Clocks, latency and energy efficiency in duty cycled, multi-hop Wireless Sensor Networks

To achieve extended low-power operation in multi-hop Wireless Sensor Networks, networked nodes are often radio duty cycled to decrease power consumption incurred by energy intensive modes of the wireless transceiver. These nodes, spending the majority of their lifetime in a `sleep' state, can introduce large latencies into data transmission and reception. This latency becomes particularly impactful as the number of hops required to transmit data packets to the destination node increases. We investigate the impact of oscillator drift on the end-to-end latency of packet transmission over multiple hops. We show how drift impacts upon the choice of the receive check interval for the networked devices. We illustrate the effects of choosing crystal oscillators with varying degrees of ppm accuracy. We present analytical models, simulation and extensive empirical evaluation to support our evaluation. Finally, we demonstrate how optimal initial operating parameters may be derived to minimize power consumption. This work provides further practical knowledge of the fundamental capabilities and limitations of radio duty cycled wireless sensor networks.