Visible Light Communication Networks Research Articles

MSAM: Modular Statistical Analytical Model for MAC and Queuing Latency of VLC Networks under ICS Conditions

Visible Light Communication (VLC) offers distinctive advantages over conventional radio frequency; wide unlicensed spectrum, resistance to electrometric interference and low susceptibility to security risks, are few to name. Excitingly, VLC becomes a cornerstone in several communication systems such as light fidelity, optical camera communication and the Internet of Radio Light. Most of these networks adopt the Carrier Sensing Multiple Access-Collision Avoidance (CSMA-CA) of IEEE 802.15.7, the official standard for the VLC, as a Medium Access Control (MAC) protocol. Motivated by the crucial roles of MAC in shaping the performance of the VLC and the wide variety of operational conditions demanded by the enormous applications, this paper proposes a Modular Statistical Analytical Model (MSAM). The fundamental approach of MSAM is to segregate the interacting stochastic processes imposed by the CSMA-CA protocol into a set of its elementary subprocesses. The MSAM then synthesises these processes in such a way that quantifies their mutual dependency without making a strict assumption on their characteristics; thus, different operational conditions can be assessed without a need to reconstruct the model. Besides, MSAM employs the radiometry and photometry of VLC to derive mathematical expressions describing the hidden and exposed nodes from which the Imperfect Carrier Sensing (ICS) conditions are defined. The MSAM exploits statistical and queuing theorems to model a VLC as a network of G/G/1 queues from which several probability distributions, characterising the operations of VLC from different perspectives, are derived. Inter-departure, queuing, service time and successful service time are the main distributions in conjunction with throughput, total delay, probability of exposed and hidden node collisions, which are the main outputs of MSAM. Validation for the integrity of the MSAM under different scenarios is carried out by conducting a head-to-head comparison between its results and simulation outcomes.

LED adaptive deployment optimization in indoor VLC networks

Driven by the continuous penetration of high data rate services and applications, a large amount of unregulated visible light spectrum is used for communication to fully meet the needs of 6th generation (6G) mobile technologies. Visible light communication (VLC) faces many challenges as a solution that complements existing radio frequency (RF) networks. This paper studies the optimal configuration of LEDs in indoor environments under the constraints of illumination and quality of experience (QoE). Based on the Voronoi tessellation(VT) and centroidal Voronoi tessellation (CVT) theory, combined with the Lloyd's algorithm, we propose two approaches for optimizing LED deployments to meet the illumination and QoE requirements of all users. Focusing on (i) the minimization of the number of LEDs to be installed in order to meet illumination and average QoE constraints, and (ii) the maximization of the average QoE of users to be served with a fixed number of LEDs. Monte Carlo simulations are carried out for different user distribution compared with hexagonal, square and VT deployment. The simulation results illustrate that under the same conditions, the proposed deployment approach can provide less LEDs and achieve better QoE performance.

On the Achievable Max-Min User Rates in Multi-Carrier Centralized NOMA-VLC Networks.

Visible light communications (VLC) is gaining interest as one of the enablers of short-distance, high-data-rate applications, in future beyond 5G networks. Moreover, non-orthogonal multiple-access (NOMA)-enabled schemes have recently emerged as a promising multiple-access scheme for these networks that would allow realization of the target spectral efficiency and user fairness requirements. The integration of NOMA in the widely adopted orthogonal frequency-division multiplexing (OFDM)-based VLC networks would require an optimal resource allocation for the pair or the cluster of users sharing the same subcarrier(s). In this paper, the max-min rate of a multi-cell indoor centralized VLC network is maximized through optimizing user pairing, subcarrier allocation, and power allocation. The joint complex optimization problem is tackled using a low-complexity solution. At first, the user pairing is assumed to follow the divide-and-next-largest-difference user-pairing algorithm (D-NLUPA) that can ensure fairness among the different clusters. Then, subcarrier allocation and power allocation are solved iteratively through both the Simulated Annealing (SA) meta-heuristic algorithm and the bisection method. The obtained results quantify the achievable max-min user rates for the different relevant variants of NOMA-enabled schemes and shed new light on both the performance and design of multi-user multi-carrier NOMA-enabled centralized VLC networks.

