Title:  Efficient Service Channel Utilization in Multichannel Vehicular Adhoc Networks

Committee:

Dr. John Copeland, ECE, Chair , Advisor

Dr. Yusun Chang, ECE, Co-Advisor

Dr. Gee-Kung Chang, ECE

Dr. Henry Owen, ECE

Dr. Jeffrey Davis, ECE

Dr. David Bader, CoC

Abstract:

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. Conforming to 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. Following the broadcast scenario, this dissertation focusses also on unicast transmission in the IEEE 1609.4 multi-channel environment. Unlike the CCH interval, during the SCH interval, the RTS/CTS/data/ACK handshake can be triggered to transmit large size of data without the hidden node problem. However, it can cause the exposed node problem that hinders concurrent transmissions, which is fatal in highly dynamic VANETs. Even though judicious SCH selection in a multi-channel environment can mitigate the exposed node problem, IEEE 1609.4 does not specify how to select a SCH, which can cause the randomly selected SCHs to be biased. Without modifying the current standards, this dissertation proposed a novel scheme that enables the exposed vehicles to avoid selecting the same SCH. Through extensive simulations, it is verified that the average throughput can be improved by up to 26%. Building upon the unicast scenario using the omnidirectional antennas, this dissertation further developed the unicast transmission using the directional antenna. When a large amount of data is transmitted in unicast, it is a waste of energy to broadcast the data toward all the directions using omnidirectional antennas, which can also increase unnecessary interference to other vehicles. However, if directional antennas can be utilized, a service provider can narrow down the beamwidth of the directional antenna and focus only on its target vehicle with higher data rate. The proposed solution is compared with other possible approaches: the least congested SCH selection method and the random SCH selection method. Theoretical analysis and extensive simulation results demonstrate that the proposed method outperforms the two schemes.