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Predictable and Scalable Medium Access Control for Vehicular Ad Hoc Networks
Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Embedded Systems (CERES).
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. , p. 21
Series
Technical report R, ISSN 1403-266X ; 2009:16
Keywords [en]
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: urn:nbn:se:hh:diva-5482OAI: oai:DiVA.org:hh-5482DiVA, id: diva2:346006
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: 2018-03-23Bibliographically approved
List of papers
1. On the ability of the IEEE 802.11p and STDMA to provide predictable channel access
Open this publication in new window or tab >>On the ability of the IEEE 802.11p and STDMA to provide predictable channel access
2009 (English)In: Proceedings of the 16th World Congress on Intelligent Transport Systems (ITS), 2009, p. 10-Conference paper, Published paper (Refereed)
Abstract [en]

Emerging traffic safety applications requiring low delay communications will need vehicle ad-hoc networks. The only communication standard currently supporting this is IEEE 802.11p. However, 802.11p uses the medium access method CSMA/CA, which has a major drawback: unbounded worst case channel access delay. We therefore propose an algorithm already in commercial use in the shipping industry: STDMA. With STDMA, nodes always get predictable channel access regardless of the number of competing nodes and the maximum delay is deterministic. In this paper we elaborated with different parameter settings for the two protocols with the aim of improving performance without altering the standards.

 

Keywords
IEEE 802.11p, vehicla ad hoc, V2V, MAC, VANET, predictable channel access, vehicular communications, STDMA
National Category
Telecommunications
Identifiers
urn:nbn:se:hh:diva-4034 (URN)
Conference
16th World Congress on Intelligent Transport Systems (ITS), 21-25 september, Stockholm, Sweden, 2009
Available from: 2010-03-09 Created: 2010-03-05 Last updated: 2018-03-23Bibliographically approved
2. On the ability of the 802.11p MAC method and STDMA to support real-time vehicle-to-vehicle communications
Open this publication in new window or tab >>On the ability of the 802.11p MAC method and STDMA to support real-time vehicle-to-vehicle communications
2009 (English)In: EURASIP Journal on Wireless Communications and Networking, ISSN 1687-1472, E-ISSN 1687-1499, Vol. 2009, no 902414, p. 1-14Article 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
Keywords
Vehicle-to-vehicle communications, MAC, Real-time, Traffic safety, STDMA, IEEE 802.11p, Performance evaluation, Simulation
National Category
Telecommunications
Identifiers
urn:nbn:se:hh:diva-2460 (URN)10.1155/2009/902414 (DOI)000264966100001 ()2-s2.0-63749083930 (Scopus ID)2082/2862 (Local ID)2082/2862 (Archive number)2082/2862 (OAI)
Available from: 2009-04-16 Created: 2009-04-16 Last updated: 2018-03-23Bibliographically approved
3. Scalability issues of the MAC methods STDMA and CSMA of IEEE 802.11p when used in VANETs
Open this publication in new window or tab >>Scalability issues of the MAC methods STDMA and CSMA of IEEE 802.11p when used in VANETs
2010 (English)In: 2010 IEEE International Conference on Communications Workshops (ICC), Cape Town, South Africa: IEEE Computer Society, 2010, p. 1-5Conference paper, Published paper (Refereed)
Abstract [en]

 

Position messages will be the foundation for many emerging traffic safety applications based on wireless communications. These messages contain information about the vehicle’s position, speed, direction, etc. and are broadcasted periodically by each vehicle. The upcoming IEEE 802.11p standard, intended for vehicle unpredictable behavior of its medium access control (MAC) scheme, which imply that traffic safety applications cannot be supported satisfactorily when the network load increases. We study the MAC mechanism within IEEE 802.11p being a carrier sense multiple access (CSMA) algorithm and compare it with a self-organizing time division multiple access (STDMA) scheme when used for broadcasting periodic position messages in a realistic highway scenario. We investigate their scalability in terms of the number of vehicles that the VANET can support using metrics such as channel access delay, probability of concurrent transmissions and interference distance. The results show that STDMA outperforms CSMA of 802.11p even when the network is not saturated.

 

Place, publisher, year, edition, pages
Cape Town, South Africa: IEEE Computer Society, 2010
Keywords
VANET, MAC, 802.11p, STDMA, CSMA, scalability
National Category
Telecommunications
Identifiers
urn:nbn:se:hh:diva-5250 (URN)10.1109/ICCW.2010.5503941 (DOI)2-s2.0-77954928450 (Scopus ID)978-1-4244-6824-9 (ISBN)
Conference
IEEE International Conference on Communications Workshops, Cape Town, South Africa, May 2010
Note

Copyright © 2010 IEEE. Reprinted from the ICC 2010 proceedings. This material is posted here with permission of the IEEE. Such permission of the IEEE does not in any way imply IEEE endorsement of any of the University of Halmstads's products or services. Internal or personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution must be obtained from the IEEE by writing to pubs-permissions@ieee.org. By choosing to view this document, you agree to all provisions of the copyright laws protecting it.

Available from: 2010-08-29 Created: 2010-08-01 Last updated: 2018-03-23Bibliographically approved

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Sjöberg Bilstrup, Katrin

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