Coalition Formation for Interference Management in Visible Light Communication Networks

Handover management in Visible Light Communications (VLC) networks is an open issue due to the need of maintaining alignment between a transmitting Light Emitting Diode (LED) and a receiver PhotoDetector (PD). Mobility strongly affects VLC connectivity links, as well as occlusions that may obstruct the Line-of-Sight (LoS) propagation. In this paper we present a proactive handover solution, which is able to switch connectivity links from a serving VLC “lighting” cell to a candidate one, in case of blockage that affects the VLC link. Differently from conventional handover mechanisms, where a handover is trigged by quality of service metrics or localization information, our technique is dedicated to VLC networks which can be affected by occlusions causing blockages. The proposed approach has been implemented both in hard and soft mode, and assessed in terms of achievable data rate and hand over latency for a user walking in a given reference room at different speeds.

The growing energy consumption of communication systems raises economical and environmental concerns. Indoor visible light communication (VLC) systems are energy friendly as they exploit the illumination power of LED luminaries for data transmission. However, the VLC systems suffer from service disruptions due to the limited coverage of light. To alleviate this problem, hybrid RF#x002F;VLC architecture has been recently proposed for indoor networks where the RF networks can be exploited to resolve the limited VLC coverage. In this paper, we consider a network composed of multiple VLC access points and an RF access points. We develop resource allocation algorithms to maximize the system's power efficiency defined as the total system throughput per unit power. Simulations show that deploying VLC access points improves the power efficiency of the system and increases the minimum guaranteed rate per user. Simulations also show that higher power efficiency can be obtained using the same number of operating VLC access points by redistributing them more uniformly across the room.

Due to directional propagation of light signals, visible light communication (VLC) channel quality is sensitive to the distance and the angle between a VLC access point (AP) and a VLC terminal. When a terminal is mobile, VLC channel gain varies with the position of the terminal. Considering rotations of a terminal during mobility, channel variations are even more severe. As a result, data rates need to be adapted according to variable link qualities. The commonly used feedback-based adaptive modulation and coding (AMC) scheme cannot catch up with channel variations in VLC, resulting in staircase-shaped adaptation results. Smoother adaptation can be achieved by the seamless rate adaptation (SRA) scheme via rate compatible modulation (RCM). However, SRA does not provide an effective way to increase symbol distances, so the improvement on spectral efficiency is small. To address the shortcomings in the existing schemes, rateless adaptation (RLA) is developed for VLC systems in this paper based on spinal codes. With RLA, smooth rate adaptation is accomplished without channel state information (CSI) feedback, and spectral efficiency is also greatly improved. Simulation results show that, in mobile scenarios, RLA achieves at least 46% improvement over AMC and 19% improvement over SRA in terms of spectral efficiency.

Visible Light Communications (VLC) technology is restricted by the transmission coverage, which is short by nature. This is imposed by the lighting range which barely reaches a couple of hundred meters. The number of applications of VLC technology is therefore limited by this specific characteristic of the light propagation. As a result, VLC cannot be used in long and medium distance communication systems. The technology is suitable for exploitation in optical wireless personal area networks (OWPAN) in which the mobile terminal (MT) and the VLC access point (VLC AP) are placed in the same room. It is then essential that the access point is fed by a backhaul network. In this paper, we propose an access network in which the backhaul or backbone network exploits fibre optic (FO) technology to feed the VLC access point with data to be retransmitted. The channel is analyzed for a few parameters of the entire system including the FO attenuation factor, α, the transmission range, L, and the indoor VLC wall, ceiling and floor reflection coefficient, ρ.

Machine-to-machine (M2M) visible light communication (VLC) is a communication architecture that makes it possible for heterogeneous devices to interact without human intervention using visible light modulated at certain frequency to enable communication. M2M VLC based is one of the feasible applications of internet of things (IoTs). This paper proposed a machine type communication (MTC) for M2M VLC based with an incorporation of energy harvesting system using a power transfer unit (PTU) with a centralized VLC access point (AP) with a probabilistic model, where an investigation is performed to show the signal to noise ratio (SNR) distribution with a semi angle at half power of a chosen link. This is done by varying some parameters.This model considers the channel analysis and light emitting diodes (LEDs) are place at the ceiling showing how bit rate can be effected for VLC AP with equal separation for a mobile devices or users. Such network aims at interconnecting billions of devices while investing the throughput performance of the M2M VLC based where a cluster of energy harvesting devices communicating with a VLC AP. This paper aims at proposing a design at the physical layer using various modulation schemes, demodulation, synchronization, error correction and so forth to ensure optimal communication can be made to the internet. Both LEDs-based analog transceiver devices and photo-detectors are exploited. The method is implemented in simulation and considering the performance and flexibility of the system.

