Pierpaolo Salvo

Road Side Unit coverage extension for data dissemination in VANETs

Data dissemination is a key component of Infotainment and safety services in Vehicular Ad Hoc Networks. For infotainment services data dissemination starts from a Road Side Unit (RSU) and propagates to a multiplicity of On Board Units (OBU). A RSU typically can reach with a single hop only a fraction of the interested vehicles. Multi-hop, inter-vehicle communications is necessary to reach vehicles in the whole area that could be interested in the service. For an efficient data dissemination both the number of forwarding vehicles and the number of not covered ones shall be kept down. In this work we study the extension of the RSU coverage area via a simple data dissemination defined for urban scenarios. The proposed forwarding algorithm relies only on information local to the forwarding OBU. We show that in our case studies representing urban structures the protocol guarantees a good RSU coverage extension (in the order of 20 times the transmission area of the RSU) with a very low percentage of vehicles not reached by the disseminated data.

Enhanced VANET broadcast throughput capacity via a dynamic backbone architecture

We propose a high throughput dissemination scheme for Vehicular Ad Hoc Networks (VANET) based on the dynamic formation of a multi-hop backbone network. We describe and analyze such a networking protocol when used to broadcast message flows generated by a Road Side Unit along a linear road, forming a VANET structure that is identified as a Vehicular Backbone Network (VBN). The VBN is based on elected vehicles that reside at preferred locations to act as backbone relay nodes, jointly optimally configured to operate at designated link data rates and spatial reuse factors. We present both an analytical evaluation of the broadcast throughput capacity that can be achieved by using the VBN mechanism and a simulative analysis based on the IEEE 802.11p CSMA/CA MAC protocol, standardized for VANET. The results demonstrate the significant performance enhancement achieved under VBN in attaining enhanced throughput capacity rate and in providing for a wider dissemination coverage span. Admitted packets are assured low end-to-end packet delays through the employment of a flow control scheme.

Timer-Based Distributed Dissemination Protocols for VANETs and Their Interaction with MAC Layer

A key paradigm enabled by Vehicular Ad hoc NET- works is the support of location aware push-mode info-tainment services, besides the safety services that motivate the deployment of the technology in the first place. Message and advertisements are spread via multi-hop communications from the originating Road Side Units connected to the Internet. Support of such services relies on robust and efficient dissemination protocols. We define a timer-based vehicular backbone network protocol, where each vehicle can take forwarding decisions only based on the information read in the message header, its current state and local measurements. We analyze its performance taking into account the effect of the IEEE 802.11p MAC layer. A comparison with other literature dissemination protocols is carried out in a highway setting.

Infotainment traffic flow dissemination in an urban VANET

Inter-vehicle communications will play an important role in future cars and traffic management in general. Many different services have been proposed in the literature using vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communications. These services include safety applications like collision warning, up-to-date traffic information, active navigation, and also infotainment. Efficient data dissemination in vehicular networks (VANET) is of particular interest for both safety and infotainment services. In case of infotainment services, which are the object of our study, data dissemination is used to extend the radio coverage area of a Road Side Unit (RSU) to reach all users that can be interested in a given service. In this work, we propose a family of algorithms to extend the RSU coverage area in VANETs. These algorithms apply simple geometrical rules based on the position of the sending nodes. The algorithms are used to allow the data to cross road junctions and to propagate towards multiple directions, without using beacon or hello messages. By applying a simple geometrical analysis we show that the proposed solutions are able to increase the number of nodes reached by a broadcast message. Moreover, we study the performance of our solution through message flows injected in a dynamic scenario, where a Manhattan street grid is reproduced and populated through SUMO, which is able to provide realistic vehicle flows. The effect of traffic lights on vehicle flows in relation to network performance is also discussed.

GPS aided inter-vehicular wireless networking

To support in an efficient way infotainment and public safety multicast applications in Vehicular Ad-Hoc Networks (VANET), a fundamental aspect is the optimization of the broadcast capacity. The objective is to disseminate packet flows to a wide set of vehicles by extending the coverage area of the broadcast packet flows distributed from a Road Side Unit through the use of vehicle-to-vehicle multi-hop communications. To this aim, we synthesize and study Vehicular Backbone Network (VBN) systems. Several vehicles that are situated along the highway are dynamically self elected based on their locations along the highway, to act as relay nodes that disseminate and forward flow packets. We analytically provide rationale for the criteria to be used in electing relay nodes. This is based on the computation of targeted optimal geographical positions for them under which the systems broadcast capacity is maximized, while striving also to reduce the number of elected relay nodes.

Probabilistic relay selection in timer-based dissemination protocols for VANETs

Implementations of data dissemination protocols in Vehicular Ad-Hoc Networks (VANETs) typically use multi-hopping approaches at the network layer, employing timers whose expiration times determine whether a vehicle should relay a message. These protocols, when they interact with lower access layers, such as the IEEE 802.11p MAC, are often affected by phenomena that impair the performance of the dissemination process. In this paper, we highlight the spurious forwarding phenomenon that arises when using timer-based protocols. We demonstrate the degradation incurred in the packet dissemination performance when the VANET is loaded by a high rate of packet flows. We then propose a probabilistic decimation approach, demonstrate its ability to alleviate the spurious forwarding problem, and discuss its performance as a function of vehicular traffic density and packet flow rate. Comparisons with other probabilistic dissemination protocols highlight the significant performance improvement attained by using our approach, assuring the realization of high throughput rate and packet delivery ratio.

