energy efficient network protocols for wireless networks

Energy Efficient Network Protocols for Wireless Networks

Kiran MuthabatullaKiran Muthabatulla

Microsoft Confidential

IntroductionIntroduction

Wireless Networking exploding in Wireless Networking exploding in Mobile and personal Mobile and personal communicationscommunications

Cell Phones, Personal Computing Cell Phones, Personal Computing Systems, Wireless LAN'sSystems, Wireless LAN's

As a result… As a result…

Energy Efficiency is an important Energy Efficiency is an important design consideration due to limited design consideration due to limited battery life of Mobile terminals.battery life of Mobile terminals.


IntroductionIntroduction

Network Interface : significant consumer Network Interface : significant consumer of power. of power.

Power consumption : On an Average Power consumption : On an Average system CPU-21%, 36% LCD. 18% system CPU-21%, 36% LCD. 18% Wireless Interface 18% Hard Disk, Power Wireless Interface 18% Hard Disk, Power consumption. consumption.

Hence.. Hence..

Low Power design of the Entire Network Low Power design of the Entire Network Stack is needed to enhance energy Stack is needed to enhance energy efficiency. efficiency.


Infrastructure NetworkInfrastructure Network


Base Stations in BSS Base Stations in BSS ModeMode Coordinate Access to one or more Coordinate Access to one or more

transmission channels for mobiles transmission channels for mobiles within the coverage cell. within the coverage cell.

Wireless Access to and from the Wireless Access to and from the wired host occurs in the last hop wired host occurs in the last hop between base stations and mobile between base stations and mobile hosts that share the bandwidth of hosts that share the bandwidth of the wireless channel. the wireless channel.


Ad hoc Network Ad hoc Network


Ad-HocAd-Hoc

Multi Hop wireless Networks, in Multi Hop wireless Networks, in which a set of mobiles which a set of mobiles cooperatively maintain network cooperatively maintain network connectivity. connectivity.

On-demand network, dynamic On-demand network, dynamic unpredictable, random, multi hop unpredictable, random, multi hop topologies which has no topologies which has no infrastructure support. infrastructure support.

Mobiles must periodically update Mobiles must periodically update topology information for routing. topology information for routing.


Protocol StackProtocol Stack


Responsibilities Data LinkResponsibilities Data Link

Data Link: reliable and secure Data Link: reliable and secure Logical Layer over unreliable Logical Layer over unreliable Wireless Link. Wireless Link.

Security : Encryption and Security : Encryption and DecryptionDecryption

Network layer packet conversion Network layer packet conversion into framesinto frames

Packet re-transmissions.Packet re-transmissions. MAC: Allocates the time-frequency MAC: Allocates the time-frequency

or code space modulations among or code space modulations among mobiles sharing wireless channels mobiles sharing wireless channels in a region. in a region.


Low Power at PHY LayerLow Power at PHY Layer

Increase Battery capacityIncrease Battery capacity Slow progress. Developments in Slow progress. Developments in

Battery technology is very slowBattery technology is very slow

Decrease amount of energy Decrease amount of energy consumed at the Wireless terminal. consumed at the Wireless terminal.

Hardware means: Hardware means: Variable Clock Speed CPU’s, flash Variable Clock Speed CPU’s, flash

memory, disk spin down. memory, disk spin down.


Sources of Power Sources of Power ConsumptionConsumption Communication related.Communication related.

Transceiver at the source, intermediate and Transceiver at the source, intermediate and destination nodes. destination nodes.

Transmitter is used for sending control, Transmitter is used for sending control, route request and response, as well as data route request and response, as well as data packets originating at the sender. packets originating at the sender.

Receiver is used to receive data and control Receiver is used to receive data and control packets destined for the node. packets destined for the node.

Computation related: Usage of CPU, Computation related: Usage of CPU, Main Memory, disk, data compression Main Memory, disk, data compression techniques. techniques.


