A Remote Code Update Mechanism for Wireless Sensor Networks

Wireless sensor networks consist of collections of small, low-power nodes that interface or interact with the physical environment. The ability to add new functionality or perform software maintenance without having to physically reach each individual node is already an essential service, even at the limited scale at which current sensor networks are deployed. TinyOS supports single-hop over-the-air reprogramming today, but the need to reprogram sensors in a multihop network will become particularly critical as sensor networks mature and move toward larger deployment sizes. In this paper we present Multihop Over-the-Air Programming (MOAP), a code distribution mechanism specifically targeted for Mica-2 Motes. We discuss and analyze the design goals, constraints, choices and optimizations focusing in particular on dissemination strategies and retransmission policies. We have implemented MOAP on Mica-2 motes and we evaluate that implementation using both emulation and testbed experiments. We show that our dissemination mechanism obtains a 60--90% performance improvement in terms of required transmissions compared to flooding. We also show that a very simple windowed retransmission tracking scheme is nearly as e#ective as arbitrary repairs and yet is much better suited to energy and memory constrained embedded systems