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Worcester Polytechnic Institute 1
Exploiting Idle Communication Power to Improve Network Performance and Energy
Efficiency
Lei Guo, Xiaoning Ding, Haining Wang, Qun Li, Songqing Chen, Xiaodong Zhang
Proceedings of the 25th IEEE Annual Conference on Computer Communications (IEEE INFOCOM 2006), Barcelona, Spain, April 23-29, 2006.
Presented by Michael Putnam
(Some images and slides taken from INFOCOM presentation - http://www.cse.ohio-state.edu/~lguo/ )
Worcester Polytechnic Institute 2
Author Bio’s
• Ohio State University– Lei Guo
Ph.D. candidate in CSE Member of High Performance Computing and Software Lab Researches:
Internet measurements and modeling Streaming media delivery over the Internet Wireless systems and networking
– Xiaoning Ding Ph.D. candidate in CSE Researches:
Operating Systems Computer architecture Wireless systems and networking
– Xiaodong Zhang Chairman of the Department of CSE Researches:
Fast Data Accesses Resource Sharing
OUTLINE
BIOGRAPHIES
Introduction
Related Work
Motivation
System Models
Channel Allocation
System Design
Experiments
Conclusion
Worcester Polytechnic Institute 3
Author Bio’s
• College of William and Mary– Haining Wang
Assistant Professor Department of CS Researches:
Network QoS Internet architecture Wireless and sensor networks
– Qun Li Assistant Professor Department of CS Researches:
Wireless and Sensor Networks Embedded Systems
OUTLINE
BIOGRAPHIES
Introduction
Related Work
Motivation
System Models
Channel Allocation
System Design
Experiments
Conclusion
Worcester Polytechnic Institute 4
Author Bio’s
• George Mason University– Songqing Chen
Assistant Professor Department of CS Researches:
Distributed Systems High Performance Computing P2P Systems Internet Systems
OUTLINE
BIOGRAPHIES
Introduction
Related Work
Motivation
System Models
Channel Allocation
System Design
Experiments
Conclusion
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Challenges in Wireless System Design
• Energy saving is not easy– Limited battery capacity in wireless devices – High power consumption in wireless communication
• High performance costs energy and fairness – Wireless users demand high throughput, but …– A high throughput device needs less sleep. – A channel allocation mechanism can favor some but
degrade performance of others.
• Can we win both instead of addressing the trade-off?
OUTLINE
Biographies
INTRODUCTION
Related Work
Motivation
System Models
Channel Allocation
System Design
Experiments
Conclusion
Worcester Polytechnic Institute 6
• Energy consumption
• A simple way to save energy
– Put the WNI into sleep mode when idle (for a 5 V device)
> 50% total energy
up to 10%total energy
high power mode450 mA
low power mode15 mA
Power Consumption for Mobile Devices
OUTLINE
Biographies
INTRODUCTION
Related Work
Motivation
System Models
Channel Allocation
System Design
Experiments
Conclusion
Worcester Polytechnic Institute 7
802.11 Power Saving Mechanism
• Access point– Buffer data for sleeping
stations
– Broadcast beacon with TIM periodically (100 ms)
• Sleeping station– Wake up periodically to
receive beacon– Poll access point to receive
data– Sleep again
Access Point
Internet
Traffic Indication Map (TIM)
sleeping station
wake uppoll
receive data
OUTLINE
Biographies
Introduction
RELATED WORK
Motivation
System Models
Channel Allocation
System Design
Experiments
Conclusion
Worcester Polytechnic Institute 8
Observations of IEEE 802.11 Protocol
• A client/server model – Each station independently communicates with AP– AP serves a station one at a time via the channel.
• The saving mode affects TCP traffic– Increasing RTT and decreasing throughput.
• Performance anomaly (Infocom’03)– Non-uniform transfer rates between different stations to
AP due to distance and obstacle condition differences. – A low speed station has low channel utilization rate.
