A Proposal for VLC-Assisting IEEE802.11p Communication for Vehicular Environment Using a Prediction-based Handover

International audienceDespite years of development and deployment, the standardized IEEE802.11p communication for vehicular networks can be pushed toward insatiable performance demands for wireless network data access, with a remarkable increase of both latency and channel congestion levels when subjected to scenarios with a very high vehicle density. In some hard safety applications such as convoys, IEEE802.11p could seriously fail to meet the fundamental vehicular safety requirements. On the other hand, the advent of LED technologies has opened up the possibility of leveraging the more robust Visible Light Communication (VLC) technology to assist IEEE802.11p and provide seamless connectivity in dense vehicular scenarios. In this paper, we propose and validate a prediction-based vertical handover (PVHO) between VLC and IEEE802.11p meant to afford seamless switching and ensure the autonomous driving safety requirements. Algorithm validation and platoon system performance were evaluated using a specially implemented 802.11p-VLC module in the NS3 Network Simulator. The simulation results showed a speed-based dynamic redundancy before and after VLC interruptions with seamless switching. Moreover, the deployment of VLC for platoon intra-communication can achieve a 10-25% PDR gain in high-density vehicular scenarios

Mobility management in multi-tier LiFi networks

Mobility management is an important part of the analysis and design of ultra-dense LiFi networks. This paper presents a two-tier LiFi network and analyses the cross-tier handover rate between the primary and secondary cells. For different conditions of semiangle at half illuminance of the primary and secondary cells, we propose three different coverage models for the secondary cells. Using stochastic geometry, closed-form expressions are derived for the cross-tier handover rate, ping-pong rate and sojourn time in terms of the received optical signal intensity, time-to-trigger and user mobility. The analytical models are validated with simulation results

A study of visible light communication channels for high speed roadways

A visible light communication channel study is conducted for high speed roadways under clear night sky conditions in which street light poles transmit to receivers on top of moving vehicles. A detailed analysis of the communication channel is undertaken. Exact and approximate analytical DC channel responses are obtained and analyzed, and the channel capacity and RMS time delay spreads are derived. Numerical studies verify that visible light communications are feasible for high speed roadways

Communications par Lumière Visible et Radio pour la Conduite Coopéraive Autonome: application à la conduite en convois.

By realizing both low-cost implementationand dual functionality, VLC has becomean outstanding intriguing supportivetechnology by using the vehicular existedinfrastructure.This thesis aims to contribute to theautonomous vehicular communicationand urban mobility improvements. Thework addresses the main radio-basedV2V communication limitations and challengesfor ITS hard-safety applicationsand intends to deploy the vehicular lightingsystem as a supportive communicationsolution for platooning of IVCenabledautonomous vehicles. The ultimateobjectives of this Ph.D. researchare to integrate the VLC system withinthe existing C-ITS architecture by developinga VLC prototype, together withsufficient hand-over algorithms enablingVLC, RF, and perception-based solutionsin order to ensure the maximumsafety requirements and the continuousinformation exchange between vehicles.The feasibility and efficiency of thesystem implementation and hand-overalgorithms were subjects to deep investigationsusing computer simulators andtest-bed that considers applications ofautomated driving. In addition to the improvementin road capacity when platoonformations are used. The carried outsimulations followed-up by experimentalresults proved that the integration of VLCwith the existed RF solutions lead to adefinite benefit in the communicationchannel quality and safety requirementsof a platooning system when a properhand-over algorithm is used.La communication par lumière visibleVLC est devenue une technologie attractivevu qu’elle assure une implémentationà faible coût et une doublefonctionnalité. En effet, elle permetd’utiliser l’infrastructure déjà existantesur le véhicule à savoir les lampesd’arrière et frontales comme des unitésde transmission. Cette thèse s’intéresseà rendre plus efficace les communicationsdes véhicules autonomes ainsi quela gestion de la mobilité urbaine. Nousnous intéressons tout d’abord aux principaleslimitations des communicationsradio sans fil dans le contexte des applicationsde sécurité routière à hautes exigences.Nous nous concentrons ensuiteau déploiement d’un système d’éclairagesur les véhicules dans le but de fournir unmoyen de communication de soutien auxcommunications radio pour l’applicationde peloton. L’objectif primordial decette thèse est d’intégrer la technologieVLC dans l’architecture de communicationITS en implémentant un prototypede communication VLC et en concevantde nouveaux algorithmes de handoverpermettant une transition transparenteentre différents moyens de communicationinter-véhiculaires (VLC, communicationsans fil et techniques de perception).Le but est d’assurer les exigencesde sécurité requises par les applicationset l’échange continue de l’informationentre véhicules. L’efficacité de ces algorithmesa été validée à travers de nombreusessimulations et test-bed réels aucours desquels nous avons considérél’application de conduite automatisée.Ces différentes méthodes de validationont démontré que l’intégration de la technologieVLC avec les solutions de communicationsradio permet d’améliorer laqualité du canal de transmission ainsique la satisfaction des exigences de sécuritérelatives à l’application de peloton

