Decentralized fountain codes for minimum-delay data collection

This paper studies decentralized strategies for facilitating data collection in circular wireless sensor networks, which rely on the stochastic diversity of data storage. The goal is to allow for a reduced delay collection by a mobile data collector (MDC) who accesses the network at a random position and random time. We consider a two-phase data collection: the push phase is mechanized through source packet dissemination strategies based on network coding; the pull phase is based on polling of additional packets from their original source nodes. Dissemination is performed by a set of relays which form a circular route to exchange source packets. The storage nodes within the transmission range of the routeiquests relays linearly combine and store overheard relay transmissions. MDC first collects a set of packets in its physical proximity and, using a message-passing decoder, attempts recovering all original source packets from this set. Whenever the decoder stalls a source packet which restarts decoding is polled/doped from its original source. The number of doped packets can be surprisingly small and, hence, the push-pull doping strategy may have the least collection delay when the density of source nodes is sufficiently large. Furthermore, the Ideal Soliton fountain encoding is a good linear combining strategy at the storage nodes whenever doping is employed.