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On the ability of the 802.11p MAC method and STDMA to support real-time vehicle-to-vehicle communications
Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Embedded Systems (CERES).
Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Embedded Systems (CERES).ORCID iD: 0000-0001-6497-4099
Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Embedded Systems (CERES).
Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Embedded Systems (CERES).
2009 (English)In: EURASIP Journal on Wireless Communications and Networking, ISSN 1687-1472, E-ISSN 1687-1499, Vol. 2009, no 902414, 1-14 p.Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
New York: Hindawi Publishing Corporation, 2009. Vol. 2009, no 902414, 1-14 p.
Keyword [en]
Vehicle-to-vehicle communications, MAC, Real-time, Traffic safety, STDMA, IEEE 802.11p, Performance evaluation, Simulation
National Category
Telecommunications
Identifiers
URN: urn:nbn:se:hh:diva-2460DOI: 10.1155/2009/902414ISI: 000264966100001Scopus ID: 2-s2.0-63749083930Local ID: 2082/2862OAI: oai:DiVA.org:hh-2460DiVA: diva2:239678
Available from: 2009-04-16 Created: 2009-04-16 Last updated: 2014-01-13Bibliographically approved
In thesis
1. Predictable and Scalable Medium Access Control for Vehicular Ad Hoc Networks
Open this publication in new window or tab >>Predictable and Scalable Medium Access Control for Vehicular Ad Hoc Networks
2009 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

This licentiate thesis work investigates two medium access control (MAC) methods, when used in traffic safety applications over vehicular ad hoc networks (VANETs). The MAC methods are carrier sense multiple access (CSMA), as specified by the leading standard for VANETs IEEE 802.11p, and self-organizing time-division multiple access (STDMA) as used by the leading standard for transponders on ships. All vehicles in traffic safety applications periodically broadcast cooperative awareness messages (CAMs). The CAM based data traffic implies requirements on a predictable, fair and scalable medium access mechanism. The investigated performance measures are channel access delay, number of consecutive packet drops and the distance between concurrently transmitting nodes. Performance is evaluated by computer simulations of a highway scenario in which all vehicles broadcast CAMs with different update rates and packet lengths. The obtained results show that nodes in a CSMA system can experience unbounded channel access delays and further that there is a significant difference between the best case and worst case channel access delay that a node could experience. In addition, with CSMA there is a very high probability that several concurrently transmitting nodes are located close to each other. This occurs when nodes start their listening periods at the same time or when nodes choose the same backoff value, which results in nodes starting to transmit at the same time instant. The CSMA algorithm is therefore both unpredictable and unfair besides the fact that it scales badly for broadcasted CAMs. STDMA, on the other hand, will always grant channel access for all packets before a predetermined time, regardless of the number of competing nodes. Therefore, the STDMA algorithm is predictable and fair. STDMA, using parameter settings that have been adapted to the vehicular environment, is shown to outperform CSMA when considering the performance measure distance between concurrently transmitting nodes. In CSMA the distance between concurrent transmissions is random, whereas STDMA uses the side information from the CAMs to properly schedule concurrent transmissions in space. The price paid for the superior performance of STDMA is the required network synchronization through a global navigation satellite system, e.g., GPS. That aside since STDMA was shown to be scalable, predictable and fair; it is an excellent candidate for use in VANETs when complex communication requirements from traffic safety applications should be met.

Place, publisher, year, edition, pages
Göteborg: Department of Signals and Systems, Chalmers University of Technology, 2009. 21 p.
Series
Technical report R, ISSN 1403-266X ; 2009:16
Keyword
CSMA, self-organizing TDMA, STDMA, medium access control, MAC, vehicular ad hoc networks, VANET, vehicle-to-vehicle communications, V2V, V2X, IEEE 802.11p, WAVE, DSRC, ETSI ITS-G5, ISO CALM M5, real-time communications, scalability, traffic safety, cooperative system
National Category
Telecommunications
Identifiers
urn:nbn:se:hh:diva-5482 (URN)
Presentation
2009-12-16, EA, Hörsalsv. 11, Chalmers University of Technology, Göteborg, 13:15 (English)
Opponent
Supervisors
Available from: 2010-09-03 Created: 2010-08-30 Last updated: 2014-01-13Bibliographically approved

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