Planning updates in multi-application wireless sensor networks

One of the arising issues in wireless sensor networks is running multiple applications to reduce deployment, administrative and management costs. In this paper we assume a sensor network in which nodes of a group have a set of same applications in their external flash memory that some of them are loaded and running. Occasionally, these applications should be updated for reasons that are manifold ranging from fixing software bugs to retasking. It is often that updates for a subset of applications happen at the same time, for example when a routing protocol shared among a subset of applications is changed. To bring the sensor nodes up to date with the new versions of the applications, existing strategies transfer the delta code, a smaller code obtained from the differential compression between the binary representations of the old and the new version of each application, and let the sensor nodes rebuild the new version from the received delta and the old version. We discuss that these strategies are blind to the order of updates when a set of updates occurs simultaneously. We introduce a heuristic planner that yields a sequence for a set of simultaneous updates, which minimizes the total delta size without adding overhead on the sensor nodes. We illustrate the efficiency of our planner on some TinyOS applications.