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

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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

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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

Address

Switching 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 Efficiency

Real 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?

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Existing Approach•PSM

▫What’s PSM: Reducing idle listening time▫How doesn’t work: