and power consumption of the overall network on the other hand. This paper seeks to provide a detailed survey of hybrid RF/VLC systems. This paper represents an overview of the current developments in the hybrid RF/VLC systems, their benefits and limitations for both newcomers and expert researchers.

Device to device (D2D) communication is designed to accommodate high data rates required in future mobile networks. To maximize spectral efficiency of the communication, D2D pairs should reuse the same set of frequencies. However, this results in a strong interference among close D2D pairs or, in the worst case, even in outage. Both the interference and the outage can be reduced if highly interfered and highly interfering D2D pairs exploit a visible light communication (VLC) band instead of a common radio frequency (RF) band. This concept is known as RF-VLC D2D. In this paper, we target the problem of a selection between RF and VLC bands for each D2D pair in a multi user scenario. We define the RF and VLC selection as a multi-objective optimization problem targeting to minimize the outage and to maximize the system capacity. To solve this problem, we propose a low-complexity heuristic centralized algorithm choosing either RF or VLC for individual D2D pairs according to both the interference imposed by the D2D transmitters and the interference observed by the D2D receivers. For interpretation of the mutual interferences among the D2D pairs, we adopt graph theory. The simulations show that the proposed algorithm outperforms state of the art algorithms in both outage and capacity. Despite a very low complexity, the proposed algorithm reaches the performance close to the optimum.

Intelligent Transportation Systems (ITSs) are being proposed, examined, and applied to enhance road safety and traffic efficiency. However, the automotive industry has stringent criteria for safety applications that demand connections that are dependable and have low latency, and high data rates. In this paper, it is widely agreed that both Visible Light Communication (VLC) and Free Space Optics (FSO) represent promising solutions, because of their complementary advantages compared to Radio Frequency (RF). VLC technology is chosen in ITS overall other optical wireless systems primarily due to its low cost and lack of licensing or new infrastructure requirements. Hence, a comparative study is applied between standalone VLC system, and a hybrid FSO/VLC system in term of Bit Error Rate (BER), coverage distance, and Signal to Noise Ratio (SNR). The VLC/FSO system provides a reliable communication link over a long distance (900 m) compared to VLC standalone system with 10−6 BER and acceptable SNR of ∼\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim$$\\end{document} 25 dB.

Recently, visible light communication (VLC) system has gained attention due to its higher data rate, wider spectrum, higher security, lower weight, extensive lifespan of LEDs, smaller sizes of apertures and lower power consumption, lower cost, and no health issues etc. The VLC is used to strengthen the radio frequency (RF) communication and it also improves the communication performance in short range such as homes, offices, corridors, hospitals, aircrafts etc. The VLC provides dual functionality, that is, illumination and communication through the same LED simultaneously. It needs fast switching of LED (which is not detectable by human eyes) along with some appropriate modulation schemes for VLC to provide communication and illumination simultaneously. Meanwhile, LED should be powered on for the duration of communication, which conversely creates two challenges. First, the LED would consume more electrical power, which makes the system expensive. Second, LED can also be used in a dimming mode to save the power. Dimming of LED decreases the data rate. The data rate is inadequate due to modulation bandwidth of high brightness LED. The power and the data rate can be achieved by using different modulation schemes or line encoding schemes. There are a number of other factors such as interference of sun light, reflection of mirror or other fluorescent or candescent light disturbing the communication due to visible light usage in communication, interference to other VLC devices, integration of VLC with existing architecture of communication system, that is, Wi-Fi. The rest of the chapter is organized as follows. Section 1.1 gives an overview of VLC, followed by the brief discussion on the VLC system architecture in Section 1.2. Section 1.3 highlights the applications of the VLC. The general modulation schemes are given in Section 1.4. Then, Section 1.5 discusses the power efficient techniques, spectral efficient techniques are covered in Section 1.6, and Section 1.7 demonstrates the interference cancellation techniques. This chapter also discusses a comparison of different modulation techniques in terms of power efficiency, spectral efficiency, and interference cancellation and concludes with the best suited technique for power, spectrum, and interference.

Enormous applications which are enabled using Vehicular Ad Hoc Networks (VANETs) require a both efficient and reliable data delivery. Visible Light Communication (VLC), which has high transmission rate without using Radio Frequency (RF) spectrum, is regard as a candidate for data transmission in VANETs. Since a VLC system requires a line-of-sight communication, the position and the posture of LEDs and receivers play key roles in VLC. Unfortunately the position and the posture always change with vehicle motion and may make the performance of VLC become severe and even result in the outage of VLC. In this paper, we present an improved Vehicle-to-Vehicle (V2V) model and an improved Vehicle-to-Infrastructure (V2I) model in consideration of the position and the posture. In order to get diversity gains and reduce the VLC interruption caused by vehicle motion, we propose a VLC based cooperative diversity scheme. Finally simulation results show that the cooperative diversity scheme can decrease the Bit-Error-Rate (BER) significantly and reduce the VLC interruption caused by vehicle motion.

