Algorithme de récupération de porteuse pourdes systèmes de communication de lumièrevisible adaptées au contexte

International audienceLa communication parlumì ere visible (VLC) suscite beaucoup d'intérêt à la fois dans la communauté scientifique et industrielle. En dépit de cet intérêt croissant, VLC en est encorè a ses balbutiements et il a été réalisé que les techniques de communication de contrôle physique et d'accès au support (MAC) bien évaluées dans les contextes de communication traditionnels (sans fil) ne peuvent pas être appliquées dans le domaine VLC. En effet, les interférences externes sont de nature et d'impact différents. Les lumières artificielles et la lumière du soleil peuvent perturber la communication et nous avons observé que les conditions extérieures changent demanì ere imprévisible et abrupte. Sur la base de ces considérations, il a été réalisé que les émetteurs et les récepteurs doivent être équipés d'une sorte d'intelligence les rendant capables de réagir dynamiquement aux changements externes afin de rendre le système de communication plus robuste. Dans ce travail, nous avons étudié l'impact de la longueur du préambule afin de réaliser un mécanisme de récupération de porteuse efficace entre unémetteurun´unémetteur et un récepteur. Nous avons remarqué que différentes conditions externes nécessitent des longueurs de préambule différentes afin de réaliser une récupération de porteuse efficace avec un faible impact en termes de taux d'erreur de morsure (BER). Nous avons étudié les différentes conditions externes et leur impact sur le système de communication et nous avons proposé une formulation de bandit multi-bras de la définition de la longueur du préambule basée sur l'approche d' échantillonnage de Thompson. Cette logique d'intelligence artificielle a été implémentée côté récepteur et une preuve de concept a été implémentée afin de valider l'approche dans un environnement réel avec de réels changements externes. Les résultats montrent que l'approche d' échantillonnage de Thompson est très réactive aux conditions externes

A Noise Mitigation Approach for VLC Systems

International audienceVisible Light Communication (VLC) is based on the dual use of the illumination infrastructure for wireless data communication. The major interest on this communication technology lies on its specific features to be a secure, cost-effective wireless technology. Recently, this technology has gained an important role as potential candidate for complementing traditional RF communication systems. Anyway a major issue for the VLC development is a deep comprehension of the noise and its impact on the received signal at the receiver. In this work, we present a simple but effective approach to analyze the noise and drastically reduce it through a signal processing method. In order to validate the effectiveness of this analytical approach, we have developed an USRP-based testbed. Experimental results have been carried out by evaluating the symbol error rate (SER) and show the effectiveness of the noise mitigation approach in different interference conditions and at different distance between the transmitter and the receiver

Simulations of the Impact of Controlled Mobility for Routing Protocols

This paper addresses mobility control routing in wireless networks. Given a data flow request between a source-destination pair, the problem is to move nodes towards the best placement, such that the performance of the network is improved. Our purpose is to find the best nodes selection depending on the minimization of the maximum distance that nodes have to travel to reach their final position. We propose a routing protocol, the Routing Protocol based on Controlled Mobility (RPCM), where the chosen nodes' path minimizes the total travelled distance to reach desirable position. Specifically, controlled mobility is intended as a new design dimension network allowing to drive nodes to specific best position in order to achieve some common objectives. The main aim of this paper is to show by simulation the effectiveness of controlled mobility when it is used as a new design dimension in wireless networks. Extensive simulations are conducted to evaluate the proposed routing algorithm. Results show how our protocol outperforms a well-known routing protocol, the Ad hoc On Demand Distance Vector routing (AODV), in terms of throughput, average end-to-end data packet delay and energy spent to send a packet unit

Adaptive Dual Color Visible Light Communication (VLC) System

International audienceIn this work, we propose a Visible Light Communication (VLC) system dynamically adapting, through a decision-making process based on a simple fuzzy-logic, the transmitting color selection to the external environmental conditions. Transmitted Signals are opportunisti-cally treated through softwarization approaches by using basic hardware (i.e. Arduino boards and inexpensive LEDs in the transmitting stage) in order to implement an effective, end-to-end, adaptive communication system. In particular, we will show that, if a low environmental noise is added, the system keeps to be well-performing in terms of Bit Error Rate (BER) also at higher distances (up to 8-9 meters) using a warm white front-end, while, if high external interfering lights are present in the environment , a low power red front end is dynamically fed for maintaining a good-level communication (with low Bit Error Rate)

Software Defined Platforms for Visible Light Communication: State of Art and New Possibilities

International audienceThe requirement of connected devices exponentially increases day by day as well as the bandwidth needed for novel applications. As a consequence of this, radio frequency spectrum becomes more and more crowded, thus leading to serious limitations in the diffusion of novel technologies when considering challenging environments such as hospitals and airplanes, where EM interferences are particularly unwanted. The integration of Visible Light Communication (VLC) in the existing infrastructures could provide a valid tool to address these issues. In this context, Software Defined concepts could significantly simplify the integration process, leading to the development of low cost and flexible architectures. To this end, Universal Software Radio Peripheral (USRP), designed and commercialized by Ettus Company and National Instruments, is emerging as a comparatively low cost hardware platform for software defined architectures, allowing rapid prototyping and test bed validations. The aim of the present work is to exploit the current literature in the framework of Software Defined Systems based on USRP platform for VLC purposes, while briefly highlighting some useful potentialities for the development of solid and flexible architectures

Error Compensation in Indoor Positioning Systems based on Software Defined Visible Light Communication

