Bastian Bloessl

Plexe: A platooning extension for Veins

Cooperative driving in general and Cooperative Adaptive Cruise Control (CACC) or platooning in particular require blending control theory, communications and networking, as well as mechanics and physics. Given the lack of an integrated modeling framework and theory as well as the prohibitively high costs of using prototypes for what-if studies, simulation remains the fundamental instrument to evaluate entire cooperative driving systems. This work presents Plexe, an Open Source extension to Veins that offers researchers a simulation environment able to run experiments in realistic scenarios, taking into account physics and mechanics of the vehicles, communications and networking impairments, and Inter-Vehicle Communication (IVC) protocol stacks. Plexe is easily extensible and already implements protocols to support platooning and cooperative driving applications and several state of the art cruise control models. We describe the structure of the simulator and the control algorithms that Plexe implements and provide two use cases which show the potential of our framework as a powerful research tool for cooperative driving systems.

Toward Communication Strategies for Platooning: Simulative and Experimental Evaluation

Platooning, which is the idea of cars autonomously following their leaders to form a road train, has huge potential to improve traffic flow efficiency and, most importantly, road traffic safety. Wireless communication is a fundamental building block: It is needed to manage and maintain the platoons. To keep the system stable, strict constraints in terms of update frequency and communication reliability must be met. We investigate different communication strategies by explicitly taking into account the requirements of the controller, exploiting synchronized communication slots, and transmit power adaptation. As a baseline, we compared the proposed approaches to two state-of-the-art adaptive beaconing protocols that have been designed for cooperative awareness applications, namely, the European Telecommunications Standards Institute (ETSI) Decentralized Congestion Control (DCC) and Dynamic Beaconing (DynB). Our simulation models have been parameterized and validated by means of real-world experiments. Our results demonstrate that the combination of synchronized communication slots with transmit power adaptation is perfectly suited for cooperative driving applications, even on very crowded freeway scenarios.

Protocol design for ultra-low power wake-up systems for tracking bats in the wild

We present a novel concept for a wake-up system based ultra-low power communication protocol for sensor networks. The main application field is monitoring contacts and even tracks of bats in the wild. Our sensor nodes can weigh at most 2 g out of which 1 g remains for the battery. We investigate a novel communication protocol design applicable to these systems and also showing great potentials for other ultra-low power sensor networks. In particular, we investigate the bat to ground communication by combining duty cycling with a multi-stage wake-up receiver. We employ Binary Offset Carrier (BOC) modulated signals that allow to accurately localize and track the bats while transmitting data in parallel. In a first step, we evaluated the conceptual design using a software-defined radio system to demonstrate the feasibility of the protocol design.

Enabling Situation Awareness at Intersections for IVC Congestion Control Mechanisms

An Intersection Assistance System aim to assist road users in avoiding collisions at intersections, either by warning the driver or by triggering automated actions. Such a system can be realized based on passive scanning only (e.g., using LiDAR) or supported by active Inter-Vehicle Communication (IVC). The main reason to use Inter-Vehicle Communication (IVC) is its ability to provide situation awareness even when a possible crash candidate is not yet in visual range. The IVC research community has identified beaconing, i.e., one-hop broadcast, as the primary communication primitive for vehicular safety applications. Recently, adaptive beaconing approaches have been studied and different congestion control mechanisms have been proposed to cope with the diverse demands of vehicular networks. In this paper, we show that current state-of-the-art congestion control mechanisms are not able to support IAS adequately. Specifically, current approaches fail due to their inherent fairness postulation, i.e., they lack fine grained prioritization. We propose a solution that extends congestion control mechanisms by allowing temporary exceptions for vehicles in dangerous situations, that is, situation-based rate adaptation. We show the applicability for two state-of-the-art congestion control mechanisms, namely Transmit Rate Control (TRC) and Dynamic Beaconing (DynB), in two different vehicular environments, rural and downtown.

Fairness kills safety: A comparative study for intersection assistance applications

We study the ability of Inter-Vehicle Communication (IVC) solutions to handle real-time requirements in safety scenarios using beaconing as a communication primitive. One of the envisioned safety applications is intersection assistance. The objective of such applications is to either warn the driver or even to act autonomously if other approaching vehicles endanger the vehicle. Fairness, combined with aggressive channel access for low-latency safety messages, has been one of the main research line according to which state of the art congestion control mechanisms have been developed. We show that these solutions are not able to sufficiently support intersection assistance applications. Specifically, we show that current approaches fail exactly due to their fairness postulation. We propose a new situation-aware solution to this fairness dilemma by allowing temporary exceptions for vehicles in dangerous situations. We show the applicability for two state of the art congestion control mechanisms, namely ETSI Transmit Rate Control (TRC) and Dynamic Beaconing (DynB). Our investigation also reveals important research objectives for future IVC protocols, namely how much reactivity and situation-awareness is needed in the highly dynamic environment of vehicular networks.

