Investigating the Energy Consumption

of a Wireless Network Interface in an

Ad Hoc Networking EnvironmentAuthors:

Laura Marie Feeney, Martin NilssonSwedish Institute of Computer Science

Presented By:Seapahn Meguerdichian

Problem StatementNetwork interface has non-trivial energy

consumption,especially as systems become more energy

efficient.

1. Improve efficiency of physical device.2. Reduce the amount of traffic?

How to develop energy efficient protocols withouta good understanding of the energy consumptionassociated with network traffic?

Data Sheets, OEM Specs …Not so helpful.

Lucent IEEE 802.11 DSSS PC Card Characteristics

Specs Measured

2 Mbps(Bronze)

Sleep ModeIdle ModeReceive ModeTransmit Mode

9 mA--------280 mA330 mA

14 mA178 mA 200 mA280 mA

11 Mbps (Silver)

Sleep ModeIdle ModeReceive ModeTransmit Mode

10 mA--------180 mA280 mA

10 mA156 mA190 mA284 mA

Approach

Make measurements and report helpful results.

Packet orientedNetwork oriented

Use numeric results as input to network simulations.

Precise values are less important than developing insights that are useful for protocol development.

Type of Network

In structured networks, base stations usually have no special energy constraints.

In ad-hoc networks this is not the case

In IEEE 802.11:Several data transmit rates.Modes:

BSS mode: base station service setAd hoc mode: wireless link

Note: CSMA/CA protocol with optional RTS/CTS negotiation.

Investigation

Directly measure energy consumed by a packet:send vs. receive vs. discardpromiscuous mode operationbroadcast vs. point-to-point trafficfixed vs. incrementaltransmit rate

• Energy consumption is sometimes treated as synonymous with bandwidth utilization.

• Energy is sometimes treated as an abstract “commodity”.

Linear Model

• Fixed component: channel acquisition• Incremental component: packet size

Energy = m * size + b

• Linear regression is used to test the model and find values for m and b.

• Model ignores backoff and retransmissions, which are best analyzed in the context of a traffic and mobility model.

Routing protocol evaluation

•Use the linear equations in conjunction with CMU Monarch ns-2 simulation environment.

•Repeat “classic” CMU performance evaluation.•50 nodes, 1500 X 300 m•random waypoint mobility, 20 m/s (uniform)•IEEE 802.11 with RTS/CTS, 2 Mbps•20 CBR streams - 4 £ 64 byte packets/s•Consider DSR, DSR-np and AODV routing protocols.

Simulation Results

• Cost of receiving is non-negligible.• Broadcast traffic is expensive in a

relatively dense network.• Incremental costs are low, relative

to per-packet costs.• Discarding can be cheap • Promiscuous mode can be

expensive.

Conclusions

• Energy consumption is not synonymous with bandwidth utilization.

• Idle mode energy consumption is extremely high.

• RTS/CTS MAC protocol consumes significant energy.

• Collision avoidance requirements limit the applicability of power and topology control strategies.

• Violating abstraction barriers can lead to new insights