Mobile Radio : Power Mobile Radio : Power ModesModesProxim Range LAN2 2.4 GHz Proxim Range LAN2 2.4 GHz

Transmit: Transmit:

1.5 W in transmit1.5 W in transmit

Receive: Receive:

0.75 W in receive0.75 W in receive

Standby: Standby:

0.01W in Standby0.01W in Standby


General Guidelines: General Guidelines:

Collisions must be eliminated as Collisions must be eliminated as they result in re-transmissions. they result in re-transmissions.

Re-transmissions lead to Re-transmissions lead to unnecessary power consumption unnecessary power consumption and to possibly unbounded delays. and to possibly unbounded delays.

Broadcast environment, receiver Broadcast environment, receiver remains on at all times. remains on at all times. Node Receives the packets and Node Receives the packets and

forwards only if it is meant to the forwards only if it is meant to the receiving node. receiving node.

Channel status monitoring. Channel status monitoring.


SchedulingScheduling

Broadcast scheduling that contains Broadcast scheduling that contains the data transmission starting times the data transmission starting times for each mobile. for each mobile.

This enables the mobiles to switch This enables the mobiles to switch to a standby mode until the receive to a standby mode until the receive start time. start time.

Turn off the transceiver whenever Turn off the transceiver whenever the node determines that it will not the node determines that it will not be receiving data for a period of be receiving data for a period of time. time.


Scheduling.. Scheduling..

Mobile Radio Switching between TX Mobile Radio Switching between TX and RX. and RX.

A protocol that allocates A protocol that allocates permissions on a slot by slot basis permissions on a slot by slot basis suffers substantial over head. suffers substantial over head.

Mobile should be allocated Mobile should be allocated contiguous slots for TX or Rx to contiguous slots for TX or Rx to reduce turnaround. reduce turnaround.

Mobiles may request multiple Mobiles may request multiple transmission slots with a single transmission slots with a single reservation packet. reservation packet.


Scheduling.. Scheduling..

Mobiles transmit data transmission Mobiles transmit data transmission requests to the BS. The BS requests to the BS. The BS computes the system transmission computes the system transmission schedule and broadcasts each schedule and broadcasts each mobiles transmission schedule. mobiles transmission schedule.

Mobiles Wake up when its their Mobiles Wake up when its their schedule time. schedule time.

Considerations : Considerations : Battery power at stationsBattery power at stations QOSQOS Avoid TX when channel conditions are Avoid TX when channel conditions are

poor. poor.


General GuidelinesGeneral Guidelines

Load Balancing of the Battery Load Balancing of the Battery Power: Power:

Avoid routing through nodes with Avoid routing through nodes with lower battery power. lower battery power.

May want not to update routing May want not to update routing information but may suffer information but may suffer performance. performance.

Taking advantage of Broadcast Taking advantage of Broadcast Multicast packets. Multicast packets.


MAC Sub LayerMAC Sub Layer

IEEE 802.11 Standard. IEEE 802.11 Standard. CSMA/CACSMA/CA Back off timers/SlotsBack off timers/Slots Positive ACK’sPositive ACK’s RTS/CTS. RTS/CTS. PSP, NULL Data Frame.PSP, NULL Data Frame. Base Stations Store the PacketsBase Stations Store the Packets Beacon updatesBeacon updates


EC-MACEC-MAC

Based on Reservation and Based on Reservation and Scheduling Scheduling Transmission organized by the BS into Transmission organized by the BS into

Frames, and each slot equals the basic Frames, and each slot equals the basic unit of Wireless data transmission.unit of Wireless data transmission.

At the Start of Each Frame, The BS At the Start of Each Frame, The BS transmits the FSM which contains transmits the FSM which contains sync info and the uplink transmission sync info and the uplink transmission order for the subsequent information order for the subsequent information and the uplink information order for and the uplink information order for the subsequent reservation phase. the subsequent reservation phase.


