The effect of awareness at the medium access control layer of vehicular ad-hoc networks

Booysen, Marthinus J. (2013-12)

Thesis (PhD)-- Stellenbosch University, 2013.

Thesis

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.

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