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

[摘要] ENGLISH ABSTRACT: The hidden terminal problem, coupled with high node mobility apparent in vehicularnetworks, present challenges to e cient communication between vehicles at the MediumAccess Control (MAC) layer. Both of these challenges are fundamentally problems of lackof awareness, and manifest most prominently in the broadcasting of safety messages ininfrastructure-free vehicle-to-vehicle communications.The design of existing contention-free and contention-based MAC approaches generallyassumes that nodes that are in range of one another can take steps to coordinatecommunications at the MAC layer to overcome the hidden terminal problem and nodemobility. Unicasting with the existing MAC standard, IEEE 802.11p, implicitly assumesan 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 rangethat is at most equal to the transmission range, since only carrier sensing is used. Existingalternative contention-free approaches make the same assumption, with some protocolsexplicitly using a 1-hop awareness range to avoid packet collisions. This dissertation challengesthe convention of assuming that a 1-hop awareness range is su cient for networkswith high mobility, such as VANETs.In this dissertation, the impact of awareness range and management of the awarenessinformation on MAC performance is researched. The impact of the number of slots thatis 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 thee ects on performance of changes to awareness management. The second MAC uses threecompeting processes to manage awareness information. The second MAC is designed fora con gurable awareness range and con gurable number of slots, and is used to evaluatethe e ects of awareness range and number of slots on MAC performance. The third MACis random access based and is used to evaluate the impact on performance of removingawareness 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 impacton MAC performance. The results further show that optimal awareness-related designparameters exist for given scenarios.Finally, the proposed contention-free and random access MAC methods are simulatedand performance compared with IEEE 802.11p. All three outperform the contentionbasedstandard IEEE 802.11p.

[发布机构] Stellenbosch University