Snooze: Energy Management in 802.11n WLANs Ki-Young Jang, Shuai Hao, Anmol Sheth, Ramesh Govindan
Snooze: Energy Management in 802.11n WLANs
Ki-Young Jang, Shuai Hao, Anmol Sheth, Ramesh Govindan
Background
2
Evolution of Wi-Fi
Performance vs. Energy Usage
WaveLAN (1995)
802.11b (1997)
802.11g (2003)
802.11n 3x3
(2009)
802.11n 4x4
(2011)
0
200
400
600
800
1000
1200Wi-Fi Performance
8x speedup compared to
802.11a/g
Mbp
s
3
Background
802.11n Features and Energy Usage
A B
Energy management should exploit bothsleep opportunities and antenna configuration.
MIMO higher data rate spatial diversity
Additional power states:10-30% of peak power
consumption of the tablet!
# of Antenna
12 1.99 1.27 1.13 0.103 2.10 1.60 1.45 0.10
Intel Wi-Fi Link 5300(W)Tx Rx Idle Sleep
1.28 0.94 0.82 0.10
1.5x and 1.6x 1.3x and
1.7x
4Motivation Design Implementation Evaluation
Motivation
Micro-sleep Opportunities
A
B
APt
Sleep!Z ZZ
Sleep!Z ZZ
t
t
5
Micro-sleepSleep + Wakeup = ~2ms
Motivation Design Implementation Evaluation
Motivation
Micro-sleep Opportunities
# of STATraffic
1 1 2 1 2VoIP File HD Video
0.00.20.40.60.81.0
EXPLOITABLE NON-EXPLOITABLE TX RX
Nor
mal
ized
Tim
eSleeping while AP is servicing others1Sleeping during inter-frame gaps2
Depending on the traffic and number of clients, we can get energy savings of 30% ~ 90%.
6Motivation Design Implementation Evaluation
Motivation
1 2 30
5
10
15
RX Antennas
Tim
e (s
econ
ds)
1 2 305
101520
RX Antennas
Ener
gy (J
)
Internet as bottleneck: SISO is best
1 2 302468
10
RX Antennas
Tim
e (s
econ
ds)
1 2 302468
10
RX Antennas
Ener
gy (J
)
High bandwidth scenario: MIMO3 is best
Antenna Configuration
Antenna configuration should be adaptive based on traffic demand and link quality.
7
Challenges
• Micro-sleep with minimal impact on delay and throughput-sensitive traffic
• Adaptive antenna configuration management• Joint design of both mechanisms• Application agnostic
Time (ms)
Pow
er(W
)
100 200 300
Sleep for 50ms
Sleep for 70ms
8
Contribution
Design and Implementation of Snooze
Joint, application-agnostic design of client micro-sleep and antenna configuration management.
Extensive experiments that demonstrate 30~85% energy-savings over CAM across a wide range of traffic scenarios.
9Motivation Design Implementation Evaluation
AP-Directed Design
Snooze AP
Snooze Client
• Shapes traffic to create sleep opportunities• Minimal impact on traffic• Minimizes the number of active
clients
• Manages antenna configurations• Minimizes antennas needed
Goal: Reduce client energy consumption by jointly controlling sleep and antenna configuration
10
Sleep duration: based on measured packet arrival rate Awake duration: based on average airtime consumption
Motivation Design Implementation Evaluation
Snooze Components
Micro-sleepScheduling
AntennaMgmt.
If measured airtime utilization is
< 0.3: high link quality or more antennas -> turn off 1 antenna
> 0.7: low link quality or less antennas -> turn on 1 antenna
Rate Adaptation: AP uses default rate-control algorithm with restricted search space
Hysteresis and moving averages
SleepAwake
25.50 25.51 25.52 25.53 25.54 25.55Sleep
Awake
A: 1Mbps
B: 20Mbps
Time (Second)
11Motivation Design Implementation Evaluation
Implementation
AP Client
Driv
erKe
rnel
RateTable
AirtimeUsage
iwlagn
Airtime Scheduling
Sleep/WakeupComputation
mac80211...
Per client traffic queue
Sleep/Wakeup
Antenna Configuration
iwlagn
mac80211
12Motivation Design Implementation Evaluation
Evaluation
Applications used for evaluation
Delay/Jitter Sensitivity
High Low
Bandwidth Requirement
High HD video streaming File downloading
Low VoIP Chat
Overview and Setup
Performance comparisonConstantly Awake Mode (CAM)
802.11 Power Save Mode (PSM)
Evaluation metricTotal energy usage of NIC
Application throughput and delay
13Motivation Design Implementation Evaluation
Evaluation
High Definition Video Streaming
More than 25% low-power sleeping compared with both CAM and PSM
About 50% energy savings compared with both CAM and PSM
Average delayCAM : 2.5ms, PSM : 4ms, Snooze : 8ms
14Motivation Design Implementation Evaluation
Evaluation
Heterogeneous Traffic
Snooze can accommodate multiple concurrent applications.
Client
Mode
HD
Chat
VoIP File HD
Chat
VoIP File HD
Chat
VoIP File
CAM PSM Snooze
0
50
100
150
200 SLEEP IDLE TX RX
Ener
gy(J
)
One app per client
Both techniques contribute significantly to energy savings, but contribution varies across traffic.
Energy saving breakdown
37%
63%
File80%
20%
VoIP
69%
31%
HD90%
10%
Chat
micro-sleepantenna config.
15
Related Work
Energy Management Techniques for 802.11
uPM C-PSM Catnap NAPman Snooze
AP-directed
Traffic types
HB-DS
HB-DI
LB-DS
LB-DI
802.11n
Rate adaptation
Multiple apps per client
16
Conclusion
Client micro-sleep and antenna configuration managementApplication agnostic30~85% energy saving across a wide range of traffic scenarios
Snooze: Energy Management Scheme for 802.11n
Future Work
Multi-AP settingHighly bursty workloadsParameter sensitivity