Riccardo Scopigno

Mobile Slotted Aloha for Vanets

Vanet literature is mainly focused on CSMA and CSMA-like access protocols. Actually a deep study on how a slotted approach could be adopted in Vanet is missing. This is mainly due to the lack of a distributed MAC able to guarantee a scalable resource reservation without involving a central poller. In this paper we propose a novel protocol, MS-Aloha, which is based on recent RR-Aloha extensions, in order to overcome its most critical limitations. The protocol is studied theoretically and validated by simulations. Even if an extensive analysis is far from being achieved, some relevant results are discussed as important enabling steps. Index Terms—Vanet, Slotted-ALOHA, Distributed Protocol, Resource Optimisation, Collision Avoidance I. INTRODUCTION

An insight into Decentralized Congestion Control techniques for VANETs from ETSI TS 102 687 V1.1.1

Many cooperative applications designed to improve road safety rely on the frequent exchange of awareness messages among vehicles. Therefore, under high vehicle density, the channel medium is expected to get congested. To tackle this situation, the European Telecommunications Standards Institute (ETSI) specified a set of Decentralized Congestion Control (DCC) mechanisms that adapt the transmission parameters based on channel load measures. Due to some concerns about its effectiveness and stability, DCC and its overall philosophy are currently being revised and extended: all in all, DCC deserves additional investigations. For this purpose, in this paper a simulation analysis is presented, aiming at enriching the insight into the DCC behaviour, under a variety of channel load conditions and through the definition of both link- and application-layer performance metrics. Achieved results show that the DCC techniques are not really effective with the currently specified parameters settings; hence some hints are given to improve their performance.

From today's VANETs to tomorrow's planning and the bets for the day after

After more than a decade of research and investments, the first release of standards for cooperative Intelligent Transportation Systems (C-ITS) is going to be finalized. Preliminary field-trials have already demonstrated the high potentials of short-range wireless communication in vehicular environments for many basic day-one C-ITS applications (e.g., hazardous location and road works warnings). In the meanwhile, stakeholders are working on Release 2 of the standards to augment the portfolio of offered services with increased cooperative awareness and driving automation. The related higher C-ITS market penetration and the strict latency and robustness requirements of after day-one applications (e.g., platooning and autonomous driving) are going to question the capability of the current standard technology, mainly based on IEEE 802.11, to cope with scalability and congestion issues at the radio access level.In this paper, we analyze the topic of vehicular networks in the context of C-ITS from an evolutionary point of view, scanning early concepts and enabling technologies, current status and future opportunities, with a look on a future fully networked vehicular environment.

Augmenting Vehicle-to-Roadside connectivity in multi-channel vehicular Ad Hoc Networks

Abstract Vehicle-to-Roadside (V2R) wireless communication is a cornerstone for providing a wide plethora of intelligent transportation system (ITS) applications in the near future. Initial investment costs could discourage the deployment of a ubiquitous roadside infrastructure to support on-the-road networks; this would imply discontinuous coverage and short-lived connectivity. The purpose of this paper is to design techniques that make the best of sparse road-side unit (RSU) placement by supporting the spreading of network initialization advertisements from RSUs, when considering the multichannel features of the recently published IEEE 802.11p/IEEE 1609.4 standards for wireless access in vehicular environment (WAVE). The proposed techniques leverage time, space and channel diversity to improve efficiency and robustness of the network advertisement procedure in a urban scenario where obstructions to signal propagation due to buildings and traffic jam could hinder successful message spreading. Simulation under different RSU density, vehicular networking technology penetration rate, data rate, and packet size, aims at assessing effectiveness and efficiency of the proposed solutions.

