Energy Consumption of Visual Sensor Networks: Impact of Spatio-Temporal Coverage Based on Single-Hop Topologies

Wireless visual sensor networks (VSNs) are expected to play a major role in future IEEE 802.15.4 personal area networks (PAN) under recently-established collision-free medium access control (MAC) protocols. In such environments, the trade-off between the number of camera sensors to deploy (spatial coverage) and the frame rate to use for each camera sensor (temporal coverage) plays a major role in the VSN energy consumption. In this paper, we address this aspect for single-hop VSNs, i.e. networks comprising independent and identical wireless visual sensor nodes connected to a collection node via a star topology. We derive analytic results for the energy-optimal spatio-temporal coverage parameters of such VSNs under a-priori known bounds for the minimum frame rate per sensor and the minimum and maximum possible number of nodes to deploy. Our results are parametric to the probability density function characterizing the data-production rate per node and the energy consumption parameters of the system of interest. Experimental results using TelosB motes under: a collision-free transmission protocol, the IEEE 802.15.4 PAN physical layer (CC2420 transceiver) and Monte-Carlo-generated data sets, reveal that our analytic results are within 7% of the energy consumption measurements for a wide range of settings. In addition, results obtained via a multimedia subsystem performing visual feature extraction in video frames show that the optimal spatio-temporal settings derived by the proposed framework allow for up to 48% of reduction of energy consumption in comparison to ad-hoc settings. As such, our analytic modeling is useful for early-stage studies of possible VSN deployments under collision-free MAC protocols prior to costly and time-consuming experiments in the field.