EC-MACEC-MAC


PAMAS ProtocolPAMAS Protocol

Power Aware Multiple Access Power Aware Multiple Access For Ad hoc Networks. For Ad hoc Networks. Separate Channels for RTS/CTS and Separate Channels for RTS/CTS and

data packets.data packets. Mobile sends RTS, Waits CTS, if Mobile sends RTS, Waits CTS, if

received, the mobile sends over Data received, the mobile sends over Data Channel. Channel.

Sets the Control Channel to busy. Sets the Control Channel to busy.


PAMAS ProtocolPAMAS Protocol

Mobiles not receiving and sending Mobiles not receiving and sending packets turn off the wireless interface. packets turn off the wireless interface. Data transmissions need not be overheard by Data transmissions need not be overheard by

all the neighbors of the transmitter. all the neighbors of the transmitter. Separate control channel determines when Separate control channel determines when

and how long to power off. and how long to power off. Mobile should power itself offMobile should power itself off

No packets to TX and neighbor begins to No packets to TX and neighbor begins to send packet not for it.send packet not for it.

Has packets to send, but some other pair Has packets to send, but some other pair already started to communicate. already started to communicate.

Probe protocol to see how long to sleep. Probe protocol to see how long to sleep.


Automatic Repeat Request (ARQ)Automatic Repeat Request (ARQ) A type of communications link where A type of communications link where

the receiver asks the transmitter to re-the receiver asks the transmitter to re-send a block of data when errors are send a block of data when errors are detected detected

Forward Error Correction (FEC)Forward Error Correction (FEC) A method of error control where the A method of error control where the

receiving node automatically corrects receiving node automatically corrects as many channel errors as it can as many channel errors as it can without referring to the sending node.without referring to the sending node.

LLC : Error Control. LLC : Error Control.


DisadvantagesDisadvantages

Both of them waste network bandwidth Both of them waste network bandwidth and consume power resources due to and consume power resources due to retransmissions of data packets retransmissions of data packets

Greater overhead necessary in error Greater overhead necessary in error correction. correction.


Adaptive Error Control Adaptive Error Control With ARQ.With ARQ.

New Design Metric : Energy New Design Metric : Energy efficiency of a protocol which is efficiency of a protocol which is defined as the ratio between total defined as the ratio between total amount of data delivered and total amount of data delivered and total amount of energy consumed. amount of energy consumed. If more data is transmitted for a given If more data is transmitted for a given

amount of energy consumption, the amount of energy consumption, the energy efficiency increases. energy efficiency increases.


GuidelinesGuidelines

Avoid Persistence in Retransmitting Avoid Persistence in Retransmitting Data. Data.

Trade off number of re-transmission Trade off number of re-transmission attempts for probability of attempts for probability of successful transmissionsuccessful transmission

Inhibit transmissions when channel Inhibit transmissions when channel conditions are poor. conditions are poor.


Guidelines.. Guidelines..

Probing Protocol that slows data Probing Protocol that slows data transmission when degraded channel transmission when degraded channel conditions are encountered. conditions are encountered.

ARQ works normal until the Transmitter ARQ works normal until the Transmitter detects an error in either the data or detects an error in either the data or control channel due to lack of an ACK.control channel due to lack of an ACK.

At this time, the protocol enters a At this time, the protocol enters a probing mode, in which the probing probing mode, in which the probing packet is transmitted every t-slots. packet is transmitted every t-slots.

This mode is continued until ACKs start This mode is continued until ACKs start to show up. to show up.

Then protocol returns to normal mode. Then protocol returns to normal mode.


Other Schemes proposed.Other Schemes proposed.

Adaptive Error control with Adaptive Error control with ARQ/FEC combinationARQ/FEC combination

Adaptive Power control and coding Adaptive Power control and coding schemescheme


Network LayerNetwork Layer

Routing PacketsRouting Packets Mobiles cooperate to maintain Mobiles cooperate to maintain

Topology informationTopology information Use Multi hop packet routingUse Multi hop packet routing

Usual Approaches : Usual Approaches : Frequent topology results in Frequent topology results in

improved routingimproved routing Infrequent topology results in Infrequent topology results in

decreased update messages. decreased update messages.

