Models and Performance of VANET based Emergency Braking

The network research community is working in the field of automotive to provide VANET based safety applications to reduce the number of accidents, deaths, injuries and loss of money. Several approaches are proposed and investigated in VANET literature, but in a completely network-oriented fashion. Most of them do not take into account application requirements and no one considers the dynamics of the vehicles. Moreover, message repropagation schemes are widely proposed without investigating their benefits and using very complicated approaches. This technical report, which is derived from the Master Thesis of Michele Segata, focuses on the Emergency Electronic Brake Lights (EEBL) safety application, meant to send warning messages in the case of an emergency brake, in particular performing a joint analysis of network requirements and provided application level benefits. The EEBL application is integrated within a Collaborative Adaptive Cruise Control (CACC) which uses network-provided information to automatically brake the car if the driver does not react to the warning. Moreover, an information aggregation scheme is proposed to analyze the benefits of repropagation together with the consequent increase of network load. This protocol is compared to a protocol without repropagation and to a rebroadcast protocol found in the literature (namely the weighted p-persistent rebroadcast). The scenario is a highway stretch in which a platoon of vehicles brake down to a complete stop. Simulations are performed using the NS_3 network simulation in which two mobility models have been embedded. The first one, which is called Intelligent Driver Model (IDM) emulates the behavior of a driver trying to reach a desired speed and braking when approaching vehicles in front. The second one (Minimizing Overall Braking Induced by Lane change (MOBIL)), instead, decides when a vehicle has to change lane in order to perform an overtake or optimize its path. The original simulator has been modified by - introducing real physical limits to naturally reproduce real crashes; - implementing a CACC; - implementing the driver reaction when a warning is received; - implementing different network protocols. The tests are performed in different situations, such as different number of lanes (one to five), different average speeds, different network protocols and different market penetration rates and they show that: - the adoption of this technology considerably decreases car accidents since the overall average maximum deceleration is reduced; - network load depends on application-level details, such as the implementation of the CACC; - VANET safety application can improve safety even with a partial market penetration rate; - message repropagation is important to reduce the risk of accidents when not all vehicles are equipped; - benefits are gained not only by equipped vehicles but also by unequipped ones

Vehicles or Pedestrians: On the gNB Placement in Ultradense Urban Areas

This paper tackles the problem of base stations placement to guarantee line of sight connectivity to vehicles in urban areas, when high frequency communications (mmWave or TeraHertz) are used. We introduce a novel methodology mixing vehicular networks simulations and show that the density of base stations per squared km is low enough to be feasibly reached. However, optimizing the placement for vehicles coverage provides an advantage but may not be enough for pedestrians coverage

Multi-Technology Cooperative Driving: An Analysis Based on PLEXE

Cooperative Driving requires ultra-reliable communications, and it is now clear that no single technology will ever be able to satisfy such stringent requirements, if only because active jamming can kill (almost) any wireless technology. Cooperative driving with multiple communication technologies which complement each other opens new spaces for research and development, but also poses several challenges. The work we present tackles the fallback and recovery mechanisms that the longitudinal controlling system of a platoon of vehicles can implement as a distributed system with multiple communication interfaces. We present a protocol and procedure to correctly compute the safe transition between different controlling algorithms, down to autonomous (or manual) driving when no communication is possible. To empower the study, we also develop a new version of PLEXE, which is an integral part of this contribution as the only Open Source, free simulation tool that enables the study of such systems with a modular approach, and that we deem offers the community the possibility of boosting research in this field. The results we present demonstrate the feasibility of safe fallback, but also highlight that such complex systems require careful design choices, as naive approaches can lead to instabilities or even collisions, and that such design can only be done with appropriate in-silico experiments

A Vehicular Networking Perspective on Estimating Vehicle Collision Probability at Intersections

Abstract-Finding viable metrics to assess the effectiveness of intelligent transportation systems (ITSs) in terms of safety is one of the major challenges in vehicular networking research. We aim to provide a metric, i.e., an estimation of the vehicle collision probability at intersections, that can be used for evaluating intervehicle communication (IVC) concepts. In the last years, the vehicular networking community reported in several studies that safety-enhancing protocols and applications cannot be evaluated based only on networking metrics such as delays and packet loss rates. We present an evaluation scheme that addresses this need by quantifying the probability of a future crash, depending on the situation in which a vehicle is receiving a beacon message [e.g., a cooperative awareness message (CAM) or a basic safety message (BSM)]. Thus, our criticality metric also allows for fully distributed situation assessment. We investigate the impact of safety messaging between cars approaching an intersection using a modified road traffic simulator that allows selected vehicles to disregard traffic rules. As a direct result, we show that simple beaconing is not as effective as anticipated in suburban environments. More profoundly, however, our simulation results reveal more details about the timeliness (regarding the criticality assessment) of beacon messages, and as such, they can be used to develop more sophisticated beaconing solutions. Index Terms-Vehicle safety, vehicular ad hoc networks, wireless communication