• Waste energy while a station is waiting for its turn.– Idle communication power due to strong dependency
OUTLINE
Biographies
Introduction
RELATED WORK
Motivation
System Models
Channel Allocation
System Design
Experiments
Conclusion
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Performance Anomaly in WLAN
• Multiple channel rates in PHY– Larger coverage– Varying channel conditions
• Same MAC control for all channel rates– Same opportunity to get channel– Different channel holding time for sending frame
Performance anomaly (INFOCOM’03)– All stations have the same flow rate– Unfair to high channel rate stations– Low channel utilization
OUTLINE
Biographies
Introduction
RELATED WORK
Motivation
System Models
Channel Allocation
System Design
Experiments
Conclusion
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Existing Solutions to address the Limits
• Reducing idle communication power by– Traffic prediction: bounded slowdown (MOBICOM’02)– Self-tuning with application hints (MOBICOM’03)– Limits: case by case, and accuracy can vary.
• Address the performance anomaly– Time-based fairness scheduling: a constant time unit is
given to each device (USENIX 04) – Limits: poorly conditioned devices suffer: fast is faster,
and slow is slower.
Purpose of this paper: to win both performance and energy
OUTLINE
Biographies
Introduction
RELATED WORK
Motivation
System Models
Channel Allocation
System Design
Experiments
Conclusion
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Source of Idle Communication Power
While the channel is used by one station, idle communication power is wasted in many other stations
AP
Wireless performance anomaly makes this power waste worse, but also with an opportunity.
OUTLINE
Biographies
Introduction
Related Work
MOTIVATION
System Models
Channel Allocation
System Design
Experiments
Conclusion
Worcester Polytechnic Institute 12
Multi-hop Relay
To help low channel rate stations to Increase throughput and extend network coverage
AP
X
OUTLINE
Biographies
Introduction
Related Work
MOTIVATION
System Models
Channel Allocation
System Design
Experiments
Conclusion
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Multi-hop Relays Leverage Strong Dependency
• Slow stations become faster– Completing the data transfer ahead of the unit time.– Equivalent to move the station closer to AP or improve the
station’s communication condition.
• Faster stations serve as proxies for slow stations– Performance improvement of slow stations reduced the
waste of idle communication powers of fast stations --- shortening the waiting time.
• Effective P2P coordination among stations is the key.
OUTLINE
Biographies
Introduction
Related Work
MOTIVATION
System Models
Channel Allocation
System Design
Experiments
Conclusion
Worcester Polytechnic Institute 14
Incentive and Fairness to Fast Stations
• Why not sleep or wait, but proxy/relay for others?– Sleep lowers throughput, and wait wastes energy. – Idle communication energy can be used – The saved time in slow stations should be contributed.
• How much service is fair in a shared radio channel?– A proxy should be paid for its service– For either proxy or client, the throughput and energy
utilization should be improved.
