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SNU INC Lab.SNU INC Lab.

A Survey of Energy Efficient NetworkProtocols for Wireless Networks

Hayoung, Oh

20 Nov 2006


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Contents

Introduction

Background

Power consumption and conservation mechanisms

MAC sublayer

LLC sublayer

Network layer

Transport layer

OS/middleware and application layers Summary


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Introduction

Power management is one of the most challengingproblem in wireless communication

This paper addresses

Incorporation of energy conservation at all layers of the protocolstack for wireless networks


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Background

Wireless network architecture Protocol layers


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Power consumption

and conservation mechanisms(1)

Sources of power consumption

Communication

Transmit(1.5W)>receive(0.75W)>standby(0.01w)

Goal is to optimize the transceiver usage

Computation

Protocol processing aspects

Ex) usage of CPU and main memory, data compression..

Tradeoff btw communication costs and computation

communication costs computation needs

Goal is to balance btw communication and computation


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Power consumption

and conservation mechanisms(2)

General conservation guidelines and mechanisms Network layer

Balance the amount of traffic carried by each node

MAC layer : collisions should be eliminated Using a small packet size for registration and bandwidth request

Link layer Transmissions may be avoided when channel are poor Error control schemes (ARQ + FEC)

In a typical broadcast environment Broadcast a schedule that contains data transmission starting times for each

mobile Turn off the transceiver whenever the node determines that it will not be

receiving data for a period of time

In switching from transmit to receive modes, and vice versa Continuous allocation Aggregate packet requests


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MAC sublayer(1)

IEEE 802.11 standard

CSMA/CA (Collision Sense Multiple Access/Collision Avoidance)

For power conservation (QoS problem)

A mobile Active mode/Power Saving mode

Base station buffering for PS mode mobile

Per-packet energy consumption

Energy cost

= fixed cost (MAC operation) + incremental cost (packet size)

Fixed cost of Unicast > Fixed cost of broadcast

receiverd s CTS/AcK messages Incremental cost of Unicast = Incremental cost of broa cast


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MAC sublayer(2)

EC-MAC protocol (Energy Conserving) Using centralized scheduler

optimize the transmission schedule

FSM-Frame synchronizationmessage (BS->mobile)


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MAC sublayer(3)

PAMSA protocol (Power Aware Multi-Access) For Ad hoc network

Separate channels to determine when and how long to power off

RTS/CTS control packets

Data packets

1. RTS

Data

A

B

Control channel

Data channel

2. CTSX

2. backoff

1. RTS

Data

A

B

2. CTS

3. Data

4. transmits a busytone over thecontrol channel

C CDo not overhear

Turn off


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LLC sublayer(1)

Adaptive error control with ARQ i ARQ (Automatic Repeat Request) The new metric for energy efficiency

total amount of data delivered ,total energy consumed()

To maximize the energy efficiency of the protocol

Avoid persistence in retransmission data

Trade off # of retransmission attempts for probability of successfultransmission

Inhibit transmission when channel conditions are poor

ARQ works as normaluntil the transmitter detects an error

(lack of AcK)

ARQ enters a probing mode (a probing packet istransmitted every t slots)

until a properly received AcK isencountered


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LLC sublayer(2)

Adaptive error control with ARQ+FEC (Forward

Error Correction)

To keep energy consumption at a minimum

The error control scheme associated with each stream may need tobe modified as channel conditions change

Certain setup parameters and a channel model

Packetsize, QoS requirements (used by MAC sublayer) and packetscheduler are associated with each data stream


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Network layer(1)

Typical routing algorithms for Ad hoc Frequent topology updates

Improved routing but consume precious bandwidth

Infrequent topology updates

Decrease update messages but inefficient routing

Typical metrics Shortest-hop, shortest-delay, and locality stability

In wireless additional metrics

Energy resources, network life time


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Network layer(3)

Broadcast traffic Each mobile s ra io turns off

after receiving a packet if its neighbors have already received acopy of the packet

Power-aware broadcast tree approach

The tree is constructed starting from a source and expanding to theneighbors

have consumed lower amounts of power

have not already received the data transmission


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Transport layer(1)

TCP degrades significantly over a wireless link (handoff) A larger # of retransmissions

Frequently invoke congestion control measures

throughput , delay , energy consumption

Three schemes for reducing retransmission

Split connection protocols

Link layer approach (ex: ARQ+FEC)

End-to-End protocol


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Transport layer(2)

Energy consumption analysis of TCP The average # of successes per transmission attempt

Error correlation

Congestion control of TCP

By backing off and waiting during error bursts

TCP Probing

A probe cycle is initiated during error instead of congestion control

If persistent error conditions are detected

Sender invokes standard TCP congestion control

If transient random error

Sender resumes transmission using available network bandwidth


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OS/middleware

and application layers(1)

OS/middleware for energy efficiency

Mobility impacts the design of OS, middleware

Mobile computersd processing is expensive (battery power)

Architecture techniques

pipelining and parallelism

Predictive shutdown

during periods of inactivity

Separation both computation activity (External events) and inactivity


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OS/middleware

and application layers(2)

Application layer for energy efficiency Load partitioning

Selectively partitioned btw the mobile and base station

Mobile host : display, acquire multimedia data

Base station : Intensive computations

Proxies Middleware automatically adapt the applications to changes in

battery power and bandwidth

Databases

Access time (probe wait, bcast wait) minimization

Video processing Under severe bandwidth constraints or low-power situations

Carefully discarding selected packets

Decreasing the # of transmitted bits


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References

CE. Jones, et al, "A Survey of Energy Efficient Network Protocols forWireless Networksf , Wireless Networks, 2001.

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