Date of Award

8-2007

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Computer Engineering

Advisor

Wang, Kuang-Ching

Committee Member

Russell , Harlan

Committee Member

Chowdhury , Mashrur

Abstract

Wireless sensor networks have been deployed along highways for traffic monitoring. The thesis studies a set of transmission scheduling methods for optimizing network throughput, message transfer delay, and energy efficiency. Today's traffic monitoring systems are centrally managed. Several studies have envisioned the advantages of distributed traffic management techniques. The thesis is based on previously proposed hierarchical sensor network architecture, for which the routing and transmission scheduling methods are derived.
Wireless sensor networks have a lifetime limited by battery energy of the sensors. The thesis proposes to assign schedules for nodes to transmit and receive packets and turning off their radios during other times to save energy. The schedules are assigned to minimize the end-to-end packet delivery latency and maximize the network throughput. Conflict-free transmission slots are assigned to sensors along road segments leading to a common intersection based on locally discovered topology. The slot assignment adopts a heuristic that rotates among segments, assigns closest possible slots to neighboring nodes in a pipelined fashion, and exploits radio capture effects when possible. Based on the single-intersection approach, centralized and distributed multi-intersection scheduling methods are proposed to resolve conflicts among nodes belonging to different intersections. The centralized approach designates a controller as the leader to collect topology information of a set of contiguous intersections and assign schedules using the same single-intersection algorithm. The distributed approach has each intersection determine its own schedule independently and then exchange the topology information and schedules with its adjacent intersections to resolve conflicts locally. Based on simulation studies in ns-2, the centralized approach achieves better performance, while the distributed approach tries to approach the centralized performance at much lower communication costs. A communication cost analysis is performed to assess the trade-off between the centralized and distributed approaches.

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