Visible Light Communication Access Points Research Articles

Energy-Efficient Resource Allocation for Aggregated RF/VLC Systems

Visible light communication (VLC) is envisioned as a core component of future wireless communication networks due to, among others, the huge unlicensed bandwidth it offers and the fact that it does not cause any interference to existing radio frequency (RF) communication systems. In order to take advantage of both RF and VLC, most research on their coexistence has focused on hybrid designs where data transmission to any user could originate from either an RF or a VLC access point (AP). However, hybrid RF/VLC systems fail to exploit the distinct transmission characteristics (e.g., susceptibility of VLC transmissions to blockages, limited field-of-view of VLC APs and receivers, more coverage and better reliability of RF systems, etc.) of RF and VLC systems to fully reap the benefits they can offer. Aggregated RF/VLC systems, in which any user can be served simultaneously by both RF and VLC APs, have recently emerged as a more promising and robust design for the coexistence of RF and VLC systems. To this end, this paper, for the first time, investigates AP assignment, subchannel allocation (SA), and transmit power allocation (PA) to optimize the energy efficiency (EE) of aggregated RF/VLC systems while considering the effects of interference and VLC line-of-sight link blockages. A novel and challenging EE optimization problem is formulated for which an efficient joint solution based on alternating optimization is developed. More particularly, an energy-efficient AP assignment algorithm based on matching theory is proposed. Then, a low-complexity SA scheme that allocates subchannels to users based on their channel conditions is developed. Finally, an effective PA algorithm is presented by utilizing the quadratic transform approach and a multi-objective optimization framework. Extensive simulation results reveal that: 1) the proposed joint AP assignment, SA, and PA solution obtains significant EE, sum-rate, and outage performance gains with low complexity, and 2) the aggregated RF/VLC system provides considerable performance improvement compared to hybrid RF/VLC systems.

CSMA/CA protocol design in hybrid network of Visible Light Communication and RF Femtocell systems

In this article, an access protocol based on the CSMA/CA algorithm and the IEEE 802.11n standard is proposed for a network composed of a hybrid Visible Light Communication (VLC) and Radio Frequency (RF) Femtocell in an indoor scenario. To evaluate the performance of the proposer protocol, a hybrid network comprised of VLC access points (APs) distributed on the ceiling, an RF AP located in the center of the room, and n users was modeled. The network considered that the VLC channel was used only for the downlink, while the RF Femtocell was used for the uplink, exchange of information with the server, and downlink. The benefits of solutions associated with hybrid Femtocells between VLC and RF that guarantee the natural use of the users are studied. The performance of the proposed protocol was studied in terms of delay, throughput, and transmission efficiency. Numerical results show that the increase in the number of users on the network leads to an exponential decrease in the average delay. In addition, it was observed that the throughput obtained by the hybrid VLC/RF Femtocell system was superior to the traditional throughput of both independent networks. The combination of VLC and RF Femtocell channels depending on the location of the users allow for increasing transmission efficiency of the hybrid VLC/RF Femtocell network.

Resource allocation based on differentiated user services for indoor hybrid multi-color VLC/WiFi networks

Multi-color visible light communication (VLC) and wireless fidelity (WiFi) networks provide a promising solution for the indoor wireless communication, while the hybrid networks face the challenge of imbalanced access point (AP) load and resource allocation. A resource allocation method based on user service differentiation (RAMUSD) is proposed for multi-color VLC/WiFi hybrid networks. In our design, the user’s premium level is defined according to the user’s channel conditions and requested data rate. The heterogeneous network selects the service AP for the users according to its premium level, user with high premium level is served by one of VLC access points (APs), while user with low premium level is served by WiFi AP. Then, the average satisfaction is used as the load index to adjust the number of users served by the WiFi AP or the VLC AP to achieve load balance among APs. Furthermore, the RAMUSD uses the potential game theory to optimize user’s migration and resource allocation among APs for improving the load balancing index. In the potential game, user can improve its return value by changing access AP. So, it makes user who pursue more resources give up the congested APs. Simulation results show that the proposed RAMUSD can achieve better system throughput and user satisfaction than an enhanced proportional fairness algorithm based on evolutionary game theory (EPF-EGT).

