Date Added: Mar 2011
With the advances in micro-electronics, wireless sensor devices have been made much smaller and more integrated, and large-scale Wireless Sensor Networks (WSNs) based the cooperation among the significant amount of nodes have become a hot topic. "Large-scale" means mainly large area or high density of a network. Accordingly the routing protocols must scale well to the network scope extension and node density increases. A sensor node is normally energy-limited and cannot be recharged, and thus its energy consumption has a quite significant effect on the scalability of the protocol. To the best of the authors' knowledge, currently the mainstream methods to solve the energy problem in large-scale WSNs are the hierarchical routing protocols.