| Summary: | 碩士 === 國立臺北科技大學 === 電腦與通訊研究所 === 94 === ABSTRACT
Title：Passive Broadcast in Mobile Ad hoc Networks Pages：93
School：National Taipei University of Technology
Department：Electronic Engineering & Institute of Computer and Communication
Time：July, 2006 Degree：Master
Researcher：Kwei-Yeh Huang Advisor：Chiu-Ching Tuan
Keywords：flooding broadcast, broadcast, mobile ad-hoc network, wireless networks.
A wireless ad-hoc network needs no infrastructure. Its characteristics of network include self-creating, self-organizing and self-administrating. Broadcasting is one of basic operations in wireless ad-hoc networks; especially, it is usually used to discover a route in the beginning of route establishment. Conventional flooding broadcast possibly generates a great deal of control packets in a wireless network; therefore, it may result in a broadcast storm problem under the network with high density of nodes.
The efficiency of wireless broadcasts directly impacts the power consumption of nodes, and indirectly affects both the use of bandwidth and the probability of signal collision. A high efficiency of broadcast means that fewer forwarding nodes can achieve as much coverage as possible in the network. Moreover, the coverage of broadcasting will vary with the mobility of nodes. When nodes move with a higher speed, the link breakage between nodes may occur frequently, which likely diminishes the broadcast coverage. Thus, a better broadcast policy should also take the mobility of nodes into account.
In this thesis, we proposed a new on-demand broadcast policy, called passive broadcast. Base on the proposed broadcast, whenever a node receives broadcast packets from neighboring nodes, the node first analyze the received packets, and then decide whether to forward the packets or not. The radio coverage of a node is logically partitioned into internal and external zones. To make the external nodes to forward packets earlier, the packets to be forwarded by internal nodes will be delayed at random. Whether the packets need to be forwarded by internal nodes is decided after the random delay time. In most cases, our policy effectively lowers the overall forwarding packets; thus, makes the broadcast efficiency and coverage rate more better than others.
We conducted simulation experiments for comparing the performance among flooding-based, probability-based, distance-based, counting-based, cluster-based and passive-based broadcasts. Three metrics: broadcast coverage, forwarding nodes and propagation time were formulated to evaluate and analyze these broadcast policies. From experimental results, the passive broadcast has higher coverage rate and lower forwarding rate. We considered that the proposed passive-based policy may be a better broadcast mode in wireless networks.
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