Power-Saving Collaborative Strategy For Large-Scale Wireless Sensor Networks

Wireless sensor networks are constructed by nodes equipped with sensor, data processing unit and wireless communication unit in an ad-hoc mode, and their main function is to collect, process, transmit and broadcast activities of the objects in the observed area by the collaboration of all the network nodes. With the development of Micro-Electro-Mechanical systems(MEMS), Very-Large-Scale-Integration systems(VLSI), and wireless communication techniques, the application of wireless sensor networks has appeared in many fields, including military, civil, scientific, etc. However, due to their compact form factors, network nodes have limited communication, computation and storage capability, and are always severely energy constrained, which makes the study of wireless sensor networks both challenging and promising. Many advanced countries have put great efforts into the study of wireless sensor networks, while this research is still underway in our country. Therefore, the author explored the status of application and research of wireless sensor networks in detail.Large-scale wireless sensor networks composed of thousands of nodes have much broader application because of their superior information quality, better stability and higher adaptability. However, their tiny nodes have much severer energy constraint, and therefore, extending the lifetime of these networks has become pivotal for extending their application. Researches for extending the lifetime of wireless sensor networks fall into two categories. One trend is to consider the design of the power supply system as well as the physical layer of the nodes, while the other trend focuses on the collaborative strategies of the network. The latter has been put more emphasis nowadays, and the research of this thesis goes along this way.The author first presented a detailed definition of sensor networks'lifetime and power consumption model, and then explored the best routine for selecting relay nodes in a multi-hop network. Based on this result, the author focused on the wireless sensor networks with a single information source, and analyzed the theoretical upperbound of the lifetime that could be realized by using the best collaborative strategies under several representative source distributions and activities. Afterwards, the author introduced the technique of maximizing network lifetime with flow control methods for the networks with a central control part or distributed central control function, proved its feasibility and advantages, and listed the detailed object functions and constraints for some representative networks.Considering the specific characteristics of wireless sensor networks, the author pointed out the necessary properties for a feasible collaborative strategy, that is, network functions are carried out by nodes only with local knowledge in a distributed way, the strategy is essentially loop-free, the strategy has some energy-related parameters and is sensitive to the energy consumption as well as the energy level of the nodes. Afterwards, the author introduced and proved the reasonability of three assumptions, namely, the network has high-density, each node is aware of its position according to the sink, and each node keeps track of its neighbors' positions and current energy levels. Based on these assumptions, the rules of our adaptive distributed collaborative strategy are presented thoroughly. Finally, this strategy's feasibility and effectiveness in extending the lifetimeof large-scale wireless sensor networks are shown by simulations.