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Optimization of Visible-Light Optical Wireless Systems: Network-Centric Versus User-Centric Designs
Abstract
In order to counteract the explosive escalation of wireless tele-traffic, the communication spectrum has been gradually expanded from the conventional radio frequency (RF) band to the optical wireless (OW) domain. By integrating the classic RF band relying on diverse radio techniques and optical bands, the next-generation heterogeneous networks (HetNets) are expected to offer a potential solution for supporting the ever-increasing wireless tele-traffic. Owing to its abundant unlicensed spectral resources, visible light communications (VLC) combined with advanced illumination constitute a competent candidate for complementing the existing RF networks. Although the advantages of VLC are multi-fold, some challenges arise when incorporating VLC into the classic RF HetNet environments, which may require new system architectures. The user-centric (UC) design principle for VLCVLC environments constitutes a novel and competitive design paradigm for the super dense multi-tier cell combinations of HetNets. The UC concept may be expected to become one of the disruptive techniques to be used in the forthcoming fifth-generation era. This paper provides a comprehensive survey of visible-light-aided OW systems with special emphasis on the design and optimization of VLC networks, where the radically new UC design philosophy is reviewed. Finally, design guidelines are provided for VLC systems.
... Due to the great interest shown in hybrid VLC/RF networks, several authors have conducted reviews of the history of these networks [2,17,[26][27][28][29]. However, the dynamic and changing characteristics depending on the deployment scenario and the extensive evolution of VLC/RF networks in recent times have produced the need to delve deeper into issues that have not been fully analyzed by the existing reviews. ...
... In addition, the main challenges faced by hybrid VLC/RF networks and future research directions are discussed. Outdoor Applications [27] 2016 [28] 2018 [29] 2018 [30] 2019 [17] 2020 [2] 2021 [26] 2021 [31] 2022 This paper The rest of this paper is organized as follows. In Section 2, the state of the art of hybrid VLC/RF networks in indoor scenarios with ideal conditions is reviewed, including analysis of aspects such as lighting requirements, hybrid channel model, load balancing, network selection, and resource allocation, and hybrid network topologies. ...
The expectation for communication systems beyond 5G/6G is to provide high reliability, high throughput, low latency, and high energy efficiency services. The integration between systems based on radio frequency (RF) and visible light communication (VLC) promises the design of hybrid systems capable of addressing and largely satisfying these requirements. Hybrid network design enables complementary cooperation without interference between the two technologies, thereby increasing the overall system data rate, improving load balancing, and reducing non-coverage areas. VLC/RF hybrid networks can offer reliable and efficient communication solutions for Internet of Things (IoT) applications such as smart lighting, location-based services, home automation, smart healthcare, and industrial IoT. Therefore, hybrid VLC/RF networks are key technologies for next-generation communication systems. In this paper, a comprehensive state-of-the-art study of hybrid VLC/RF networks is carried out, divided into four areas. First, indoor scenarios are studied considering lighting requirements, hybrid channel models, load balancing, resource allocation, and hybrid network topologies. Second, the characteristics and implementation of these hybrid networks in outdoor scenarios with adverse conditions are analyzed. Third, we address the main applications of hybrid VLC/RF networks in technological, economic, and socio-environmental domains. Finally, we outline the main challenges and future research lines of hybrid VLC/RF networks.
