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

In multihop wireless networks, hop-by-hop reliability is generally achieved through positive acknowledgments at the MAC layer. However, positive acknowledgments introduce significant energy inefficiencies on battery-constrained devices. This inefficiency becomes particularly significant on high error rate channels. We propose to reduce the energy consumption during retransmissions using a novel protocol that localizes bit-errors at the MAC layer. The proposed protocol, referred to as Selective Retransmission using Virtual Fragmentation (SRVF), requires simple modifications to the positive-ACK-based reliability mechanism but provides substantial improvements in energy efficiency. The main premise of the 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 develop stochastic models of the Simple Positive-ACK-based reliability, the previously-proposed Packet Length Optimization (PLO) protocol, and the SRVF protocol operating over an arbitrary-order Markov wireless channel. Our analytical models show that SRVF provides significant theoretical improvements in energy efficiency over existing protocols. We then use biterror traces collected over different real networks to empirically compare the proposed and existing protocols. These experimental results further substantiate that SRVF provides considerably better energy efficiency than Simple Positive-ACK and Packet Length Optimization protocols.