André Cardote

On the connection availability between relay nodes in a VANET

Vehicular Ad-hoc NETworks (VANET) are emerging as a promising way to disseminate information among vehicles. As this information can range from safety to infotainment application content, and the vehicular environment has very particular characteristics, the behavior of the network must be effectively studied in order to adapt the transmission mechanisms. This work presents a model for the connectivity patterns of chains of vehicles traveling in a highway. This information will be crucial to provide insight in the design of VANET protocols and applications, which will be dependent on the connectivity characteristics. The accuracy of the model is shown through its application to specific case studies. The obtained results show that, in highway scenarios, the connectivity availability between relay nodes can last for a significant amount of time (in the order of tens of seconds).

An IEEE 802.11p/WAVE implementation with synchronous channel switching for seamless dual-channel access (poster)

The emerging interest in vehicular networks (VANET) led to the deployment of several small and medium-scale testbeds to evaluate the characteristics of this technology in real-world scenarios. Despite this, due to the low availability and high cost of IEEE 802.11p/WAVE fully compliant hardware and software, many of these experiments have been performed with other communication standards, which generate, in many cases, misleading results, that are not representative of real-world vehicular communications. As a mean of solving this problem, this paper presents the implementation and validation of a fully compliant MAC/PHY solution developed in the scope of the DRIVE-IN project, which will be used in a 500-node testbed. Contrarily to what happens with most of the solutions existent in the market, our system complies with the strict channel switching timings using GPS time synchronization, providing access to two different types of wireless channels (e.g. control and service channels as defined in IEEE 1609.4) in a seamless way for the end user. This feature allows safety-critical and control messages to be sent in a dedicated channel, with very low latency, while another channel may be used for less critical services (e.g. infotainment applications, advertisement). The results of the conducted tests show that indeed it is possible to assure the support of critical safety services in the presence of other traffic.

Harbornet: a real-world testbed for vehicular networks

We present a real-world testbed for research and development in vehicular networking that has been deployed successfully in the seaport of Leixoes in Portugal. The testbed allows cloudbased code deployment, remote network control and distributed data collection from moving container trucks, cranes, tow boats, patrol vessels, and roadside units, thereby enabling a wide range of experiments and performance analyses. After describing the testbed architecture and its various modes of operation, we give concrete examples of its use and offer insights on how to build effective testbeds for wireless networking with moving vehicles.

Real-world evaluation of IEEE 802.11p for vehicular networks

This paper presents a set of experiments, performed using an IEEE 802.11p physical layer implementation based on the open-source ath5k driver, in both line of sight (LOS) and non-line of sight (NLOS) conditions. The results are compared against theoretical models and simulation of the same scenarios with proper propagation and channel models. The communication range in LOS can reach values larger than 1Km, while in NLOS scenarios, this communication range is decreased to the order of hundreds of meters.

Seamless horizontal and vertical mobility in VANET

In a near future, vehicles will be equipped with WAVE-compliant communication technology, enabling not only safety message exchange, but also infotainment and Internet access. However, without complete market penetration, other technologies must still be used, such as IEEE 802.11g/n to connect to public Wi-Fi hotspots in the city, or even 3G and 4G cellular networks. Due to the high mobility of nodes in Vehicular Ad-hoc NETworks (VANETs), the connectivity time between nodes becomes very short; therefore, it is essential to ensure the lowest handover time when moving between Road Side Units (RSUs) and other vehicles. In this paper, we implemented a multi-technology seamless handover mechanism for vehicular networks that integrates extended mobility protocols based on MIPv6 and PMIPv6, with a mobility manager that provides seamless communication between vehicles and the infrastructure, electing the best technology to maintain the vehicle connected without breaking any active sessions. To validate and evaluate the proposed handover approaches, a real-world vehicular testbed was setup, combining three technologies: IEEE 802.11p, IEEE 802.11g and 3G; handover metrics were obtained for all the combinations of these technologies. The results show that, if IEEE 802.11p is used in both vehicles and RSUs, the proposed approach is able to perform seamless handover with very low delay and no packet loss. The same conclusions apply for handovers between different technologies.

