1. E-MiLi: Energy-Minimizing Idle Listening in Wireless Networks Xinyu Zhang and Kang G. Shin Dept. of EECS Univ. Michigan 1 Presented by: Fenggang Wu 2011/11/04

2. Author HIT(01)-> Toronto(05)->U Michigan(08)- >(11)Princeton NEC Lab 2 Name:Xinyu Zhang Gender:Male Birthyear:1984 Place of Birth:Baotou, Inner-Mongolia, China Nationality:Chinese

3. Agenda Background Related Work Solution ▫SRID ▫oDoc Evaluation Conclusoin Comments 3

4. 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? 4

5. 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 5

6. The E-MiLi Approach 6

7. Overview of E-MiLi 7 What’s M-preamble How to detect it? When it is safe to downclock?

8. 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 8

9. SRID (1/3) M-preamble 9 Duplicated Sequence (Gold Sequence) Check the self-correlation Able to be detected arriving packet even when down sampled Embedded Address Switching Time

10. SRID (2/3) 10

11. SRID (3/3) 11

12. Address Allocation 12

13. Odoc (Opportunistic Downclocking) 13

14. Evaluation (1/5) Two Questions: ▫Packet detecting accuracy ▫IL energy saving Setups ▫E-MiLi implementation on GNURadio ▫Network level simulator on real WiFi trace 14

15. Evaluation (2/5) - Packet-Detection Performance 15 Single link

16. Evaluation (3/5) - Packet-Detection Performance 16 9 USRP Testbed

17. Evaluation (4/5) – Energy Efficiency 17 Real WiFi traffic Trace: SIGCOMM’08, PDX-powell

18. Evaluation (5/5) – Energy Efficiency 18 Synthetic traffic NS-2: HTTP FTP traffic generator

19. 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) 19

20. Conclusion Goal: reducing the IL energy by downclocking ▫Sampling-Rate Invariant packet Detector ▫Opportunistic downclocking scheme Future works ▫ZigBee extension ▫Changing working voltage 20

21. 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 21

22. Thank you for your attention! Questions? 22/20

23. Existing Approach PSM ▫What’s PSM: Reducing idle listening time ▫How doesn’t work: 23