Browsing and exploration of video sequences: A new scheme for key frame extraction and 3D visualization using entropy based Jensen divergence

Abstract This paper proposes a unified scheme for video browsing and exploration. Our scheme involves two components, video key frame extraction and 3D visualization. For key frame extraction, we develop a generic approach in which the Jensen–Shannon divergence (JSD), Jensen–Renyi divergence (JRD) and Jensen–Tsallis divergence (JTD) are investigated for measuring the difference between neighboring video frames, segmenting a video clip into shots then possibly into sub-shots, and choosing key frames in each shot. Our novel approach is computationally inexpensive and yet effective, as shown by experimental results. As for 3D visualization, an innovative prototype, in which key frames, their related information and video contexts are displayed, is created for video exploration. Our visualization tool also contributes to easily locating, highlighting and removing the possible redundant key frames. The key frames selected by our proposed approach and their corresponding visualization interface are combined to lead to a fast grasp of video contents.

A Methodology for the Analysis of 802.11a Links in Industrial Environments

Wireless solutions are becoming more and more attractive for the communication systems of manufacturing plants. If the advantages of wireless are clear and have been extensively discussed, also the drawbacks need to be considered and, among them, the impact of an industrial environment on error rate and throughput of the wireless links. These performance aspects get even more critical when developing wireless solutions for safety-critical industrial communications and using off-the-shelf components. The first step in evaluating these solutions is to characterize the channel behavior of the selected wireless platform for a set of real-life scenarios representative of different operating conditions. We present a methodology and software tool aimed at analyzing WLAN channel behaviors and we apply it to evaluate the use of 802.11a consumer chipsets for a typical safety critical industrial plant application.

Signal Shadowing in Simulation of Urban Vehicular Communications

Vehicular communications have been demonstrated to strongly depend on the general setting of the scenario: a heavy impact on bit-error-rate and packet-error-rate may come from physical layer phenomena which are typically simulated on software platforms different from those used for protocol validation. As a result, current protocol simulations do not take into account environmental constraints: some effects are considered by statistical models (such as Nakagami model), other ones – such as shadowing – remain uncovered phenomena. This paper proposes a simple but effective model for the shadowing raised by large buildings and blocks in urban areas: we demonstrate that the proposed solution improves the realism of simulations and significantly improves the results.

RR-Aloha+: A slotted and distributed MAC protocol for vehicular communications

The state of the art of vehicular communications includes extensive investigations on distributed-contention approaches (mostly focused on WiFi CSMA/CA optimal and/or custom configurations), while scalable solutions for a distributed but contention-free wireless architecture remain unexplored. In this paper, starting from an existing protocol called RR-Aloha, we propose some novel extensions to it, in order to solve some technical open issues, improve its scalability and overcome some criticalities concerning the dynamic setting of vehicular mobility. The study is based both on conceptual tests and on PC simulations on NS-2 (Network Simulator). The proposed scenarios are meant to validate the extensions and confirm the feasibility; the preliminary results show that the enhanced RR-Aloha+ 1 may actually exert a potentially relevant role in the vehicular communications, with a deterministic, reservation-based, QoS-capable and distributed access channel.

Urban VANETs and hidden terminals: Evaluation through a realistic urban grid propagation model

Despite the large number of active field-trials, network simulations still play a vital role in the development and validation of new protocols for vehicular networks. This role still motivates the improvement of simulation tools, especially in terms of realism, so to yield accurate results. One of the major gaps which still needs to be filled is urban propagation: an adequate modeling of obstructions is still missing and has come to light as a critical feature, potentially leading to arguable results. Here a new urban model (called Reliable Urban Grid - RUG) is proposed as an extension of an already validated propagation model of urban corners to more complex grid topologies. Achieved results show the higher impact of collisions by hidden terminals on standard contention-based medium access control protocols when compared to slotted solutions.

GNSS Synchronization in Vanets

The literature about GNSS in vehicular networks is usually restricted to the mutual interaction between positioning and routing (respectively with georouting and services of GNSS assistance). However, despite the apparent contradiction, also asynchronous Vehicular Ad-hoc networks (Vanets) built on the top of IEEE 802.11p require an absolute synchronization: this could be easily provided by the time information embedded in GNSS systems. This position paper analyses the issue of synchronization in Vanet both for the emerging asynchronous standard and for alternative synchronous solutions. The technical discussion adds also new elements useful for the comparative analysis among protocols for Vanets.