Dynamic Route Discovery Using Modified Grasshopper Optimization Algorithm in Wireless Ad-Hoc Visible Light Communication Network

In recent times, visible light communication is an emerging technology that supports high speed data communication for wireless communication systems. However, the performance of the visible light communication system is impaired by inter symbol interference, the time dispersive nature of the channel, and nonlinear features of the light emitting diode that significantly reduces the bit error rate performance. To address these problems, many environments offer a rich infrastructure of light sources for end-to-end communication. In this research paper, an effective routing protocol named the modified grasshopper optimization algorithm is proposed to reduce communication interruptions, and to provide alternative routes in the network without the need of previous topology knowledge. In this research paper, the proposed routing protocol is implemented and analyzed using the MATLAB environment. The experimental result showed that the proposed routing protocol adapts to dynamic changes in the communication networks, like obstacles and shadows. Hence, the proposed protocol achieved better performance in data transmission in terms of throughput, packet delivery ratio, end-to-end delay, and routing overhead. In addition, the performance is analyzed by varying the number of nodes like 50, 100, 250, and 500. From the experimental analysis, the proposed routing protocol achieved maximum of 16.69% and minimum of 2.20% improvement in packet delivery ratio, and minimized 0.80 milliseconds of end-to-end delay compared to the existing optimization algorithms.

A hybrid next-generation passive optical network and visible light communication for future hospital applications

The advancement in the latest healthcare technologies have shown a growing interest in 10/10 Gbps per channel hybrid next generation passive optical network (NG-PON) and visible light communication (VLC) networks to achieve the aim of future hospital applications. This paper investigates the use of hybrid time and wavelength division multiplexing PON (TWDM-PON), wavelength division multiplexing optical code division multiple access PON (WDM-OCDMA PON) using zero cross-correlation (ZCC) code and VLC for the hospitals scenario. The proposed bidirectional system is investigated for four TWDM, six WDM-OCDMA and three VLC information channels in terms of variable fiber length, bit rate, different OCDMA codes and multi-hospital systems. It is investigated that upstream channels performs better than downstream channels and provides the successful 10/10 Gbps hybrid system over 50 km fiber and 10 m VLC link serving 53 users in single hospital system. It also provides the high eye-height, optical signal to noise ratio (OSNR) and received power. Moreover, the performance of the proposed system can be further enhanced by using modified quadratic congruence (MQC) code and high transmission power. Also the comparative analysis with existing systems show the superiority of the hybrid NG-PON/VLC system using fiber/wireless links over the conventional radio access networks in healthcare applications.

A Cross-Layer Design for Dynamic Resource Management of VLC Networks

In this article, we propose a cross-layer resource management mechanism for an indoor multiuser visible light communication (VLC) access network. The physical layer builds upon DC-biased orthogonal frequency division multiple access. Channel state information at the physical layer serves as a performance indicator for better data rate opportunity while queue state information at medium access control layer provides the information about packet urgency. A packet based traffic arrival model is considered such that incoming packets with random inter arrival times join a separate queue dedicated to each user if the admission control accepts them, otherwise packets are dropped. We formulate and solve a stochastic cross-layer optimization problem to optimize the network resources under the constraints of queue stability and power to maximize the average system throughput. By using the Lyapunov optimization technique, we convert the long term time-average optimization problem into series of single time slot online problem. Then, we decompose the problem into independent sub problems and propose packet admission, resource (access point and subcarrier) allocation and power control solutions. We present simulation results to demonstrate the superiority of proposed scheme over existing solutions in the literature.

Lights and Shadows: A Comprehensive Survey on Cooperative and Precoding Schemes to Overcome LOS Blockage and Interference in Indoor VLC.

