Enhancement of throughput and energy efficiency in sensor networks with mobile access points

Abstract

In sensor networks with mobile access points (SENMA), sensor nodes should operate for very long time and send sensed information to the mobile access points efficiently. Hence, in this thesis, we study on the enhancement of SENMA, considering the different characteristic from conventional sensor networks. We focus on throughput enhancement and energy efficiency in SENMA. First, we propose a permission-based access scheme to enhance throughput in SENMA. With the permission-based access, only the sensor nodes which obtain permission can access to the mobile access point and collisions can be reduced by the transmission of orthogonal signatures in random access phase. For performance evaluation, we suggest a discrete-time Markov chain, which can be used widely in the performance analysis of SENMA. In dense and large scale networks, this analysis method can be used for the performance estimation and optimal parameters selection. Second, we propose a sentinel node operation for energy-efficient and robust operation, which greatly reduces the energy consumption in idle listening. The proposed scheme does not require any election procedure, which is used in the previous algorithms of sensor networks. We also present a role-exchange scheme in addition to the sentinel node operation to ensure that energy load is fairly distributed among nodes. Consequently, the lifetime of sensor network increases so much that sensor nodes can continue performing mission for very long time. In addition, we propose a sentinel-minimization scheme to prolong lifetime more, especially when event rate is low. Third, we propose an enhanced power-saving scheme for broadcast packet delivery in interactive SENMA applications. Since sensor nodes are extremely dependent on battery life in SENMA, we focus on the low-battery nodes to which more energy-efficient chemes are necessary. The double-buffering of broadcast packets is proposed to guarantee longer sleep time without loss...