A statistical channel model for realistic simulation in VANET

Vehicular Ad-hoc NETwork (VANET) simulation is crucial for the development of new protocols and applications. Even though real-world experimentation is the de facto benchmarking solution for any of these, the first evaluations must be made through simulation, due to the ease of changing parameters and scenarios. In this work, we propose a statistical channel model for VANET simulation based on the observation of data from real-world experiments, obtained from an IEEE 802.11p / WAVE compliant testbed. We statistically characterize fading in VANET communication and propose a combination of models for Line-of-Sight (LoS) transmission. Simulations using the proposed model were compared with real-world experiment results and, furthermore, the model was validated against a set of measurements from an independent research group, fitting it with a high concordance level, thus proving to be effective and general.

REINVENT: Accessing vehicular networks in mobile applications

This paper proposes REINVENT, a software architectural solution to decouple the specificities of using vehicular network communication resources in Android smartphone applications. REINVENT provides a REST based message passing interface based on Androids content provider to abstract vehicular network communication services. Using REINVENT, Android applications can use transparently the communication resources avoiding network transport layer details. REINVENT was tested in both laboratory and real world scenarios in the road with WAVE/IEEE 802.11p technology, to assess its usefulness in two Android applications, (VNChat and iThere). The real experiments also assess how REINVENT supports a mobile application to log relevant parameters in typical vehicular networks testing in different network scenarios.

Context classifier for position-based user association control in vehicular hotspots

Abstract Unintentional associations of mobile devices to on-board WiFi access points (APs) can affect the outdoor Internet experience of mobile device users, as the on-going cellular connection is broken and a short-lived WiFi connection is initiated. This disruption of the user experience can be avoided if the on-board AP learns whether the user device is inside or outside the bus and decides to accept its connection request or not. In this article, we present a classifier-based mechanism for on-board APs that accepts or denies user device associations based on a classification of the relative position of the device. An analysis of the problem in terms of connection duration and RSSI is presented to motivate the selected approach. We then describe a classifier to identify the user relative position trained on features extracted from contextual information. The classifier was trained with a large dataset of real-world WiFi-usage and mobility patterns of a public bus fleet from Porto, Portugal. The training procedure indicated bus speed as the most relevant feature, and that the RSSI measured at the on-board AP does not contribute. Finally, we propose a mechanism that grants or denies connection access to users based on the classifier output. We discuss how to integrate this mechanism in the AP network stack and evaluate its performance in real-world tests. Our solution can avoid 40% of the associations from users outside of the bus.

Detecting relative position of user devices and mobile access points

Free Internet access in urban public transportation fleets by means of WiFi hotspots is becoming a common service in a growing number of cities. Users of the public bus WiFi service will get the network memorised in their mobile devices and, as they move from buses to streets, their devices will switch Internet access from WiFi to cellular. If a bus passes by the user while he or she is on the street, the mobile device will connect to the bus WiFi hotspot, breaking the cellular connection and initiating a short-lived WiFi connection. This disruption of the user experience can be avoided if the mobile access point (AP) learns whether the user device is inside or outside the bus and decides to accept its connection request or not. In this paper, we evaluate if a mobile AP (installed on the buses) can detect the relative position of a user device. We collected a large dataset of WiFi-usage and mobility patterns from a real-world public bus fleet in Porto, Portugal, to identify features from which the mobile AP can detect if a user device is inside or outside the bus. We tested RSSI and bus speed as features feed into a classifier, and observed that RSSI is a poor indicator whereas bus speed presents some correlation to whether a connection is established inside or outside the bus. Finally, we propose and evaluate the trade-offs of a mechanism (running on the mobile AP) that decides whether a device should be allowed to connect or not.

Vehicular testbed management

The deployment of vehicular network testbeds encompasses a myriad of new challenges regarding resource management, execution of experiments on the nodes, and the collection of the resulting data, when compared to traditional testbeds. Vehicular nodes have very unpredictable mobility patterns, especially in cities, and use a specific communication protocol; therefore, the commonly used solutions for large scale testbeds are not directly applicable. This is the case of our vehicular network testbed developed in the framework of the DRIVE-IN and Future Cities! (DRIVE-IN and Future Cities!)1 projects. This paper tackles the aforementioned issues by proposing the design and implementation of a testbed management system based on the cOntrol and Management Framework (OMF). The base functionalities of OMF were extended to integrate node control over cellular networks, as well as to guarantee that experiments are always safely deployed, minimizing the risk of node corruption and malfunctioning. The management platform is capable of uploading new software to the vehicular nodes, conduct experiments using the specific vehicular wireless (IEEE 802.11p) interface, collect the resulting data, as well as storing and managing information about all the nodes. The results obtained from real-world experiments show that the the proposed platform is able to manage a Vehicular Ad-hoc NETwork (VANET) testbed.