Meta-Reinforcement Learning for Reliable Communication in THz/VLC Wireless VR Networks

In this paper, the problem of enhancing the quality of virtual reality (VR) services is studied for an indoor terahertz (THz)/visible light communication (VLC) wireless network. In the studied model, small base stations (SBSs) transmit high-quality VR images to VR users over THz bands and light-emitting diodes (LEDs) provide accurate indoor positioning services for them using VLC. Here, VR users move in real time and their movement patterns change over time according to their applications, where both THz and VLC links can be blocked by the bodies of VR users. To control the energy consumption of the studied THz/VLC wireless VR network, VLC access points (VAPs) must be selectively turned on so as to ensure accurate and extensive positioning for VR users. Based on the user positions, each SBS must generate corresponding VR images and establish THz links without body blockage to transmit the VR content. The problem is formulated as an optimization problem whose goal is to maximize the average number of successfully served VR users by selecting the appropriate VAPs to be turned on and controlling the user association with SBSs. To solve this problem, a policy gradient-based reinforcement learning (RL) algorithm that adopts a meta-learning approach is proposed. The proposed meta policy gradient (MPG) algorithm enables the trained policy to quickly adapt to new user movement patterns. In order to solve the problem of maximizing the average number of successfully served users for VR scenarios with large numbers of users, a low-complexity dual method based MPG algorithm (D-MPG) with a low complexity is proposed. Simulation results demonstrate that, compared to a baseline trust region policy optimization algorithm (TRPO), the proposed MPG and D-MPG algorithms yield up to 26.8% and 21.9% improvement in the average number of successfully served users as well as 81.2% and 87.5% gains in the convergence speed, respectively.

Distributed DRL-Based Downlink Power Allocation for Hybrid RF/VLC Networks

Hybrid radio frequency (RF) and visible light communication (VLC) networks can provide high throughput and energy efficiency with VLC access points (APs) while ensuring ubiquitous coverage with RF APs. Due to dynamic channel conditions and limited resources, the hybrid RF/VLC networks’ resource allocation problem is complex and challenging. Conventional resource allocation techniques fail to overcome these challenges. Heuristic methods can solve high complexity problems; however, they are not robust against changes such as dynamic channel conditions or alternating user requirements. Heuristic methods require centralized control for stability which adds communication overhead between APs. Deep Reinforcement Learning (DRL) based solutions can solve high complexity, dynamic channel conditions, and alternating user requirements while not requiring centralized control. In this paper, we formulate a distributed downlink power allocation problem to optimize the transmit power for users to reach target data rates in hybrid RF/VLC networks. Then, we propose a distributed DRL-based algorithm Deep Deterministic Policy Gradient (DDPG), to solve the formulated computationally-intensive problem. We implement a simulation environment to benchmark the proposed distributed DRL-based method against other methods such as Q-Learning (QL) and Deep Q-Networks (DQN), and centralized heuristic power allocation algorithms. Our simulation results show that the distributed DDPG-based algorithm learns to adapt against changes in the channel or user requirements, while centralized Genetic Algorithm and Particle Swarm Optimization-based algorithms fail to endure against these changes even with coordination between APs. Additionally, we quantify the performance of the DDPG-based algorithm to prevail amid DRL-based algorithms at the expense of higher implementation complexity.

VLC Network Design for High Mobility Users in Urban Tunnels.

