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Visible Light Communication, Networking and Sensing: Potential and Challenges
Abstract
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.
... Nowadays, the incandescent bulb is gradually being eliminated as it has a low energy efficiency. LEDs are the best choice for illumination and also for communication purposes and it is fit for changing to various light power levels at a quick rate and the exchanging rate is sufficiently quick to be noticed by a human eye [3]. The information is encoded in radiating light in different ways and a photodetector at the receiver receives and decodes the modulated signal fulfilling the criteria of the dual purposes of illumination and communication. ...
... Visible light communication operating in the visible light range, which incorporates hundreds of terahertz of license free bandwidth shown in Fig. 1 [3], can correlate the RF based mobile communication systems in designing high capacity mobile data networks. Visible light cannot infiltrate through walls and objects which permits to generate small cells of LED transmitters with no inter-cell interference issues over the walls and parcels and feeds an inherent security for wireless data communications and can also increase the capacity of the available wireless channel. ...
... The flow of current through the LEDs is controlled by a driver circuit and in turn brightness of transmitting light can be controlled. For communication purposes in both indoor and outdoor applications, white light is the most widely used forms of illumination because of color rendering [3]. Two types of LEDs are used to produce white light. ...
Visible Light Communication is the emerging field in the area of Indoor Optical Wireless Communication which uses white light LEDs for transmitting data and light simultaneously. LEDs can be modulated at very high speeds which increases its efficiency and enabling it for the dual purposes of data communication and illumination simultaneously. Radio Frequency have some limitations which is not at par with the current demand of bandwidth but using visible light, it is possible to achieve higher data rates per user. In this paper, we discuss some challenges, potentials and possible future applications for this new technology. Basically, visible light communication is for indoor application capable of multiuser access. We also design a very basic illumination pattern inside a room using uniform power distribution.
... The current overuse of the spectrum and projected growth of users and data rates [1,2] have led to an increasing interest on finding new wireless technologies to either complement or replace current wireless networks. One of the most promising alternatives in the recent years has been Visible Light Communication (VLC) technology [3][4][5][6]. ...
... In general, a blue gallium nitride HB-LED in combination with a yellow inorganic phosphor is the preferred approach for obtaining white light in SSL. However, this phosphor limits the HB-LED bandwidth to a few MHz (3)(4)(5) [14,15]. ...
... To test the communication capability of the proposed TIBuck DC/DC converter as a VLC driver, a 64-QAM modulation scheme was used. The communication signal modulates the amplitude and phase and, due to its high complexity and wide use in VLC [3][4][5], it allows proof of concept of the communication capability of the prototype. The carrier frequency must lie within the HB-LED bandwidth, hence a carrier frequency, f sig , of 1 MHz was used. ...
This work proposes a high-efficiency High-Brightness LED (HB-LED) driver for Visible Light Communication (VLC) based on a Two-Input Buck (TIBuck) DC/DC converter. This solution not only outperforms previous approaches based on Buck DC/DC converters, but also simplifies previous proposals for VLC drivers that use the split power technique with two DC/DC converters: one is in charge of the communication tasks and the other controls the biasing of the HB-LED (i.e., lighting tasks). The real implementation of this scheme requires either two input voltage sources, one of which is isolated, or one DC/DC converter with galvanic isolation. The proposed implementation of splitting the power is based on a TIBuck DC/DC converter that avoids the isolation requirement, overcoming the major drawback of this technique, keeping high-efficiency and high communication capability thanks to the lower voltage stress both across the switches and at the switching node. This fact allows for the operation at very high frequency for communication purposes, minimizing switching power losses, achieving high efficiency and providing lower filtering effort. Moreover, the duty ratio range can also be adapted to the useful voltage range of the HB-LED load to maximize the resolution on the tracking of the output volage. The power is split by means of an auxiliary Buck DC/DC converter operating at low switching frequency, which generates the secondary voltage source needed by the TIBuck DC/DC converter. This defines a natural split of power by only processing the power delivered for communications purposes at high frequency. A 7 W output-power experimental prototype of the proposed VLC driver was built and tested. Based on the experimental results, the prototype achieved 94% efficiency, reproducing a 64-QAM digital modulation scheme and achieving a bit rate of 1.5 Mbps with error in communication of 12%.
... Research on light-based communication systems has just recently been apparent, despite the increasing interest in VLC [1]. Light has always been one of the essential components that people have utilized to connect with one another throughout history. ...
... LED luminaires are the emitters used in visible light communication systems [1]. A full lighting device made up of an LED, a ballast, a housing, and additional parts is called an LED luminaire. ...
... There are two primary types of VLC receivers designed to capture signals emitted by LED luminaires: 1) the photo detector, also known as a photodiode or non-imaging receiver, and 2) the imaging sensor, commonly referred to as a camera sensor [1]. The photo detector, a semiconductor device, plays a crucial role in converting received light into electrical current. ...
In recent years, the rapid growth of mobile devices and wireless services has created a significant demand for RF-based technologies. Among the various emerging wireless communication forms, Visible Light Communications (VLC) stands out as a potentially transformative technology that not only complements RF communications but also introduces innovative possibilities for mobile wireless device applications. VLC utilizes visible light for communication, offering high-speed data transmission, improved energy efficiency, and enhanced communication security and privacy. This article thoroughly explores VLC, discussing its core concepts, fundamental principles, and essential technologies that define this rapidly developing field. By providing insights into the intricacies of VLC, readers can gain a better understanding of its mechanisms and capabilities. The exploration also extends to elucidating the diverse application scenarios where VLC can be effectively applied, showcasing its versatility and potential impact on various sectors. This comprehensive survey not only presents the current state of VLC but also predicts future development trends, providing a forward-looking perspective on the evolution of this technology. As the demand for efficient and secure wireless communications continues to rise, VLC emerges as a promising frontier, poised to play a pivotal role in shaping the landscape of communication technologies in the years to come.
... Furthermore, VLC is less harmful than other wireless communication technologies for human health, provided the illumination level is below the eye safety level [11,12]. VLC can also be integrated into existing lighting infrastructure, making it a cost-effective solution for smart lighting and communication systems [13,14]. VLC systems can provide precise indoor positioning and navigation services, which are advantageous in various applications, including retail and healthcare [15,16]. ...
... In addition, LED arrays are designed in this paper to increase the received power rather than reduce the background noise. In arrays with better performance, the received power is larger and the background noise is higher, as expected from the shot noise formula given in Equation (13). However, since the received power is higher, the SNR values of these arrays are also better. ...
In this paper, a novel method is introduced to enhance the performance of vehicle-to-vehicle (V2V) visible light communication (VLC) by employing different transmitter (Tx) light-emitting diode (LED) array arrangements with different LED orientations. Improving the signal-to-noise ratio (SNR) is crucial for V2V VLC systems to provide long communication ranges. For this purpose, six transmitter configurations are proposed: single-LED transmitters, as well as 3 × 3 square-, single hexagonal-, octagonal-, 5 × 5 square-, and honeycomb hexagonal-shaped LED arrays. Indoor VLC studies using LED arrays offer a uniform SNR, while outdoor studies focus on optimizing the receiver side to enhance system performance. This paper optimizes system performance by increasing the SNR and communication range of V2V VLC systems by changing the geometry of the Tx LED array and LED orientations. A V2V VLC system using on–off keying (OOK) is modeled in MATLAB, and the SNR and bit error rate (BER) are simulated for different Tx configurations. Our results show that the honeycomb hexagonal transmitter design provides a 19% improvement in system performance with a spacing of 1 cm, and maintains a 16% improvement when the array size is reduced by a factor of 100, making it smaller than one of the smallest industrial headlight modules.
... The fifth-generation (5G) networks aim to revolutionize the Internet of Things (IoT) with enhanced speed, connectivity, and capacity. A potential technology for this transformation is Optical Wireless Communication (OWC) [1], specifically Visible Light Communication (VLC), which utilizes ubiquitous light-emitting diodes (LEDs) for dual purposes: illumination and high-speed data transmission [2]. Operating in the 400-800 THz spectrum, VLC faces challenges in signal communication at these frequencies, particularly affecting device performance at the transmitting and receiving ends. ...
... This feature allows for the mapping of received optical signals to distinct scalar values, each corresponding to the wavelengths of the individual RGB LEDs. With the SPD configuration, the received signal model, initially formulated in (2), is adapted to the following: ...
Visible Light Communication (VLC) is emerging as a promising technology to meet the demands of fifth-generation (5G) networks and the Internet of Things (IoT). This study introduces a novel RGB-LED-based VLC system design that leverages autoencoders, addressing the often overlooked impact of optical-to-electrical (O/E) conversion efficiency. Unlike traditional methods, our autoencoder-based system not only improves communication performance but also mitigates the negative effects of O/E conversion. Through comprehensive simulations, we show that the proposed autoencoder structure enhances system robustness, achieving superior performance compared to traditional VLC systems. By quantitatively assessing the impact of O/E conversion—a critical aspect previously overlooked in the literature—our work bridges a crucial gap in VLC research. This contribution not only advances the understanding of VLC systems but also provides a strong foundation for future enhancements in 5G and IoT connectivity.
