Visible Light Communication Networks Research Articles

Speed-Adaptive PI Collection and PP Adjustment in Indoor VLC Network

In this paper, a novel adjustment algorithm of the position-predicted period (PP) in an indoor visible light communication (VLC) network is proposed. The algorithm is adaptive to the movement speed. It contains two key parts: speed-adaptive position information (PI) collection and speed-adaptive PP adjustment. By the user’s mobile characteristics, speed-adaptive PI collection is realized to lift prediction accuracy. By distribution characteristics of received power, speed-adaptive PP adjustment is achieved to avoid unnecessary predictions. By the access point (AP) selection, based on position prediction and the PP adjustment algorithm adaptive to movement speed, the user’s transmission quality under different movement speeds can be improved. Finally, by simulation, the effectiveness of this algorithm is demonstrated.

A dynamic multicast routing protocol for visible light communication networks

Due to the current challenges of wireless communications, optical wireless communications, like visible light communication (VLC), have become very popular in the last decade for local area networks. However, current VLC systems focus mainly on one-hop direct transmissions, ignoring that many networking applications require multicast communications. In this sense, we propose MCAST-VLC, a fully functional cross-layer dynamic multicast scheme over a dynamic routing protocol for VLC. MCAST-VLC considers the particular characteristics of the VLC as the need for group management, traffic isolation, a challenging multi-hop route discovery protocol, and a complex cross-layer VLC mechanism to maintain the proper system state. We evaluate our protocol following close real indoor VLC scenarios, previously discussed in the literature, where a light source in a room streams data to a few other VLC devices, and we extend our results numerically. Our results show that MCAST-VLC can handle considerably more network flows than a unicast VLC system under a negligible overhead.

Asynchronous Code Division Multiplexing-Based Visible Light Positioning and Communication Network Using Successive Interference Cancellation Decoding.

In the evolving landscape of sixth-generation wireless communication, the integration of visible light communication (VLC) and visible light positioning (VLP), known as visible light positioning and communication (VLPC), emerges as a pivotal technology. This study addresses the challenges of asynchronous code division multiplexing (ACDM) in VLPC networks, focusing on the enhancement of data transmission quality and positioning accuracy. Firstly, we propose an orthogonal pseudo-random code (OPRC) for ACDM-based VLP systems. Leveraging its excellent correlation properties, VLP signals preserve orthogonality even amidst asynchronous transmissions, achieving sub-centimeter average positioning errors. Next, by combining OPRC with successive interference cancellation decoding (SICD), we propose an enhanced ACDM-based VLPC system that utilizes OPRC for improved signal orthogonality and SICD for progressive elimination of multiple access interference (MAI) among VLPC signals. The results show substantial improvements in bit-error rate (BER) and positioning error (PE), approaching the performance levels observed in synchronized VLPC systems. Specifically, the SICD-OPRC scheme reduces average BER to 4.3 × 10-4 and average PE to 2.7 cm, demonstrating its robustness and superiority in complex asynchronous scenarios.

Optically powered FiWi system for B5G hybrid VLC/RF access networks

This paper proposes the concept and reports the demonstrator of an optically powered fiber/wireless (FiWi) system based on a hybrid visible light communication (VLC) and RF access network for beyond 5G (B5G) indoor applications. The power-over-fiber (PoF) technology is properly applied to simultaneously energize two components from the remote site, namely: a radio-over-fiber (RoF) module, which contains a photodetector and an RF amplifier; a red laser from the VLC system. The proposed PoF system is composed of a 500 m conventional multimode optical fiber (MMF) with a 62.5 μm core diameter, which enables the transmission of up to 12 W optical power with a power transmission efficiency (PTE) of 14%. In the proof of concept, 8.1 W optical power is generated to feed the 5G system components. Regarding the communication setup, a 5G new radio (5G NR) signal is initially transported through a RoF fronthaul, composed of 10 km of single-mode fiber (SMF), followed by the hybrid VLC/RF access network. The performance investigation of the B5G communication system is based on an analysis of the root mean square error vector magnitude (EVMRMS) parameter. Experimental results indicate 1.2 Gbps throughput in the VLC link using a 200 MHz bandwidth and 64-quadrature amplitude modulation (64-QAM), resulting in approximately 4.02% of EVMRMS. Moreover, the RF link at 3.5 GHz provides 360 Mbps with an EVMRMS of 2.67%. Finally, a comparison between the PoF system and conventional power supply validates the proposed approach's applicability for B5G wireless communications.

