Title:  Efficient Service Channel Utilization in Multichannel Vehicular Adhoc Networks

Committee: 

Dr. Copeland, Y. ChangAdvisor     

Dr. Owen, Chair

Dr. G.K. Chang

Abstract: The objective of the proposed research is to design efficient service channel utilization schemes for IEEE 1609.4 multi-channel environments in Vehicular Ad Hoc Networks. The current IEEE 1609.4 standard defines multi-channel operations to alternate control and service channel intervals during a period of 100ms. However, there is no mention of service channel selection for a service provider, which allows hidden service providers to select the same service channel (SCH). This limitation can cause the hidden terminal problem during the SCH intervals, leading to significant performance deterioration. Without modifying the existing standards, the proposed scheme enables hidden service providers to avoid selecting the same SCH by delivering their candidate service channel number in the optional field of the basic safety message (BSM). Through extensive simulations, it is verified that the packet reception ratio can be improved by up to 23% in typical broadcast scenarios.  During the SCH intervals, the IEEE 802.11 RTS/CTS handshake can solve the hidden node problem while it can cause the exposed node problem. This limitation is fatal in highly dynamic VANETs because vehicles can exceed each other’s transmission range even during the short gagged time. If the SCHs to which the exposed vehicles switch are different from each other, the exposed vehicles do not have to defer their channel access, which can lead to the concurrent transmission. Conforming to the current standards, a novel scheme is proposed for the exposed vehicles to be able to avoid selecting the same SCH. Through extensive simulations, it is verified that the average throughput can be improved by up to 26%.