Visible light communications (VLC) is emerging as a new alternative to the use of the existing and increasingly crowded radio frequency (RF) spectrum. VLC is unlicensed, has wide bandwidth, supports new levels of security due to the opacity of walls, and can be combined to provide both lighting and data communications for little net increase in energy cost. As part of a lighting system, VLC is ideal as a downlink technology in which data are delivered from overhead luminaries to receivers in the lighting field. However, realizing a symmetric optical channel is problematic because most receivers, such as mobile devices, are ill-suited for an optical uplink due to glare, device orientation, energy constraints. In this paper we propose and implement a hybrid solution in which the uplink challenge is resolved by the use of an asymmetric RF-VLC combination. VLC is used as a downlink, RF is used as an uplink, and the hybrid solution realizes full duplex communication without performance glare or throughput degradation expected in an all-VLC-based approach. Our proposed approach utilizes a software defined VLC platform (SDVLC) to implement the unidirectional optical wireless channel and a WiFi link as the back-channel. Experiments with the implemented prototype reveal that the integrated system outperforms conventional WiFi for crowded (congested) multiuser environments in term of throughput, and demonstrate functional access to full-duplex interactive applications such as web browsing with HTTP.

Visible light communication (VLC) reuses illumination devices, particularly light-emitting diodes (LEDs), for communication purposes. It has great potential to alleviate the strain on radio-frequency spectrum in indoor environments. VLC-enabled LED luminaries form VLC attocells that carry downlink data traffic to indoor mobile or stationary terminals. While one of the advantages of indoor VLC is low interference due to natural cell boundaries such as walls, multiple VLC attocells within a room would interfere. This is because illumination requirements often mandate a rich overlap of emissions of luminaries in a room. In this paper, we suggest the coordination of multiple VLC attocells (i.e., VLC-enabled LED luminaries) to turn the problem of overlap and thus interference into an advantage. We stipulate that this coordination can be accomplished through power line communication, which has been considered before as a means to transport data to VLC transmitters. Borrowing from concepts developed for radio-frequency wireless communications, we develop several precoding schemes for the new coordinated VLC broadcasting architecture. These include designs for the case of imperfect channel knowledge at the VLC transmitter, since channel information is usually provided through a low-rate feedback channel. The performance advantages for VLC transmission due to the proposed coordination and precoding designs are demonstrated based on a set of numerical results.

5G networks have to offer extremely high capacity for novel streaming applications. One of the most promising approaches is to embed large numbers of cooperating small cells into the macro-cell coverage area. Alternatively, optical wireless based technologies can be adopted as an alternative physical layer offering higher data rates. Visible light communications (VLC) is an emerging technology for future high capacity communication links (it has been accepted to 5GPP) in the visible range of the electromagnetic spectrum (~370–780 nm) utilizing light-emitting diodes (LEDs) simultaneously provide data transmission and room illumination. A major challenge in VLC is the LED modulation bandwidths, which are limited to a few MHz. However, myriad gigabit speed transmission links have already been demonstrated. Non line-of-sight (NLOS) optical wireless is resistant to blocking by people and obstacles and is capable of adapting its’ throughput according to the current channel state information. Concurrently, organic polymer LEDs (PLEDs) have become the focus of enormous attention for solid-state lighting applications due to their advantages over conventional white LEDs such as ultra-low costs, low heating temperature, mechanical flexibility and large photoactive areas when produced with wet processing methods. This paper discusses development of such VLC links with a view to implementing ubiquitous broadcasting networks featuring advanced modulation formats such as orthogonal frequency division multiplexing (OFDM) or carrier-less amplitude and phase modulation (CAP) in conjunction with equalization techniques. Finally, this paper will also summarize the results of the European project ICT COST IC1101 OPTICWISE (Optical Wireless Communications - An Emerging Technology) dealing VLC and OLEDs towards 5G networks.

Evolution of optical wireless communication for B5G/6G

We demonstrate the possibility of using 3D‐printed, see‐through planar elements built with commercially available materials as fluorescent Optical Antennas (OAs) for fast Optical Wireless Communication (OWC). OWC represents a key technology in the forthcoming next‐generation communication services (6G), given its intrinsic combination of bandwidth (BW), security, and pervasiveness. In the Visible Light Communication (VLC) approach, ubiquitous white or colored LED sources can also be used as optical transmitters besides providing indoor/outdoor illumination and signaling, strongly fostering the implementation of the Internet of Things (IoT) paradigm. Here, the intrinsic optical properties (such as BW, field of View (FoV), and collection efficiency) of four different fluorescent slabs grown with commercial, non‐optical resins typically employed to realize transparent objects are fully characterized, unveiling for the first time their large potential as receivers in VLC applications. Complete VLC communication tests are reported, demonstrating attainable bit rates larger than 70 Mb s −1 with On‐Off Keying (OOK) modulation, which could be largely increased toward the Gb s −1 target exploiting high‐order modulation schemes. This work can have a profound impact toward the full‐fledged implementation of the IoT paradigm, showing that transparent 3D‐printed objects can be exploited as optical front ends in a new class of VLC and OWC receivers.

