Online code compression in Wireless Sensor Networks

A problem in Wireless Sensor Networks (WSN), an extremely resource-limited system, is that re-tasking by replacing complete or partial code images is both disruptive and energy intensive. In this paper we report on a dynamic code compression scheme for mobile code that we implemented for a WSN. We use a fine-grained code mobility scheme based on capsules, ChameleonVM, where network functionality can be deployed on demand and for several tasks in parallel. Within a task's virtual network segment we let our ChameleonVM optimize the assignment of instruction bits: Mobile code instructions are re-coded on a regional basis and depending on the actual code sequences used, incrementally leading to smaller capsules. We demonstrate the operation of our online compression scheme with a time-sync protocol and discuss its performance.