| Summary: | 博士 === 國立中正大學 === 資訊工程研究所 === 99 === To provide an efficient and stable framework to vehicles is an emerging issue. Since
conventional communication schemes in Vehicular Ad Hoc Networks (VANETs)
only support short transmission range, vehicles need to switch to different roadside
units frequently in order to disseminate data. It is difficult to deliver an emergency
message to other vehicles in time and provide real-time multimedia services in
VANETs. Fortunately, a new version of Worldwide Interoperability for Microwave
Access (WiMAX), known as IEEE 802.16j, can support long transmission range and
high mobility using mobile multi-relay node. This dissertation fist develops an efficient
framework, termed SIP-Based Safety/Vehicular Information Delivery (SVID),
by using WiMAX mobile multi-relay techniques. SVID also introduces several crosslayer
mechanisms to maintain the proposed framework and satisfy the characteristics
of VANETs. With SVID, Vehicles can communicate with each other and connect
to the Internet through a relay vehicle. However, the proposed framework still faces
two mobility problems: (1) imbalanced traffic load among relay vehicles; (2) long
handover latency for vehicles. In load balancing problem, a SRV may become overloaded
once too many vehicles choose it as their relay vehicle. Thus, mechanisms
are needed to distribute vehicles to nearby relay vehicles to avoid the overloading
problem. This dissertation investigates two threshold-based schemes to help vehicles
to select their relay vehicles dynamically to balance the traffic load among
SRVs based on Markov chain model. To solve the long handover latency problem,
this dissertation presents a cross-layer fast handover scheme, called vehicular fast
handover scheme (VFHS), where the physical layer information is shared with the
MAC layer, to reduce the handover delay. The key idea of VFHS is to utilize oncoming
side vehicles (OSVs) to accumulate physical and MAC layers information
of passing through relay vehicles and broadcast the information to vehicles that are
temporarily disconnected, referred to as disconnected vehicles (DVs). Simulations
are conducted to verify the feasibility and stability of the proposed schemes. The
simulation results indicate that the proposed schemes can yield better system performance
and low handover latency. The main contribution of this dissertation is
to develop an efficient and stable communication framework for VANETs based on
the WiMAX relay network.
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