OUTLINE
Biographies
Introduction
Related Work
MOTIVATION
System Models
Channel Allocation
System Design
Experiments
Conclusion
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Rationale
• Energy efficiency: what does a user care about?– Energy per second
– Energy per bit: time is energy• Self-incentive multi-hop relay with TBF
– Use channel time to pay the relay service
A win-win solution
Throughput Energy efficiency
Proxy Increase No loss
Client Increase Increase
OUTLINE
Biographies
Introduction
Related Work
MOTIVATION
System Models
Channel Allocation
System Design
Experiments
Conclusion
Worcester Polytechnic Institute 16
System Model
• Time based fairness in shared radio channel
• Principle of proxy forwarding
– Proxy: throughput idle time energy/bit – Client: channel rate throughput
S1 S2 … Si … Sn
ti = t = 1/n
1 roundidle idle
Sq
Client
Sp
Proxy
S0
AP
OUTLINE
Biographies
Introduction
Related Work
Motivation
SYSTEM MODELS
Channel Allocation
System Design
Experiments
Conclusion
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Analytic Definitions
• Power Consumption – P(Si)– Joules / sec
• Throughput – T(Si)– The number or effective bits a station transmits per unit
time (not including retransmissions, or forwarding data for other stations)
• Energy Utility – E(Si)– Average number of effective bits per unit energy
OUTLINE
Biographies
Introduction
Related Work
Motivation
SYSTEM MODELS
Channel Allocation
System Design
Experiments
Conclusion
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Analytic Definitions
• Throughput Gain
• Energy Gain
OUTLINE
Biographies
Introduction
Related Work
Motivation
SYSTEM MODELS
Channel Allocation
System Design
Experiments
Conclusion
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Channel Time Allocation (single-hop)
OUTLINE
Biographies
Introduction
Related Work
Motivation
System Models
CHANNEL ALLOCATION
System Design
Experiments
Conclusion
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Lemma 1 (single-hop)
• Time utilization of a client Sq when it pays the cost price to its proxy Sp for the forwarding service is
OUTLINE
Biographies
Introduction
Related Work
Motivation
System Models
CHANNEL ALLOCATION
System Design
Experiments
Conclusion
Worcester Polytechnic Institute 21
Lemma 1 (single-hop)
• Rewarding time of a client Sq when it pays the cost price to its proxy Sp for the forwarding service are
• Amount needed to keep energy utility of proxy unchanged
• Cost for the proxy to listen to the client and talk to the AP
OUTLINE
Biographies
Introduction
Related Work
Motivation
System Models
CHANNEL ALLOCATION
System Design
Experiments
Conclusion
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Lemma 1 (single-hop)
• Throughput gain of a client Sq when it pays the cost price to its proxy Sp for the forwarding service are
• Energy Utility gain of a client Sq when it pays the cost price to its proxy Sp for the forwarding service is
OUTLINE
Biographies
Introduction
Related Work
Motivation
System Models
CHANNEL ALLOCATION
System Design
Experiments
Conclusion
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Lemma 1 (single-hop)
• Relaying is only useful when the Throughput Gain
• Since U(Sq) < 1, Note that
Which Implies
• Relaying can increase the Energy Utility of a client station as long as its Throughput can be improved
OUTLINE
Biographies
Introduction
Related Work
Motivation
System Models
CHANNEL ALLOCATION
System Design
Experiments
Conclusion
Worcester Polytechnic Institute 24
Lemma 2 (single-hop)
• Assume station Sp provides forwarding services to k client stations, Sq1 , Sq2 , ..., Sqk (k > 1), and these client stations independently contribute their rewarding time to Sp to keep the energy utility of Sp unchanged, we have
• U(Sp) = 1 and = 1: “…easy to see…” – authors
OUTLINE
Biographies
Introduction
Related Work
Motivation
System Models
CHANNEL ALLOCATION
System Design
Experiments
Conclusion
Worcester Polytechnic Institute 25
Lemma 2 (single-hop)
• Throughput Gain– The effective time of Sp is
• Thus,
OUTLINE
Biographies
Introduction
Related Work
Motivation
System Models
CHANNEL ALLOCATION
System Design
Experiments
Conclusion
Worcester Polytechnic Institute 26
Channel Time Allocation (multi-hop)
S0 S1 Si-1 Si
OUTLINE
Biographies
Introduction
Related Work
Motivation
System Models
CHANNEL ALLOCATION
System Design
Experiments
Conclusion
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Lemma 3 (multi-hop)
• Assume each station has at most one immediate relaying station in a WLAN, and each station rewards its relaying stations independently to keep their energy utilities unchanged. For station Si that is relayed by i – 1 (i ≥ 1) stations along the path S0 → S1 → ... → Si – 1 → Si, and Si has mi indirect or direct clients (Sq1 , Sq2 , ..., Sqmi), we have
Where
and
OUTLINE
Biographies
Introduction
Related Work
Motivation
System Models
CHANNEL ALLOCATION
System Design
Experiments
Conclusion
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Selfish Forwarding - SFW
• Proxy discovery and selection– A poorly conditioned client broadcasts a request to relay
his packets
– AP assigns a relaying station for clients based on the game theory (second price auction) to provide fairness for competition among proxy candidates
HELP!
