Master Thesis - 2011

In recent years, the number of applications of wireless sensor networks (WSNs) has been increasing. In WSN, one of the problems is that nodes around a sink die earlier than the other nodes because such nodes tend to transmit many more packets than the others. To solve this problem, Clustering is proposed as a load balancing method.

Moreover, overlapped WSNs have been constructed within the same geographic area. In this situation, it is expected for the overlapped WSNs to cooperate in communication. Some researchers have focused on sharing resources and proposed methods to construct WSNs suitable to requested services on common platforms. Such a cooperation enables WSNs to reduce redundant paths and the number of nodes, so that this is efficient in the point of reducing resources.

On the other hand, there is another case that independent WSNs cooperate with each other. Each WSN is managed respectively, so that the location of a sink is different. Then, we focus on load balancing by cooperation in overlapped WSNs.

In this thesis, we focus the difference of the location of a sink in overlapped WSN. We propose a cooperative routing method to balance load around each sink. When a node is far from a sink in its own network and near to a sink in another network, it is able to forward packets from a node in another WSN to the corresponding sink. As a result, our method enables each WSN to prolong the lifetime. Finally, we show the effectiveness of the proposed method by simulation experiments.