Visible light communications (VLC) have received significant attention as a way of moving part of the saturated indoor wireless traffic to the wide and unregulated visible optical spectrum. Nowadays, VLC are considered as a suitable technology, for several applications such as high-rate data transmission, supporting internet of things communications or positioning. The signal processing originally derived from radio-frequency (RF) systems such as cooperative or precoding schemes can be applied to VLC. However, its implementation is not straightforward. Furthermore, unlike RF transmission, VLC present a predominant line-of-sight link, although a weak non-LoS component may appear due to the reflection of the light on walls, floor, ceiling and nearby objects. Blocking effects may compromise the performance of the aforementioned transmission schemes. There exist several surveys in the literature focused on VLC and its applications, but the management of the shadowing and interference in VLC requires a comprehensive study. To fill this gap, this work introduces the implementation of cooperative and precoding schemes to VLC, while remarking their benefits and drawbacks for overcoming the shadowing effects. After that, the combination of both cooperative and precoding schemes is analyzed as a way of providing resilient VLC networks. Finally, we propose several open issues that the cooperative and precoding schemes must face in order to provide satisfactory VLC performance in indoor scenarios.

Design and Demonstration of a TDD-Based Central-Coordinated Resource-Reserved Multiple Access (CRMA) Scheme for Bidirectional VLC Networking

The sharply growing demand for increased transmission capacity and bandwidth in last meter and last mile access networks together with the commercialization of fifth generation (5G) wireless systems has been opening up new opportunities for non-radio frequency (RF)-based wireless technologies. Visible light communications (VLC) technology is a potential candidate for access networking in 5G, which offers a higher spectral efficiency than RF-based Femtocell networks by three orders of magnitude. This paper proposes an all wireless optical bidirectional VLC multiple access scheme for pure VLC network access points in terminals. Centralized coordination is adopted to reduce the system complexity. And reservation of resource is introduced to guarantee collision avoidance during data frame transmission. The proposed multiple access scheme introduces special system parameters to achieve the balance of system throughput and access latency. The feasibility of the proposed scheme is verified by both theoretical analysis and experimental investigation. We show that the proposed scheme is suitable for a bidirectional pure VLC access network and can be used as a supplement in the IEEE 802.11 bb for 5G+bidirectional VLC application scenarios.

Capacity Analysis of NOMA-Enabled Underwater VLC Networks

Visible light communication (VLC) has recently emerged as an enabling technology for high capacity underwater wireless sensor networks. Non-orthogonal multiple access (NOMA) has been also proven capable of handling a massive number of sensor nodes while increasing the sum capacity. In this paper, we consider a VLC-based underwater sensor network where a clusterhead communicates with several underwater sensor nodes based on NOMA. We derive a closed-form expression for the NOMA system capacity over underwater turbulence channels modeled by lognormal distribution. NOMA sum capacity in the absence of underwater optical turbulence is also considered as a benchmark. Our results reveal that the overall capacity of NOMA-enabled Underwater VLC networks is significantly affected by the propagation distance in underwater environments. As a result, effective wireless transmission at high and moderate spectral efficiency levels can be practically achieved in underwater environments only in the context of local area networks. Moreover, we compare the achievable capacity of NOMA system with its counterpart, i.e., orthogonal frequency division multiple access (OFDMA). Our results reveal that NOMA system is not only characterized by achieving higher sum capacity than the sum capacity of its counterpart, OFDMA system. But also, the distances between sensor nodes and the clusterhead for achieving the highest sum capacity in these two multiple access systems are different.

Joint Synchronization and Attocell Identification With Received Power Estimation in VLC Networks

Optical attocell networks building upon visible light communication (VLC) offer several advanced features including load balancing, mobility management etc. as in radio-frequency networks. Attocell identification is crucial to perform the features' functionalities. Attocells are allocated with identities and their own synchronization signals (SSs) are generated accordingly. The signal is periodically broadcasted and used for cell identification and synchronization in receiver side. In this letter, we revise SS design for VLC domain and propose a joint synchronization and cell identification including SS received power estimation mechanism. The performance of proposed mechanisms is then evaluated though Monte-Carlo simulations.

