E-MiLi: Energy-Minimizing Idle Listening in Wireless Networks
Xinyu Zhang and Kang G. ShinDept. of EECS Univ. Michigan
Presented by: Fenggang Wu2011/11/04
2/20
Author
•HIT(01)-> Toronto(05)->U Michigan(08)->(11)Princeton NEC Lab
Name: Xinyu Zhang
Gender: Male
Birthyear: 1984
Place of Birth: Baotou, Inner-Mongolia, China
Nationality: Chinese
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Agenda•Background•Related Work•Solution
▫SRID▫oDoc
•Evaluation•Conclusoin•Comments
4/20
Background•Scenario:
▫WiFi AP-client senario•Idle listening (IL) in CSMA
▫Why listening? (transmit, receive)▫Energy waste
•Problem▫How to reduce the energy consumption in
IL?
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Existing Work•PSM
▫Reducing IL energy cost by reducing IL time
▫Yet IL still dominate clients’ energy consumption even with PSM enabled 80% busy network, 60% idle network
•Another dimension▫Reducing IL energy cost by reducing IL
power
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The E-MiLi Approach•E-MiLi: Energy-Minimizing idle Listening•Key Idea:
▫Reduce the IL energy cost by downclocking.•Challenge:
▫Nyquist’s Theorem: ▫How to put the radio in a subconscious mode
while it can still respond to incoming packets properly?
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Overview of E-MiLiWhat’s M-preambleHow to detect it?
When it is safe to
downclock?
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Solutions•SRID (Sampling Rate Invariant Detection)
▫How to perceive arriving packet in low sampling rate?
▫Key: separate detecting and decoding•Odoc (Opportunistic Downclocking)
▫When safe to downclock?▫Key: predict the possibility of coming
packet
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SRID (1/3)•M-preamble
Duplicated Sequence
(Gold Sequence)
Check the self-correlation
Able to be detected arriving packet even when down
sampled
Embedded
AddressSwitching
Time
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SRID (2/3)Self-correlation of
samples
Energy level of samples
|𝑅 (𝑘 )|≈ {𝐸 (𝑘) , 𝑖𝑓 𝑐𝑜𝑟𝑟𝑒𝑙𝑎𝑡𝑒𝑑0 ,𝑖𝑓 𝑛𝑜𝑡 𝑐𝑜𝑟𝑟𝑒𝑙𝑎𝑡𝑒𝑑
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SRID (3/3)
•Considering CGS•SNR squelch
|𝑅 (𝑘 )|≈ {𝐸 (𝑘) , 𝑖𝑓 𝑐𝑜𝑟𝑟𝑒𝑙𝑎𝑡𝑒𝑑0 ,𝑖𝑓 𝑛𝑜𝑡 𝑐𝑜𝑟𝑟𝑒𝑙𝑎𝑡𝑒𝑑
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Address Allocation• as the embedded address
▫Multiple user?▫What if is large?
• Minimum-cost address sharing▫Multiple clients share a limited number of addresses▫Clients tx/rx more frequently share the addr. with less
other clients• Broadcast address
▫, clients maintain a self-correlator with offset and ▫For carrier sensing purpose, double preamble is
needed.
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Odoc (Opportunistic Downclocking)•Switching time (~)
▫Compared to SIFS()•Arrival prediction (Outage prediction)
▫Key intuition: Burstininess of WiFi▫Deterministic operation
CTS, DATA, ACK are all deterministic operations after RTS
▫Non-deterministic operation recorded if the arriving interval if shorter
than
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Evaluation (1/5)•Two Questions:
▫Packet detecting accuracy▫IL energy saving
•Setups▫E-MiLi implementation on GNURadio▫Network level simulator on real WiFi trace
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Evaluation (2/5) -Packet-Detection Performance
Single link
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Evaluation (3/5) -Packet-Detection Performance
9 USRP Testbed
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Evaluation (4/5) – Energy EfficiencyReal WiFi trafficTrace: SIGCOMM’08, PDX-
powell
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Evaluation (5/5) – Energy Efficiency
Synthetic traffic
NS-2: HTTP FTP traffic generator
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Related Work•Energy-efficient protocols for WiFi
▫PSM and its variants (can be integrated with E-MiLi)▫Wakeup on demand approach (second radio needed)
•Packet detection▫Self-correlate (problem when down-sampled)▫Cross-correlate (down-sampled prob and offset-
sensitive)•Dynamic voltage-frequency scaling
▫In multi-processor design▫SampleWidth (tx and rx agree on same clock rate)
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Conclusion•Goal: reducing the IL energy by
downclocking▫Sampling-Rate Invariant packet Detector▫Opportunistic downclocking scheme
•Future works▫ZigBee extension▫Changing working voltage
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Comments•Pros:
▫Novel idea▫Practical use
•Cons:▫Overhead: doesn’t consider the delay
caused by the additional preamble.•Take home message:
▫From simple questions▫Learn from real practice▫Paper writer skill
Thank you for your attention!
Questions?
22/20
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Existing Approach•PSM
▫What’s PSM: Reducing idle listening time▫How doesn’t work: