Traffic safety applications using vehicle-to-vehicle (V2V) communication is an emerging and promising area within the intelligent transportation systems (ITS) sphere. Many of these new applications require real-time communication with high reliability, meaning that packets must be successfully delivered before a certain deadline. Applications with early deadlines are expected to require direct V2V communications, and the only standard currently supporting this is the upcoming IEEE 802.11p, included in the wireless access in vehicular environment (WAVE) stack. To meet a real-time deadline, timely and predictable access to the channel is paramount. However, the medium access method used in 802.11p, carrier sense multiple access with collision avoidance (CSMA/CA), does not guarantee channel access before a finite deadline. In this paper, we analyze the communication requirements introduced by traffic safety applications, namely, low delay, reliable, real-time communications. We show by simulation of a simple, but realistic, highway scenario, that vehicles using CSMA/CA can experience unacceptable channel access delays and, therefore, 802.11p does not support real-time communications. In addition, we present a potential remedy for this problem, namely, the use of self-organizing time division multiple access (STDMA). The real-time properties of STDMA are investigated by means of the same highway simulation scenario, with promising results.

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On the ability of the 802.11p MAC method and STDMA to support real-time vehicle-to-vehicle communication

The IEEE-1588 standard for a high precision time synchronization now exists since 2002. For using this standard in bridged networks a so-called boundary clock is defined, where the local clock adjustment can be modeled by a corresponding control loop. At the field level of industrial automation systems, the line topology is very important. By using Ethernet at the field level, the resulting chain of bridges leads to a cascade of control loops and may lead to instabilities and deviations of the distributed clocks, which are not acceptable. For this application a bypass clock instead of the boundary clock is proposed as an enhancement of the IEEE-1588 standard. The effectiveness of this extension to be evaluated by simulation technique.

Enhancements to the time synchronization standard IEEE-1588 for a system of cascaded bridges

The evolution of industrial communication inexorably moves to Industrial Ethernet networks. One important reason for using Ethernet at the shop floor is to participate on the continuous advancements of standard Ethernet. Thus it seems to be the logical next step to change the bit rate from Fast Ethernet to Gigabit Ethernet to achieve better performance. The question is, how the cycle time as a relevant performance metrics of industrial automation systems can profit from increasing the bit rate to 1 Gbps. Because of its importance for the industrial automation domain this paper focuses on line topology. The analysis is based on EtherCAT and PROFINET, which are two popular representatives of different architectures for high performance Industrial Ethernet networks.

Limits of increasing the performance of Industrial Ethernet protocols

In current vehicles, a large number of control units are connected by several automotive specific communication buses, facilitating innovative distributed applications. At the same time, computers and entertainment devices use IP and commodity communications technology like Ethernet to connect to the Internet, allowing for innovative solutions and maintaining fast innovation cycles. Today, one can see first applications of Ethernet for in-vehicle communication in contemporary cars. In next generation vehicles, many innovative applications could benefit from the increased bandwidth Ethernet can offer. Therefore, a examination of Ethernet usage for additional in-vehicle communication use cases is needed. In this paper, we show simulation results of promising use cases for in-car Ethernet, while looking at different realistic topologies, types of traffic, and configurations.

Challenges in a future IP/ethernet-based in-car network for real-time applications

PROFIBUS is an international standard (IEC 61158) for factory-floor communications, with some hundreds of thousands of world-wide installations. However, it does not include any wireless capabilities. In this paper we propose a hybrid wired/wireless PROFIBUS solution where most of the design options are made in order to guarantee the proper real-time behaviour of the overall network. We address the timing unpredictability problems placed by the co-existence of heterogeneous transmission media in the same network. Moreover, we propose a novel solution to provide inter-cell mobility to PROFIBUS wireless nodes.

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Real-time communications over hybrid wired/wireless PROFIBUS-based networks

Ethernet is the most famous type of communication network used for office applications. Currently, networks used on field level and on office level are different due to their specific requirements. Especially for real-time systems, the deterministic behavior of the network is very important. Now Switched Ethernet seems to be applicable also on field level, because collisions can be avoided and priorities can be used. In this paper Switched Ethernet networks with different topologies are analyzed concerning the transmission delays. Therefore a typical master-slave scenario of an automation system is investigated.

S. Rüping

Papers

Analysis of Switched Ethernet Networks with Different Topologies Used in Automation Systems