Review of advanced techniques for multi‐gigabit visible light communication

Visible light communication (VLC) is a promising candidate for future indoor wireless communication. Light emitting diodes (LEDs) are popular choices as transmitters for VLC, since they are energy efficient and have the ability to provide illumination and data transmission simultaneously. VLC is attractive for reasons such as security, the ability to use a licence free spectrum, and broad bandwidth. Previous review articles on VLC mainly focused on VLC network algorithms, implementation challenges, system design, applications, and physical layer technologies. Unlike the existing reviews, this study presents state-of-the-art VLC systems for high-speed data communication in the gigabit range and the techniques to achieve such high data rates. In addition, concepts such as LED modelling and fabrication process, recent commercial advancements of VLC products, and hybrid/heterogeneous networks to achieve high data rate are highlighted in this study. For this purpose, some key technologies of VLC systems, including channel equalisation from both transmitter and receiver sides, higher-order modulation techniques, wavelength division multiplexing, multiple input multiple output technology, LED modelling, and advanced fabrication processes are discussed. This study also covers recent advancements in commercialisation of VLC technology, and recent progress made by various research groups.

User Pairing, Link Selection, and Power Allocation for Cooperative NOMA Hybrid VLC/RF Systems

Despite the promising high-data rate features of visible light communications (VLC), they still suffer from unbalanced services due to blockages and channel fluctuation among users. This paper introduces and evaluates a new transmission scheme which adopts cooperative non-orthogonal multiple access (Co-NOMA) in hybrid VLC/radio-frequency (RF) systems, so as to improve both system sum-rate and fairness. Consider a network consisting of one VLC access point (AP) and multiple strong and weak users, where each weak user is paired with a strong user. Each weak user can be served either directly by the VLC AP, or via the strong user which converts light information received through the VLC link, and forwards the information to the weak user via the RF link. The paper then maximizes a network-wide weighted sum-rate, so as to jointly determine the strong-weak user-pairs, the serving link of each weak user (i.e., either direct VLC or hybrid VLC/RF), and the power of each user message, subject to user connectivity and transmit power constraints. The paper tackles such a mixed-integer non-convex optimization problem using an iterative approach. Simulations show that the proposed scheme significantly improves the VLC network performance (i.e., sum-rate and fairness) as compared to the conventional NOMA scheme.

Power Allocation and Link Selection for Multicell Cooperative NOMA Hybrid VLC/RF Systems

This letter proposes and optimizes a cooperative non-orthogonal multiple-access (Co-NOMA) scheme in the context of multicell visible light communications (VLC) networks to mitigate inter-cell interference. Consider a network where each access-point (AP) serves two users. In each cell, the weak user (cell-edge user) can be served either directly by the VLC AP, or through the strong user that decodes the weak user message and forwards it through the radio-frequency (RF) link. The paper then considers the problem of maximizing the sum-rate under quality-of-service constraints by allocating the powers of the messages and APs, and determining the links serving each weak user. The paper solves this non-convex problem by first finding closed-form solutions of the users' powers and link selection for fixed APs powers. The APs powers are then iteratively solved in an outer loop. Simulation results show that the proposed scheme improves the sum-rate and fairness as compared to non-orthogonal multiple-access (NOMA) scheme.

Support vector machine based machine learning method for GS 8QAM constellation classification in seamless integrated fiber and visible light communication system

Visible light communication (VLC) network over optical fiber has become a potential candidate in ultra-high speed indoor wireless communication. To mitigate signal distortion accumulated in optical fiber and VLC channel, we present to utilize support vector machine (SVM) for constellation classification in two kinds of geometrically-shaped 8QAM (quadrature amplitude modulation) seamless integrated fiber and VLC system. We introduce 4 sub-bands to simulate multi-user. Experimental results show that system performance can be significantly improved, and transmission at −2.5 dBm input optical power under 7% forward error correction (FEC) threshold can be realized employing Circular (7, 1) geometrically-shaped 8QAM and SVM. At overall capacity of 960 Mbps, Q-factor increases by up to 11.5 dB.