... By exploring transmission technologies beyond traditional RF and mmWave, this research opens up possibilities for providing high-speed internet access in space, underground, underwater, and remote terrestrial regions, enabling digital inclusion and empowering communities. The improved spectral efficiency and network capacity offered by MBN solutions can support the growing demand [41] 2018 BMF ✓ [47] 2020 BMF ✓ ✓ [27] 2022 CM, CP ✓ ✓ [3] 2021 CM, BMF ✓ ✓ [22] 2021 CM, C& M ✓ [32] 2022 CEM, CP ✓ [33] 2022 CEM, CP ✓ [28] 2022 CEM ✓ ✓ ✓ mmWave [43] 2016 BMF ✓ [4] 2018 CM, CP ✓ [45] 2018 BMF ✓ ✓ [44] 2018 BMF ✓ [5] 2018 CM, CEM, CP, C&M ✓ ✓ [37] 2018 C&M, BMF, MAC ✓ ✓ [29] 2019 BMF ✓ ✓ [6] 2020 CM, CP ✓ [30] 2021 CEM, C&M ✓ [31] 2022 CEM, BMF ✓ [7] 2022 CM, CEM, CP, BMF ✓ [8] 2022 CM ✓ VLC [26] 2015 ✓ [9] 2015 CM, CP ✓ ✓ [10] 2016 CM ✓ ✓ [46] 2017 ✓ [11] 2018 CM, C&M ✓ [12] 2018 CM ✓ [39] 2019 ✓ ✓ ✓ [40] 2019 ✓ ✓ [13] 2019 CM ✓ ✓ [14] 2020 CM ✓ [15] 2020 CM ✓ [16] 2020 CM, C&M ✓ [34] 2023 C&M ✓ FSO [17] 2014 CM ✓ ✓ [18] 2017 CM ✓ ✓ [35] 2017 C&M ✓ [36] 2019 C&M ✓ [19] 2019 CM, C&M ✓ ✓ [25] 2020 C&M ✓ [2] 2020 CM ✓ [23] 2022 CEM ✓ ✓ [38] 2022 C&M ✓ Multi-Band [20] 2013 FSO/VLC: CM, CP, C&M ✓ [54] 2020 RF/Optical, Optical/Optical [21] 2020 mmWave, THz, Optical: CM, CP ✓ ✓ [48] 2021 WiFi/VLC ✓ [24] 2022 THz-mmWave: CP ✓ [42] 2023 THZ-mmWave: BMF ✓ CM: channel modeling; CEM : channel estimation and measurement; CP: channel propagation; C&M: coding and modulation; BMF: beam management and beamforming; MAC: MAC protocols Ref. ...
This paper explores the evolution of wireless communication networks from utilizing the sub-6 GHz spectrum and the millimeter wave frequency band to incorporating extremely high frequencies like optical and terahertz for 6G and beyond. While these higher frequencies offer broader bandwidths and extreme data rate capabilities, the transition from single-band and heterogeneous networks to multi-band networks (MBNs), where various frequency bands coexist introduces novel challenges in channel modeling, transceiver and antenna design, programmable simulation platforms, standardization, and resource allocation. This paper provides a tutorial overview from the communication design perspective of the various frequency bands, elaborating on the above issues. Then, we introduce and examine typical MBN architectures for future networks and provide a detailed overview of state-of-the-art resource allocation problems for existing MBNs that typically operate on two frequency bands. The considered resource allocation optimization problems and solution techniques are discussed comprehensively. We then identify key performance metrics and constraint sets that should be considered for resource allocation optimization in future MBNs and provide numerical results to depict how various system parameters and user behaviors can influence their performance. Finally, we present several potential research issues as future work for the design and performance optimization of MBNs.
... LEDs have several advantages such as low power consumption, low heat generation, high bandwidth, and high energy conversion efficiency. Micro-LEDs, multi-chip LEDs (MC-LEDs), phosphorconverted LEDs (PC-LEDs), and organic LEDs (OLEDs) are commercially available in various types/structures [274]. Photodiodes (PDs) are often used in VLC systems as receivers and are responsible for collecting and transforming light into electric currents. ...
This review paper discusses the complete evolution of free-space optical (FSO) communication, also known as unguided optical communication (UOC) technologies, all the way back to ancient man’s fire to today’s machine-learning-supported UOC systems. The principles, significance, and developments that have happened over the past several decades, as well as installation methodologies, technological limitations, and today’s challenges of UOCs are presented. All the subsets of UOC: FSO communication, underwater optical wireless communication (UOWC), and visible light communication (VLC), with their technology/system developments, potential applications, and limitations are reviewed. The state-of-the-art developments/achievements in (i) FSO channel effects and their mitigation techniques; (ii) radio-over-FSO techniques; (iii) wavelength division multiplexing and sub-carrier multiplexing techniques; (iv) FSO for worldwide interoperability for microwave access applications; (v) space optical satellite communication (SOSC); (vi) UWOC; (vii) photoacoustic communication (PAC); (viii) light-fidelity; (ix) VLC; (x) vehicular VLC (V2LC); and (xi) optical camera communication are reviewed. In addition, the current developments on emerging technologies such as artificial intelligence (to improve the performance of UOC systems), energy harvesting (for the effective utilization of UOC channels), and near-future communication network scenarios (mandatory for secured broadband digital links) are covered. Finally, in brief, to achieve the full potential of UOC systems, challenges that require immediate research attention are summarized.
