| As new fabrication and integration technologies reduce the cost and size of micro-sensors and wireless sensors, we will witness another revolution that involves observation and control of our physical world, as what networking technologies have done for the ways individuals and organization exchange information. In the power constraint, application specific sensor networks, energy efficiency is always one of the most crucial design goals. In this thesis, we first propose a general metric to evaluate the performance of the protocols in terms of energy efficiency, then explore the energy efficiency problem from the perspective of data consistency.; To systematically evaluate the performance of protocols in terms of energy efficiency, a formal definition for the lifetime of the wireless sensor network has been modeled, by considering the relationship between individual sensors and the whole sensor network, the importance of different sensors based on their positions, the link quality in transmission, and the connectivity and coverage of the sensor network. Based on our model, we have compared two types of query protocols, the direct query protocol and the indirect query protocol using mathematical analysis.; Lots of work has been done to save energy so that to extend the lifetime of wireless sensor networks, however, these efforts focus on the energy efficient routing protocols, MAC protocols and duty cycle managements. We reexamine the energy efficient data collection problem from the perspective of data consistency. After analyzing the specific data consistency requirements from applications and the feature of data dynamics, we first formally model the energy-efficiency problem in the scenario of a passive monitoring application with the goal of delivering minimum number of messages under the constraint of data consistency. Then, we give the formal definition of data consistency in wireless sensor networks. To achieve this goal, we propose a data collection protocol named Alep, which adapts the data sampling rate to the data dynamics in the data field and keeps lazy when the data consistency is maintained. From the results of a comprehensive simulation using PowerTOSSIM, we find that the proposed approach indeed reduces the number of delivered messages by more than 20%, extends the lifetime of the wireless sensor network by more than 50%, and improves the accuracy of the sampled data. Furthermore, we show that the tradeoff between the energy efficiency and data consistency should be tuned based on the specific requirements of different applications. |