Time-division multiplexing wireless light communication network

Owing to emission-detection spectral overlap, a quantum well (QW) diode can detect shorter-wavelength photons emitted from another diode sharing the same QW active region. Therefore, a wireless light communication system can be established by using identical QW diodes that function separately as transmitters and receivers. Here, we investigate the irreversibility between light emission and detection of the QW diode and present a time-division multiplexing (TDM) visible light communication (VLC) network using five identical blue QW diodes that are defined by software as transmitters or receivers to achieve real-time TDM-integrated interconnection via the same optical paths. These results indicate the great potential of realizing an advanced TDM VLC network for diverse applications.

Outage and Rate Analysis for Industrial Internet of Things in Multitier Visible Light Communication Networks Inside Finite 3-D Space

Outage and Rate Analysis for Industrial Internet of Things in Multitier Visible Light Communication Networks Inside Finite 3-D Space

Experimental validation of the appropriate channel model for an indoor Visible Light Communication system

Visible light communication (VLC) is a technology with significant potential to revolutionize indoor communication performance and satisfy the demands of fifth-generation (5G) and beyond technologies. To achieve an efficient VLC system that delivers optimal performance and coverage, it is imperative to create a reliable channel model. As a result, this research is centered around the evaluation of existing channel models for planning the VLC network coverage within indoor environments. The primary focus of this study is to enforce three types of channel models, Line of Sight (LoS), Nakagawa’s first reflection model, and the Spherical model through MATLAB simulations and obtain simulation results by varying the distance parameter. Furthermore, this research intends to implement a physical prototype representing a real-world scenario, and thereby determine the nearest channel model that aligns with the physical measurements obtained from the physical prototype.

The Latency Performance Analysis and Effective Relay Selection for Visible Light Networks.

In visible light communication (VLC), the precise latency evaluation of wireless access networks and the efficient forwarding strategy of core networks are the crux for end-to-end reliability provisioning. Leveraging martingale theory, an elegant latency-bounded reliability analysis framework is studied for the VLC network. Considering the characteristic that VLC links are easy to block, the martingale of the service process is constructed. Based on the time shift features, the martingale process related to latency is proposed for the VLC system, which models the influence of entanglement between aggregate arrivals and random service on latency. A stopping time event about latency is defined. Renting the stopping time theory, a tight upper bound of the unreliability with regard to latency is derived. In the core network, a dynamic forward backhaul framework is proposed, which uses the relay selection algorithm based on back-pressure theory to improve data transmission quality. The theoretical latency-bounded reliability matches the simulation results well, which verifies the effectiveness of the proposed analysis framework, and the proposed relay selection algorithm can also improve network performance under data-intensive transmission.

An Emergency Message Routing Protocol for Improved Congestion Management in Hybrid RF/VLC VANETs

Unexpected traffic incidents cause safety concerns and intense traffic congestion on crowded urban road networks. Vehicular ad-hoc network (VANET)-aided Intelligent Transport Systems (ITS) aim to mitigate these risks through timely dissemination of alert messages. However, conventional Radio frequency (RF) mobile ad-hoc routing protocols are ill-suited for dynamic VANET environments due to high mutual interference, packet collisions, high end-to-end delay from frequent route discoveries, and periodic beaconing requirements. Fortunately, the quickly emerging Visible Light Communications (VLC) provide complementary short-range connectivity with high bandwidth and low interference. This paper proposes an efficient adaptive routing protocol for emergency messages in dense VANET scenarios leveraging a hybrid RF/VLC system. When an incident or congestion happens, the source vehicle disseminates the information to the incoming vehicles as quickly as possible using a combination of VLC and RF communication networks. Multi-hop relays extend the connectivity if the direct links are blocked. The coverage area is partitioned into zones based on road segments, intersections, and traffic flows. The Road Side Units (RSU)s are intelligently assigned to zones and they analyze the historical traffic data to characterize each zone and decide a response strategy. We also propose a congestion detection scheme that utilizes traffic simulations to forecast the clearance times under different response strategies. The highest-scoring strategy is selected based on the predicted impacts on travel time, emissions, and driver stress levels. The proposed algorithm adaptively uses the selected strategy to proactively alleviate the predicted congestion through optimized routing and control. Overall, the protocol maximizes safety and efficiency during emergencies by leveraging the hybrid RF/VLC, incorporating real-time congestion forecasting and dynamic rerouting into the response strategies.

