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Energy Models. David Holmer dholmer@jhu.edu. Energy Model. Captures the effect of the limited energy reserves of mobile devices (i.e. batteries) Models the power levels of the device during operation so that total energy consumption can be calculated

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## Energy Models

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**Energy Models**David Holmer dholmer@jhu.edu**Energy Model**• Captures the effect of the limited energy reserves of mobile devices (i.e. batteries) • Models the power levels of the device during operation so that total energy consumption can be calculated • A number of different models are used in the literature • Transmission Power Model • Transmission & Reception Model • Power State Model**Transmission Power Model**• Assumes energy consumption is directly related to wireless output power • Output power in typical cards range from 1mW to 200mW • Output power is related to the square of range • Cutting transmission range in half cuts output power requirement by ¼ • In some environments related by greater exponent (depends on path loss constant = 1.8 to 6) • This means by choosing shorter hops, the total output power can be reduced (¼ + ¼ < 1) • Used by many papers (particularly theory papers) • Minimum energy routing • Minimum energy broadcast • Topology control • Flawed model ignores MANY sources of energy consumption • Fixed transmission consumption overhead • Consumption by receiver • Consumption by idle nodes**Transmission & Reception Model**• Energy consumption depends on the number of packets sent & received • Energy consumption of a packet is calculated using several constants • Not very commonly used • Increased accuracy but still missing a significant contribution to energy consumption (idle power)**Power State Model**• Uses different power levels depending on state of wireless card • Transmit (1.33 Watts) • Receive (0.97 Watts) • Idle (0.84 Watts) • Sleep (.07 Watts) • Based on measurements of a real wireless card on lab equipment • Captures the majority of card power consumption effects (most accurate model in general use) • Measured values only apply for the exact model of card • Does not take into account transient consumption from mode switches • Does not take into account power consumption of host(i.e. from packet processing) • Usually assumes fixed output power(not normally used with transmission power control)**Sending Power Example**Receiving Sending**Sleep Mode**• High consumption while active • High transmit power constant • High idle & receive power • Sleep mode allows much of the electronics to be turned off • Radio cannot send or receive packets • Can be activated again by host in a small amount of time • SIGNIFICANTLY lower power levels (.07 Watts) • Only protocols that make extensive use of sleep mode can save a large fraction (>50%) of the card power consumption • Sleep mode limit = <90% savings • Transmit power control limit = <<35% savings

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