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In this work we characterize the energy consumption of a visual sensor network testbed. Each node in the testbed consists of a "single-board computer", namely Crossbow's Stargate, equipped with a wireless network card and a webcam. We assess energy consumption of activities representative of the target application (e.g., perimeter surveillance) using a benchmark that runs (individual and combinations of) "basic" tasks such as processing, flash memory access, image acquisition, and communication over the network. In our characterization, we consider the various hardware states the system switches through as it executes these benchmarks, e.g., different radio modes (sleep, idle, transmission, reception), and webcam modes (off, on, and acquiring image). We report both steady-state and transient energy consumption behavior obtained by direct measurements of current with a digital multimeter. We validate our measurements against results obtained using the Stargate's on-board energy consumption measuring capabilities.

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Absfmcf-This paper presents an analytical model to predict energy consumption in saturated IEEE 802.11 single-hop ad hoc networks under ideal channel conditions. The model we introduce takes into account the different operational modes of Ule IEEE 802.11 DCF MAC, and is against packetlevel simn~ations, I,, contrast to previous works that attempted to characterize the energy consumption of IEEE 802.11 cards in isolated, contention-free channels (i.e., single sendedreceiver pair), this paper investigates the extreme opposite case, i.e., when nodes need to contend for channel access under saturation conditions. In such scenarios, to what most mode has marginal impact on overall energy consumption, while other modes (receive, idle, etc.) are responsible for most of the energy This paper presents advances in two fundamental aspects of energy-aware protocols: it introduces an analytical model to predict energy consumption in single.hop EEE 802.11 ad hoc networks (under ideal channel conditions), and it validates this model with discrete-event simulations using Qualnet v3.6 [4], for which an extended and improved energy consumption accounting was implemented [ 5 ] . In particular,we are interested in the following questions: (1) How accurate is the analytical model compared to discreteevent simulations? (2) What is the relative energy consumption among the MAC operational modes (e.g., transmit, receive, idle, etc) when nodes are activelv contendine for channel main findings include:indicate, the radio's

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