The Department of Computer Science at the University of Cyprus cordially invites you to the PhD Defense entitled:

Performance Aware Congestion Control in Wireless Sensor Networks using Resource Control

Speaker: Charalambos Sergiou
Affiliation: University of Cyprus, Cyprus
Category: PhD Defense
Location: Room 148, Faculty of Pure and Applied Sciences (FST-01), 1 University Avenue, 2109 Nicosia, Cyprus (directions)
Date: Thursday, October 25, 2012
Time: 09.30-10.30 EET
Host: Vasos Vassiliou (

Recent advances in Wireless Sensor Networks (WSNs) lead to applications with increased traffic demands. Performance, in terms of throughput, time delay and power consumption, is now a dominating factor that leads research in WSNs. There are many cases in the fields of automation, health, and disaster response that demand WSNs with strict performance assurances. Congestion occurrence is a key factor that can negatively affect the performance of WSNs. The overwhelming majority of approaches that deal with congestion control in WSNs attempt to control congestion, by reducing the rate with which sources inject packets in the network. This method is called “traffic control”. Although “traffic control” seems to be an effective method for controlling congestion, it presents a number of drawbacks which are not easy to ignore. The most important drawback steams from the fact that higher traffic load occurs when the monitored event takes place. At this instance there is a higher probability of congestion occurrence in the network. By controlling the rate with which packets are injected in the network, the amount of information that reaches the data sinks reduces. This fact can jeopardize the network’s mission. Moreover, network connectivity issues arise since in most cases, this approach utilizes the shortest path from source to sink. Thus, in case of heavy data load, this path of nodes can easily become power exhausted. This leads to energy “holes” in the network. In this work we approach congestion control and avoidance in WSNs with a different perspective. Hence, when congestion occurs, instead of reducing the rate with which packets are injected in the network, we program nodes to route a number packets, through alternative paths, in order to avoid the congested areas. This method is called “resource control”. To achieve this, we take advantage of the fact that wireless sensor nodes are frequently redundantly and/or densely deployed. Thus, initially, we prove with mathematical analysis using a traffic flow model that the “traffic control” method can be proven inefficient in specific scenarios where performance assurances are needed and the inefficiencies of this method can be handled effectively by the “resource control” method. Then, we argue on the importance of topology control algorithms and study how tree forming schemes can assist the purpose of congestion control with specific performance bounds. After this study, we propose an algorithm called HTAP (Hierarchical Tree Alternative Path), which is an efficient algorithm for congestion control and avoidance, in terms of throughput and power consumption. Moreover, we study the effectiveness and power performance of this algorithm under specific node placements. Then, we propose an alternative algorithm, called DAlPaS (Dynamic Alternative Path Selection), which keeps the advantages of HTAP algorithm but presents higher and more stable performance in terms of time delay, power consumption and throughput. Finally we close with conclusions and future work.

Short Bio:
Charalambos Sergiou is a PhD Candidate at the Department of Computer Science, of University of Cyprus under the supervision of Dr. Vasos Vassiliou. He received his Diploma in Telecommunication and Electronics Engineering (Dipl.- Ing) from Hellenic Air- Force Academy in Greece, in 2000. In 2007 he received MSc in Advanced Information Technologies from the Department of Computer Science of University of Cyprus. Since 2000, he serves as Aviation Engineer Officer in Cyprus National Guard, specialized in various aircrafts Avionics Systems. His research interests include wireless ad-hoc and sensor networks, focusing on overload and congestion control.

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