| Summary: | 碩士 === 國立交通大學 === 電信工程研究所 === 104 === A wireless network based on a wide area deployment of low power and low cost user equipments (UEs) can be found in many applications. Most of these applications require each UE to maintain its clock synchronized with at least neighboring nodes in order to coordinate message exchanges. Most of the known synchronization protocols for wireless networks, however, lack the physical layer (PHY) considerations which causes collisions of message-carrying packets and confusion in determining the time-ow of the designed operations. The lack of PHY considerations also lead to unrealistic assumptions and assessments on the message delivery and related algorithms. The so-called broadcast storm problem is an obvious example.
We first present a new wireless broadcast protocol with which a relay node uses a carrier-sense like approach and the received signal to interference plus noise ratio (SINR) to make a relay or unicast decision so that duplicate or redundant message relaying is minimized. We take into account PHY issues such as packet collision and statistical signal propagation and acquisition to obtain realistic performance assessments.
Based on the proposed broadcast protocol we propose a three-phase tree-based network timing protocol. The timing synchronization protocol establish timing synchronization among network nodes while building a tree structure for the network. In the first phase, each UE discovers its neighbors and creates local parent-children connections via local broadcasting. Those nodes having children but no parents are designated as local tree roots from which we build local trees using the parent-children relations derived from them. Using a gossip procedure, local roots exchange its offspring size information and reach a consensus on the global root which has the largest family size. After finding a global root, we then enter the final phase and start construct a global tree that connects all nodes. The tree-building process will start at the root node and terminates at the point when the root receives a notification from all childless UEs. Network timing synchronization is obtained in the final tree-building phase as a byproduct.
The proposed scheme provides a practical approach which takes PHY issue into account. The transmission resource can be single-channel and multiple orthogonal channels. As expected, the mean network synchronization time performance is improved with additional transmission resources although the energy consumption is not necessarily reduced. We use the flooding time synchronization protocol (FTSP) as a reference for performance comparison.
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