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Medium Access Control for Wireless Networks with Diverse Real-Time and Reliability Requirements
Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems. TTTech Computertechnik AG. (Data Communication)
2016 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Wireless real-time networks are a natural step for deployments in industrial automation, automotive, avionics, or robotics targeting features such as improved mobility, reduced wiring costs, and easier more flexible network developments. However, the open transmission medium where wireless networks operate is generally more prone to interference and transmission errors caused by fading. Due to this, real-time communications is in general still provided by wired networks in many of these application fields. At the same time, wired and wireless standards traditionally associated with the consumer electronics application field (e.g., IEEE 802.3 "Ethernet" and IEEE 802.11 “WiFi”) are trying to find their way into industrial automation, automotive, avionics, and robotics use cases, since they provide features like high throughput and cheap hardware. Many times, applications with diverse real-time and reliability requirements have to co-exist, and often in hybrid wired-wireless networks to ensure compatibility with existing systems. Given this scenario, it is essential to provide support for data traffic with requirements ranging from real-time time-triggered and event-driven to non-real-time, and enable high reliability with respect to timing constraints, in the context of hybrid wired-wireless networks. This thesis aims at covering the aforementioned requirements by proposing a medium access control (MAC) solution suitable for wireless communications, with support for real-time traffic with diverse time and reliability requirements. The MAC layer is in charge of providing timely access to the transmission medium, and can be effectively used to increase reliability by means of, e.g., avoiding concurrent transmissions and performing retransmissions. To this end, a set of evaluation criteria is proposed to determine the suitability of a particular MAC method to meet the identified emerging requirements. These criteria include channel access delay, reliability, protocol overhead, capability to integrate with wired networks, and sensitivity to interference from collocated systems. Next, based on these requirements, a MAC protocol with a set of tunable features is proposed, and evaluated in terms of support for data traffic with different loads and distributions, i.e., emanating from different traffic classes, and from different number of senders. The evaluation is made both analytically, by calculating the worst case delay and, with the help of real-time schedulability analysis, determining the effective load required to guarantee real-time deadlines, as well as by means of computer simulations using the INET framework for OMNeT++ to determine the average delay. Finally, the thesis proposes a set of retransmission schemes to be used together with the proposed MAC protocols in order to improve the resistance against interference and transmission errors. For this, a set of interference patterns with different characteristics is proposed and applied in the simulator. The resulting MAC layer solution is designed to be used at the wireless segment of a hybrid wired-wireless network, and is able to schedule data traffic originating from three different classes: time-triggered, rate-constrained and best-effort. To achieve this, an additional collision domain introducing wireless segments is added to the real-time scheduler, as well as support for real-time retransmissions, to enable high reliability while keeping real-time deadlines.

Place, publisher, year, edition, pages
Västerås: Mälardalen University , 2016.
Series
Mälardalen University Press Licentiate Theses, ISSN 1651-9256 ; 243
National Category
Computer Science
Research subject
Computer Science
Identifiers
URN: urn:nbn:se:mdh:diva-33264ISBN: 978-91-7485-287-5 (print)OAI: oai:DiVA.org:mdh-33264DiVA: diva2:1001865
Presentation
2016-11-11, Lambda, Mälardalen University, Västerås, 13:15 (English)
Opponent
Supervisors
Projects
RetNet - The European Industrial Doctorate Programme on Future Real-Time Networks
Funder
EU, FP7, Seventh Framework Programme, 607727
Available from: 2016-09-30 Created: 2016-09-27 Last updated: 2016-10-14Bibliographically approved
List of papers
1. Towards a Reliable and High-Speed Wireless Complement to TTEthernet
Open this publication in new window or tab >>Towards a Reliable and High-Speed Wireless Complement to TTEthernet
2014 (English)In: The 19th IEEE International Conference on Emerging Technologies and Factory Automation ETFA'14, 2014, Article number 7005311- p.Conference paper, Published paper (Refereed)
Abstract [en]

TTEthernet is a general purpose communication infrastructure for applications with real-time and/or fault-tolerance requirements. It is based on Ethernet as standardized by the IEEE and allows the integration of mixed-criticality applications in a single physical network. However, currently TTEthernet only operates in wired network settings. With growing industrial demand of the design freedom that comes with wireless communication solutions we are interested in extending TTEthernet to a wireless communication paradigm. In this paper we review the state of the art in deterministic wireless communication approaches. We deduce quality criteria for wireless networks from industrial use cases and outline candidates for a wireless complement to wired TTEthernet.

National Category
Computer Systems
Identifiers
urn:nbn:se:mdh:diva-29220 (URN)10.1109/ETFA.2014.7005311 (DOI)9781479948468 (ISBN)
Conference
19th IEEE International Conference on Emerging Technologies and Factory Automation, ETFA 2014; Barcelona; Spain; 16 September 2014 through 19 September 2014
Projects
RetNet - The European Industrial Doctorate Programme on Future Real-Time Networks
Available from: 2015-10-06 Created: 2015-09-29 Last updated: 2016-12-28Bibliographically approved
2. A Wireless MAC Method with Support for Heterogeneous Data Traffic
Open this publication in new window or tab >>A Wireless MAC Method with Support for Heterogeneous Data Traffic
2015 (English)In: IECON 2015 - 41st Annual Conference of the IEEE Industrial Electronics Society, 2015, 3869-3874 p., 7392703Conference paper, Published paper (Refereed)
Abstract [en]