... The layout of optical attocells plays a crucial role in the indoor VLC system, especially to ascertain the uniform distribution of received power and SNR over the communication plane [18][19][20][21]. Random movement of mobile terminals is a hindrance to mobile networking [22], in which performance parameters (e.g., received power & SNR) are not fairly distributed across the entire environment. ...
Visible light communication (VLC), which is a prominent emerging solution that complements the radio frequency (RF) technology, exhibits the potential to meet the demands of fifth-generation (5G) and beyond technologies. The random movement of mobile terminals in the indoor environment is a challenge in the VLC system. The model of optical attocells has a critical role in the uniform distribution and the quality of communication links in terms of received power and signal-to-noise ratio (SNR). As such, the optical attocells positions were optimized in this study with a developed try and error (TE) algorithm. The optimized optical attocells were examined and compared with previous models. This novel approach had successfully increased minimum received power from −1.29 to −0.225 dBm, along with enhanced SNR performance by 2.06 dB. The bit error rate (BER) was reduced to 4.42×10−8 and 6.63×10−14 by utilizing OOK-NRZ and BPSK modulation techniques, respectively. The optimized attocells positions displayed better uniform distribution, as both received power and SNR performances improved by 0.45 and 0.026, respectively. As the results of the proposed model are optimal, it is suitable for standard office and room model applications.
... As a benefit of the sparse and quasi-stationary nature of the DD-domain, convenient low-overhead DD-domain channel estimation becomes possible [211], but there are numerous open problems to be addressed by future research in [210,212,250], such as the choice of the most appropriate near-capacity channel codes and multiple access techniques, just to name a few. In contrast to traditional radio transmission, advanced next-generation technologies will include non-radio frequency (Non-RF) solutions relying on laser based optical communications, visible light communications (VLC) and quantum communications [25,44,128,236]. The pertinent research issues consist of power control and modulation design for laser based optical wireless communications (OWC) and VLC [271]. ...
Whilst the fifth-generation (5G) systems are being rolled out across the globe, researchers have turned their attention to the exploration of radical next-generation solutions. At this early evolutionary stage we survey five main research facets of this field, namely Facet 1: next-generation architectures, spectrum and services, Facet 2: next-generation networking, Facet 3: Internet of Things (IoT), Facet 4: wireless positioning and sensing, as well as Facet 5: applications of deep learning in 6G networks. In this paper, we have provided a critical appraisal of the literature of promising techniques ranging from the associated architectures, networking, applications as well as designs. We have portrayed a plethora of heterogeneous architectures relying on cooperative hybrid networks supported by diverse access and transmission mechanisms. The vulnerabilities of these techniques are also addressed and carefully considered for highlighting the most of promising future research directions. Additionally, we have listed a rich suite of learning-driven optimization techniques. We conclude by observing the evolutionary paradigm-shift that has taken place from pure single-component bandwidth-efficiency, power-efficiency or delay-optimization towards multi-component designs, as exemplified by the twin-component ultra-reliable low-latency mode of the 5G system. We advocate a further evolutionary step towards multi-component Pareto optimization, which requires the exploration of the entire Pareto front of all optiomal solutions, where none of the components of the objective function may be improved without degrading at least one of the other components.
This article introduces the general concepts of light fidelity (LiFi) 2.0 for sixth generation (6G) of wireless networks that will be based on indoor laser-based wireless networks capable of achieving aggregate data-rates of terabits per second as widely accepted as a 6G key performance indicator. The main focus of this article is on the technologies supporting the near infrared region of the optical spectrum. The main challenges in the design of the transmitter and receiver systems and communication/networking schemes are identified and new insights are provided. This article also covers the previous and recent standards as well as industrial applications for optical wireless communications (OWC) and LiFi.