Timings matter: standard compliant ieee 802.11 channel access for a fully software-based SDR architecture

We present a solution for enabling standard compliant channel access for a fully software-based Software Defined Radio (SDR) architecture. With the availability of a GNU Radio implementation of an Orthogonal Frequency Division Multiplexing (OFDM) transceiver, there is substantial demand for standard compliant channel access. It has been shown that implementation of CSMA on a host PC is infeasible due to system-inherent delays. The common approach is to fully implement the protocol stack on the FPGA, which makes further updates or modifications to the protocols a complex and time consuming task. We take another approach and investigate the feasibility of a fully software-based solution and show that standard compliant broadcast transmissions are possible with marginal modifications of the FPGA. We envision the use of our system for example in the vehicular networking domain, where broadcast is the main communication paradigm. We show that our SDR solution exactly complies with the IEEE 802.11 Distributed Coordination Function (DCF) as well as Enhanced Distributed Channel Access (EDCA) timings. We were even able to identify shortcomings of commercial systems and prototypes.

Power matters: Automatic Gain Control for a Software Defined Radio IEEE 802.11a/g/p receiver

Software Defined Radios (SDRs) have become a fundamental building block for research on wireless networks. Yet, using this platform for experiments in the field is hindered by many practical difficulties, an important one being the need for Automatic Gain Control (AGC). We demonstrate a way of implementing an AGC algorithm directly in the FPGA where we are able to meet tough timing constraints. This allows using SDRs not just for lab experiments but also for measurement campaigns or deployments in the field.With extending our GNURadio-based Open Source stack for IEEE 802.11a/g/p WLAN with AGC, we provide an SDR platform that can be integrated into existing WiFi networks just as well as into future vehicular networks.

Demo: simulating the impact of communication performance on road traffic safety at intersections

Performance evaluation of communication protocols is usually carried out using typical network metrics as delay, jitter, or goodput. However, recent studies in the context of Inter-Vehicle Communication (IVC) have shown that using these metrics is not sufficient for evaluating vehicular safety applications. To highlight the importance of safety metrics and their applicability, we extended our existing simulation framework Veins to visualize these metrics live while the road traffic and network simulation are running in parallel. In particular, we demonstrate the impact of communication on intersection assistance applications. To simulate different intersection approaches, we implemented a simulation model that resembles different kinds of driver behavior and enables crashes at intersections. The resulting situations are displayed in the road traffic simulator and give the visitor insights on the current state of endangered vehicles. Furthermore, an autonomous controller has been implemented which tries to avoid accidents and hence shows the real-world impact, i.e., accidents can be avoided using advanced beaconing techniques. To increase interactivity of the demo, visitors will have the possibility to interact with and take control over endangered vehicles.

Low-Complexity Soft-Bit Diversity Combining for Ultra-Low Power Wildlife Monitoring

Diversity combining is a popular technique to in- crease the robustness of wireless communications. Multiple independent paths are needed for successful combining to recover a signal; which is particularly helpful in fading scenarios. Typically, this is achieved using multiple, sufficiently spaced apart antennas at a single receiver. We consider a Wireless Sensor Network (WSN) to monitor bats in the wild by equipping them with sensor nodes weighing only 2g and, therefore, having very tight energy budgets. A distributed ground network is used to receive the signals from bats at multiple nodes. We propose to exploit the distributed nature of these receivers to cooperatively decode the received signal. This scenario poses a number of research challenges related to the necessary synchronization of the receivers as well as the very limited energy budget at the nodes. To optimize link utilization in the ground network, we study the performance of low-complexity soft-bit diversity and unequal gain combining for robust packet-based communication. To assess the performance of diversity combining strategies, we conduct simulations and measurements using MATLAB as well as a Software Defined Radio (SDR)-based prototype. Finally, our application-specific diversity techniques are adapted to provide a more general solution.

Assessing the impact of inter-vehicle communication protocols on road traffic safety

Intelligent Transportation Systems (ITS) will change the experience of driving in the near future. Most applications will use wireless communication (cellular or ad-hoc) for being able to provide the required services. Usually performance evaluations of communication protocols are conducted with typical network metrics like delay, jitter, or goodput for example. However, in the context of ITS it has been shown that network metrics are not sufficient to evaluate vehicular safety applications. Therefore, we extended our existing simulation framework Veins with a model that allows to simulate dangerous road traffic safety situations, i.e., we implemented a driver behavior model for intersection approaches. Furthermore, we implemented an autonomous controller which tries to avoid crashes at intersections. We showcase the impact of different Inter-Vehicle Communication (IVC) protocols, although the intersection approach model and autonomous controller could be also employed to carry out safety evaluations of other communication technologies.