— This paper presents a two-level strategy for topology control in wireless sensor networks. The energy saving methods in most of the existing research work can be categorized into two types: active subnetwork and short hops. The active subnetwork method reduces the nodes’ average idle time which may consume significant amount of energy in a wireless sensor network. The short hops method reduces the energy consumption during packet delivery by choosing a route with many short hops instead of one with a few long hops. The active subnetwork and short hops methods have different network conditions for them to perform well. We propose a two-level topology control strategy which integrates the above two methods to achieve further energy saving. We first apply an active subnetwork algorithm on the whole network to generate an active subnetwork, then use a short hops algorithm in each node of the network to adjust its transmission power according to its local knowledge about the active ...