Heterogeneous cellular and DSRC networking for Floating Car Data collection in urban areas

Abstract Vehicular traffic monitoring is a major enabler for a whole range of Intelligent Transportation System services. Real time, high spatial and temporal resolution vehicular traffic monitoring is becoming a reality thanks to the variety of communication platforms that are being deployed. Dedicated Short Range Communications (DSRC) and cellular communications like Long Term Evolution (LTE) are the major technologies. The former is specifically tailored for Vehicular Ad-hoc Network, the second one is pervasive. We propose a fully distributed Floating Car Data (FCD) collection protocol that exploits the heterogeneous network provided by DSRC and LTE. The proposed approach adapts automatically to the penetration degree of DSRC, achieving the maximum possible LTE offloading, given the VANET connectivity achieved via DSRC. Extensive simulations in real urban scenarios are used to evaluate the protocol performance and LTE offloading, as compared to baseline and literature approaches.

Vehicular Backbone Network Approach to Vehicular Military Ad Hoc Networks

We consider a tactical command center that issues broadcast data message flows for dissemination to all vehicles traveling as team members of a convoy, or along a multilane linear road segment. We propose a networking protocol which uses location aware data to identify and elect certain vehicles that reside at preferred locations to act as relay nodes, forming a dynamic multi-hop backbone network. The presented mechanism, identified as a Vehicular Backbone Network (VBN), optimally sets the rate of the adaptive coding scheme for the backbone links, while jointly configuring the targeted inter-relay distances and the proper reuse level for a reuse-M spatial-TDMA medium access control (MAC) scheme. We present a fast and efficient mechanism for the dynamic and spatially distributed implementation of the backbone-node election process. For this purpose, we make use of the spatial structure governing the mobility of vehicles across a multi-lane linear highway. To assure the robustness of the election scheme, we assume the backbone synthesis process to be performed at a Forwarding Layer, above the MAC layer, and thus be transparent to the character and operation of the employed (whether contention-less or contention oriented) MAC layer protocol. We present a mathematical model for the determination of the VBN systems parameters that serve to produce the highest throughput capacity rate.

Vehicular Backbone Networking Protocol for Highway Broadcasting using Directional Antennas

Vehicular Ad Hoc Network technology facilitates real time information dissemination by enabling efficient inter-vehicle communications for the wide broadcasting of public safety and other message flows. A key challenge in VANET broadcasting is to develop a networking mechanism to coordinate data transmissions among moving vehicles. We propose a Directional Vehicular Backbone Network (DVBN) protocol for the distribution of messages generated by a Road Side Unit located at a position along a linear highway to vehicles that travel along this highway. Using GPS (Global Positioning System), an election algorithm is used so that vehicles that are positioned close to those nominal positions are elected to act as relay nodes. The aim of this paper is two-fold: a. We examine the utility of using varying inter-RN nominal position ranges in contributing to the enhancement of the systems broadcast throughput rate. We show that when minimum inter-vehicular spacing requirements are imposed, it is effective to select equal inter-RN distance levels. b. We demonstrate the superior performance offered by this DVBN protocol when compared with a corresponding (VBN) protocol that employs omni-directional antennas. We illustrate scenarios under which broadcast throughput capacity rate gains as high as three to ten fold are achieved by the DVBN scheme.

Investigating VANET dissemination protocols performance under high throughput conditions

Abstract The use of Vehicular Ad-Hoc Networks (VANETs) for the dissemination of data flows to mobile highway vehicles has gained recently attention. For this purpose, vehicle-to-vehicle multi-hop communications are employed. For the effective networking of packets among highway vehicles, it is necessary to implement efficient algorithms that vehicles use to elect themselves as relay nodes to forward packets that they receive from other vehicles. In this work, we investigate the behavior of distributed relay node election protocols. In particular, we consider a class of such protocols whose actions are determined at time instants induced by the expiration of properly calibrated timers. We then investigate the high throughput regime of dissemination protocols. We show that a key factor that limits the achievable throughput rate is the occurrence of spurious forwarding events. These events are shown to lead to message duplications and consequent throughput degradation. We characterize this phenomenon by considering a VANET system that is configured to disseminate a single message flow along a road, as well as a scenario that involves the dissemination of two data flows that are originated by two distinct source nodes. We propose the integration into the protocol of a probabilistic decimation logic, with minimal impact on the protocol complexity. We show that, combined with the use of timers, the probabilistic mechanism serves to alleviate the occurrence of spurious forwarding events and consequently enhances the systems throughput rate and packet delivery ratios. The results of our study provide key guidelines for the design and calibration of such high performance networking protocols for VANET systems.