CoMP-Based Dynamic Handover for Vehicular VLC Networks

Visible light communication (VLC) has emerged as a potential wireless connectivity solution for infrastructure-to-vehicle networks where street lights can be configured to serve as access points. In this letter, we propose dynamic soft handover algorithm based on coordinated multipoint (CoMP) transmission. The proposed algorithm takes the rate of change in the received power as an input and accordingly revises the handover margin and time-to-trigger value without explicit information of the vehicle velocity. Our simulation results demonstrate that the proposed algorithm outperforms conventional CoMP and hard handover and maintains a stable signal quality regardless of vehicle velocity.

Beamforming Design for Secure MISO Visible Light Communication Networks With SLIPT

Visible light communication (VLC) is a promising technology for the next generation wireless communication systems due to its high spectral efficiency and energy efficiency. In this article, a secure multiple-input single-output (MISO) VLC network is studied, where simultaneous lightwave information and power transfer (SLIPT) is exploited to support multiple energy-limited devices tacking into account a practical non-linear energy harvesting model. The transmit power minimization and the minimum secrecy rate maximization problems are formulated under both perfect and imperfect channel state information, respectively. To further improve the user connectivity, those problems are also investigated in MISO-VLC networks with non-orthogonal multiple access (NOMA). To tackle these challenging non-convex problems, semidefinite program relaxation and $\mathcal {S}$ -Procedure are exploited. It is proved that optimal beamforming schemes can be obtained for the considered two types problems in MISO-VLC SLIPT networks, while a sub-optimal solution can be obtained for the transmit power minimization problem in those networks with NOMA. It is found that there is a non-trivial trade-off between the average harvested power and maximum-minimum secrecy rate. Moreover, it is shown that the performance achieved with NOMA outperforms that of conventional orthogonal multiple access in MISO-VLC SLIPT networks, despite the existence of imperfect channel state information.

Framework of IoT Services over Unidirectional Visible Lights Communication Networks

Visible Light Communication (VLC) has been noted as an emerging technology for communications in wireless local area networks. VLC provides some distinctive features over the conventional wireless access technologies, such as Wi-Fi, Bluetooth, or ZigBee. The most prominent feature of VLC is that it can provide more exact location information, since it is based on a particular light. In addition, VLC can reduce the frequency interferences from numerous wireless channels, since it uses a completely different radio frequency channel from the conventional wireless access technologies. Thus, VLC can be used for Internet-of-Things (IoT) services. Nevertheless, up to now, not enough studies on how to provide IoT services over VLC networks have been conducted. In this paper, we propose a framework to provide IoT services in VLC networks. In particular, we will consider the unidirectional VLC network, in which the downlink channel from the VLC transmitter to the VLC receiver is given by using VLC communication, whereas the uplink channel from the VLC receiver to the VLC transmitter is implemented by using another wireless access technology, such as Wi-Fi. This is because most of the VLC receivers, such as mobile phones, cannot support the uplink VLC communication. Based on the framework of IoT services over unidirectional VLC, in this paper, we also propose the VLC–IoT protocol (VIP) which is an application layer protocol for data transport with the session management functionality that can be used to effectively provide IoT services among IoT servers, VLC transmitters and VLC receivers in the networks. The proposed VIP protocol is implemented by using the Cooja simulator. For performance analysis, the proposed scheme is compared with the existing CoAP-based scheme that does not provide the session management. From a variety of simulation experiments, we see that the proposed scheme can provide lower data transmission and handover delays, compared to the existing scheme.