... The ray-optical simulations in this work provide essential input for the implementation in vehicular communication scenarios, as they reveal insights into the signal strength variation while a vehicle is approaching an intersection equipped with a stationary RIS and the impact of the surface size. When some vehicles of a platoon have already turned, but others are still on the initial road, the communication distances between the vehicles are not covered by the common Light Emitting Diode (LED) approach [11]. Therefore, in this work, laser diodes are assumed as the transmitter source instead of LEDs, as they have a sufficient range depending on the angular divergence of the laser beam [12]. ...
... The second step is sending the requested information from B to A. In the following the first step is investigated, therefore A is set as the transmitter, and B as the receiver. LEDs [11] are often not sufficient as the communication channel is not only between two close vehicles behind each other but over the RIS in a far-off distance. Thus, the parameters of the light source of the transmitting vehicle are selected as a laser diode. ...
For Visible Light Communication (VLC) between vehicles, maintaining Line of Sight (LoS) is a fundamental requirement. Especially when a sequentially communicating convoy (platoon) is turning at an intersection within a city, the direct line-of-sight connection can be interrupted, leading to a disruption of VLC communication. Particularly in urban locations with obstructed view, it is crucial for future autonomous driving to convey critical information, such as crossing pedestrians and other obstacles like partial road closures due to construction sites, to following vehicles. Within the development of Sixth-Generation (6G) wireless networks, the use of Reconfigurable Intelligent Surfaces (RIS) is proposed as one option to address the LoS issue. In this work, a conceivable use case is investigated to examine through ray-optical simulations the requirements for the update rate of such systems when RIS elements are reconfigured discontinuously. Additionally, the influence of the size of the device surface area on the resulting signal strength in the described traffic situation is provided. The findings suggest that delays in updating array elements significantly impact situations where the transmitter is far from the intersection, offering crucial insights for autonomous driving system development. Please note: This is a preprint of the publication which is accepted at the 2024 IEEE 99th Vehicular Technology Conference (VTC Spring) in the Workshop on Optical Wireless Communications (OWC'24) for 6G. The final version will be available soon.
... However, a single high-resolution camera typically meets several limitations: 1) lack of depth information (Chen et al. 2017), and 2) heavy reliance on visible light (Pathak et al. 2015). The lack of depth measurement brings the inconvenience of monitoring some specific construction activities like excavation. ...
Traditional 2D surveillance video has been widely adopted in construction project management, yet facing several challenges. An emerging surveillance technology is the latest Light Detection and Ranging (LiDAR) that streams time-dynamic 4D point cloud (4DPC), which gained wide attention in the automobile and engineering sectors. However, one of the major defects of LiDAR surveillance streaming is the huge data volume. This paper presents a novel 4DPC data compression method to ease the problem. First, the 4DPC data frame is transformed into a depth image; then, the depth and laser intensity information are coded in the RGB color spectrum. As a result, a stationed 4DPC data stream is converted into a 3D surveillance video coded in H.264. A pilot test was conducted on the 4DPC data collected in a real-world project. The results confirmed that the presented method effectively encodes the 4DPC data stream with a high (1:0.08) compression ratio at a very low (0.5%) loss ratio at 5-cm resolution to common point cloud formats such as .ply and .pcd. The result of 4DPC LiDAR surveillance video can be played in 3D view mode by a designated player. The contribution of this paper lies in a novel video-based 4DPC data compression for LiDAR surveillance video streaming in construction project management.
... Visible light communication (VLC) [1][2][3] refers to a method of data transmission that uses light waves within the visible spectrum, ranging from 380 nm to 750 nm. A key feature of this communication method is its ability to transfer data unobtrusively, without affecting the perceived illumination of the environment. ...
Display field communication (DFC) is an emerging technology that enables seamless communication between electronic displays and cameras. It utilizes the frequency-domain characteristics of image frames to embed and transmit data, which are then decoded and interpreted by a camera. DFC offers a novel solution for screen-to-camera data communication, leveraging existing displays and camera infrastructures. This makes it a cost-effective and easily deployable solution. DFC can be applied in various fields, including secure data transfer, mobile payments, and interactive advertising, where data can be exchanged by simply pointing a camera at a screen. This article provides a comprehensive survey of DFC, highlighting significant milestones achieved in recent years and discussing future challenges in establishing a fully functional DFC system. We begin by introducing the broader topic of screen–camera communication (SCC), classifying it into visible and hidden SCC. DFC, a type of spectral-domain hidden SCC, is then explored in detail. Various DFC variants are introduced, with a focus on the physical layer. Finally, we present promising experimental results from our lab and outline further research directions and challenges.
... Lambertian intensity profiles are mathematically well-governed and are established in optics literature as a reasonable fit for modeling light-emitting diodes (LEDs) [22,23]. The Lambertian model assumes the total optical power of the source P tx is radiated from a point. ...
An experimental testbed was constructed to rigorously assess the fundamental limits of light-wave sensing—an economic, non-contact vitals monitoring approach previously reported. We improve the testbed using lock-in amplification and demonstrate that a photodetector and a commonplace array of infrared LEDs are sufficient to detect respiratory motion and quantify respiration rate up to 2.5 meters away. We propose a novel scattering model, from which we derive the performance limits of the light-wave sensing system in terms of a theoretical range resolution limited by the dynamic range of the system. Using a robotic breathing phantom, we experimentally assess, for the first time, the range resolution of the testbed system and compare this to theoretical predictions. This work also introduces a process for generating stochastic respiration patterns, which may prove broadly useful to the designers of breathing phantoms. Holistically exploring practical challenges and analytical models, this paper serves as a unique and comprehensive tutorial for understanding and designing light-wave sensing systems.
... Additionally, VLC offers the utilization of already existing illumination infrastructure for communication. This indicates that such systems may be implemented with comparatively less time and at a reduced expense [6]. ...
In recent years, the integration of intelligent transportation systems (ITS) has gained popularity as a means of enhancing the safety of roadways and underground tunnels and reducing traffic congestion. Given the fact that conventional radio frequency (RF) communication systems are vulnerable to significant limitations as a result of a variety of factors, including signal attenuation and interference, which affect their application, the emerging visible light communication (VLC) technology is an exciting potential candidate for facilitating wireless access in such environments. This study investigates the deployment of VLC systems in underground vehicular tunnels involving a handover strategy based on the software-defined network (SDN) approach, with the objective of addressing the fundamental challenges faced by communication systems in such scenarios. The Optisystem software is used to simulate and investigate the performance of the proposed system, which is based on orthogonal frequency division multiplexing (OFDM) technology in both line-of-sight (LOS) and non-line-of-sight (NLOS) conditions. The simulated scenario is capable of achieving a data rate of 10 Gbps within a link range of 3 meters in the LOS approach. In the NLOS propagation model, a data rate of 2 Gbps can be attained without any error. The simulation results reveal a particular perspective on the viability of VLC systems in improving the communication infrastructure in underground vehicular tunnels and promoting efficient tunnel operations. The evaluation of the simulated system is conducted based on bit error rate (BER), signal-to-noise ratio (SNR), and the constellation diagram.
... Infrared spectra can also be specifically applied in human signal measurement [37]. In addition to infrared technology, industry and the research community have developed numerous visible-light positioning (VLP) systems [38] and visible-light sensing (VLS) systems [39], which require commonly used light emitting diodes (LED) as lighting sources and light sensors to form the systems [40]. Similarly, utilizing visible light for screen sensing involves using ambient light sensors to capture light intensity information from external light sources at various angles relative to the screen [41]. ...
Human–computer interaction (HCI) with screens through gestures is a pivotal method amidst the digitalization trend. In this work, a gesture recognition method is proposed that combines multi-band spectral features with spatial characteristics of screen-reflected light. Based on the method, a red-green-blue (RGB) three-channel spectral gesture recognition system has been developed, composed of a display screen integrated with narrowband spectral receivers as the hardware setup. During system operation, emitted light from the screen is reflected by gestures and received by the narrowband spectral receivers. These receivers at various locations are tasked with capturing multiple narrowband spectra and converting them into light-intensity series. The availability of multi-narrowband spectral data integrates multidimensional features from frequency and spatial domains, enhancing classification capabilities. Based on the RGB three-channel spectral features, this work formulates an RGB multi-channel convolutional neural network long short-term memory (CNN-LSTM) gesture recognition model. It achieves accuracies of 99.93% in darkness and 99.89% in illuminated conditions. This indicates the system’s capability for stable operation across different lighting conditions and accurate interaction. The intelligent gesture recognition method can be widely applied for interactive purposes on various screens such as computers and mobile phones, facilitating more convenient and precise HCI.
