Thesis (PhD)-- Stellenbosch University, 2013. / ENGLISH ABSTRACT: The hidden terminal problem, coupled with high node mobility apparent in vehicular
networks, present challenges to e cient communication between vehicles at the Medium
Access Control (MAC) layer. Both of these challenges are fundamentally problems of lack
of awareness, and manifest most prominently in the broadcasting of safety messages in
infrastructure-free vehicle-to-vehicle communications.
The design of existing contention-free and contention-based MAC approaches generally
assumes that nodes that are in range of one another can take steps to coordinate
communications at the MAC layer to overcome the hidden terminal problem and node
mobility. Unicasting with the existing MAC standard, IEEE 802.11p, implicitly assumes
an awareness range of twice the transmission range (a 1-hop awareness range) at most,
since handshaking is used. For broadcasting, the assumption implies an awareness range
that is at most equal to the transmission range, since only carrier sensing is used. Existing
alternative contention-free approaches make the same assumption, with some protocols
explicitly using a 1-hop awareness range to avoid packet collisions. This dissertation challenges
the convention of assuming that a 1-hop awareness range is su cient for networks
with high mobility, such as VANETs.
In this dissertation, the impact of awareness range and management of the awareness
information on MAC performance is researched. The impact of the number of slots that
is required to support the awareness range is also evaluated.
Three contention-free MAC protocols are introduced to support the research. The
rst is an improved version of an existing MAC method, which is used to demonstrate the
e ects on performance of changes to awareness management. The second MAC uses three
competing processes to manage awareness information. The second MAC is designed for
a con gurable awareness range and con gurable number of slots, and is used to evaluate
the e ects of awareness range and number of slots on MAC performance. The third MAC
is random access based and is used to evaluate the impact on performance of removing
awareness completely. An analytical model is developed to support the simulated results.
The simulation results demonstrate that awareness range, awareness information management,
and number of slots used are key design parameters that signi cantly impact
on MAC performance. The results further show that optimal awareness-related design
parameters exist for given scenarios.
Finally, the proposed contention-free and random access MAC methods are simulated
and performance compared with IEEE 802.11p. All three outperform the contentionbased
standard IEEE 802.11p. / AFRIKAANSE OPSOMMING: Die versteekte-nodus-probleem, gekoppel met die hoë vlakke van nodusbeweging teenwoordig
in voertuignetwerke, bied uitdagings vir doeltre ende kommunikasie tussen voertuie
in die medium-toegangbeheer- (MAC) vlak. Beide van hierdie probleme spruit uit
beperkte bewustheid, en manifesteer veral in die uitsaai van veiligheidsboodskappe in
infrastruktuurvrye voertuig-na-voertuig-kommunikasie.
Die ontwerp van bestaande wedywerende en nie-wedywerende MAC benaderings neem
aan dat nodusse wat binne bereik van mekaar is, stappe kan neem om kommunikasie op
die MAC-vlak te koördineer, ten einde probleme met versteekte nodusse en mobiliteit te
oorkom. Vir punt-tot-puntkommunikasie met IEEE 802.11p, impliseer dié aanname 'n bewustheidstrekking
van hoogstens twee keer die radiobereik (1-hop bewustheidstrekking),
aangesien bladskud gebruik word. In die geval van uitsaai, impliseer die aanname 'n bewustheidstrekking
hoogstens gelyk is aan die radiobereik, aangesien slegs draeropsporing
gebruik word. Nie-wedywerende metodes maak dieselfde aanname, met sommiges wat
eksplisiet 1-hop-bewustheidstrekking gebruik om pakkieverliese te voorkom. Hierdie verhandeling
wys dat hierdie aanname nie geld vir netwerke met hoë mobiliteit nie, soos wat
die geval is vir VANET.
In hierdie verhandeling word die impak van bewustheidstrekking en bestuur van die
bewustheidsinligting in die MAC-vlak ondersoek. Die impak van die aantal tydgleuwe
wat nodig is om die bewustheidstrekking te ondersteun word ook ondersoek.
Drie nie-wedywerende metodes word bekendgestel om die navorsing te ondersteun.
Die eerste is 'n verbeterde weergawe van 'n bestaande MAC, wat gebruik word om die
e ekte van bewustheidsbestuur op MAC-werkverrigting te beoordeel. Die tweede MAC is
ontwerp om veranderbare bewustheidstrekking en hoeveelheid tydgleuwe te ondersteun,
en word gebruik om die e ekte van bewustheidstrekking en hoeveelheid tydgleuwe op
MAC werkverrigting aan te beoordeel. Die derde MAC is ewetoeganklik (onbewus van
omliggende nodusse) en word gebruik om die impak van die verwydering van bewustheid
op werkverrigting te ondersoek. 'n Analitiese model is ontwikkel om die simulasieresultate
te ondersteun.
Die simulasieresultate dui aan dat bewustheidstrekking, bestuur van bewustheidsinligting,
en hoeveelheid tydsgleuwe sleutel-ontwerpsveranderlikes is wat 'n beduidende impak
het op MAC werkverrigting. Die resultate wys verder dat optimale ontwerpsveranderlikes,
in terme van bewustheid, bestaan vir gegewe scenario's.
Laastens, word die nie-wedywerende en ewetoeganklike MAC-metodes wat gesimuleer
word se werkverrigting vergelyk met IEEE 802.11p. Al drie MAC metodes vaar beter as
die wedywerende standaard, IEEE 802.11p.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/95480 |
| Date | 12 1900 |
| Creators | Booysen, Marthinus J. |
| Contributors | Van Rooyen, G-J., Zeadallly, S., Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | xv, 110 p. : ill. |
| Rights | Stellenbosch University |
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