Proactive link handover deploying coordinated transmission for indoor visible light communications (VLC) networks

Abstract Visible Light Communications (VLC) is considered as an emerging technology for indoor wireless communications to achieve high-speed and secure data transmission. Instead of using radio frequency (RF) spectrum, VLC uses the visible light spectrum to perform lighting and communications functions simultaneously. Multiple access points VLC (multi-AP VLC) networks use ceiling access point (ceiling-AP) and desk access point (desk-AP) to provide both uniform and spot lighting in order to achieve full coverage and high spectral efficiency. Because mobile user equipment (UE) require seamless connectivity when moving, fast link handover between VLC access points (VLC-AP) has to be supported in the VLC networks. In this paper, we present a coordinated multi-channel transmission method (CMcT) used to improve quality of service (QoS) of cell-edge UEs and propose a novel proactive link handover scheme deploying the CMcT method for multi-AP VLC networks. Performance results obtained by computer simulation show that the proactive link handover scheme deploying the CMcT method can significantly improve user throughput and packet delay comparing with those of other link handover schemes.

A Novel Semi-Distributed OFDMA for Indoor Visible Light Communications

In this paper, a novel OFDMA architecture based on the characteristics of the indoor visible light communication network is introduced. It is characterized by a microcell structure and frequent terminal switching. The OFDM proposed in this paper adopts DCO-OFDM modulation technology, which is determined by the consideration of the nonlinear and non-negative signal transmission characteristics of LEDs, and the SLM algorithm is also introduced to reduce PAPR. The simulation results demonstrate that the SLM algorithm can effectively reduce the PAPR of DCO-OFDM, which increases the probability that the signal in the entire system is lower than the PAPR threshold. Compared with the SLM algorithm, its CDF probability is increased by about 40%, and the SNR is also improved by 2.5 dB. The proposed OFDMA is a semi-distributed structure that is controlled by the DME to allocate subcarriers to each AP, and each has the ability to allocate subcarriers independently. Based on this architecture, an idea of dynamic subcarrier allocation is proposed, and uses the optical power received by the terminal as the SIR index to allocate different subcarriers to different SIR terminals and optimize the utilization of resources. The results of the modeling and simulation indicate that when the subcarrier allocation algorithm and method of reducing PAPR via SLM are combined, the BER of the system is significantly improved; when the SNR is 13 dB, the BER can be reduced to less than 10-6. This method can help the system reach the perfect communication target with a lower SNR, allowing the system to achieve better BER performance with less power consumption.

Optimal Placement of Access Points in Cellular Visible Light Communication Networks: An Adaptive Gradient Projection Method

In this paper, a new approach toward the optimization of Access Point (AP) placement in cellular Visible light Communication (VLC) networks is proposed based on the projected gradient algorithm. The objective of the optimal placement problem is to maximize the average throughput of the network subject to constraints on the minimum illumination level and the minimum rate of the users. This optimization framework gives the enhanced AP deployment in case of users with static, nomadic, or completely mobile behavior. Taking the distribution of users, the receiver's field of view, reflection from walls and interference from neighboring APs into account makes the deployment problem complicated. To solve the arising intricate optimization problem, we derive analytical expressions for gradients of the objective and use them in the gradient ascent algorithm. The proposed adaptive gradient projection method then realizes the constraints. This method relaxes the projection onto a high dimensional space to planar projections, which are implemented using efficient tools from computational geometry. The proposed method eliminates the need for an intractable exhaustive search to find the optimal placement of VLC APs in cellular VLC networks, while it gives either exact optimum or very close approximations to the optimal placement. It is shown, with the aid of properties of convolution of parametric concave functions, that in some practical cases the objective function is unimodal and has no local optimum. Simulation results show a significant improvement in the throughput, SINR and outage probability of the system when the access points are deployed according to their optimized placement, determined by the algorithm. On the other hand, proper constraints on the minimum achievable rate and minimum illumination level improve the worst-case performance of the network to the desired extent.