Scheduling on sensor hybrid network

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 out-performs the RTS/CTS based distributed algorithm (up to 30%) and exhibits stable scheduling behavior.