Current vehicular systems require real-time information to keep drivers safer and more secure on the road. In addition to the radio frequency (RF) based communication technologies, Visible Light Communication (VLC) has emerged as a complementary way to enable wireless access in intelligent transportation systems (ITS) with a simple design and low-cost deployment. However, integrating VLC in vehicular networks poses some fundamental challenges. In particular, the limited coverage range of the VLC access points and the high speed of vehicles create time-limited links that the existing handover procedures of VLC networks can not be accomplished timely. Therefore, this paper addresses the problem of designing a vehicular VLC network that supports high mobility users. We first modify the traditional VLC network topology to increase uplink reliability. Then, a low-latency handover scheme is proposed to enable mobility in a VLC network. Furthermore, we validate the functionality of the proposed VLC network design method by using system-level simulations of a vehicular tunnel scenario. The analysis and the results show that the proposed method provides a steady connection, where the vehicular node is available more than 99% of the time regardless of the number of vehicular nodes on this network. Additionally, the system is able to achieve a Frame-Error-Rate (FER) performance lower than 10−3.

Mobility aware of WDM-based CMO OFDM communication system

Abstract The continued increase in several mobile applications forces to replace existing limited spectrum indoor radio frequency wireless connections with high-speed ones. Visible light communications (VLC) technology has gained prominence in the development of high data rate transmission for fifth-generation networks. In optical wireless communications, light-emitting diode (LED) transmitters are used in applications that desire mobility as LED divergence enables larger coverage. Since each VLC access point covers a small area, handovers of mobile users are inevitable. Wavelength division multiplexing (WDM) can be used in VLC systems to tackle the above issue and to meet the increasing demand for indoor connectivity with high bit rates. In this paper, a new system architecture for WDM with coded modulated optical in orthogonal frequency division multiplexing (OFDM) VLC system in conjunction with red, green, blue, and yellow (RGBY) LEDs is proposed to reduce the impact of random receiver orientation of indoor mobile users over VLC downlink channels and improves the system’s bit-error-rate (BER) performance. Simulation results show that the proposed method is not affected by the user’s mobility and hence it performs better than other approaches, in terms of BER for all scenarios and at all positions. This study reveals that using WDM-OFDM-VLC with RGBY LEDs to construct a VLC system is very promising.

Cooperative Hybrid VLC/RF Systems With SLIPT

A hybrid downlink system that simultaneously uses visible light communication (VLC) and radio frequency (RF) is investigated, assuming that only one of the two considered users is capable of receiving information over the optical band. In order to facilitate information transmissions from the VLC access point to the RF user, mixed VLC/RF relaying and simultaneous lightwave information and power transfer (SLIPT) are utilized. Moreover, a cognitive-based resource allocation policy and tractable bounds for the harvested energy are introduced. Furthermore, by taking into account the random location of the VLC and RF user terminals, the closed-form outage probability for the VLC user is given, while for the RF user, the outage probability is derived in terms of infinite-series, which is also approximated by a tractable closed-form expression. In addition, the outage probability of the RF user is minimized by optimizing the direct current (DC) component. Finally, simulations are provided to verify the accuracy of the theoretical analysis and demonstrate the effectiveness of the proposed optimization framework.

Impact of Multiple Shadows on Visible Light Communication Channel

This letter investigates the impact of multiple shadows for indoor visible light communication (VLC) systems composed of a VLC access point and multiple terminals. The blockage is a crucial problem in the VLC system, which would result in great deterioration of users' communication quality due to the shadow area caused by the blockage. Considering the room boundaries and overlap between shadows, we derive the mathematical expressions of the shadow area and position. In the simulation part, the effect of multiple shadows on throughput and outage performance is appraised. Furthermore, we also take the effect of the room size into account.

Deep Reinforcement Learning-Based Adaptive Handover Mechanism for VLC in a Hybrid 6G Network Architecture

Visible light communication (VLC) is considered an important complementary technology for extremely high sixth-generation (6G) data transmission and has become part of a hybrid 6G indoor network architecture with an ultradense deployment of VLC access points (APs) that presents severe challenges to user mobility. An adaptive handover mechanism, which includes a seamless handover protocol and a selection algorithm optimized with a deep reinforcement learning (DRL) method, is proposed to overcome these challenges. Experimental simulation results reveal that the average downlink data rate with the proposed algorithm is up to 48% better than those with traditional RL algorithms and that this algorithm also outperforms the deep Q-network (DQN), Sarsa and Q-learning algorithms by 8%, 13% and 13%, respectively.