... Meanwhile, the prolonged exposure to flashing lights with frequencies below 200 Hz can pose risks to human health. To address this concern, OCC systems have turned to utilize the rolling shutter technique that scans the image sensor pixel row by row at high frequencies so that illumination and communication can be realized simultaneously [6]. At the same time, the utilization of image sensors enables easy implementation of spatial division multiplexing (SDM) and wavelength division multiplexing (WDM), when a large number of pixels and color filters in current image sensors are comprehensively used. ...
Optical camera communication (OCC) has garnered worldwide research attention, due to its immunity to electromagnetic interference (EMI) and efficient utilization of spectrum resources. However, the limited bandwidth of the OCC system and the timing offset of the camera result in low system throughput. To enhance the OCC throughput, we propose and experimentally demonstrate a frame-rate adaptive fractionally spaced equalization algorithm (FA-FSE) for the joint mitigation of severe inter-symbol interference (ISI) and timing offset arising in OCC. Experimental results validate its correct and power-efficient function, leading to a record aggregated throughput of 250.96 kbit/s, when the 8-level pulse amplitude modulation (PAM-8) signals are independently modulated to eight chip-on-board light emitting diode (COB-LED) light strips, while simultaneously received by a smartphone 10 cm away.
... PoF systems have been applied to OWC towards 6G. OWC covers the entire optical spectrum of ultraviolet (UV), visible, and infrared (IR) [37,38]. It offers high-speed data transfer and secure communication channels. ...
This paper reports two implementations of power-over-fiber (PoF) solutions applied to radio-over-fiber (RoF) and optical wireless communication (OWC) systems, in the context of an industrial environment. We employ a conventional 62.5-µm multimode fiber (MMF) to deliver optical power to different communication links based on RoF, free-space optics (FSO), and visible light communication (VLC) technologies aiming beyond 5G (B5G) and 6G applications. First, a 3.5-GHz 5G New Radio (5G NR) signal is transmitted throughout a 20-km single-mode optical fiber (SMF) link using RoF technology. Regarding the PoF system, a 5-W optical power is transmitted through a 100-m MMF link. A photovoltaic power converter (PPC) and a DC/DC converter are employed to convert the power from the optical to the electrical domain and adjust the voltage level, respectively, with the purpose of energizing a remote RoF module. The attainable optical and electrical power transmission efficiencies (OPTE and PTE) are 80% and 19%, respectively. Posterior, a second PoF system is implemented to power a hybrid RoF/FSO/VLC B5G system, comprising a 200-m MMF and an additional DC/DC converter. Over 10.5 W of optical power is transmitted to feed an electrical amplifier (EA) and a white LED from the VLC link. In this configuration, we achieve 78% and 18.5% of OPTE and PTE, respectively. Furthermore, a performance investigation based on the root mean square error vector magnitude ( E V M R M S ) metric is conducted to evaluate the signal using the implemented PoF systems and a conventional electrical power supply. In the first implementation, a throughput of 600 Mbps is achieved with 100-MHz bandwidth without performance degradation, when compared to the conventional-powered RoF system, whereas, in the second implementation, 60-Mbps throughput is achieved when employing the FSO and VLC technologies simultaneously, demonstrating the applicability and potential of the PoF technique for B5G and 6G industrial communications.
... The communication protocol, outlined in Table 1, governs information exchange, covering synchronization, identification, and payload sections of the transmitted frame. The frame structure is systematic and standardized, contingent on the type of communication (1)(2)(3)(4)(5)(6), and includes the following components: Table 1 Communication protocol: synchronization (Sync), type of communication (COM), identification (position and time) and payload sections of the transmitted frame. • Other ID Blocks: These include vehicle number (Veic. ...
Li-Fi (Light Fidelity) is the transmission of data through light, it is secure, efficient, and cheaper than other data transmission technologies such as Bluetooth, Wi-Fi, GiFi, etc. Also, data transmission in Li-Fi is around 100 × faster than the data transmission through Wi-Fi, i.e., it can send data at a very high speed. This chapter discusses the overview of Li-Fi, its characteristics, a comparison of various data transfer technologies such as Wi-Fi, Li-Fi and its applications such as underwater data transmission, its usage in thermal power plants, hotels, hospitals, malls, etc. and also contains its limitations and advantages over other technologies. Li-Fi technology has vast application and development potential because light is widely available and free. Each Li-Fi bulb could be used to transmit data if this technology matures. It would be a future communication system that is safer, greener, less expensive, and more cost-effective.
The design and simulation of indoor visible light communication (VLC) system with preemphasis is proposed for 5 m transmission of signal at the data rate of 10 Gbps for receiving only applications like smart TV, smart speaker, and smart home appliance control. The preemphasis driver circuit is designed to reduce the intersymbol interference by pulse shaping the signal and transimpedance amplifier is used to amplify the signal for longer distance transmission. Intensity modulation at the sender side and direct detection at the receiver-side are adopted in this work for the improvement of the system’s overall performance and to decrease its implementation cost. The system performance is analyzed in terms of BER, data-rate, Q-factor, and eye diagrams. The setup is developed, which includes a nonreturn-to-zero (NRZ) generator, preemphasis driver, light-emitting-diode, VLC channel, and receiver with an avalanche photodiode and Gaussian LPF. At 10 Gbps data rate, the maximum transmission distance that can be obtained is 5 m with a BER of less than 10 ⁻³¹ .
Telemedicine has emerged as a critical tool in modern healthcare, allowing remote diagnostics, treatment, and consultation. The growing demand for efficient, reliable, and high-speed communication networks for telemedicine services necessitates advanced solutions. Hybrid networks that combine Radio Frequency (RF) and Free Space Optics (FSO) offer the potential to enhance communication systems by leveraging the strengths of both technologies. This review explores the challenges associated with RF and FSO hybrid networks, particularly in telemedicine, and provides potential solutions for optimizing these networks. By investigating technological, environmental, and operational challenges, as well as analyzing the integration of RF and FSO, this article aims to provide a comprehensive understanding of how these networks can revolutionize telemedicine.
This paper introduces the use of Visible Light Communication (VLC) to enhance traffic signal efficiency and vehicle trajectory management at urban intersections. By integrating VLC localization with learning-based traffic signal control, a multi-intersection traffic system is proposed. VLC enables communication between connected vehicles and infrastructure through mobile optical receivers. The primary objectives are to reduce waiting times and improve overall traffic safety by accommodating diverse traffic movements during multiple signal phases. Cooperative mechanisms and queue/response interactions balance traffic flow between intersections, enhancing road network performance. A reinforcement learning scheme optimally schedules traffic signals, with agents at each intersection using VLC-enabled vehicle communication to improve traffic flow and overall system optimization. Evaluated using the SUMO urban mobility simulator, the system demonstrates reduced waiting and travel times. The decentralized and scalable nature of this approach highlights its potential applicability in real-world traffic scenarios.
Wireless optical communication plays a vital role in mobile communication networks, and both drones and vehicles are essential mobile communication nodes. Here, image identification technology, gimbal, and full-duplex optical communication systems are integrated to manage the challenging issues of light alignment and target tracking for mobile full-duplex optical communication under the transmission control protocol/internet protocol (TCP/IP) scheme. Both drones and vehicles are equipped with the proposed setup to realize full-duplex wireless optical data transmission at a communication rate of 2 Mbps in both air-to-ground and air-to-air scenarios. By further integrating wireless-fidelity (Wi-Fi) modules, drone-based mobile optical communication systems (MOCSs) can be interconnected with the network via the TCP/IP scheme, and real-time video transmission can be demonstrated. This work provides a feasible route toward a mobile optical communication network (MOCN) for diverse applications.
This paper presents a novel concept for joint light source identification and localization (JLIL) with subsequent interference suppression using a liquid crystal display (LCD)-based receiver. The JLIL concept is particularly suitable for multiple-input single-output visible-light-communication settings, where an LCD-based receiver must be able to identify a desired light source before suppressing interfering ones. Given a basic visible-light-communication setup, in a first step modifications required both on the transmitter and the receiver side are identified. Subsequently, the concept for LCD-based JLIL is introduced, and its performance is illustrated by means of simulation results. In this context, intersymbol interference effects are investigated and a known ambiguity problem is overcome. Finally, results of an experimental verification are reported as a proof of concept. It is shown that the derived simulation model accurately predicts measurement results. The latter confirm a virtually error-free light source identification and precise localization within system accuracy range. Furthermore, an improved peak detection is reported. Signal-to-noise ratio measurements suggest good performance for up to 3 m using the developed hardware demonstrator.
