Energy-efficient collaborative data transmissions in wireless sensor networks

Wireless sensor networks provide great potential for environment monitoring and military missions. In many applications, sensor nodes need to be deployed far away from the base station, where the data are collected, stored, and analyzed. Long distance transmissions are often required in wireless sensor networks and they consume significant amounts of energy. Collaborative beamforming achieve long distance, yet low energy consuming, transmissions by means of multiple simultaneous nodes transmitting the same data to the same receiver. However, each type of collaborative transmission introduces some energy overhead due to additional steps. This dissertation presents several techniques in achieving energy-efficient collaborative transmissions in wireless sensor networks. It addresses the following questions: (1) whether collaborative transmissions save energy, and what are the determining key factors, (2) how to perform collaborative transmissions in order to prolong the network lifetime, and (3) how to perform collaborative transmissions to extend the transmission distance. The first question is addressed by studying the various steps in achieving collaborative beamforming transmissions using different approaches. This dissertation analyzes the factors that affect the energy savings for beamforming transmissions. The second question is addressed by proposing an energy-efficient transmitter scheduling algorithm to balance the energy consumption over the network, hence prolonging the network lifetime. Finally, the third question is addressed by proposing a method to use beamforming in multi-hop transmissions to extend the transmission distance between hops.