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.

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.

Q-Learning Based Two-Timescale Power Allocation for Multi-Homing Hybrid RF/VLC Networks

This letter investigates hybrid networks composed of a radio frequency (RF) access point (AP) and multiple visible light communication (VLC) APs. We consider mobile multi-homing users that can aggregate resources from both RF and VLC APs. In hybrid RF/VLC networks, RF channel gains vary faster than VLC channels due to small scale fading. By leveraging multi-agent Q-learning to interact with the dynamics of wireless environments, we develop an online two-timescale power allocation strategy that optimizes the transmit powers at the RF and VLC APs to ensure quality-of-service satisfaction. Simulation results demonstrate the effectiveness of the proposed Q-learning based strategy.

Reflection-Based Relaying Techniques in Visible Light Communications: Will it Work?

Visible light communication (VLC) is capable of satisfying the escalating data rate demand in indoor scenarios. The lighting infrastructure may also be exploited in the downlink of a wireless local area network (WLAN), where light-emitting diodes are used for transmitting information. The backhaul of VLC access points (APs) constitutes a potential bottleneck in WLANs, especially in large rooms where the number of APs is high. Thus, an alternative reflection-based cooperative wireless system concept is proposed, where no wired connections are required for connecting the APs. Then, its data rate analysis is developed based on the signal-to-noise ratio attained. The results show that the performance of the cooperative wireless system advocated closely approximates the performance of the traditional wired backhaul. Finally, we demonstrate by using Jain's index of fairness that the proposed scheme provides fair coverage quality for all users.

QoS-Driven Optimized Design-Based Integrated Visible Light Communication and Positioning for Indoor IoT Networks

With the rapid development of the Internet of Things (IoT) in the smart city, smart grid, and smart industry, indoor communication and positioning are important for IoT. However, radio-frequency (RF)-based wireless networks may fail to guarantee different quality-of-service (QoS) requirements of devices, due to the limited bandwidth, severe interference, and multipath reflections. Hence, this article presents a new integrated visible light communication (VLC) and VLC positioning (VLCP) network for IoT to provide both high-speed communication and high-accuracy positioning services. As the network consists of multiple VLC access points (APs), we propose jointly optimizing the AP selection, bandwidth allocation, adaptive modulation, and power allocation approach to satisfy different QoS requirements of indoor devices while maximizing the network data rate. A low-complexity iterative algorithm is presented to solve the resource management (RM) optimization problem by decomposing it into two subproblems. Finally, a robust handover mechanism and a pedestrian dead reckoning (PDR)-assisted VLCP scheme are presented to maintain good performance under line-of-sight (LOS) blockages. The simulation results verify that the proposed solutions outperform other existing solutions in terms of effectively enhancing the data rate, improving the positioning accuracy, and guaranteeing devices’ QoS requirements. In detail, the mean position error is reduced from 20 to 4.3 cm by using our presented integrated VLCP model. The proposed RM approach achieves a satisfied QoS level improvement of up to 20.3% compared with the non-QoS-driven RM approach, and it achieves the high data rate up to 1.31 Gb/s.

Design of Energy Efficient Hybrid VLC/RF/PLC Communication System for Indoor Networks

Integrating visible light communication (VLC) system with indoor radio frequency (RF) network is seen as a possible way of increasing the capacity and coverage of indoor networks. In such a hybrid network, the traffic generated at the indoor RF and VLC access points must be backhauled to the core network. Power line communication (PLC) technology is seen as a cost-effective backhaul (BH) solution due to its infrastructure availability in every home. In this letter, a novel system model that captures the joint effect of power and BH flow optimization for hybrid VLC/RF/PLC indoor communication network is proposed. For the proposed system model, the problem of energy efficiency (EE) maximization via power and BH flow optimization is formulated as a non-convex problem, and then transformed into a convex problem via the Dinkelbach’s approach. An energy efficient algorithm is proposed to solve this joint problem with guaranteed optimality. Simulation results are used to verify the superiority of the proposed hybrid VLC/RF/PLC system and algorithm over a conventional indoor RF system and equal power allocation benchmark scheme, respectively, in terms of network throughput, power consumption, and EE.