Achieving fairness in power allocation is crucial for maximizing the performance of Non-Orthogonal Multiple Access (NOMA) systems in Visible Light Communication (VLC). However, existing power allocation methods for NOMA-VLC often struggle to maintain fairness. This paper addresses this challenge by introducing the Empirical Fair Optical Power Allocation (EFOPA) method. EFOPA leverages a simplified mathematical model to achieve maximum fairness among users, ensuring equitable data rates even when channel conditions and illumination levels vary. Furthermore, EFOPA significantly reduces computational complexity compared to optimisation based approaches, making it suitable for dynamic environments where users move frequently. Simulation results demonstrate that EFOPA outperforms existing methods GRPA and NGDPA in terms of fairness and maintains comparable sum-rate performance, offering a robust and efficient solution for power allocation in NOMA-VLC systems.
This study presents visible‐light chiral photonic synaptic devices based on 2D chiral hybrid organic‐inorganic perovskites (HOIPs), composed of Si/SiO₂/chiral HOIPs/poly(methyl methacrylate)/pentacene/Au, designed for circularly polarized light (CPL)‐active peripheral nervous system (PNS) applications. In the heterostructure of 2D chiral HOIPs and pentacene, chiral HOIPs effectively distinguish the direction of CPL and the pentacene layer extracts photoinduced charge carriers to achieve synaptic properties, as confirmed by circular dichroism and photoluminescence analyses. The devices exhibit a photocurrent dissymmetry factor of up to 0.3 and a photoresponsivity of 130 mA W⁻¹. Logic operations using a 3 × 4 pixel array of chiral HOIP‐based heterostructures are demonstrated, achieving pattern recognition based on the direction of CPL and pulse interval time. Notably, the efficiency to discriminate CPL direction increases with longer pulse intervals. This improvement enhances the learning capability by amplifying CPL direction discrimination ratios. Leveraging these properties, neural network simulations for neuromorphic applications are conducted, and artificial neural networks are trained for image recognition using the devices as CPL filters, achieving a 92% recognition accuracy. These results signify the beginning of chiral PNS devices communicating with visible CPL based on 2D chiral HOIPs.
Visible light communication (VLC) gains significant attention from researchers due to its broad optical spectrum and numerous advantages. VLC is considered a potential alternative wireless communication solution that meets the high demand for devices and service types, particularly in indoor environments, leveraging existing light-emitting diode (LED) infrastructure. However, limitations associated with conventional modulation schemes and LED characteristics necessitate alternative approaches. Mainly, there are two main modulation techniques commonly used in VLC: single-carrier and multi-carrier. Multi-carrier modulations, such as orthogonal frequency division multiplexing (OFDM), are particularly interesting due to their immunity to inter-symbol interference (ISI) at high data rates. Indeed, OFDM produces a high peak-to-average power ratio (PAPR), which can affect the LED's lifespan and produce clipping distortion. Generalized frequency division multiplexing (GFDM) can be an alternative, providing better performance. This paper explores the potential of optical GFDM (OGFDM) for indoor VLC due to its flexibility and high efficiency. Despite its promising capabilities, OGFDM in VLC systems still faces challenges, including complexity and practical implementation considerations. This paper concludes by outlining these challenges and emphasizing the need for further research to unlock the full potential of OGFDM for future VLC advancements.
This paper considers multiuser downlink transmission and detection in a multiple input‐multiple output (MIMO) visible light communication (VLC) system. We combine two promising techniques: space‐shift keying (SSK) and optical orthogonal codes (OOCs). Multiuser downlink transmission is realized by allowing each activated LED to transmit user‐specific OOC simultaneously. An OOC despreader is implemented at the front end of each user terminal (UT) to extract the desired signal and mitigate multiuser interference (MUI). The second part of UT receiver aims to extract the index of the corresponding active LED based on maximum likelihood (ML) or zero‐forcing (ZF) algorithm. The figure of merit we used to access the performance of the proposed downlink multiuser SSK system is the average symbol error rate (SER). Comprehensive Monte Carlo simulations have been undertaken for different system setup to evaluate SER at UT receiver. It is demonstrated that for a specified SER, the required SNR for ML‐based detection algorithm is 3 dB less than the ZF detector in the MUI‐free scenario. On the other hand, the ZF detector outperforms ML detector in the case with residual MUI and limited channel state information (CSI). Both algorithms are computationally attractive, hence can be put into practice in multiuser VLC MIMO system.
This study aims to enhance the efficiency of Visible Light Communication (VLC) channels and contribute to the reduction of carbon emissions in underground communications by leveraging Polar Codes and Multiresolution Analysis (MRA). It uses a specific configuration of frozen bits for the implementation of Polar codes. Additionally, it integrates the Daubechies Wavelet family with a five-level decomposition into the MRA filters. The effectiveness of these methodologies is evaluated separately, without incorporating additional techniques into the communication channel. The results depicted a significant improvement, around of 19 dB in channel performance. This represent a considerable reduction in carbon emissions in a underground copper production context.
The challenges of high latency and interference plaguing Radio Frequency (RF) communication have sparked a quest for alternative solutions. Visible Light Communication (VLC) emerges as a promising alternative due to its distinct advantages. Unlike RF communication, which requires separate configurations for transmission and reception of RF waves, VLC operates seamlessly, utilizing visible light for both transmission and reception. Light Emitting Diodes (LEDs) replace fluorescent lamps as a result of the solid-state lighting revolution, further encouraging the use of VLC. In contemporary discussions, there’s been a noticeable surge in interest surrounding the application of VLC within underwater settings, particularly for applications like oceanographic data collection and other underwater tasks. The collected data must be transmitted to an inland base station for further analysis, especially for time-critical applications in military and scientific domains. The aim is to analyse the performance of the RF with Underwater VLC (UVLC) link, with particular purpose of data speed and signal strength in under water environments. By strategically integrating acoustic and VLC technologies, the system attains high-speed data transmission capabilities alongside long-range communication capabilities. This research aims to address the complex challenges of underwater communication and provide insights into the most effective communication protocols and link combinations for real-time data streaming in underwater environments.
We examine the feasibility of human identification using purely the ubiquitous visible light. Empowered by the Visible Light Communication (VLC), the identification system consists of VLC-enabled LED lights on the ceiling emitting light beacons, and photodiodes on the floor capturing a continuous stream of shadow maps each corresponding to an LED light. We leverage these shadow maps to localize a user's key boy joints in the 3D space and recognize the user based on the estimated body parameters (e.g., shoulder width, arm length). Preliminary results with 10 participants show 80\% success rate, i.e., correctly identifying 8 participants out of 10. The mean error of the body parameter estimation is 0.03 m. To extend the system to diverse practical settings, we discuss the our plan of incorporating advanced behavioral features to enhance the identification accuracy and robustness.
We present LiSense, the first-of-its-kind system that enables both data communication and fine-grained, real-time human skeleton reconstruction using Visible Light Communication (VLC). LiSense uses shadows created by the human body from blocked light and reconstructs 3D human skeleton postures in real time. We overcome two key challenges to realize shadow-based human sensing. First, multiple lights on the ceiling lead to diminished and complex shadow patterns on the floor. We design light beacons enabled by VLC to separate light rays from different light sources and recover the shadow pattern cast by each individual light. Second, we design an efficient inference algorithm to reconstruct user postures using 2D shadow information with a limited resolution collected by photodiodes embedded in the floor. We build a 3 m x 3 m LiSense testbed using off-the-shelf LEDs and photodiodes. Experiments show that LiSense reconstructs the 3D user skeleton at 60 Hz in real time with 10 degrees mean angular error for five body joints.
The study investigates on Light Emitting Diode (LED) based Visible Light Communication (VLC) systems. Starting with a short review on High Brightness (HB) LEDs and their recent performances reaching up to 100 Lm W -1, the researchers examine the processes and techniques of using light emitted by LEDs as a mediwn for carrying data. The technology exploits the inherent high rate switching characteristic of these devices. In addition, investigation on different modulation techniques is explained. Recent developments in VLC and its potential application areas are discussed. A prognosis for future trend, functional requirements and challenges are also discussed.
We present HiLight, a new form of screen-camera communication without the need of any coded images (e.g. barcodes) for off-the-shelf smart devices. HiLight hides information underlying any images shown on a LED or an OLED screen, so that camera-equipped smart devices can fetch the information by turning their cameras to the screen. HiLight achieves this by leveraging the orthogonal transparency (alpha) channel, a well-known concept in computer graphics, to embed bits into pixel translucency changes without the need of modifying pixel color (RGB) values. We demonstrated HiLight's feasibility using smartphones. By offering an unobtrusive, flexible, and lightweight communication channel between screens and cameras, HiLight opens up opportunities for new HCI and context-aware applications to emerge, e.g. smart glass communicates with screens for additional personalized information to realize augmented reality.