Congestion ControlCongestion Control


Network LayerNetwork Layer

Typical Metrics: Typical Metrics: Shortest HopShortest Hop

Shortest DelayShortest Delay

Locality stabilityLocality stability


Unicast TrafficUnicast Traffic : Metrics : Metrics

Energy Consumed per packet : MinEnergy Consumed per packet : Min Time to network PartitionTime to network Partition : Max : Max

Critical Nodes drain their power at equal rates.Critical Nodes drain their power at equal rates. Variance in power levels across mobiles : MinVariance in power levels across mobiles : Min

All nodes are at the same priority levelAll nodes are at the same priority level All mobiles are equal and no one mobile is penalized All mobiles are equal and no one mobile is penalized

or privileged over the other.or privileged over the other.

Cost per packetCost per packet : Min: Min Routes with depleted energy reserves don’t lie in Routes with depleted energy reserves don’t lie in

many routes. many routes. Maximum Mobile costMaximum Mobile cost : Min: Min

Minimize cost to move the packet through this node.Minimize cost to move the packet through this node.


Broadcast TrafficBroadcast Traffic

Single transmission, a mobile is Single transmission, a mobile is able to broadcast a packet to all able to broadcast a packet to all immediate neighbors. immediate neighbors. Intermediate Nodes re-transmit the Intermediate Nodes re-transmit the

packet to all its immediate. packet to all its immediate.

Turn off after receiving the packet if Turn off after receiving the packet if the neighbor already received the the neighbor already received the packet. packet.


Broadcast TrafficBroadcast Traffic Traditional : FloodingTraditional : Flooding

No Global topology information No Global topology information requiring little control overhead and requiring little control overhead and completes the broadcast with completes the broadcast with minimum number of hops. minimum number of hops.

Solution:Solution: Collect topology information. Collect topology information. Ensure that transmission reaches as Ensure that transmission reaches as

many new nodes as possible. many new nodes as possible. Construct trees with lowest cost per Construct trees with lowest cost per

outgoing degree. outgoing degree.


Transport LayerTransport Layer

TCP degrades over Wireless LinkTCP degrades over Wireless Link Large number of Re-transmissionsLarge number of Re-transmissions Frequently invoke congestion control Frequently invoke congestion control

measures.measures. Confusing Wireless Link Errors Confusing Wireless Link Errors Loss due to handoff as channel Loss due to handoff as channel

congestion. congestion. Significantly reduces throughput and Significantly reduces throughput and

introduce unacceptable delays. introduce unacceptable delays.


New SchemesNew Schemes

TO reduce RetransmissionsTO reduce Retransmissions Split connection protocolsSplit connection protocols

Hide the wireless link from the wired Hide the wireless link from the wired network by terminating the Tcp network by terminating the Tcp connection at the Base station. connection at the Base station.

Link Layer protocolsLink Layer protocols Hide link related Losses from the TCP Hide link related Losses from the TCP

source by using a combination of local source by using a combination of local retransmissions and FEC.retransmissions and FEC.

End to End Protocols. End to End Protocols. Modified versions of TCP sensitive to Modified versions of TCP sensitive to

Wireless environmentWireless environment


Split ConnectionSplit Connection


Link Layer ProtocolsLink Layer Protocols


ReferencesReferences

This presentation is a This presentation is a understanding based on the understanding based on the research paper.research paper.

A survey of energy efficient network A survey of energy efficient network protocols for wireless networks. protocols for wireless networks. Wireless Networks, 7(4):343--358, Wireless Networks, 7(4):343--358, July 2001. by C. E. Jones, K. M. July 2001. by C. E. Jones, K. M. Sivalingam, P. Agrawal, and J. C. Sivalingam, P. Agrawal, and J. C. Chen. Chen.

energy efficient network protocols for wireless networks

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