Energy Models

David Holmerdholmer@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)

DataLengthDataOverheadEnergy

DataLengthDataOverheadEnergy

RXRXRX

TXTXTX

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

Sending Receiving

Receiving Power Example

Different Transmit Options

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

PRISM Sleep Power Ramp Up