The indoor visible light propagation characteristics are simulated and analyzed using the method of SBR/Image (shooting and bounding ray tracing/Image). A good agreement is achieved between the results simulated and the results given in published literature. So the correctness of the method has been validated. Some propagation parameters are obtained in the simulation, such as the indoor received power distribution, statistical distribution of phase angle of received power, RMS (root mean square) delay spread, direction of arrival, and Doppler shift. The foundation for the wireless network coverage of indoor visible light communication system is provided by the analysis of the above results.
Light-emitting diodes (LEDs) have been deployed for various applications in our daily lives. Similarly, image sensors or cameras integrated into mobile phones have become common. Hence, visible light communication (VLC) using LED and mobile phone cameras is attractive and provides low-cost wireless communication. In this paper, we propose and demonstrate a VLC system using color-shift-keying (CSK) modulation and code-division multiple-access (CDMA) technology simultaneously for the first time; a mobile phone camera is used as the receiver (Rx). CSK is used to enhance the VLC system capacity and to mitigate the single color light interference, whereas CDMA allows multiple users to access the network. The system design and operation mechanism of the proposed CSK-CDMA VLC system are discussed. A proof-of-concept demonstration is performed, and error-free transmission is achieved for multiple-access users. A 3-dB transmission gain is also obtained in each user when compared with the traditional on-off keying (OOK) modulation.
Optical wireless communication (OWC) refers to transmission in unguided propagation media through the use of optical carriers, i.e., visible, infrared (IR), and ultraviolet (UV) bands. In this survey, we focus on outdoor terrestrial OWC links which operate in near IR band. These are widely referred to as free space optical (FSO) communication in the literature. FSO systems are used for high rate communication between two fixed points over distances up to several kilometers. In com- parison to radio-frequency (RF) counterparts, FSO links have a very high optical bandwidth available, allowing much higher data rates. They are appealing for a wide range of applications such as metropolitan area network (MAN) extension, local area network (LAN)-to-LAN connectivity, fiber back-up, backhaul for wireless cellular networks, disaster recovery, high definition TV and medical image/video transmission, wireless video surveillance/ monitoring, and quantum key distribution among others. De- spite the major advantages of FSO technology and variety of its application areas, its widespread use has been hampered by its rather disappointing link reliability particularly in long ranges due to atmospheric turbulence-induced fading and sensitivity to weather conditions. In the last five years or so, there has been a surge of interest in FSO research to address these major technical challenges. Several innovative physical layer concepts, originally introduced in the context of RF systems, such as multiple-input multiple-output communication, cooperative diversity, and adap- tive transmission have been recently explored for the design of next generation FSO systems. In this paper, we present an up-to-date survey on FSO communication systems. The first part describes FSO channel models and transmitter/receiver structures. In the second part, we provide details on information theoretical limits of FSO channels and algorithmic-level system design research activities to approach these limits. Specific topics include advances in modulation, channel coding, spatial/cooperative diversity tech- niques, adaptive transmission, and hybrid RF/FSO systems.
The present paper proposes a novel multiple-LED-arrays acquisition for an infrastructure-to-vehicle visible light communication (I2V-VLC) using LED arrays (transmitter) and an in-vehicle high-speed image sensor (receiver). In order to achieve a robust detection of LED arrays, we employ the block matching algorithm, which is a way of finding a corresponding position between two successive frames. The proposed method divides a captured image into a number of small domains (blocks) and determines if the LED array is present or absent using the block matching. We perform I2V-VLC experiments with multiple-LED arrays and evaluate the acquisition capability of the proposed method.
In recent years, visible light communication (VLC) has emerged as a complementary technique to overcome limitations of the crowded radio frequency (RF) spectrum. Its superior characteristics include unlicensed wide bandwidth, high security and dual-use nature. Nevertheless, mobile devices are not equipped with illuminating components, which are utilized as transmitters in downlink data transmission. Targeting a high quality and robust uplink channel, high power light sources turn to be unsuitable for mobile devices with limited battery life. Furthermore, VLC uplink requires a directional optical transmission beam that can lead to significant deterioration of throughput given the potential rotation and/or movement of devices. With the above-mentioned design challenges, the uplink mechanism becomes a fundamental problem for bidirectionalVLC. In order to alleviate congestion in the RF shared medium as well as resolve the back-channel issue of VLC networking, we propose a real-time indoor hybrid WiFi and VLC system for realizing Internet surfing. In this hybrid system, downstream data flow is transmitted by light emitting diodes (LED), whereas the upstream data flow is forwarded through WiFi connectivity. Our designed system utilizes flexible software defined VLC (SDVLC) to implement the unidirectional optical wireless channel. Experimental results reveal that the integrated system outperforms conventional WiFi for crowded environments in term of throughput.
Visible light communications (VLC) can be adopted in lighting infrastructure to provide ubiquitous wireless access in spaces where light is consumed by humans. Unfortunately, the requirement to provide high-quality diffuse illumination reduces the potential capacity of the free space links and we seek ways to accommodate both the lighting and data rate goals. We investigate the combination of multiple VLC transmissions through spatial multiplexing (SM), a MIMO technique, to meet our data rate goals. Specifically, this paper deals with receiver designs intended to receive and decode increasing numbers of SM/MIMO VLC data streams.
Conventional imaging (camera) receivers have been used as VLC receivers; however, they are intended to capture frames at relatively low speeds and their architectures do not translate well for receiving multiple high-rate VLC streams. Thus we consider new techniques to optimize imaging receivers to meet the capacity requirements of multiple SM streams.
In this paper, we propose token-based pixel selection (TBPS) for CMOS image sensors as a scalable alternative to mitigate this decrease in sampling rate. We show that in many cases, TBPS-based image sensors sample transmissions several times more frequently than windowing image sensors, yielding higher VLC data rates. Assuming the same reset, integration, and read times, TBPS always performs as well as, and often better than, windowing.
Though there has been a lot of interest in Visible Light Communication (VLC) in recent years, a reference platform based on commercial off-the-shelf components is still missing. We believe that an open-source platform would lower the barriers of entry to VLC research and help the VLC community gain momentum. In this paper we take an initial step toward the goal of a VLC reference platform - OpenVLC, and present our design and implementation. Built around a credit-card-sized embedded Linux platform with an LED front-end, OpenVLC offers a basic physical layer, a set of essential medium access primitives, as well as interaction with Internet protocols. We investigate the performance of OpenVLC and show how it can be used along with standard networking diagnostics tools.
We present HiLight, a new form of screen-camera communication without the need of any coded images (e.g. barcodes) for off-the-shelf smart devices. HiLight hides information underlying any images shown on a LED or an OLED screen, so that camera-equipped smart devices can fetch the information by turning their cameras to the screen. HiLight achieves this by leveraging the orthogonal transparency (alpha) channel, a well-known concept in computer graphics, to embed bits into pixel translucency changes without the need of modifying pixel color (RGB) values. We demonstrated HiLight's feasibility using smartphones. By offering an unobtrusive, flexible, and lightweight communication channel between screens and cameras, HiLight opens up opportunities for new HCI and context-aware applications to emerge, e.g. smart glass communicates with screens for additional personalized information to realize augmented reality.
After years of development, cost-effective, energy-efficient, and long-lasting solid-state lighting technology is finally a viable alternative to incandescent and fluorescent lights. Unfortunately, the remarkable march of semiconductor technology into the lighting industry is almost entirely in the form of a substitute good - one kind of lighting technology that replaces another - but this, we argue, squanders a unique opportunity for lighting to enable a bevy of new applications. In this paper, we discuss applications in health, energy efficiency, entertainment, communications, indoor positioning, device configuration, and time synchronization. We then prototype several of the indoor applications to explore a software-defined lighting (SDL) architecture that could support them.
Using our prototyped applications, we next take a primitive stab at demonstrating application coexistence, multiplexing multiple applications on a single lighting network. A major question raised by this effort is how to multiplex these various applications in a more principled manner on a shared lighting infrastructure whose primary role is illumination (implying that any human-perceptible flicker or flashing will be unacceptable). Looking ahead, we draw inspiration from software-defined networking's approach to sharing the network, and software-defined radios' approach to processing waveforms, to sketch the beginnings of an SDL architecture and its application programming interfaces.
With the rapid proliferation of camera-equipped smart devices (e.g., smartphones, pads, tablets), visible light communication (VLC) over screen-camera links emerges as a novel form of near-field communication. Such communication via smart devices is highly competitive for its user-friendliness, security, and infrastructure-less (i.e., no dependency on WiFi or cellular infrastructure). However, existing approaches mostly focus on improving the transmission speed and ignore the transmission reliability. Considering the interplay between the transmission speed and reliability towards effective end-to-end communication, in this paper, we aim to boost the throughput over screen-camera links by enhancing the transmission reliability. To this end, we propose RDCode, a robust dynamic barcode which enables a novel packet-frame-block structure. Based on the layered structure, we design different error correction schemes at three levels: intra-blocks, inter-blocks and inter-frames, in order to verify and recover the lost blocks and frames. Finally, we implement RDCode and experimentally show that RDCode reaches a high level of transmission reliability (e.g., reducing the error rate to 10%) and yields a at least doubled transmission rate, compared with the existing state-of-the-art approach COBRA.
