Study on optimal energy-efficient routing algorithm and high-precision localization system in wireless sensor networks

Wireless sensor networks (WSNs), which is formed by numerous sensing devices (or called sensor nodes) capable of computing and wireless communication. Due to the compact size of the sensor nodes, WSNs have soon becoming a revolutionary technology suitable with applications in wide areas of interest. However, limited energy supply in each sensor node brought new challenges and operational problems to the field of distributed and collaborative information processing in WSNs. In this dissertation, we concentrate on three essential problems within this extensive topic, including energy-efficient routing protocol, dynamic radio power control and two-dimensional sensor node localization. The first two topics emphasize on efficient use of limited energy in each sensor node. The primary goal is to prolong the network lifetime. The later part of this dissertation presents a rotational antenna configuration for accurate localization of sensor nodes. Localization is an essential function since it is meaningless to collect sensor data without knowing the position of the event.
In Chapter 2, an adaptive routing protocol was presented to construct network topology and transmit sensor data to the sink. Each node acts as an independent router. Due to this key feature, the proposed routing algorithm determines the path to transmit data packets from its source nodes to the destination node (sink) with minimum delay time, and also balances the power consumption of all sensor nodes in the network. The routing protocol also applied to a hybrid network that consists of packet switching network and WSN to show its wide applicability in various types of networks.
A dynamic radio power control method is proposed in Chapter 3. Radio transmissions are major sources of energy consumption in WSNs. In order to reduce redundant power consumptions and to prevent generating any orphan nodes in the WSN, a dynamic radio power management mechanism was developed to collaborate with the energy-efficient routing protocol proposed in Chapter 2. To maximize the merit of the radio power control, developing an accurate localization method for sensor nodes in a WSN is necessary.
In Chapter 4, an RSSI-based collaborative localization method that makes use of the irregularity of the EM wave is proposed. First, we coupled external low-cost omnidirectional antennas with sensor nodes and reference nodes using specific antenna configurations. The omnidirectional antenna of the reference node rotates in the horizontal plane to measure the RSSI pattern between the sensor node and the reference node to estimate their relative angular direction and distance. A robust estimation technique is also presented to analyze the RSSI patterns obtained by the reference node. The proposed algorithm is thus able to provide the localization results with higher precision. In addition, a collaborative localization scheme is presented to integrate the information obtained by multiple reference nodes.
All presented methods are evaluated via computer simulation and/or real-world field test. The experimental results show that the proposed algorithm outperforms existing algorithms with better performance in terms of energy efficiency and localization accuracy.