OUTLINE
Biographies
Introduction
Related Work
Motivation
System Models
Channel Allocation
SYSTEM DESIGN
Experiments
Conclusion
AP
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Selfish Forwarding - SFW
• Proxy discovery and selection– AP collects the bids within a bidding time window– AP selects winner based on “second price sealed bid” rule
(highest bidder wins, but only pays second highest price)
– Client sends a request to the proxy– Proxy ACKs, and notifies the AP of the association
HELP!
OUTLINE
Biographies
Introduction
Related Work
Motivation
System Models
Channel Allocation
SYSTEM DESIGN
Experiments
Conclusion
Worcester Polytechnic Institute 30
Selfish Forwarding - SFW
• Channel allocation and scheduling
– Easy to do under PCF - but since most commercial products only support DCF, there is a need for a scheduling algorithm
– AP distributes tokens for fairness without any enforcement.
– The relaying actions are determined by token exchanges among stations.
OUTLINE
Biographies
Introduction
Related Work
Motivation
System Models
Channel Allocation
SYSTEM DESIGN
Experiments
Conclusion
Worcester Polytechnic Institute 31
Basic Idea of Token-based Channel Scheduling
• A token is a ticket for a data transfer (RX/TX) in one time unit
• AP initially distributes an equal amount of tokens to each station (fairness).
• A pair of RX & TX consumes one token.
• Token bucket model to fully use transmission channel.
• Multi-hop forwarding to increase throughput
• Incentive rewards to proxies
OUTLINE
Biographies
Introduction
Related Work
Motivation
System Models
Channel Allocation
SYSTEM DESIGN
Experiments
Conclusion
Worcester Polytechnic Institute 32
Token and Token Bucket Model
packets
tokens from AP
Overflow!Re-allocate to other
stations by AP
Token Bucket
Packet Queue
Transmitter 1 token per packet
OUTLINE
Biographies
Introduction
Related Work
Motivation
System Models
Channel Allocation
SYSTEM DESIGN
Experiments
Conclusion
Worcester Polytechnic Institute 33
Multi-hop Forwarding
APS1
STA Proxy Rate
S1--- R(0,1)
S2--- R(0,2)
S3 S2R(0,3)
S4 S2R(0,4)
S2
S3
S4
Hop Station Rate
1 Self R(0,2)
2 S3R(2,3)
S4R(2,4)
Hop Station Rate
1 S2R(0,2)
2 Self R(2,3)
OUTLINE
Biographies
Introduction
Related Work
Motivation
System Models
Channel Allocation
SYSTEM DESIGN
Experiments
Conclusion
Worcester Polytechnic Institute 34
Multi-hop Forwarding
APS1
R(0,4)S2S4
R(0,3)S2S3
R(0,2)---S2
R(0,1)---S1
RateProxySTA
S2
S3
S4
R(2,3)S3
R(2,4)S4
2
R(0,2)Self1
RateStationHop
R(2,3)Self2
R(0,2)S21
RateStationHop
• Each frame has Src / Dest MAC address
• Upon receipt of frame, node looks up Dest in table to see who to send to next
• Puts that addy in the Dest field and forwards the frame
• Then updates its channel rate field for the link received on to compute cost price of forwarding service.