We explore the indoor positioning problem with unmodified smartphones and slightly-modified commercial LED luminaires. The luminaires-modified to allow rapid, on-off keying-transmit their identifiers and/or locations encoded in human-imperceptible optical pulses. A camera-equipped smartphone, using just a single image frame capture, can detect the presence of the luminaires in the image, decode their transmitted identifiers and/or locations, and determine the smartphone's location and orientation relative to the luminaires. Continuous image capture and processing enables continuous position updates. The key insights underlying this work are (i) the driver circuits of emerging LED lighting systems can be easily modified to transmit data through on-off keying; (ii) the rolling shutter effect of CMOS imagers can be leveraged to receive many bits of data encoded in the optical transmissions with just a single frame capture, (iii) a camera is intrinsically an angle-of-arrival sensor, so the projection of multiple nearby light sources with known positions onto a camera's image plane can be framed as an instance of a sufficiently-constrained angle-of-arrival localization problem, and (iv) this problem can be solved with optimization techniques. We explore the feasibility of the design through an analytical model, demonstrate the viability of the design through a prototype system, discuss the challenges to a practical deployment including usability and scalability, and demonstrate decimeter-level accuracy in both carefully controlled and more realistic human mobility scenarios.
Despite the growing interest in Visible Light Communication (VLC), a
reference networking platform based on commercial off-the-shelf components is
not available yet. An open-source platform would lower the barriers to entry to
VLC network research and help the VLC community gain momentum. We introduce
OpenVLC, an open-source VLC research platform based on software-defined
implementation. Built around a credit-card-sized embedded Linux platform with a
simple opto-electronic transceiver front-end, OpenVLC offers a basic physical
layer, a set of essential medium access primitives, as well as interoperability
with Internet protocols. We investigate the performance of OpenVLC and show
examples of how it can be used along with standard network diagnostics tools.
Our software-defined implementation can currently reach throughput in the order
of the basic rate of IEEE 802.15.7 standard. We discuss several techniques that
researchers and engineers could introduce to improve the performance of OpenVLC
and envision several directions that can benefit from OpenVLC by adopting it as
a reference platform.
A two phase hybrid algorithm for estimating the location of a mobile node, which has the capability of measuring signal strength, azimuth, and elevation, in a smart space environment over the visible light channel is proposed. In contrast to conventional triangulation approaches which are performed in a simplified plane, the smart room architecture requires a non-planar solu-tion due to the illumination requirement. Furthermore, conventional triangulation approaches can at times produce numerically ill-defined solutions, thereby prohibiting a notion of target location. Instead of solely relying on triangulation, the mobile nodes estimate their locations through a two phase approach in which they firstly exploit the signal strength observables with unique IDs to establish a coarse estimate, and secondly use the azimuth and elevation observables to establish a fine estimate. In many cases, the fine estimate will improve upon the coarse estimate; however when triangulation fails, the algorithm yields the coarse estimate rather than a localization failure. Since the environment model relies on the primary requirement of adequate illumination, the num-ber of LED anchors and transmit power for communication functions are determined. Simulation results confirm the effectiveness of the hybrid two phase localization approach in a smart space in-door environment by having a median coarse phase accuracy of 34.88 cm and a fine phase median accuracy of 13.95 cm.
With the emergence of Light Emitting Diodes (LEDs), Visible Light Communication (VLC) has become an emerging technology for short range data communication. In this paper, a complete VLC software defined radio (SDR) transceiver is implemented on National Instrument (NI) cDAQ modules programmed in LabVIEW/MATLAB. The transceiver design mainly consists of VLC transmitter, receiver and interfacing of cDAQ modules. The major blocks of VLC transmitter comprise Optical Code Division Multiple Access (OCDMA) to improve the signal quality. The novelty in the designed prototype is that it is capable of compensating errors over a distance of 1 meter in a brightly lit room. Over and above physical system, simulation programs are also developed to investigate the impact of line-ofsight (LOS) VLC channel. In order to investigate VLC channel, Bit-Error-Rate (BER) performance is carried out to compare the proposed system with traditional VLC system.
2D barcodes have enjoyed a significant penetration rate in mobile applications. This is largely due to the extremely low barrier to adoption-almost every camera-enabled smartphone can scan 2D barcodes. As an alternative to NFC technology, 2D barcodes have been increasingly used for security-sensitive mobile applications including mobile payments and personal identification. However, the security of barcode-based communication in mobile applications has not been systematically studied. Due to the visual nature, 2D barcodes are subject to eavesdropping when they are displayed on the smartphone screens. On the other hand, the fundamental design principles of 2D barcodes make it difficult to add security features. In this paper, we propose SBVLC-a secure system for barcode-based visible light communication (VLC) between smartphones. We formally analyze the security of SBVLC based on geometric models and propose physical security enhancement mechanisms for barcode communication by manipulating screen view angles and leveraging user-induced motions. We then develop three secure data exchange schemes that encode information in barcode streams. These schemes are useful in many security-sensitive mobile applications including private information sharing, secure device pairing, and contactless payment. SBVLC is evaluated through extensive experiments on both Android and iOS smartphones.
Wireless networks based on visible light communication (VLC) are often considered to be resilient to eavesdropping by design, since light cannot penetrate most walls and objects. In this paper, we experimentally study the ability of a VLC eavesdropper to intercept and decode a transmission even while being outside of the direct beam. We design a testbed using software defined radios (SDRs) and evaluate different VLC eavesdropping scenarios. We find that a small gap under a door can be sufficient for an eavesdropper to decode high-order modulated (DCO-OFDM 64-QAM) reflected signals outside of a room. Likewise, neither Victorian keyholes nor window coatings provide any significant protection against information leakage to the outside. Furthermore, eavesdroppers located in the same room but not facing the sender can profit from reflections on walls.
Mobile devices are shrinking their form factors for portability, but user-mobile interaction is becoming increasingly challenging. In this paper, we propose a novel system called Okuli to meet this challenge. Okuli is a compact, low-cost system that can augment a mobile device and extend its interaction workspace to any nearby surface area. Okuli piggybacks on visible light communication modules, and uses a low-power LED and two light sensors to locate user's finger within the workspace. It is built on a light propagation/reflection model that achieves around one-centimeter location precision, with zero run-time training overhead. We have prototyped Okuli as an Android peripheral, with a 3D-printed shroud to host the LED and light sensors. Our experiments demonstrate Okuli's accuracy, stability, energy efficiency, as well as its potential in serving virtual keyboard and trackpad applications.
We analyze the error performance of overlapping multipulse pulse position modulation (OMPPM) in optical direct-detection channel with existing noise. Moreover we analyze the error performance of trellis-coded OMPPM with the small overlap index N = 2 in optical direct-detection channel to achieve significant coding gains over uncoded PPM, uncoded MPPM and the trellis coded overlapping PPM (OPPM) with the same pulsewidth. First we analyze the symbol error probability of OMPPM in both the quantum-limited case and the quantum and background noise case by using the distance defined as the number of nonoverlapped pulsed chips between symbols. Second by using this distance, we partition the OMPPM signals and apply the four-state and the eight-state codes described by Ungerboeck, to OMPPM. It is shown that the trellis coding over OMPPM is effective in optical direct-detection channel: the eight-state trellis coded (4,2,2) OMPPM can achieve gains of 3.92 dB and 3.23 dB over uncoded binary PPM in the quantum-limited case and in the quantum and background noise case with noise photons per slot time is one, respectively.
Overlapping multi-pulse pulse position modulation (OMPPM) is a modulation scheme having higher capacity and cutoff rate than other conventional modulation schemes when both off-duration between pulses shorter than a laser pulsewidth and resolution better than a laser pulsewidth are realized [1], [2]. In Refs. [1], [2] erasure events of a few chips that can be decoded correctly is defined as an erasure event. This results in lower bounds on the performance of OMPPM in optical-direct-detection channel in quantum limited case. This paper analyzes more exact performance of OMPPM in optical direct-detection channel in quantum limited case when both off-duration between pulses shorter than a laser pulsewidth and resolution better than a laser pulsewidth are realized. First we derive the error probability of OMPPM with considering what chips are detected or erased. Then we derive the capacity and the cutoff rate of OMPPM using the error probability. It is shown that OMPPM outperforms on-off keying (OOK), pulse position modulation (PPM), multipulse PPM (MPPM), and overlapping PPM (OPPM) in terms of both capacity and cutoff rate for the same pulsewidth and the same duty cycle. Moreover, it is shown that OMPPM with fewer slots and more pulses per block has better cutoff rate performance when the average received power per slot is somewhat large.