Optical Wireless Communication for Mobile Platforms

The past few decades have witnessed the widespread adaptation of wireless devices such as cellular phones and Wifi-connected laptops, and demand for wireless communication is expected to continue to increase. Though radio frequency (RF) communication has traditionally dominated in this application space, recent decades have seen an increasing interest in the use of optical wireless (OW) communication to supplement RF communications. In contrast to RF communication technology, OW systems offer the use of largely unregulated electromagnetic spectrum and large bandwidths for communication. They also offer the potential to be highly secure against jamming and eavesdropping. Interest in OW has become especially keen in light of the maturation of light-emitting diode (LED) technology. This maturation, and the consequent emerging ubiquity of LED technology in lighting systems, has motivated the exploration of LEDs for wireless communication purposes in a wide variety of applications. Recent interest in this field has largely focused on the potential for indoor local area networks (LANs) to be realized with increasingly common LED-based lighting systems. We envision the use of LED-based OW to serve as a supplement to RF technology in communication between mobile platforms, which may include automobiles, robots, or unmanned aerial vehicles (UAVs). OW technology may be especially useful in what are known as RF-denied environments, in which RF communication may be prohibited or undesirable. The use of OW in these settings presents major challenges. In contrast to many RF systems, OWsystems that operate at ranges beyond a few meters typically require relatively precise alignment. For example, some laser-based optical wireless communication systems require alignment precision to within small fractions of a degree. This level of alignment precision can be difficult to maintain between mobile platforms. Additionally, the use of OW systems in outdoor settings presents the challenge of interference from ambient light, which can be much brighter than any LED transmitter. This thesis addresses these challenges to the use of LED-based communication between mobile platforms. We propose and analyze a dual-link LED-based system that uses one link with a wide transmission beam and relaxed alignment constraints to support a more narrow, precisely aligned, higher-data-rate link. The use of an optical link with relaxed alignment constraints to support the alignment of a more precisely aligned link motivates our exploration of a panoramic imaging receiver for estimating the range and bearing of neighboring nodes. The precision of such a system is analyzed and an experimental system is realized. Finally, we present an experimental prototype of a self-aligning LED-based link

Exploiting Heterogeneity in Networks of Aerial and Ground Robotic Agents

By taking advantage of complementary communication technologies, distinct sensing functionalities and varied motion dynamics present in a heterogeneous multi-robotic network, it is possible to accomplish a main mission objective by assigning specialized sub-tasks to specific members of a robotic team. An adequate selection of the team members and an effective coordination are some of the challenges to fully exploit the unique capabilities that these types of systems can offer. Motivated by real world applications, we focus on a multi-robotic network consisting off aerial and ground agents which has the potential to provide critical support to humans in complex settings. For instance, aerial robotic relays are capable of transporting small ground mobile sensors to expand the communication range and the situational awareness of first responders in hazardous environments. In the first part of this dissertation, we extend work on manipulation of cable-suspended loads using aerial robots by solving the problem of lifting the cable-suspended load from the ground before proceeding to transport it. Since the suspended load-quadrotor system experiences switching conditions during this critical maneuver, we define a hybrid system and show that it is differentially-flat. This property facilitates the design of a nonlinear controller which tracks a waypoint-based trajectory associated with the discrete states of the hybrid system. In addition, we address the case of unknown payload mass by combining a least-squares estimation method with the designed controller. Second, we focus on the coordination of a heterogeneous team formed by a group of ground mobile sensors and a flying communication router which is deployed to sense areas of interest in a cluttered environment. Using potential field methods, we propose a controller for the coordinated mobility of the team to guarantee inter-robot and obstacle collision avoidance as well as connectivity maintenance among the ground agents while the main goal of sensing is carried out. For the case of the aerial communications relays, we combine antenna diversity with reinforcement learning to dynamically re-locate these relays so that the received signal strength is maintained above a desired threshold. Motivated by the recent interest of combining radio frequency and optical wireless communications, we envision the implementation of an optical link between micro-scale aerial and ground robots. This type of link requires maintaining a sufficient relative transmitter-receiver position for reliable communications. In the third part of this thesis, we tackle this problem. Based on the link model, we define a connectivity cone where a minimum transmission rate is guaranteed. For example, the aerial robot has to track the ground vehicle to stay inside this cone. The control must be robust to noisy measurements. Thus, we use particle filters to obtain a better estimation of the receiver position and we design a control algorithm for the flying robot to enhance the transmission rate. Also, we consider the problem of pairing a ground sensor with an aerial vehicle, both equipped with a hybrid radio-frequency/optical wireless communication system. A challenge is positioning the flying robot within optical range when the sensor location is unknown. Thus, we take advantage of the hybrid communication scheme by developing a control strategy that uses the radio signal to guide the aerial platform to the ground sensor. Once the optical-based signal strength has achieved a certain threshold, the robot hovers within optical range. Finally, we investigate the problem of building an alliance of agents with different skills in order to satisfy the requirements imposed by a given task. We find this alliance, known also as a coalition, by using a bipartite graph in which edges represent the relation between agent capabilities and required resources for task execution. Using this graph, we build a coalition whose total capability resources can satisfy the task resource requirements. Also, we study the heterogeneity of the formed coalition to analyze how it is affected for instance by the amount of capability resources present in the agents