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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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