Unlike traditional radio frequency communication of con- sumer devices, the\optical antenna"direction of Visible Light Communication (VLC), i.e., the Field-Of-View (FOV), varies greatly from device to device. This encompasses wide FOVs of ambient infrastructure and directional FOVs of light emit- ted by low-end embedded devices. This variety of light wave propagation can severely affect the transmission reliability, despite \pointing" devices to each other may seem enough for a reliable link. In particular, the fact that FOVs are un- known makes traditional access protocols in VLC unreliable in presence of interference among nodes of different FOVs and exacerbates the hidden-node problem. In this paper, we propose a Carrier Sensing Multiple Access/Collision De- tection&Hidden Avoidance (CSMA/CD-HA) Medium Ac- cess Control protocol for a network where each node solely uses one Light Emitting Diode (LED) to transmit and re- ceive data. The CSMA/CD-HA can enable in-band intra- frame bidirectional transmission with just one optical an- tenna. The key idea is to exploit the intra-frame data sym- bols without emission of light to introduce an embedded communication channel. This approach enables the trans- mission of additional data while receiving in the same opti- cal channel and it makes the communication robust to dif- ferent types of FOVs. We build a software-deffned embed- ded platform running on Linux operating system, implement the CSMA/CD-HA protocol, and evaluate its performance through experiments. Results show that collisions caused by hidden nodes can be reduced and our protocol can increase the saturation throughput by nearly up to 50% and 100% under the two-node and four-node scenarios, respectively.
A precoding multi-user MIMO model was proposed for the multi-user indoor visible light communication system. The multi-user interference was eliminated by data pre-processing in transmitter, leading to the reduction of complexity and power consumption of terminals in the VLC system. Based on a 4×[2, 2] indoor MU-MIMO VLC system, the limitation of block diagonalization precoding algorithm in VLC system was figured out. The corresponding solution by utilizing receivers with different field of view was analyzed. The impact of the terminals' location to BER and SNR performances of the proposed system was also investigated. Based on the numerical results of the proposed indoor VLC system, the terminals can achieve 100 Mb/s at a BER of 10-6 in the most indoor area when single LED chip's power is 10 mW.
This paper presents results of a practical implementation of a spatial shift keying (SSK) visible light communication (VLC) system. This is the first practical proof-of-concept realtime implementation of SSK for VLC to the best knowledge of the authors. The system uses four transmitter light emitting diodes (LEDs) to encode information, and four receiver photo diodes (PDs) to decode the spatial signatures and decode the incoming data signal. The achieved bit error ratio (BER) of less than 2 × 10-3 allows for error-free communication if forward error correction (FEC) is to be applied. The main challenge with practical implementations of SSK in VLC is identified, namely maintaining symbol separation in the received constellation, and solutions are proposed.
RF wireless communications will be unable to meet all the demands for wireless capacity that will be faced in the future, and some of these will be met using optical frequencies. In this chapter we outline the key characteristics of Optical Wireless (OW) communications, contrast it with Radio Frequency (RF) techniques and discuss how cooperation between the two techniques might improve the capabilities of both.
Visible light communications is an energy efficient and cost effective solution for indoor wireless connectivity. In this paper we explore algorithms for supporting many users concurrently by optimizing the use of individual LEDs in each luminary. The directionality of LEDs is considered when assigning multiple LEDs to a user, forming a multiple input single output (MISO) system. Exploiting the spatial separation of detectors, MISO techniques using code division multiple access and minimum mean square error detection can offer high performance to simultaneous users while preserving the properties of the lighting system, such as spatially and temporally continuous dimmable illumination.
Multiple input and multiple output (MIMO) technique offers advantage of high data rate parallel transmission for indoor visible light communication (VLC) systems. As multiple decentralized user terminals are generally employed in typical indoor environment, the main difficulty for multi-user MIMO indoor VLC systems lies in the separation of data for different user terminals. We have proposed a linear precoding multi-user (MU) MIMO indoor VLC system to eliminate multi-user interference (MUI), by utilizing block diagonalization (BD) algorithm. However, nonlinear Tomlinson-Harashima precoding (THP) algorithm is generally considered as much better scheme in a practical MIMO system. Besides, channel capacity based on THP algorithm is better than that of BD precoding algorithm. Therefore, in this paper, we utilize THP optimization scheme to eliminate MUI in MU-MIMO indoor VLC system. The performances of conventional THP algorithm and THP optimization scheme in VLC systems are investigated. In addition, based on the limitation analysis of THP algorithm in VLC system, optical detectors with different fields of view (FOV) are utilized to further improve system performance. Numerical simulation results show that nonlinear precoding based on THP algorithm can achieve better BER performance than that with linear BD precoding.
Future electric lights will be comprised of white LEDs (Light Emitting Diodes). White LEDs with a high power output are expected to serve in the next generation of lamps. In this paper, an indoor visible data transmission system utilizing white LED lights is proposed. In the proposed system, these devices are used not only for illuminating rooms but also for an optical wireless communication system. This system is suitable for private networks such as consumer communication networks. However, it remains necessary to investigate the properties of white LEDs when they are used as optical transmitters. Based on numerical analyses and computer simulations, it was confirmed that the proposed system could be used for indoor optical transmission.
Visible Light Communication (VLC) is an emerging field in Optical Wireless Communication (OWC) which utilizes the superior modulation bandwidth of Light Emitting Diodes (LEDs) to transmit data. In modern day communication systems, the most popular frequency band is Radio Frequency (RF) mainly due to little interference and good coverage. However, the rapidly dwindling RF spectrum along with increasing wireless network traffic has substantiated the need for greater bandwidth and spectral relief. By combining illumination and communication, VLC provides ubiquitous communication while addressing the shortfalls and limitations of RF communication. This paper provides a comprehensive survey on VLC with an emphasis on challenges faced in indoor applications over the period 1979-2014. VLC is compared with Infrared (IR) and RF systems and the necessity for using this beneficial technology in communication systems is justified. The advantages of LEDs compared to traditional lighting technologies are discussed and comparison is done between different types of LEDs currently available. Modulation schemes and dimming techniques for indoor VLC are discussed in detail. Methods needed to improve VLC system performance such as filtering, equalization, compensation and beamforming are also presented. The recent progress made by various research groups in this field is discussed along with the possible applications of this technology. Finally, the limitations of VLC as well as the probable future directions are presented.
In recent years, the rapid growth of visible light communications (VLC) is driven the interest into new applications of this technology. While single-user VLC systems are widely studied in the literature, less attention is given to multiuser scenarios which are likely to be deployed. Thus, this paper studies a new low-complexity multiuser structure for indoor VLC systems using RGB channels. In this scheme, a time-based approach is employed to separate the users' signals which is combined with a three-dimensional signal constellation design to enhance the throughput on each user. The uncomplicated architecture of this multiuser system proves to be effective and appealing for low-cost implementations such as wireless sensor networks. Numerical simulations are carried out to evaluate the performance of the proposed scheme.
Spatial modulation (SM) and spatial multiplexing (SMP) are two multiple-input multiple-output (MIMO) techniques for transmitting data over an indoor optical wireless channel. Receivers for SM and SMP can be of the non-imaging type, in which case the channel matrix coefficients can be highly correlated, or of the imaging type, which can reduce the degree of correlation and improve overall system performance. In this work, we propose a new framework to analyze the performance of imaging MIMO systems. This framework is applied to characterize the performance of SM and SMP under both imaging and non-imaging receivers. Results of our analysis indicate that imaging receivers can provide significant signal-to-noise ratio (SNR) improvements up to 45dB under SM and SMP as compared to the use of non-imaging receivers. Finally, the application of the proposed analysis framework indicates specific design principles to optimize imaging receiver parameters.
This paper focuses on transmit beamforming for multiple-input multiple-output optical wireless communication (OWC) systems with intensity modulation and direct detection (IM/DD). OWC with IM/DD requires the transmitted signals to be nonnegative, for which existing beamforming schemes developed for radio frequency systems cannot be applied directly. We propose effective schemes for OWC over frequency flat and frequency selective channels. For frequency flat fading, the property of the beamforming vector is derived. For frequency selective fading, bit-error rate performances of the proposed scheme with zero-forcing and minimum mean-square error frequency domain equalization receivers are derived, and a suboptimal beamforming vector for frequency selective fading channels is proposed. Compared with asymmetrically clipped optical orthogonal frequency division multiplexing based frequency domain beamforming, the proposed scheme needs much less feedback information and has a better error performance.