Channel-Independent Quantum Mapping-Substitution OFDM-Based Spatial Modulation for Physical-Layer Encryption in VLC Networks

Physical-layer encryption has lately been highlighted as a promising security approach for visible light communications (VLC). Orthogonal frequency-division multiplexing (OFDM) is the main structural entity of multiple-carrier modulation in most modern communication systems, including vehicle ad hoc networks, 5G systems, and the Internet of Things. The integration of OFDM and spatial modulation (SM) can improve the capacity of low-complication VLC systems. Two common methods have been proposed for OFDM-based SM schemes: frequency-domain SM (FD-SM) and time-domain SM (TD-SM). TD-SM supports higher spectral efficiency than FD-SM with low complication. In this paper, we propose a physical-layer encryption method, referred to as channel-independent quantum mapping-substitution (CIQMS) TD-SM, for enhancing VLC's confidentiality. The random properties of the input data are used for generating dynamic cypher keys that are updated for each frame using hashing and stream cypher methods. The proposed approach performs four encryption operations: quantum noise stream cypher, substitution of radiated data symbols mapping, substitution of light-emitting-diode information mapping, and polarity encryption of time-domain OFDM subcarriers. The findings show that our CIQMS method provides a considerably higher secrecy rate than channel-dependent methods proposed in the literature. Also, it provides high robustness against both authorized and non-authorized eavesdroppers. In addition to that, the results show that the CIQMS method provides high confidentiality against several attacks, e.g., statistical attacks, chosen-/known-plaintexts, and brute-force attacks.

Visible light communication and WiFi hybrid networks based on dynamic resource allocation algorithm

Visible light communication and WiFi hybrid networks based on dynamic resource allocation algorithm

Homology Theory-Based Coverage Hole Localization and Area Estimation for Visible Light Communication Networks

Homology Theory-Based Coverage Hole Localization and Area Estimation for Visible Light Communication Networks

Low-Latency Network Slicing for VLC-Based Industrial Internet of Things: Superframe Duration Minimization and Delay Violation Probability Analysis

Visible light communication (VLC) is promising for the future application in industrial internet of things (IIoT) due to limited inter-user interference from directional transmission, which can provide a good guarantee for the delay and reliability of communication. In this work, we consider the model of a downlink indoor VLC network covered by multiple lighting emitting diodes (LEDs). We reduce the delay violation probability via minimizing the superframe duration, and analyze the delay violation probability based on the optimized superframe duration. We analyze the delay violation probability using stochastic network calculus (SNC). More specifically, we propose a low-complexity resource slicing scheme, and exploit LED layout characteristics to minimize the superframe duration. Then, assuming that the users are uniformly distributed in each served area, we obtain the achievable rate distribution for each served area. Our results show that the proposed resource slicing scheme yields a shorter superframe duration than random scheme and the delay violation probability increases with traffic arrival rate, LED spacing and the coverage radius.