IEEE 802.15.7 visible light communication (VLC) networks suffer from performance degradation caused by the hidden device problems due to the directional transmission with narrow beamwidth. One of the solutions for the hidden device is to apply a full-duplex transmission technique to the VLC networks. This approach enables to mitigate collisions induced by hidden devices. As a side effect of applying the full-duplex transmission, however, the data-packet discard by reaching the retransmission limit occurs frequently in the networks. This paper proposes an improved backoff scheme to suppress the packet discard. In the proposed backoff scheme, the values of the backoff exponent (BE) and the number of backoff stage (NB) in IEEE 802.15.7 are increased only when the data packet transmission fails. To evaluate the system performance theoretically, in addition, this paper establishes the analytical models, including operations of the improved backoff scheme. The results from simulation and theoretical analysis show the effectiveness of the proposed scheme.

This paper introduces an optical orthogonal frequency division multiplexing (OFDM)‐based hyperchaotic key generation encryption approach that can improve confidentiality in visible light communication (VLC) networks. Using a hyperchaotic four‐dimensional method, the bipolar real‐valued OFDM signal can be used for constructing dynamic cipher keys modified at every frame over the communication time, resulting in a superior degree of protection against malicious attacks. In accordance with our findings, this approach decreases the ratio of peak‐to‐average power of the transmitted signal, and enhances the bit error rate efficiency and secrecy capacity of the OFDM‐based VLC network, which improves confidentiality. © 2022 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

A room division multiplexing (RDM)-based hybrid visible light communication (VLC) network for realizing indoor broadband communication within a multi-room house is presented.The downlink information is transmitted by light-emitting diode lamps, whereas the uplink information is transmitted through WiFi.RDM is introduced to improve the VLC network throughput; in addition, the associated signaling localization and active handoff mechanisms are designed for implementation.The experimental platform demonstrates the effectiveness of the proposed hybrid architecture, along with the RDM and active handoff mechanisms.

Cross-layer analysis has been gaining an increasing attention as a powerful tool to study and assess different quality-of-service (QoS) mechanisms in wireless networks. Regarding the physical and data-link layers, in this paper we provide a cross-layer study for visible light communication (VLC) systems operating under statistical QoS constraints, which are inflicted as limits on the delay violation and buffer overflow probabilities. We assume that the VLC access point (AP) is unaware of the channel conditions, thus the AP sends the data at a fixed rate. Under this assumption, and considering an ON-OFF data source, we employ the maximum average data arrival rate at the AP buffer and the non-asymptotic bounds on buffering delay as the main performance measures. Through numerical results, we illustrate the impacts of different physical and data-link parameters on the system performance.

Visible light communication (VLC) uses huge license-free spectral bandwidth of visible light for high-speed wireless communication. Since each VLC access point covers a small area, handovers of mobile users are inevitable. In order to deal with these handovers, developing fast and effective resource allocation algorithms is a challenge. This paper introduces the problem of mobility-aware optimization of resources in VLC networks using the T-step look-ahead policy and employing the notion of handover efficiency. It is shown that the handover efficiency can correlate the overall performance of the network with future actions based on the mobility of users. Due to the stationary nature of indoor optical wireless channels, future channel state information (CSI) can be predicted by anticipating the future locations of users. A resource allocation algorithm is thus proposed, which uses CSI to dynamically allocate network resources to users. To solve this mathematically intractable problem, a novel relaxation method is proposed, which proves to be a useful tool to develop efficient algorithms for network optimization problems with a proportional fairness utility function. The resulting algorithm is extremely faster than the previous method and awareness of mobility enhances the overall performance of the network in terms of rate and fairness utility function.