In future visible light communication (VLC) systems, networked multi-cell operation is required to achieve seamless coverage and high data rate in typical indoor environments. We refer to this type of cellular network as optical atto-cell network. In such network, co-channel interference (CCI) between adjacent optical atto-cells limits the performance of the network. In order to maximise system throughput and improve signal quality in the whole coverage area, it is necessary to mitigate CCI. In this paper, the concept of multi-point joint transmission (JT) is adapted to a VLC cellular network. It can generally be described as concurrent data transmission from multiple cooperating base stations (BSs) to a mobile station (MS). In a VLC JT system, strong CCI is avoided by co-ordinated transmission and, in addition, we exploit a particular characteristic of intensity modulation (IM) systems. This is that signals always superimpose constructively which is in stark contrast to radio frequency (RF)-based systems. Therefore, the cell-edge user signal to interference plus noise ratios (SINRs) can be improved. The results show that the JT scheme improves the median SINR by 16.4 dB compared to a full frequency reuse system. Additionally, a JT system exhibits a 67.6% improvement in terms of median system throughput compared to a static resource partitioning system with a reuse factor of 3.
Motivated by the looming radio frequency (RF) spectrum crisis, this paper aims at demonstrating that optical wireless communication (OWC) has now reached a state where it can demonstrate that it is a viable and matured solution to this fundamental problem. In particular, for indoor communications where most mobile data traffic is consumed, light fidelity (Li-Fi) which is related to visible light communication (VLC) offers many key advantages, and effective solutions to the issues that have been posed in the last decade. This paper discusses all key component technologies required to realize optical cellular communication systems referred to here as optical attocell networks. Optical attocells are the next step in the progression towards ever smaller cells, a progression which is known to be the most significant contributor to the improvements in network spectral efficiencies in RF wireless networks.
Cameras are ubiquitous and increasingly being used not just for capturing images but also for communicating information. For example, the pervasive QR codes can be viewed as communicating a short code to camera-equipped sensors and recent research has explored using screen-to-camera communications for larger data transfers. Such communications could be particularly attractive in pervasive camera based applications, where such camera communications can reuse the existing camera hardware and also leverage from the large pixel array structure for high data-rate communication. While several prototypes have been constructed, the fundamental capacity limits of this novel communication channel in all but the simplest scenarios remains unknown. The visual medium differs from RF in that the information capacity of this channel largely depends on the perspective distortions while multipath becomes negligible. In this paper, we create a model of this communication system to allow predicting the capacity based on receiver perspective (distance and angle to the transmitter). We calibrate and validate this model through lab experiments wherein information is transmitted from a screen and received with a tablet camera. Our capacity estimates indicate that tens of Mbps is possible using a smartphone camera even when the short code on the screen images onto only 15% of the camera frame. Our estimates also indicate that there is room for at least 2.5x improvement in throughput of existing screen - camera communication prototypes.
Visible Light Communication (VLC) is a fast-growing technology that provides free-space wireless communications using LEDs and photodiodes. As LED becomes common in automotive lighting, Vehicular VLC (V2LC) becomes a new and low-cost solution to implement vehicle-to-vehicle (V2V) communications, in order to support many new safety and infotainment applications. In this paper, we take an experimental approach to measure the distribution of V2LC link duration. A video recorder was mounted on a taxi car while it was driven around the city, and the recorded video was post-processed to identify the taillights of other vehicles. Then, the duration of a taillight that stays in the video can be used as an approximation of the link duration of a V2LC link, if some vehicles were equipped with VLC-capable taillights. Our measurement results suggest that on average the V2LC link duration is on the order of several seconds, while the numbers could significantly vary in different scenarios. It was also found that generalized Pareto distribution can be used to model the V2LC link duration. Finally, the empirical distributions of link duration reported in this paper will be useful for future system design and performance evaluation.
As an alternative to NFC technology, 2D barcodes have been increasingly used for security-sensitive applications including payments and personal identification. However, the security of barcode-based communication in mobile applications has not been systematically studied. Due to the visual nature, 2D barcodes are subject to eavesdropping when they are displayed on the screen of a smartphone. On the other hand, the fundamental design principles of 2D barcodes make it difficult to add security features. In this paper, we propose SBVLC - a secure system for barcode-based visible light communication (VLC) between smartphones. We formally analyze the security of SBVLC based on geometric models and propose physical security enhancement mechanisms for barcode communication by manipulating screen view angles and leveraging user-induced motions. We then develop two secure data exchange schemes. These schemes are useful in many security-sensitive mobile applications including private information sharing, secure device pairing, and mobile payment. SBVLC is evaluated through extensive experiments on both Android and iOS smartphones.
We experimentally demonstrated a high-speed multi-user multi-carrier code-division multiple access (MC-CDMA) visible light communication (VLC) system. By employing a commercially available red light emitting diode (LED) and an avalanche photo diode (APD), we achieved a 16-user VLC system enabled by MC-CDMA, pre- and post-equalization, with an overall bit rate of 750 Mb/s over 1.5 m free-space transmission. The measured bit error ratio (BER) of each user is below the 7% pre-forward-error-correction (pre-FEC) threshold of 3.8×10−3.
Recent WiFi standards use Channel State Information (CSI) feedback for better MIMO and rate adaptation. CSI provides detailed information about current channel conditions for different subcarriers and spatial streams. In this paper, we show that CSI feedback from a client to the AP can be used to recognize different fine-grained motions of the client. We find that CSI can not only identify if the client is in motion or not, but also classify different types of motions. To this end, we propose APsense, a framework that uses CSI to estimate the sensor patterns of the client. It is observed that client's sensor (e.g. accelerometer) values are correlated to CSI values available at the AP. We show that using simple machine learning classifiers, APsense can classify different motions with accuracy as high as 90%.
Screen-to-camera visible-light communication links are fundamentally limited by inter-symbol interference, in which the camera receives multiple overlapping symbols in a single capture exposure. By determining interference constraints, we are able to decode symbols with multi-bit depth across all three color channels. We present Styrofoam, a coding scheme which optimally satisfies the constraints by inserting blank frames into the transmission pattern. The coding scheme improves upon the state-of-the-art in camera-based visible light communication by: (1) ensuring a decode with at least half exposure of colored multi-bit symbols, (2) limiting decode latency to two transmission frames, and (3) transmitting 0.4 bytes per grid block at the slowest camera's frame rate. In doing so, we outperform peer unsynchronized VLC transmission schemes by 2.9x. Our implementation on smartphone displays and cameras achieves 69.1 kbps.
We propose for the first time an integrated Visible Light Communication (iVLC) system, which combines scalable VLC networking and accurate VLC sensing of mobile users. To meet this goal, we envision using modulated LED lights for communications between networked devices, while at the same time using the very same lights to accurately identify and track users, and importantly, sense and infer their gestures (e.g., pointing to an object in the room) as a means of collecting user analytics and enabling interactions with objects in smart spaces. Enabling the iVLC vision requires reliable VLC networking and robust VLC sensing. We discuss the key research components and open challenges in realizing this vision. By combining VLC networking and sensing, iVLC opens the way for a new class of context-aware applications and a new HCI paradigm not possible before.
Existing code designs for display-camera based visual communication all have an all-or-nothing behavior, i.e., they assume the entire code must be decoded. However, diverse operational conditions due to device hardware diversity (in camera resolution and frame rate) and distance range motivate more scalable designs. In this paper, we borrow the notion of hierarchical modulation from traditional RF communication, and design Strata, a layered coding scheme for visual communication. Strata can support a range of frame capture resolutions and rates, and deliver information rates correspondingly. Strata embeds information at multiple granularity into the same code area spatially or the same frame interval temporally. It ensures all layers are decodable independently, by controlling the amount of interference between adjacent layers. Further, our design is recursive and extends readily to generate more layers. Compared with existing codes, it significantly extends the operational range, though at the expense of less capacity than a single-layer code.
Prior work in RF-based positioning has mainly focused on discovering the absolute location of an RF source, where state-of-the-art systems can achieve an accuracy on the order of tens of centimeters using a large number of antennas. However, many applications in gaming and gesture based interface see more benefits in knowing the detailed shape of a motion. Such trajectory tracing requires a resolution several fold higher than what existing RF-based positioning systems can offer.
This paper shows that one can provide a dramatic increase in trajectory tracing accuracy, even with a small number of antennas. The key enabler for our design is a multi-resolution positioning technique that exploits an intrinsic tradeoff between improving the resolution and resolving ambiguity in the location of the RF source. The unique property of this design is its ability to precisely reconstruct the minute details in the trajectory shape, even when the absolute position might have an offset. We built a prototype of our design with commercial off-the-shelf RFID readers and tags and used it to enable a virtual touch screen, which allows a user to interact with a desired computing device by gesturing or writing her commands in the air, where each letter is only a few centimeters wide.