OUTLINE
Biographies
Introduction
Related Work
Motivation
System Models
Channel Allocation
SYSTEM DESIGN
Experiments
Conclusion
Worcester Polytechnic Institute 35
Multi-hop Path Maintenance
• Channel rates vary due to mobility or changes in the environment conditions – possible broken paths
• Each client periodically re-evaluates the forwarding service
• If the service quality is degraded, looks for a new proxy
• ( What threshold determines significantly degraded service? )
OUTLINE
Biographies
Introduction
Related Work
Motivation
System Models
Channel Allocation
SYSTEM DESIGN
Experiments
Conclusion
Worcester Polytechnic Institute 36
Multi-hop Power Management
• Power saving mode (no clients)– notify the AP directly
• Power saving mode (with clients)– Notify immediate children– Children recursively notify their children– After receiving all ACK’s – notify the AP– Clients look for new proxies
OUTLINE
Biographies
Introduction
Related Work
Motivation
System Models
Channel Allocation
SYSTEM DESIGN
Experiments
Conclusion
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Implementation and Experiments
• AP– NetGear MA311 802.11b PCI wireless adaptor– Linux kernel 2.4.20– HostAP linux driver v0.1.3
• Wireless Stations (6)– NetGear MA401 802.11b PCMCIA wireless adaptor– ORiNOCO Linux driver v0.15rc2
• Traffic– FTP (presented in the paper)– Web (results in tech report)
OUTLINE
Biographies
Introduction
Related Work
Motivation
System Models
Channel Allocation
System Design
EXPERIMENTS
Conclusion
Worcester Polytechnic Institute 38
Implementation
• Bidding time – 50 ms
• Token distribution interval – 100 ms
• Token value – 20 µs channel time
• Host AP distributes tokens evenly based on number of stations, then transfers rewarding tokens from clients to proxies
OUTLINE
Biographies
Introduction
Related Work
Motivation
System Models
Channel Allocation
System Design
EXPERIMENTS
Conclusion
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Protocols Compared
• DCF– Most widely used protocol in 802.11b network– Distributed Coordination Function
• TBF– Time-based Fairness (proposed USENIX 2004)
• SFW– Selfish Forwarding (authors’ homebrew)
OUTLINE
Biographies
Introduction
Related Work
Motivation
System Models
Channel Allocation
System Design
EXPERIMENTS
Conclusion
Worcester Polytechnic Institute 40
Single Client Experiment
AP
11Mbps
11Mbps
1Mbps
• Large file download from AP to proxy / clients
• Throughput measured at each hop
• Energy consumption computed (not measured)– Tx time * power consumption
(as provided by the manufacturer)
OUTLINE
Biographies
Introduction
Related Work
Motivation
System Models
Channel Allocation
System Design
EXPERIMENTS
Conclusion
Worcester Polytechnic Institute 41
Performance Evaluation
Channel allocation scheme
Channel allocation scheme
1 proxy (P), 1 client (Q)OUTLINE
Biographies
Introduction
Related Work
Motivation
System Models
Channel Allocation
System Design
EXPERIMENTS
Conclusion
Worcester Polytechnic Institute 42
Multi-clients Experiment
AP
11Mbps
1Mbps
OUTLINE
Biographies
Introduction
Related Work
Motivation
System Models
Channel Allocation
System Design
EXPERIMENTS
Conclusion
Worcester Polytechnic Institute 43
Performance Evaluation
1 proxy (P), 5 clients (Q)OUTLINE
Biographies
Introduction
Related Work
Motivation
System Models
Channel Allocation
System Design
EXPERIMENTS
Conclusion
Worcester Polytechnic Institute 44
Performance Evaluation
Proxy throughput gain
1 proxy, multiple clients
OUTLINE
Biographies
Introduction
Related Work
Motivation
System Models
Channel Allocation
System Design
EXPERIMENTS
Conclusion
Worcester Polytechnic Institute 45
Conclusion
• Address throughput degradation caused by low-rate stations (Performance Anomaly ’03)
• Utilize energy waste in idle channel listening
• High Channel-rate station forwards data for low-rate station
• Clients reward proxy with additional channel time
• Everyone’s throughput can increase without suffering energy efficiency
OUTLINE
Biographies
Introduction
Related Work
Motivation
System Models
Channel Allocation
System Design
Experiments
CONCLUSION
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