This chapter explores the integration of energy-harvesting techniques in wireless communication systems, focusing on two prominent methods: radio frequency (RF) energy harvesting and visible light communication (VLC) energy harvesting. RF energy harvesting leverages ambient electromagnetic waves from sources such as cellular networks, Wi-Fi, and television broadcasts to convert RF signals into usable electrical energy, providing a sustainable power solution for low-energy devices in applications like wireless sensor networks and the Internet of Things (IoT). The chapter discusses the architecture of RF energy-harvesting systems, including antennas, rectifiers, and energy storage units, highlighting their efficiency and adaptability in various environments. In contrast, VLC energy harvesting utilizes light emitted from LEDs and other light sources to generate power through photovoltaic cells. This method not only facilitates energy collection but also enables simultaneous data transmission, thereby enhancing the overall functionality of communication systems. The chapter examines the advantages and challenges associated with VLC, such as light intensity variations and low conversion efficiency. By comparing these two energies harvesting techniques, we aim to provide insights into their complementary roles in developing self-sustaining wireless communication networks that can operate efficiently in diverse conditions while minimizing reliance on traditional power sources.

The radio frequency spectrum has become very congested and scarce. A response to this dilemma is the implementation of visible light communications (VLC) technology, which is enabled by the dramatic development of light emitting diodes (LEDs) and laser diodes (LDs). VLC has become the most popular emerging telecommunication technology. This is due to the interesting advantages that it provides, which include an unlicensed and large bandwidth, a high throughput capability and a low implementation cost. VLC needs a pivot network in medium and long distance transmissions. The amplify‐and‐forward scenario between the backbone network and VLC is cost‐effective owing to its simplicity when compared to the decode‐and‐forward scenario. MPSK‐CSK is a typical example of cascaded systems in AF scenario with VLC where the backbone channel utilises PSK to convey the message. In this paper, we investigate a forward error correction scheme for cascaded MPSK‐CSK systems. A convolutional encoder is added to the MPSK‐CSK scheme to construct the hybrid trellis coded modulation scheme. Selected 8HTCM systems using set partitioning are investigated and results for a Gaussian channel are presented. Numerical results reveal that 8HTCM achieves up to 2.129 dB of asymptotic coding gain when compared to the corresponding un‐coded MPSK‐CSK system.

Visible light communication (VLC) has emerged as a viable complement to traditional radio frequency (RF) based systems and as an enabler for high data rate communications for beyond-5G (B5G) indoor communication systems. In particular, the emergence of new B5G-based applications with quality of service (QoS) requirements and massive connectivity has recently led to research on the required service-levels and the development of improved physical (PHY) layer methods. As part of recent VLC standards development activities, the IEEE has formed the 802.11bb “Light Communications (LC) for Wireless Local Area Networking” standardization group. This paper investigates the network requirements of 5G indoor services such as virtual reality (VR) and high-definition (HD) video for residential environments using VLC. In this paper, we consider such typical VLC scenarios with additional impairments such as light-emitting diode (LED) nonlinearity and imperfect channel feedback, and propose hyperparameter-free mitigation techniques using Reproducing Kernel Hilbert Space (RKHS) methods. In this context, we also propose using a direct current biased optical orthogonal frequency division multiplexing (DCO-OFDM)-based adaptive VLC transmission method that uses precomputed bit error rate (BER) expressions for these RKHS-based detection methods and performs adaptive BER-based modulation-order switching. Simulations of channel impulse responses (CIRs) show that the adaptive transmission method provides significantly improved error rate performance, which makes it promising for high data rate VLC-based 5G indoor services.

Visible Light Communication (VLC) is an optical wireless communication technology that can be used for data communication over optical wireless link. In this paper, a complete state-of-the-art Visible Light Communication (VLC) transceiver prototype has been physically designed. The developed VLC transceiver prototype can serve the purpose of both illumination and data communication simultaneously. The novelty of the design lies in the fact that it uses STM32F4Discovery board which is customizable over the Universal Synchronous/Asynchronous Receiver/Transmitter (USART) TX and RX protocols. The work covers complete hardware design of the transceiver including LED driving circuit, and full configuration of the STM32F4Discovery board. Furthermore, the proposed VLC design can also be used for audio communication.