This paper investigates the sum-capacity of two-user optical intensity multiple access channels with per-user peak-or/ and average-intensity constraints. By leveraging tools from the decomposition of certain distributions, we derive several lower bounds on the sum-capacity. In the high signal-to-noise ratio (SNR) regime, some bounds asymptotically match or approach the sum-capacity, thus closing or reducing the existing gaps to the high-SNR asymptotic sum-capacity. At moderate SNR, some bounds are also fairly close to the sum-capacity.
Recent intensive and extensive development of the fifth-generation (5G) of cellular networks has led to their deployment throughout much of the world. As part of this implementation, one of the challenges that must be addressed is the skip-zone problem, which occurs when objects such as trees, people, animals, and vehicles obstruct the transmission of signals. In free-space optical (FSO) and radio frequency (RF) systems, dead zones are most often caused by buildings and trees, while in visible light communications (VLC), obstructions are caused by individuals moving around a room or objects placed in the room. A signal obstruction can significantly reduce the signal-to-noise ratio in RF and indoor VLC systems, whereas in FSO systems, where the transmitted signals are directional, the obstruction can completely disrupt data transmission. Therefore, the skip-zone dilemma must be resolved to ensure the smooth and efficient operation of 5G and beyond networks. By placing a relay between a transmitter and a receiver, the effects of obstacles can be mitigated. As a result, the signal from the transmitter will reach the receiver. In recent years, reconfigurable intelligent surfaces (RISs) that are more efficient than relays have become widely accepted as a method of mitigating skip-zones and providing reconfigurable radio environments. However, there have been limited studies on RISs for optical wireless communication (OWC) systems. Through the RIS technology, OWC and RF communication channels can be reconfigured. This paper aims to provide a comprehensive tutorial on indoor VLC systems utilizing RIS technology. The article discusses the basics of VLC and RISs and reintroduces RISs for OWC systems, focusing on RIS-assisted indoor VLC systems. We also provide a comprehensive overview of optical RISs and examine the differences between optical RISs, RF-RISs, and optical relays. Furthermore, we discuss in detail how RISs can be used to overcome line-of-sight blockages and the device orientation issue in VLC systems while revealing key challenges such as RIS element orientation design, RIS elements to access point/user assignment design, and RIS array positioning design problems that need to be studied. Moreover, we discuss and propose several research problems on integrating optical RISs with other emerging technologies, including non-orthogonal multiple access, multiple-input multiple-output systems, physical layer security, and simultaneous lightwave and power transfer in VLC systems. Finally, we highlight other important research directions that can further improve the performance of RIS-assisted VLC systems.
Bridging the gap between the video compression and communication communities, this unique volume provides an all-encompassing treatment of wireless video communications, compression, channel coding, and wireless transmission as a joint subject. WIRELESS VIDEO COMMUNICATIONS begins with relatively simple compression and information theoretical principles, continues through state-of-the-art and future concepts, and concludes with implementation-ready system solutions. This book's deductive presentation and broad scope make it essential for anyone interested in wireless communications. It systematically converts the lessons of Shannon's information theory into design principles applicable to practical wireless systems. It provides in a comprehensive manner "implementation-ready" overall system design and performance studies, giving cognizance to the contradictory design requirements of video quality, bit rate, delay, complexity error resilience, and other related system design aspects. Topics covered include • information theoretical foundations • block-based and convolutional channel coding • very-low-bit-rate video codecs and multimode videophone transceivers • high-resolution video coding using both proprietary and standard schemes • CDMA/OFDM systems, third-generation and beyond adaptive video systems. WIRELESS VIDEO COMMUNICATIONS is a valuable reference for postgraduate researchers, system engineers, industrialists, managers and visual communications practitioners. © 2001 by the Institute of Electricaland Electronics Engineers, Inc. All rights reserved.