Improved physical layer secrecy fairness in a realistic indoor NOMA VLC network under users’ mobility

This paper investigates the improvement of the secrecy rate fairness in a cellular non-orthogonal multiple access (NOMA) visible light communication (VLC) network. We formulate the users’ secrecy rate by taking into account the users (legitimate and illegitimate) mobility according to the random way-point (RWP) model. We propose an optimization problem to maximize the minimum secrecy rate for two legitimate users per cell, and then we generalize it for an arbitrary number of users. Moreover, utilizing secrecy considerations, we customize two well-known power allocation methods of fixed power allocation (FPA) and gain ratio power allocation (GRPA) as benchmarks for comparison of the proposed maximization power allocation method. Our numerical results demonstrate the superiority of the proposed power allocation algorithm compared with FPA and GRPA methods. Moreover, for the higher number of users, our results indicate the advantages of the proposed algorithm over modified FPA and GRPA methods. Finally, we investigate the effect of the optical receiver’s field of view fluctuations on the performance of the VLC network.

SLIPT-Enabled Multi-LED MU-MISO VLC Networks: Joint Beamforming and DC Bias Optimization

This paper studies a simultaneous lightwave information and power transfer (SLIPT)-enabled multi-user (MU) multiple input single output (MISO) visible light communication (VLC) network, where multiple user equipments (UEs) are simultaneously allowed to receive information by the photodiode (PD) and harvest energy by the solar panel, respectively. To improve the system spectral efficiency, an achievable sum rate maximization problem is formulated subject to the minimum energy harvesting (EH) requirement of each UE, the total transmit power constraint of the LEDs and the dimming control constraint of the LEDs, by jointly optimizing the beamforming vector and the direct current (DC) bias vector of the LEDs. To be general, the practical non-linear EH model and the information capacity model of the VLC channel are adopted. To solve the non-convex optimization problem, the objective function is equivalently transformed at first by using the epigraph reformulation, and then the transformed problem is relaxed with the semi-definite relaxation (SDR) method. Based on this, an iterative algorithm is designed to approximately obtain the maximal achievable sum rate based on the successive convex approximation (SCA). Simulation results indicate that there exists a non-trivial trade-off between the achievable sum rate and the harvested energy, and that DC bias vector dominates the amount of the harvested energy compared with the beamforming vector. Besides, for a given relatively high EH requirement, the achievable sum rate increases with the increment of the dimming level, especially for relatively small dimming level. Once the dimming level is larger than a specific value, with the increment of the dimming level, more transmit power will be allocated for illumination, resulting in the decrement of the achievable sum rate.

Robust Power Allocation for Integrated Visible Light Positioning and Communication Networks

Integrated visible light positioning and communication (VLPC), capable of combining advantages of visible light communications (VLC) and visible light positioning (VLP), is a promising key technology for the future Internet of Things. In VLPC networks, positioning and communications are inherently coupled, which has not been sufficiently explored in the literature. We propose a robust power allocation scheme for integrated VLPC Networks by exploiting the intrinsic relationship between positioning and communications. Specifically, we derive explicit relationships between random positioning errors, following both a Gaussian distribution and an arbitrary distribution, and channel state information errors. Then, we minimize the Cramer-Rao lower bound (CRLB) of positioning errors, subject to the rate outage constraint and the power constraints, which is a chance-constrained optimization problem and generally computationally intractable. To circumvent the nonconvex challenge, we conservatively transform the chance constraints to deterministic forms by using the Bernstein-type inequality and the conditional value-at-risk for the Gaussian and arbitrary distributed positioning errors, respectively, and then approximate them as convex semidefinite programs. Finally, simulation results verify the robustness and effectiveness of our proposed integrated VLPC design schemes.

