SRVF: An Energy-Efficient Link Layer Protocol for Reliable Transmission over Wireless Sensor Networks

The 802.15.4 WSN standard provides optional reliability through positive acknowledgments. Since positive-ACKs are not designed for energy efficiency, there is significant room for improvement in the energy usage of reliable 802.15.4. In this paper, we propose a new reliable link layer protocol, referred to as the Selective Retransmission using Virtual Fragmentation (SRVF) protocol. SRVF requires simple modifications to reliable 802.15.4, but provides substantial improvements in energy efficiency. The main premise of the proposed protocol is to localize bit-errors by performing partial checksums on disjoint parts or virtual fragments of a packet. In case of error, only the corrupted virtual fragments are retransmitted. We analytically model reliable 802.15.4 and SRVF as Markov chains operating over an arbitrary-order Markov wireless channel, and show that SRVF provides significant theoretical improvements over reliable 802.15.4. We then use bit-error traces collected over a real sensor network testbed to experimentally evaluate the two reliable protocols. These experimental results show that SRVF has consistently and considerably better energy efficiency than the reliable 802.15.4.