Ultra-dense networks (UDN) constitute one of the most promising techniques of supporting the fifth generation (5G) mobile system. By deploying more small cells in a fixed area, the average distance between users and access points can be significantly reduced, hence a dense spatial frequency reuse can be exploited. However, severe interference is the major obstacle in UDN. Most of the contributions deal with the interference by relying on cooperative game theory. This paper advocates the application of dense user-centric cloud radio access network (C-RAN) philosophy to UDN, thanks to the recent development of cloud computing techniques. Under dense C-RAN, centralized signal processing can be invoked for supporting Coordinated Multiple Points Transmission/Reception (CoMP) transmission. We summarize the main challenges in dense user-centric C-RANs. One of the most challenging issues is the requirement of the global CSI for the sake of cooperative transmission. We investigate this requirement by only relying on partial channel state information (CSI), namely, on inter-cluster large-scale CSI. Furthermore, the estimation of the intra-cluster CSI is considered, including the pilot allocation and robust transmission. Finally, we highlight several promising research directions to make the dense user-centric C-RAN become a reality, with special emphasis on the application of the 'big data' techniques. Index Terms Ultra-dense networks (UDN), user-centric C-RAN, virtual cells, DAS, imperfect CSI, pilot allocation.
This paper provides a unified framework to deal with the challenges arising in dense cloud radio access networks (C-RAN), which include huge power consumption, limited fron-thaul capacity, heavy computational complexity, unavailability of full channel state information (CSI), etc. Specifically, we aim to jointly optimize the remote radio head (RRH) selection, user equipment (UE)-RRH associations and beam-vectors to minimize the total network power consumption (NPC) for dense multi-channel downlink C-RAN with incomplete CSI subject to per-RRH power constraints, each UE's total rate requirement, and fronthaul link capacity constraints. This optimization problem is NP-hard. In addition, due to the incomplete CSI, the exact expression of UEs' rate expression is intractable. We first conservatively replace UEs' rate expression with its lower-bound. Then, based on the successive convex approximation (SCA) technique and the relationship between the data rate and the mean square error (MSE), we propose a single-layer iterative algorithm to solve the NPC minimization problem with convergence guarantee. In each iteration of the algorithm, the Lagrange dual decomposition method is used to derive the structure of the optimal beam-vectors, which facilitates the parallel computations at the Baseband unit (BBU) pool. Furthermore, a bisection UE selection algorithm is proposed to guarantee the feasibility of the problem. Simulation results show the benefits of the proposed algorithms and the fact that a limited amount of CSI is sufficient to achieve performance close to that obtained when perfect CSI is possessed. Index Terms—Cloud radio access network (C-RAN), 5G ultra-dense networks, limited fronthaul capacity, incomplete CSI.
In visible light communications (VLCs) relying on intensity-modulation and direct detection (IM/DD), the conversion from electrical signals to optical signals and the limited dynamic range of the light-emitting diodes (LEDs) constitute the fundamental impediments in the way of high-integrity communications, especially when orthogonal frequency-division multiplexing (OFDM) is employed. In IM/DD VLCs, only real-valued positive signals are used for signal transmission. However, the Fourier transform of OFDM systems is operated in the complex-domain. In order to meet the requirements of the IM/ DD VLCs, the complex-to-real conversion is achieved at the cost of reducing the bandwidth efficiency. Moreover, OFDM signals experience a high peak-to-average power ratio (PAPR), hence typically clipping is used for confining the positive-valued signals within the LED's dynamic range. However, hard clipping leads to the loss of orthogonality for O-OFDM signals, generating inter-carrier interference (ICI). As a result, the performance of the clipping-based O-OFDM (CO-OFDM) systems may be severely degraded. In this paper, the concept of piecewise companding transform (CT) is introduced into the O-OFDM system advocated, forming the CTO-OFDM arrangement. We first investigate the general principles and design criteria of the piecewise CTO-OFDM. Based on our studies, three types of piecewise companders, namely the constant probability sub-distribution function (CPsDF), linear PsDF (LPsDF) and the nonlinear PsDF (NLPsDF) based CT are designed. Furthermore, we investigate the nonlinear effect of hard clipping and of our CT on O-OFDM systems in the context of different scenarios by both analytical and simulation techniques. Our investigations show that the CTO-OFDM constitutes a promising signalling scheme conceived for VLCs, which exhibits a high bandwidth efficiency, high flexibility, high reliability, as well as a high data-rate, despite experiencing nonlinear distortions.
