Fountain Reprogramming Protocol: a Reliable Data Dissemination Scheme for Wireless Sensor Networks Using Fountain Codes

Wireless sensor network technologies enable a wide variety of applications (e.g., environmental monitoring). Such sensor networks are often deployed in regions that make it difficult to collect and redistribute the nodes for maintenance. However, there is often a need to reprogram all of the nodes in the network, either during application test phases on deployed networks, or to support software upgrades. Therefore, a reliable method of sending a relatively large amount of data to each node in the network is required to support these functions. The challenge to designing such in-network node reprogramming protocols lies in the potentially large amount of energy required to successfully transmit the entire program to every node in the network. The wireless channels used by small sensor nodes are potentially lossy and highly variable. The use of unicast retransmissions to correct errors for each node can be prohibitive in terms of traffic generation and hence transmission cost. Additionally, such retransmission techniques are known to result in feedback implosion in dense networks [1]. Therefore, coding solutions allowing different errors at various nodes to be corrected with single packet transmissions are preferable. However, many such techniques, using forward error correction codes (FEC) tend to be inefficient for wireless sensor networks. This is mainly due to the inherent computational complexity of standard codes (e.g., Reed Solomon), which involve operations on Galois fields. In addition, standard block codes have a fixed code rate, which cannot be changed on the fly according to channel errors or number of receivers. The main contribution of our work is an in-network reprogramming protocol, which uses a Fountain Code [2] we designed specifically to meet the needs of sensor network reprogramming. This code is designed to maintain a high efficiency, in terms of overhead, in the face of small packet sizes and typical program sizes. In addition Fountain Codes are rateless and have a low computational complexity, as encoding and decoding are performed efficiently through XOR operations. Our fountain code has been implemented on Tmote Sky nodes and shown to execute efficiently even with the limited available processing power. Our experiments show that we achieve reliable network programming with very low overhead compared to other current in-network reprogramming techniques [3], [4]. Codec Radio Manager Partition SingleHop MultiHop Communication BootLoader DataDissemination BootLoader