The Performance Comparison of SC-PPM Receiver Models

Visible light communication (VLC) technology has arisen as promising candidate to solve the critical challenges of wireless communication networks. In particular, the evolving explosion in use of internet services requiring high bandwidth will soon become a great potential problem among the service provider. Meanwhile, this paper describes a physical layer solution to provide data transmission in the VLC networks. In the paper, it is aim to examine the performance comparison of SC-PPM (Subcarrier Pulse Position Modulation) demodulator schemes. It is considered three receiver techniques to assemble the demodulator techniques to SC-PPM receiver system. Firstly, the traditional PPM (T-PPM) demodulator has been applied on the SC-4PPM receiver system to estimate the slot that includes high frequency signal that is referred to as subcarrier signal. To successfully detect the bits by using traditional PPM receiver, it must be known the dimming level of received SC-4PPM signal. This is a serious problem to ensure data transmission in the real-time VLC systems due to challenge of providing the variable dimming level knowledge at the receiver side. In another receiver model that is referred to as PD (Peak Detector), it is aim to detect peak values of slot with high frequency signal. The disadvantage of this system is that BER (Bit Error Rate) performance depends the difference between peak and bottom values of subcarrier filled slot. Hence, second method is improved to achieve the similar BER performance at all dimming levels between 12.5% and 87.5%. This receiver model is called as IPD in the paper. In brief, it is reported for the first time, it has been employed the PD and the IPD algorithms for the SC-PPM receiver schemes. In addition to this, it is given a theoretical framework for both the traditional PPM and the improved receiver schemes in VLC-SC-PPM schemes. Moreover, it has been investigated how the SC-PPM receiver schemes are affected by brightness level.

Threefold layered optical wireless network: illumination, communication, and positioning.

Visible light communication (VLC) technology has traditionally emerged as a complementary solution to radio frequency, due to its huge available bandwidth and high data rates. Relying on visible spectrum, VLC allows both illumination and communication, thus representing a green technology with reduced energy impact. However, VLC can also be exploited for localization, and thanks to its huge bandwidth it can reach very high accuracy (i.e., <0.1 m). In this paper, we deal with a VLC network intended as a fully integrated indoor system providing at the same time both illumination, communication, and positioning tasks. Three different optimization problems are presented, aiming to seek for the minimum number of white LEDs that can achieve different constraints of illumination, data rate, and localization accuracy. Different types of LEDs are considered, according to which tasks they are intended to pursue. We consider traditional white LEDs aiming to provide illumination, communication, and positioning; otherwise, we distinguish between devices designed for localization-only and communication-only. Such distinction results in different optimization problems, and related solutions, as confirmed through extensive simulation results.

Energy Efficiency in Secure VLC Networks With SLIPT

This letter focuses on maximizing the energy efficiency (EE) for secure visible light communication (VLC) network with simultaneous lightwave information and power transfer (SLIPT) by optimizing the beamforming vectors and direct current (DC) bias under the constraints of the minimal rate requirement, the secure transmission requirement, the minimal energy harvesting (EH) requirement, and total power budget at the transmitters. To solve the non-convex optimization problem, we present a dual-layer iterative algorithm based on Dinkelbach’s and successive convex approximation (SCA) methods. An efficient algorithm is also designed to find a good initial point to accelerate the convergence. Simulation results show three typical phenomena: (1) the EE first remains unchanged and then decreases with the increasing EH requirement; (2) compared with the traditional sum-rate maximization design, our proposed approach achieves notable EE performance gain under the secure constraints; (3) the number of the authorized receivers, as well as the number of the unauthorized receivers, imposes significant impact on the EE performance.

R-AP's position-domain model for an RO-receiver and AP placement strategy for an uninterrupted link between the robotic arm and AP in the VLC network.

In the visible light communication (VLC) network, the optical link between the robotic arm and the access point (AP) is easily interrupted due to the random orientation of the receiver on the robotic arm. First, based on the VLC channel model, a position-domain model of reliable AP (R-AP) for a random-orientation receiver (RO-receiver) is proposed. The channel gain of the VLC link between the receiver and the R-AP is non-zero. The tilt-angle range of the RO-receiver is [0,π]. Given the field of view (FOV) angle and the orientation of the receiver, the R-AP's position domain of the receiver can be obtained by this model. Then, based on the R-AP's position-domain model for the RO-receiver, a novel AP placement strategy is proposed. Under this AP placement strategy, the number of R-APs for the RO-receiver is not less than 1, thereby effectively avoiding link interruption caused by the random orientation of receivers. Finally, it is proved by the Monte Carlo method that, under the AP placement strategy proposed in this paper, the VLC link of the receiver on the robotic arm can remain uninterrupted during the movement of the robotic arm.