International audienceVisible Light Communication (VLC) paradigm allows the reusing of existing illuminating infrastructures in order to provide data communication. VLC can be considered a promising technology also for positioning in indoor environments, due to its potentially high accuracy and low costs. However, the main obstacle to the use of VLC for localization purposes is the high level of environmental noises, mainly due to sunlight. A novel approach, for easily measuring environmental noises and compensating their effects on localization results performed by an Indoor Positioning System (IPS) based on VLC, is proposed in this work. Frequency Division Multiplexing (FDM) is adopted to divide the total bandwidth into a series of non-overlapping frequency sub-bands corresponding to each signal, while an estimation of Signal to Noise Ratio (SNR), obtained through real time Power Spectral Density measurements in the proper frequency ranges, is exploited to compensate the error in positioning due to sunlight and other wide-band external optical disturbing signals. The proposed approach has been validated through experimental tests, carried out using a simple deployment of low power lamps, low cost hardware and a software defined approach. In the region under test, receiver position has been experimentally detected with higher accuracy in comparison to classical FDM approach, confirming the correctness and effectiveness of our proposed technique. In order to further validate the proposed approach, an additive measurement campaign has been successfully carried out considering a scenario characterized by very low SNR levels

A Learning Approach for Robust Carrier Recovery in Heavily Noisy Visible Light Communication

International audienceVisible Light Communication (VLC) exploits optical frequencies, diffused by usual LED lamps, for adding data communication features to illuminating systems. This paradigm has attracted a growing interest in both scientific and industrial community in the latter decade. Nevertheless, classical wireless communication mechanisms for physical and Medium Access Control (MAC) layers are hardly available for VLC, due to the massive external interference caused by sunlight. A correct signal carrier recover in high noise conditions represent a significant challenge. In this work, it is shown that the synchronization frame length affects the performance of the system in terms of Bit Error Ratio (BER). Since different external conditions require different minimum preamble lengths, we considered an Artificial Intelligence (AI) approach, based on multi-arm bandit formulation, for obtaining a low impact in both BER and goodput of the communication. A low-cost hardware VLC system, implementing a learning algorithm on a Frequency Shift Keying Modulation (FSK), has been designed and tested in different environmental conditions. Experimental results show that a proper choice of preamble length overcomes, in terms of BER and goodput, the classical approach based on fixed preambles

Visible Light Indoor Positioning in a Noise-aware Environment

International audienceLocalization systems based on Visible Light Communication (VLC) are considered as good candidates for indoor environments, due to their high accuracy, low costs and the possibility of reusing existing infrastructures for both lighting and positioning. However, high level of environmental noises, mainly due to sunlight, significantly affect the performance of VLC positioning systems. A novel approach, for easily measuring environmental noises and compensating their effects, has been proposed in this work. Frequency Division Multiplexing (FDM) is adopted to divide the total bandwidth into a series of non-overlapping frequency sub-bands corresponding to each signal, while an estimation of Signal to Noise Ratio, obtained through real time Power Spectral Density measure, is exploited to compensate error positioning due to sunlight and other wide-band external optical nice sources. Proposed approach has been validated through experimental tests, carried out using a simple deployment of low power lamps, extremely low cost hardware and a Software Defined approach. In the region under test, receiver positions have been experimentally detected according to an improved accuracy in comparison with classical FDM approach, confirming the correctness of proposed technique, according to low Signal to Noise Ratio levels

Demo: A Context Aware Algorithm for an Adaptive Visible Light Communication System

International audienceRecently, Visible Light Communication systems have gained a lot of attention. In this work we proposea context-aware and adaptive Visible Light Communication(VLC) system, able to dynamically react to the environmentalchanges in order to keep a good communication quality.In particular, we focus on a frame synchronization techniquewhich is implemented by appending a preamble (repetitiveinsertion of sequences), to the transmitted data. At the receiver,a clean copy of the appended message is correlatedwith the received symbol stream for frame alignment. Thesize N (number of bits) of the preamble impacts on the performanceof the communication system. Indeed, a short dimensionof the preamble is to be preferred to reduce the controloverhead (i.e. it is not carrying data information) but itcould be not sufficient to perform a good carrier recovery, especiallyin the case of noisy environmental conditions. Sincedifferent external environmental conditions need differentvalues of preamble length, the system must be able to gatherinformation about its environment at any given time andadapt its behaviors accordingly (context awareness). Basedon these premises, we propose a dynamic computation of Nas ideal size of preamble for carrier recovery by modelingit as a multi-arm bandit problem and apply Thompson samplingto select in a fast and efficient way the best value of N[3]. Specifically, an agent tries to achieve as much award aspossible by playing the most rewarding arm among J arms(J in our case represents the possible choices of the size N,that could be potentially unlimited but not all the sizes aremeaningful, so we consider a limited sub-set). Each arm rewardsrandomly upon being played according to an unknowndistribution. Our goal is the minimization of the explorationto find the most rewarding arm. The learning approach hasbeen implemented to the receiver side. This choice is motivatedby the fact that in the receiving path all data needed to implement the algorithm are known. We assumed that afterthe receiver computes the ideal value of N, it communicatesthis value to the transmitter that will consequently adapt thenext frame. The algorithm has been implemented on a coupleof low cost VLC prototypes consisting in an Arduino board,a driving circuit and a led array in the transmitting stage, aphoto-diode, a trans-impedance amplifier and a second Arduinoboard in the receiving path. Transmitted signal is generatedthrough software and the received one is processedthrough a proper ”Virtual Instrument”, developed using thecommercial software LabView. Experimental results haveshown the impact played by a correct choice of the parameterN on the reduction of the recovered carrier frequencyvariance and Bit Error Ratio (BER) in different environmentalconditions