Nodes Placement for reducing Energy Consumption in Multimedia Transmissions

International audiencePower consumption is an essential issue in wireless multimedia sensor networks (WMSNs) due to the elevated processing capabilities requested by the video acquisition hardware installed on the generic sensor node. Hence, node placement scheme in WMSNs greatly impacts the overall network lifetime. In this context, the paper first proposes a suitable hardware architecture to implement a feasible WMS node based on off-the-shelf technology, then it evaluates the energy consumption obtained throughout a wise "energy-spaced" placement of the wireless nodes without affecting the video quality of multimedia traffic

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

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

Système de localisation à Lumière Visible avec compensation du bruit environnemental

International audienceLes systèmes de localisation basés sur la Communication à Lumière Visible (VLC) sont des bonnes candidates pour les environnements intérieurs, parce qu' ils offrent la possibilité de réutiliser les infrastructures existantes pour l'illumina-tion et la localisation en même temps. Toutefois, la lumière du soleil compromet les prestations de ces systèmes. Une nouvelle approche, fondée sur le paradigme "software defined", a été proposée pour évaluer facilement le bruit ambiant. Une adaptation de la technique FDM (Frequency Division Multiplexing) a été exploitée pour partager le débit total en différents sous-débits, chacun correspondant a l'intervalle de fréquences de chaque transmitteur. Le bruit ambiant et les autres sources optiques interférentes sont estimées en utilisant des mesures en temps réel. La validation expérimentale, effectuée en deployant des simple lampes LED à faible puissance, démontre une précision améliorée par rapport aux approches FDM classiques et confirme l'exactitude de la technique proposée

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

Graphene-Based Reconfigurable Intelligent Metasurface Structure for THz Communications

International audienceIn this paper, a graphene based reconfigurable intelligent metasurface structure is proposed for terahertz (THz) communication applications. The proposed structure consists of multilayer unit cells with a graphene radiating patch. By using different values of biasing voltages, the chemical potential (µc) of the graphene is changed which leads to have different reflected phases. Based on this property we are able to create different reflected phase distributions within the full structure metasurface array which can be controlled by coding pattern in processing units. The proposed unit cell can provide an acceptable reflection characteristic around 4.35 THz. In addition, by changing the biasing voltage, four states are generated which can transmit 1-bit and 2-bits data. The proposed metasurface structure has small size and high flexibility in controlling radiation patterns. The simulated results such as reflected phase distributions and reconfigurable radiation patterns show the effectiveness of the proposed design for THz communication

Error Probability Derivation in a Phonon-based Quantum Channel

International audienceQuantum communications are gaining more and more interest in the research community thanks to the recent advancements in nanotechnology. Indeed, quantum phenomena represent a natural direction for developing nanotechnology. The exploitation of quantum nature of information offers new potential solutions in the field of computing and networking, and extends the communication potentiality to levels that cannot be imagined in classical communication systems. Quantum communications can be realized in different ways. In this paper, we focus on the exploitation of quantum particles and quantum channels, in order to realize a data transmission system by means of phonons. First, we introduce the channel model of a phonon-based quantum system, and then derive the analysis of the error probability associated to such quantum channel. The application scenario is a biological environment, where phonons are exploited as information carriers. We have dealt a numerical evaluation in order to assess the performance of the quantum communication system. In particular, we have derived numerical results in terms of the error probability and the activity time, which represent how effective are phonons for communication purpose. We observe the frequency dependence of both error probability and activity time, thus allowing to tune the frequency for performance optimization

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

Controlled Mobility in Mobile Sensor Networks: Advantages, Issues and Challenges

International audienceRecently, wireless self-organizing networks are attracting a lot of interest in the research community. Moreover, in the last decade many mobile devices have appeared in the market. Exploiting mobility in a wireless environment, instead of considering it as a kind of disturbance, is a fundamental concept that the research community is beginning to appreciate now. Of course, the advantages obtainable through the use of the mobility imply the knowledge of the different types of mobility and the way to include it in the management architecture of the wireless networks. In this work we claim that mobility and wireless sensor networks can be considered as two synergetic elements of the same reality. For this purpose, we sketch a macro-classification of the different objectives which can be pursued by controlled mobility. Moreover, we identify and highlight the interactions between this specific type of mobility and the layers of the control stack. Lastly, this paper reports a case study in which we show how controlled mobility can be exploited practically

A Novel Design of Ultrathin Metasurface Structure for Terahertz Time-Domain Spectroscopy (THz-TDS) Applications

International audienceIn this paper, an ultrathin metasurface structure is proposed for terahertz time-domain spectroscopy (THz-TDS) applications. The proposed structure consists of an inverted Tshaped strip surrounded by a rectangular-shaped split ring resonator (SRR) structure on a high-resistance silicon substrate. By inserting an inverted T-shaped strip inside the SRR, the coupling between the strip and SRR is improved and the sensitivity (refractive index unit (RIU)) of the proposed unit cell is increased. The proposed unit cell can provide an acceptable transmission characteristic around 0.6 THz. In addition, by using biological analyte, in this study brain Glioma, we are able to detect this material's concentrations by calculating the sensitivity in the range of 65 GHz/RIU. The proposed metasurface structure has small size and high sensitivity characteristics. Simulation results of the transmission coefficients and radiation characteristics show the effectiveness of the proposed design for biomedical applications