An important aspect of any communication technology is its medium access method, being responsible for sharing the medium among users. For delay-sensitive applications, such as industrial control systems, timely and reliable channel access is of essence. Hence, existing protocols like HART and TTEthernet use a time-triggered medium access approach. However, as the nature of industrial control systems change and evolve, there is a growing need to provide wireless access and support data traffic with mixed requirements. While technologies like WirelessHART can offer timely and reliable access to the wireless medium, only one type of data traffic is usually supported. In this paper, we therefore propose and evaluate three different medium access methods for wireless communications, all capable of supporting three different data traffic classes: time-triggered, rate-constrained and best-effort traffic. In particular, different options on how to handle best-effort traffic, using scheduled time-slots or contention, are evaluated, showing for all the proposals different drawbacks and benefits depending on additional requirements on e.g., hardware, protocol overhead and resistance to interference.

National Category
Computer Systems
Identifiers
urn:nbn:se:mdh:diva-29631 (URN)10.1109/IECON.2015.7392703 (DOI)000382950703153 ()2-s2.0-84973162673 (Scopus ID)978-1-4799-1761-7 (ISBN)
Conference
41st Annual Conference of the IEEE Industrial Electronics Society, IECON 2015; Pacifico YokohamaYokohama; Japan; 9 November 2015 through 12 November 2015; Category numberCFP15IEC-ART; Code 119153
Projects
RetNet - The European Industrial Doctorate Programme on Future Real-Time Networks
Available from: 2015-12-10 Created: 2015-11-26 Last updated: 2016-12-22Bibliographically approved
3. Medium Access Control for Wireless Networks with Diverse Time and Safety Real-Time Requirements
Open this publication in new window or tab >>Medium Access Control for Wireless Networks with Diverse Time and Safety Real-Time Requirements
2016 (English)In: 42nd Annual Conference of the IEEE Industrial Electronics Society IECON 2016, 2016, 4665-4670 p., 7794095Conference paper, Published paper (Refereed)
Abstract [en]

The communication in-between embedded systems present in cars and planes, requires real-time networks. Up to now, fieldbus technologies like PROFIBUS and CAN have covered the demand for predictable communications in embedded systems. However, these fieldbuses do not suit some of the emerging application domains, that need more flexibility, support for dynamic traffic flows, different traffic classes, high throughput, and the inclusion of wireless capabilities. To this end, we propose several different medium access control (MAC) schemes with support for traffic with diverse time and safety requirements. We have calculated the worst case channel access delay for each proposal, and also simulated them in OMNeT++ to analyse and compare their performance in terms of average access delay and packet collisions as a function of different protocol settings and traffic patterns e.g., the channel load, data traffic emerging from one sender only versus evenly distributed between all senders. Our results indicate that the more that is known about the data traffic, the better performance can be achieved by selecting an appropriate MAC protocol. Conversely, when nothing is known, one MAC protocol emerges as the best trade-off.

Series
IECON Proceedings (Industrial Electronics Conference)
National Category
Computer Systems
Identifiers
urn:nbn:se:mdh:diva-33261 (URN)10.1109/IECON.2016.7794095 (DOI)2-s2.0-85010030958 (Scopus ID)
Conference
42nd Annual Conference of the IEEE Industrial Electronics Society IECON 2016, 24 Oct 2016, Florence, Italy
Projects
RetNet - The European Industrial Doctorate Programme on Future Real-Time NetworksREADY - Research Environment for Advancing Low Latency Internet
Available from: 2016-09-27 Created: 2016-09-27 Last updated: 2017-02-02Bibliographically approved
4. Applying Time Diversity for Improved Reliability in a Real-Time Wireless MAC Protocol
Open this publication in new window or tab >>Applying Time Diversity for Improved Reliability in a Real-Time Wireless MAC Protocol
2016 (English)Report (Other academic)
Abstract [en]

Supporting real-time applications over wireless networks is challenging for several reasons. However, the inherent advantages due to wireless access like reduced wiring or the possibility to transmit between moving components are still desirable in many application domains. In particular, wireless support to applications with traffic having diverse time and safety requirements is desirable. The medium access control (MAC) layer plays a key role in enabling real-time guarantees, since it provides access to the transmission medium. Unfortunately, even if timely access is guaranteed, transmissions can still be compromised due to the unreliable wireless medium. A common way to increase the reliability of a communication system is to apply redundancy in the form of time diversity, i.e., transmitting several copies of the same message at different points in time. In this paper we propose a wireless MAC method in where transmissions and retransmissions are tailored to deadlines, so that the reliability of the communication system is increased and real-time guarantees can be provided. The proposal enables coexistence of three different traffic classes: time-triggered, rate-constrained and best-effort. Further, we have analysed the effect of different protocol configurations subject to interference with different duration, frequency, and level of persistence. The results show that different protocol settings can be successfully applied to combat different kinds of interference to improve transmission reliability and timeliness.

Place, publisher, year, edition, pages
Sweden: Mälardalen Real-Time Research Centre, Mälardalen University, 2016
Series
MRTC Reports, ISSN 1404-3041
National Category
Computer Systems
Identifiers
urn:nbn:se:mdh:diva-33262 (URN)MDH-MRTC-311/2016-1-SE (ISRN)
Projects
RetNet - The European Industrial Doctorate Programme on Future Real-Time Networks
Available from: 2016-09-27 Created: 2016-09-27 Last updated: 2016-12-22Bibliographically approved

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