In this paper, we study the physical-layer security in a 3-D multiuser visible light communication (VLC) network. The locations of access points (APs) and mobile users are modeled as two 2-D, independent and homogeneous Poisson point processes at distinct heights. Using mathematical tools from stochastic geometry, we provide a new analytical framework to characterize the secrecy performance in multiuser VLC networks. Closed-form results for the outage probability and the ergodic secrecy rate are derived for networks without AP cooperation. Considering the cooperation among APs, we give tight lower and upper bounds on the secrecy outage probability and the ergodic secrecy rate. To further enhance the secrecy performance at the legitimate user, a disk-shaped secrecy protected zone is implemented in the vicinity of the transmit AP. Based on the obtained results, it is shown that cooperating neighboring APs in a multiuser VLC network can bring performance gains on the secrecy rate, but only to a limited extent. We also show that building an eavesdropper-free protected zone around the AP significantly improves the secrecy performance of legitimate users, which appears to be a promising solution for the design of multiuser VLC networks with high security requirements.

Visible light communications (VLC) are gaining popularity and may provide an alternative means of communications in indoor environment, due to their great advantages in high transmission rate, high bandwidth, green healthy, flexible coverage, etc. However, the past works mainly focus on the elements design, physical and MAC layer, little attention has been paid to system planning and design for VLC networking. In this paper, we design the typical architecture of indoor VLC networks based on its technical characteristic; from a point view of the evolution and development of the wireless communication system, we propose some networking schemes for the indoor visible light networking, including multi-tier cell coverage, the separation of user plane and control plane, the distributed and client-server mode coexisted. Those networking policies will effectively accelerate the application and popularization of indoor VLC networks.

Visible light communication (VLC) networks, consisting of multiple light-emitting diodes (LEDs) acting as optical access points (APs), can provide low-cost high-rate data transmission to multiple users simultaneously in indoor environments. However, the performance of VLC networks is severely limited by the interference between different users. In this paper, we establish a distributed user-centric scheduling framework based on stable marriage theory, and propose a novel decentralized scheduling method to manage interference by forming flexible amorphous cells for all users. The proposed scheduling method has provable low computational complexity and requires only the exchange of a few 1-bit messages between the APs and the users but not the feedback of the channel state information of the entire network. We further show that the proposed method can achieve both user-wise and system-wise optimality as well as a certain level of fairness. Simulation results indicate that our decentralized user-centric scheduling method outperforms existing centralized approaches in terms of throughput, fairness, and computational complexity.

We present a statistical analysis of a mixed radio-frequency (RF)-visible light communications (VLC) relaying system, where outdoor millimeter wave based RF links are utilized to provide backhaul connectivity for indoor VLC broadcasting. The multiple RF links are assumed to communicate with the VLC access point through decode-and-forward relay. Novel closed-form outage probability and average bit error rate expressions are derived and utilized to obtain numerical results. Monte Carlo simulations validate presented numerical results, which are further used to examine the effects of system and channel parameters on system performance.

In this article, we propose and experimentally demonstrate the full-duplex channel-aware adaptive physical-layer network (APNC) coding over orthogonal frequency division multiplexing (OFDM) based visible light communication (VLC) to boost the capacity of relay-assisted VLC networks. The network encoding is realized by detecting signals coming from different terminal nodes simultaneously with a single photodiode at the relay node, which then achieves the amplify-and-forward function. At the receiver of each terminal node, the desired signal can be reconstructed by applying the corresponding APNC decoding to the detected interfered signal from the relay node. The use of adaptively loaded OFDM not only addresses the inherent frequency fading issue in VLC systems but also relaxes the synchronization issue at the relay node. The detailed principles of the proposed full-duplex channel-aware APNC scheme are presented, and its performance is experimentally investigated in a two-way-relay (TWR) VLC network. Experimental results show that the proposed scheme exhibits superior BER performance to other existing network scheduling schemes. For a TWR-VLC network with a fixed 600-Mb/s throughput, we achieve around two orders of magnitude reductions in the bit-error-rate (BER) by using the proposed channel-aware APNC scheme compared to other schemes, and BERs of 3.96 × 10−4 and 5.32 × 10−4 are attained for the two transmission links in the TWR network, respectively.