Annette Böhm

Evaluating CALM M5-based vehicle-to-vehicle communication in various road settings through field trials

Future cooperative Intelligent Transport Systems (ITS) applications aimed to improve safety, efficiency and comfort on our roads put high demands on the underlying wireless communication system. To gain better understanding of the limitations of the 5.9 GHz frequency band and the set of communication protocols for medium range vehicle to vehicle (V2V) communication, a set of field trials with CALM M5 enabled prototypes has been conducted. This paper describes five different real vehicle traffic scenarios covering both urban and rural settings at varying vehicle speeds and under varying line-of-sight (LOS) conditions and discusses the connectivity (measured as Packet Reception Ratio) that could be achieved between the two test vehicles. Our measurements indicate a quite problematic LOS sensitivity that strongly influences the performance of V2V-based applications. We further discuss how the awareness of these context-based connectivity problems can be used to improve the design of possible future cooperative ITS safety applications.

Supporting real-time data traffic in safety-critical vehicle-to-infrastructure communication

Support for real-time traffic is crucial to many ITS (intelligent transport systems) safety applications. At the same time it is desirable to provide a number of non-safety services. In this paper, we propose a communication system for safety-critical V2I (vehicle-to-infrastructure) communication based on an extension to the upcoming IEEE 802.11p MAC standard. Real-time analysis provides the tool to adapt the resources set aside for collision-free, safety-critical data traffic to the communication needs of the current number of supported vehicles. The remaining bandwidth is available to other services according to the contention-based random access method defined in the standard. The performance of the proposed concept is evaluated through a simulation analysis based on a merge assistance scenario supported by roadside infrastructure.

Real-Time Communication Support for Cooperative, Infrastructure-Based Traffic Safety Applications

The implementation of ITS (Intelligent Transport Systems) services offers great potential to improve the level of safety, efficiency and comfort on our roads. Although cooperative traffic safety ap ...

Position-Based Data Traffic Prioritization in Safety-Critical, Real-Time Vehicle-to-Infrastructure Communication

Future active-safety applications in vehicular networks rely heavily on the support for real-time inter-vehicle communication. The Medium Access Control (MAC) mechanism proposed for the upcoming IE ...

Wireless Sensor Networks for Surveillance Applications A Comparative Survey of MAC Protocols

Wireless sensor nodes are made up of small electronic devices which are capable of sensing, computing and transmitting data from harsh physical environments. These sensor nodes depend on batteries for energy, which get depleted at a fast rate because of the computation and communication operations these nodes have to perform. A well designed MAC (Medium Access Control) protocol can prolong the network life. A set of previously reported MAC layer protocols has abilities to achieve some energy efficiency. In this paper, we first describe some assumptions made for the specific application area of surveillance applications. Then, we compare a set of MAC protocols in terms of their suitability to be used in wireless sensor networks for this type of applications. In addition to energy efficiency, keeping the delays reasonably low is a crucial factor when sensing and reporting an event.

Performance comparison of a platooning application using the IEEE 802.11p MAC on the control channel and a centralized MAC on a service channel

Recent advances in cooperative driving hold the potential to significantly improve safety, comfort and efficiency on our roads. An application of particular interest is platooning of trucks, where it has been shown that keeping a minimum inter-vehicle distance results in considerably reduced fuel consumption. This, however, puts high requirements on timeliness and reliability of the underlying exchange of control messages between platoon members. The European profile of IEEE 802.11p, recently adopted by ETSI, defines two message types to this end, periodic beacons for basic cooperative awareness (CAM) and event-triggered decentralized environmental notification messages (DENM), both of which will use one common control channel. IEEE 802.11p employs a random medium access protocol, which may experience excessive delays during high network loads. To mitigate these effects, ETSI standardizes a decentralized congestion control algorithm to, e.g., lower the CAM update frequency during high loads. However, this may prevent proper functionality of a platooning application. In this paper we propose a solution that instead uses a dedicated service channel for platooning applications and compare its performance to standard-compliant IEEE 802.11p inter-platoon communication on the control channel. Service channels typically have less strict requirements on send rates, data traffic types and medium access methods. Our service channel solution combines a random access phase for DENM with a centralized, scheduled access phase for CAM. Using a service channel enables us to guarantee timely channel access for all CAM packets before a specified deadline while still being able to provide a reasonable DENM dissemination delay.

