Autonomous energy efficient protocols and strategies for wireless sensor networks

The aim of this research is to develop a model of a sensor network that will endeavour to monitor a hostile environment (one where communication within the network is difficult and the network entities are under risk due to physical damage). In this context, the study identifies the following key characteristics. A wireless sensor network (WSN) is a wireless network consisting of spatially distributed devices using sensors to monitor physical or environmental conditions at different locations. In addition to one or more sensors, each node in a WSN is typically equipped with a radio transceiver or other wireless communications device, a small micro controller, and an energy source, usually a battery. The size constraints on sensor nodes result in corresponding constraints on resources such as energy, memory, computational speed and bandwidth. Of these, energy is the most important since it is required for everything else. Thus, it directly influences the life-span of the nodes, hence, that of the system as a whole. Furthermore, the environment itself, where these sensor nodes are deployed, plays a big role in influencing the entire architecture of the network hardware platform and protocols that govern its smooth functioning. As a result the protocols required for governing the actions of the sensor nodes need to be designed accordingly. Against this background, this research facilitates the developent of an environmental sensor network called GlacsWeb (deployed inside a glacier in Norway) which focuses on providing useful information about sub-glacial dynamics. GlacsWeb nodes are deployed under very hostile conditions. The strain from the moving ice may damage the nodes and the en-glacial water bodies may carry the nodes far out of transmission range from a centrally located base station. For these reasons GlacsWeb nodes have a high rate of failure. In order to effectively tackle this problem, this research develops GW-MAC (a Medium Access Control protocol) which focuses on efficiently connecting GlacsWeb nodes in an ad-hoc manner. Moreover, the poorly understood nature of the glacier imposes further challenges in the area of sensing. Sub-glacial behaviour appears vary across the entire large mass of ice. For this reason, there is a strong need for nodes to make autonomous decisions to adapt their observation patterns and communication patterns accordingly to ensure maximum data is gathered with minimum consumption in energy. The study, therefore, develops USAC (A Utility Based Sensing and Communication Model for an Agent-Based Sensor Network), that provides a measure of utility by combining the task of both sensing and communication by the sensor nodes. The model, at first, develops a sensing protocol in which each agent node locally adjusts its sensing rate based on the value (importance) of the data it believes it will observe. Then, it details a communication protocol that finds optimal routes for relaying this data back the network base station based on the cost of communicating (derived from the opportunity cost of using the battery power for relaying data) it. Both GW-MAC and USAC have been tested in simulation and have shown to perform better than other similar models.