Novel Hierarchical Routing Protocols to Improve Event Detection in Wireless Sensor Networks

The number of applications that depend on wireless sensor networks (WSNs) has risen recently. Since WSN applications are becoming more complex, more efficient routing protocols are needed. However, WSNs have limited resources in terms of restricted storage capacity, energy, and processing. The main goal of WSNs is to transmit the sensed data to the sink in an efficient way to achieve high degree of event detection reliability. The level of reliability required is determined by the nature of the application. Organising the network nodes into clusters is a common technique to improve reliability. Many clustering methods have been proposed, with LEACH (Low-Energy Adaptive Clustering Hierarchy) being the first. Many of these employ IEEE 802.15.4 which uses Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) as a technique to access the shared communication medium. However, for 802.15.4 (ZigBee) based systems CSMA/CA does not work well when the number of nodes is increased. In this thesis, firstly LEACH and direct transmission (DT) protocols are implemented and evaluated using up to 15 Waspmote wireless nodes with XBee-Pro S1 802.15.4 radio modules as a hardware testbed. These were used as a baseline to test the performance, in terms of event delivery ratio (VDR) and event reporting round time (RRT), of new clustering protocols (ToRRCH, and F-ToRRCH) which were developed to solve the conflicts between the events delivery reliability and the hardware constraints of WSNs. Clustering in both ToRRCH and F-ToRRCH are based on token ring transmission techniques. Results show that the worst VDR was achieved using DT, due to the deficiency of the backoff function in the CSMA/CA protocol implemented in the XBee-Pro S1 802.15.4 module. However, ToRRCH achieved a 100% VDR, but with longer RRT than LEACH and DT. The long RRT problem was solved by developing a new protocol called F-ToRRCH.