Abstract-We investigate a unique scheduling problem in wireless sensor networks where all nodes in a cluster send exactly one packet to a designated sink node with goal of minimized transmission time. The difficulty lies in the fact that node transmissions must be sufficiently isolated either in time or in space to avoid collisions. The problem is formulated and solved via graph representation. We prove that with specific network topologies (either line or tree), an optimal transmission schedule can be obtained efficiently through a pipeline-like schedule. The minimum time required for a line (or tree) topology with n nodes is 3(n − 2). We further prove that our scheduling problem is NP-hard for general graphs. We propose a heuristic algorithm for general graphs. Our heuristic tries to schedule as many independent segments as possible to increase the degree of parallel transmission. This algorithm is compared to an RTS/CTS based distributed algorithm. Preliminary simulated results indicate that our heuristic algorithm outperforms the RTS/CTS based distributed algorithm (up to 30%) and exhibits stable scheduling behavior. Index Terms-Sensor network, hybrid network, scheduling, allto-one information gathering I. INTRODUCTION Advances in wireless networking and the desire for real time data collection has resulted in tremendous growth in research activities in the area of wireless sensor networks. An important technology trend is the development of large-scale heterogeneous network architectures integrated with various communication technologies for better performance. In such network architectures, low cost battery powered sensor nodes are typically equipped with (several) data sensing components, limited data processing components, and short-range communication components. The baseline data collection functionality is provided by packet relaying among sensor nodes, where the data is eventually received in a central location. However, this method is not scalable and cannot handle aggregated traffic when hundreds or thousands of sensor nodes are used. To support large-scale sensor networks and the fast collection of time critical data, the network is often organized into clusters [2] where information is first gathered at the cluster head, then further collected by mobile base stations such as unmanned vehicles for example. An important link to such a network paradigm is efficient packet routing inside of the clusters. Much research has been performed on routing in sensor networks based on the ad hoc nature of sensor networks [4] , [5] , [1] , [3] resulting in distributed routing algorithms. These distributed algorithms are inherently competition-based, such as in [5] and [7] . Thus, their performance is heavily dependent on the density of the sensor nodes and on traffic patterns.
Choi et al REF shown that convergecast scheduling problem is NP-hard in a weak sense.
Scheduling on sensor hybrid network
Proceedings. 14th International Conference on Computer Communications and Networks, 2005. ICCCN 2005.
Proceedings. 14th International Conference on Computer Communications and Networks, 2005. ICCCN 2005.
Computer Science