Safe and Efficient Communication Protocols for Platooning Control

Modern vehicles are becoming smarter and smarter thanks to the continuous development of new Advanced Driving Assistance Systems (ADAS). For example, some new commercial vehicles can detect pedestrians on the road and automatically come to a stop avoiding a collision. Some others can obtain information about traffic congestion through the cellular network and suggest the driver another route to save time. Nevertheless, drivers (and our society as well) are always striving for a safer, cleaner, and more efficient way of traveling and standard, non-cooperative ADAS might not be sufficient. For this reason the research community started to design a vehicular application called “platooning”. Platooning simultaneously tackles safety and traffic congestion problems by cooperatively coordinating vehicles in an autonomous way. Traffic flow is optimized by using an advanced Adaptive Cruise Control (ACC), called Cooperative Adaptive Cruise Control (CACC), which drastically reduces inter-vehicle gaps. By being autonomously coordinated, platooning vehicles implicitly implement automated emergency braking, a fundamental application for freeway safety. The idea is to form optimized road trains of vehicles where the first drives the train, while the others autonomously follow at a close distance, without requiring the driver to steer, accelerate, or brake. Platooning can have an enormous impact on future transportation systems by increasing traffic flow (and thus reducing congestion), increasing safety, reducing CO2 emissions, and reducing the stress of driving. This application is extremely challenging due to its inter-disciplinary nature. Indeed, it involves control theory, vehicle dynamics, communication, and traffic engineering. In this thesis we are mostly concerned with the communication aspects of this application, which is fundamental for making the vehicles cooperate, improving the efficiency of the application with respect to a pure sensor-based solution. Application requirements are very tight and, given that the envisioned communication technology will be IEEE 802.11-based, there are concerns on whether these requirements can really be met. The focus of the thesis is in this direction. The first contribution is the design of PLEXE, an extension for the widely used vehicular simulation framework Veins that enables research studies on various platooning aspects, including design and evaluation of control algorithms, communication protocols, and applications. The tool is open source and free to download and use, and it realistically simulates both communication and vehicle dynamics. This makes PLEXE a valid testing platform before real world deployment. The second contribution is a set of undirected information broadcasting (beaconing) protocols that specifically take into account the requirements of the application. We initially develop four static (i.e., periodic) approaches and compare them against two state of the art dynamic protocols, showing that our approaches are capable of supporting the application even in heavily dense scenarios. Then, we propose a dynamic protocol that further improves the application (increasing safety) and the network layer (reducing resource usage) performance. The final contribution is a platooning control algorithm that, compared to state of the art approaches, is re-configurable at run-time and that can be adapted to network conditions. We thoroughly test the algorithm in highly challenging scenarios. These scenarios include a realistic network setup where the road is shared by human- and automated-driven vehicles. Human-driven vehicles interfere with automated-driven ones by sending data packets on the same channel. Moreover, we also consider a scenario with realistic vehicle dynamics, which takes into account vehicles’ engine and braking characteristics. The algorithm is shown to be robust to network and external disturbances, to have a fast convergence, and to be very stable. The results in this work thus represent a big step towards the real world implementation of platooning systems

The joint network/control design of platooning algorithms can enforce guaranteed safety constraints

4noVehicular networks supporting cooperative driving are among the most interesting and challenging ad-hoc networks. Platooning, or the act of coordinating a set of vehicles through an ad-hoc network, promises to improve traffic safety, and at the same time reduce congestion and pollution. The design of the control system for this application is challenging, especially because the coordination and cooperation between vehicles is obtained through a wireless network. So far, control and network issues of platooning have been investigated separately, but this is definitely a sub-optimal approach, as constraints of the networked control system impose bounds on the network performance, and network impairments translate into disturbances on the controlled system. In this work we design a cooperative driving system from a joint network and control perspective, determining upper bounds on the error subject to packet losses in the network, so that the actual inter-vehicle gap can be tuned depending on vehicle or network performance. Extensive simulations show that the system is very robust to packet losses and that the derived bounds are never violated. In addition, since the leader control law is part of the proposed control approach, we show that, besides taking into account external events and reacting within the given constraints to ensure the overall road safety, the system can be easily integrated into global traffic optimization tools that mandate the platoon behavior.openopenGiordano G.; Segata M.; Blanchini F.; Lo Cigno R.Goldoni, Giordano; Segata, M.; Blanchini, F.; Lo Cigno, R

Markov-modulated Models to Estimate the Age of Information in Cooperative Driving

This short paper explores for the first time the possibility to model the Age of Information (AoI) in cooperative driving applications. A heuristic analysis shows that it is possible to model the AoI as a system modulated by a Semi-Markov process, where the states depend on the mobility and the radio environment. The dwell time in typical road networks cannot be assumed exponential, so that the model is not a simple Markov Modulated Poisson Process (MMPP), but rather a generic Markov Modulated Process with general dwell time and arbitrary distribution of the AoI. Future work includes the tuning of the model parameters in different scenarios, the characterization of the AoI distribution, validation tests, and obviously its use in the design of cooperative driving applications

Emergency braking: a study of network and application performance

Safety applications are among the key drivers in VANET research. Their study is complex as it encompasses different disciplines, from wireless networking to car dynamics, to drivers' behavior, not to mention the economic and legal aspects. This work presents a simulative study of emergency braking applications tackled by embedding a mobility, cars' dynamic, and driver's behavior model into a detailed networking simulator (ns-3). The results, derived both at the network and at the application level, capture correctly the interactions of the communications and protocols with the car's adaptive cruise control system and the driver's behavior for cars that are not equipped with communication devices. The paper presents in detail the improvements we contribute in simulation techniques and model completeness. It introduces a novel and easy message aggregation technique to empower message re-propagation while controlling the network load during the peak due to the emergency braking. Finally it discusses the effectiveness of such applications as a function of the market penetration rate, showing that even cars that are not equipped with communication devices benefit from the smoother and earlier reaction of those cars that can communicate and whose adaptive cruise control implements a correct deceleration strategy