Co-existing periodic beaconing and hazard warnings in IEEE 802.11p-based platooning applications

A platoon of trucks driving at the same, mutually agreed speed while keeping a minimum inter-vehicle distance will reduce fuel consumption, enhance transport efficiency as well as improve the safety of other adjacent road users. The European profile of IEEE 802.11p for inter-vehicle communications uses a single 10 MHz control channel dedicated to safety-critical data, shared by periodic status updates, and event-triggered warnings. Coupled with the random access delay inherent to the 802.11p medium access method, the strict timing and reliability requirements of platoon applications are not easily met. To this end, we evaluate the effect of IEEE 802.11p-compliant send rate adaptations and message type prioritizations and the choice of warning dissemination strategy in a platooning scenario. Simulation studies of a platoon of 10-20 vehicles in a busy highway scenario show that a context-aware choice of send rate, priority class and dissemination strategy not only reduces the hazard warning dissemination delay but also has a significant effect on the throughput of periodic beacons.

Context-Aware Retransmission Scheme for Increased Reliability in Platooning Applications

Recent advances in cooperative driving hold the potential to significantly improve safety, comfort and efficiency on our roads. An application of particular interest is platooning of vehicles, where reduced inter-vehicle gaps lead to considerable reductions in fuel consumption. This, however, puts high requirements on timeliness and reliability of the underlying exchange of control data. Considering the difficult radio environment and potentially long distances between communicating platoon members, as well as the random channel access method used by the IEEE 802.11p standard for short-range inter-vehicle communication, those requirements are very difficult to meet. The relatively static topology of a platoon, however, enables us to preschedule communication within the platoon over a dedicated service channel. Furthermore, we are able to set aside parts of the available bandwidth for retransmission of packets in order to fulfil the reliability requirements stated by the platoon control application. In this paper, we describe the platooning framework along with the scheduling algorithm used to assign retransmission slots to control packets that are most likely to need them. This retransmission scheduling scheme offers a valuable tool for system designers when answering questions about the number of safely supported vehicles in a platoon, achievable reductions in inter-vehicle gaps and periodicity of control packets.

Data age based retransmission scheme for reliable control data exchange in platooning applications

Recent advances in cooperative driving hold the potential to significantly improve safety, comfort and efficiency on our roads. Platooning of heavy vehicles, where automated or semi-automated driving allows minimal inter-vehicle gaps, has shown considerable reductions in fuel consumption. Although using the same wireless communication technology, a platoon differs from a VANET (Vehicular Ad-hoc NETwork) in several points. It is centralized in its nature, with a well-defined group leader, its topology is fairly stable and it has very challenging requirements on timeliness and reliability of its control data exchange. Therefore, the IEEE 802.11p protocol suite and its recently defined message types do neither support the needs of a platooning application nor take advantage of its properties. A platoons control loop must continuously be fed with fresh data, so the information age is an important parameter to be closely monitored. In this paper, we therefore propose a framework for centralized channel access and retransmission capabilities for safety critical inter-platoon control data based on the data age of earlier received messages. A simulation evaluation compares our solution to a) the decentralized, standard-compliant IEEE 802.11p MAC (Medium Access Control) method, and a time-slotted scheme b) with and c) without retransmissions and shows that the centralized, data age based retransmission scheme clearly outperforms its competitors in terms of maintained data age.

Increased Communication Reliability for Delay-Sensitive Platooning Applications on Top of IEEE 802.11p

Cooperative driving in platooning applications has received much attention lately due to its potential to lower fuel consumption and improve safety and efficiency on our roads. However, the recently adopted standard for vehicular communication, IEEE 802.11p, fails to support the level of reliability and real-time properties required by highly safety-critical applications. In this paper, we propose a communication and real-time analysis framework over a dedicated frequency channel for platoon applications and show that our retransmission scheme is able to decrease the message error rate of control data exchange within a platoon of moderate size by several orders of magnitude while still guaranteeing that all delay bounds are met. Even for long platoons with up to seventeen members the message error rate is significantly reduced by retransmitting erroneous packets without jeopardizing the timely delivery of regular data traffic.