Performance of hybrid cellular-VLC link for indoor environments under dynamic user movement

Visible light communications (VLC) is an emerging technology that complements the existing cellular network in order to provide high throughput, secure and power efficient indoor communication system. In this paper, we analyze the performance of hybrid cellular-VLC downlink where the outdoor coverage is provided via cellular network, and the indoor coverage is provided through a VLC system. In the proposed framework, VLC access point (AP) helps to communicate the information between the base station (BTS) and user by acting as a decode-and-forward (DF) relay. The relay decodes the received signal from the base station and then uses the decoded signal to modulate the intensity of the optical transmitter. Multiple light emitting diode (LED) transmitters with rectangular deployment are considered for a VLC transmitter. The channel model for VLC link has been modeled as an integrating sphere VLC channel which includes both line-of-sight (LOS) and non-line-of-sight (NLOS) links. Further, the movement and density of people have also been considered while deriving the closed-form expressions for the outage probability and bit-error-rate (BER) for the hybrid cellular-VLC downlink. In addition, the proposed work also utilizes optimal Lambertian order (OLO) to achieve increased average received optical power through LOS path and uniform delay spread in an indoor environment. It has been shown that by using the proposed hybrid cellular-VLC downlink, it is possible to achieve significant amount of power saving (approximately 51%) at BTS as compared to direct cellular link. Finally, the dimming range is calculated for the proposed system under dimming constraint. Results show that dimming range up to 70% can be achieved in the hybrid cellular-VLC link.

Multi-cell VLC system design under illumination and communication constraints

Visible Light Communication (VLC) uses lamps light to convey information. As such, lamps in VLC systems work not only as illumination devices, but as VLC Access Points (VAPs) as well. This makes the choice of the lamps’ specifications and positions vital to satisfy the illumination and communication requirements. It is important that an indoor environment has the best possible VLC performance and the lowest possible power consumption while maintaining satisfactory illumination conditions. Designing multi-VAP systems is challenging due to the conflicting requirements of illumination and communication. For example, closely installed lamps give more consistent illumination but more inter-VAP interference, and vice versa. In this paper, we propose an optimal strategy to design multi-VAP systems. We consider the general design problem that aims to maximize the VLC performance while minimizing the total power consumption. This should be achieved while keeping satisfactory illumination conditions represented by the average illumination level and the degree of illumination consistency. The multi-VAP system design is formulated as a two objective design problem with constraints on illumination. The interplay between the system design parameters and the constraints and objectives is then studied. Finally, the algorithm to optimize multi-VAP design strategies is proposed.

Dynamic FOV visible light communications receiver for dense optical networks

This study explores how the field-of-view (FOV) of a visible light communications (VLCs) receiver can be manipulated to realise the best signal-to-noise ratio (SNR) while supporting device mobility and optimal access point (AP) selection. The authors propose a dynamic FOV receiver that changes its aperture according to receiver velocity, location, and device orientation. The D-FOV technique is evaluated through modelling, analysis, and experimentation in an indoor environment comprised of 15 VLC APs. The proposed approach is also realised as an algorithm that is studied through analysis and simulation. The results of the study indicate the efficacy of the approach including a 3X increase in predicted SNR over static FOV approaches based on measured received signal strength in the testbed. Additionally, the collected data reveal that D-FOV increases effectiveness in the presence of noise. Finally, the study describes the tradeoffs among the number of VLC sources, FOV, user device velocity, and SNR as a performance metric.