In orthogonal frequency division multiplexing relying on subcarrier index modulation (OFDM-SIM), the information is conveyed by both the indices of the activated subcarriers and the conventional amplitude-phase modulated (APM) symbols. It has been shown that OFDM-SIM is capable of striking a tradeoff between the attainable spectral efficiency (SE) and energy efficiency (EE). In order to further increase the EE of the OFDM-SIM system, while potentially increasing its SE, we propose a compressed sensing (CS) assisted signalling strategy for the family of OFDM-SIM systems. Correspondingly, we first consider the joint maximum likelihood (JML) detection of the CS assisted index-modulated (CSIM) and of the classic APM symbols, despite its high complexity. Then, we propose a low complexity detection algorithm, which is termed as the iterative residual check (IRC) based detector. This is based on the Greedy Pursuit concept of CS, which makes locally optimal choices at each step. Finally, both analytical and simulation results are provided for characterizing the attainable system performance of our proposed OFDM-CSIM system. We demonstrate that in comparison to the conventional OFDM-SIM system, the proposed OFDM-CSIM arrangement is capable of achieving both a higher SE as well as an increased EE. We also show that the diversity gain provided by the OFDM-CSIM system is much higher than that of the OFDM-SIM system. Furthermore, our investigation of the detection performance shows that the proposed IRC detector is capable of providing an attractive detection performance at a low complexity.
In this paper, we conceive novel symbol-based Color- Shift Keying (CSK)-aided concatenated coding schemes, which provide attractive performance gains over the comparable bitbased systems. Quantitatively, our 4CSK-aided and 16CSK-aided symbol-based concatenated systems require 0.8 dB and 0.45 dB lower SNR than the equivalent bit-based schemes. In terms of decoding complexity, the 4CSK-aided and 16CSK-aided systems reduce the decoding complexity by 67% and 33%, respectively.We have also analyzed the convergence behavior of our system with the aid of non-binary EXtrinsic Information Transfer (EXIT) charts adapted for symbol-based iterative CSK-assisted systems.
The field of visible light communications (VLC) has gained significant interest over the last decade, in both fibre and free-space embodiments. In fibre systems, the availability of low cost polymer optical fibre (POF) that is compatible with visible data communications has been a key enabler. In free-space applications, the availability of hundreds of THz of the unregulated spectrum makes VLC attractive for wireless communications. This paper provides an overview of the recent developments in VLC systems based on gallium nitride (GaN) light-emitting diodes (LEDs), covering aspects from sources to systems. The state-of-the-art technology enabling bandwidth of GaN LEDs in the range of >400 MHz is explored. Furthermore, advances in key technologies, including advanced modulation, equalisation, and multiplexing that have enabled free-space VLC data rates beyond 10 Gb s⁻¹ are also outlined.
The solid-state lighting is revolutionizing the indoor illumination. Current incandescent and fluorescent lamps are being replaced by the LEDs at a rapid pace. Apart from extremely high energy efficiency, the LEDs have other advantages such as longer lifespan, lower heat generation and improved color rendering without using harmful chemicals. One additional benefit of LEDs is that they are capable of switching to different light intensity at a very fast rate. This functionality has given rise to a novel communication technology (known as Visible Light Communication-VLC) where LED luminaires can be used for high speed data transfer. This survey provides a technology overview and review of existing literature of visible light communication and sensing. This paper provides a detailed survey of (1) visible light communication system and characteristics of its various components such as transmitter and receiver, (2) physical layer properties of visible light communication channel, modulation methods and MIMO techniques, (3) medium access techniques, (4) system design and programmable platforms and (5) visible light sensing and application such as indoor localization, gesture recognition, screen-camera communication and vehicular networking. We also outline important challenges that need to be addressed in order to design high-speed mobile networks using visible light communication.