Introduction Approaches Experiments/Results Conclusions

Power Saving in Wireless VoIP

Wei Wu, Sung Hyuck Lee, Kwan Hong Lee

6.829 Final Project

December 7, 2006

Wei Wu, Sung Hyuck Lee, Kwan Hong Lee Power Saving in Wireless VoIP

Introduction Approaches Experiments/Results Conclusions

Outline

ProblemRelated WorkApproachExperiment/AnalysisGuidelines/Conclusions

Wei Wu, Sung Hyuck Lee, Kwan Hong Lee Power Saving in Wireless VoIP

Introduction Approaches Experiments/Results Conclusions

Problem

Where does power get consumed on WiFi phones during VoIPsession?

Figure: Chen, Power Management for VoIP over IEEE 802.11 WLAN

Wei Wu, Sung Hyuck Lee, Kwan Hong Lee Power Saving in Wireless VoIP

Introduction Approaches Experiments/Results Conclusions

Power Consumption

Understanding where power is consumed

Figure: Pering, CoolSpots: reducing the power consumption ofwireless mobile devices with multiple radio interfaces

Wei Wu, Sung Hyuck Lee, Kwan Hong Lee Power Saving in Wireless VoIP

Introduction Approaches Experiments/Results Conclusions

Projections of VoWiFi

Figure: Harden,http://ntrg.cs.tcd.ie/undergrad/4ba2.05/group9/index.html

Wei Wu, Sung Hyuck Lee, Kwan Hong Lee Power Saving in Wireless VoIP

Introduction Approaches Experiments/Results Conclusions

Approaches

802.11 MAC, Power Save Mode (PSM), UnscheduledPower Save Delivery (UPSD)Silence Detection, Voice CodecHeader Compression

Current StatusA lot has been done to save power on VoWiFi!!

Wei Wu, Sung Hyuck Lee, Kwan Hong Lee Power Saving in Wireless VoIP

Introduction Approaches Experiments/Results Conclusions

802.11 Frame/Packet Format

Figure: more than 150 vs. 160/40/20, TI, Low Power Advantage of802.11a/g vs. 802.11b

Wei Wu, Sung Hyuck Lee, Kwan Hong Lee Power Saving in Wireless VoIP

Introduction Approaches Experiments/Results Conclusions

Header Compression/MAC Protocols Experiment

Measurement tool: ACPI(Advanced Configuration andPower Interface) battery information, KismetWLAN cards: Intel PRO/Wireless 2200 NetworkConnection/Mad-WiFi(Atheros)

Wei Wu, Sung Hyuck Lee, Kwan Hong Lee Power Saving in Wireless VoIP

Introduction Approaches Experiments/Results Conclusions

IP Header Compression

Emulation of IP Header Compression (ROHC)(Packet Size vs. Power Consumption)

Setting (payload size) ∆ power (mW/min)4 3540 37

Conclusion5% of energy saved by compressing header

Wei Wu, Sung Hyuck Lee, Kwan Hong Lee Power Saving in Wireless VoIP

Introduction Approaches Experiments/Results Conclusions

802.11a/b/g Power Consumption

PHY ∆ power (mW/min) Header Size (µsec)802.11a 40 20802.11g 39 20802.11b 45 96, 192

Conclusion802.11b’s larger header size and greater time for transmitting(smaller rate), it consumes more power

Wei Wu, Sung Hyuck Lee, Kwan Hong Lee Power Saving in Wireless VoIP

Introduction Approaches Experiments/Results Conclusions

802.11 Power Save Mode

Power Saving bit based

Power Saving poll based

Figure: Chen, Power Management for VoIP over IEEE 802.11 WLAN

Wei Wu, Sung Hyuck Lee, Kwan Hong Lee Power Saving in Wireless VoIP

Introduction Approaches Experiments/Results Conclusions

802.11 Power Save Mode

UPSD (Unscheduled Power Saving Delivery), part of802.11e standard

Figure: Chen, Power Management for VoIP over IEEE 802.11 WLAN

Wei Wu, Sung Hyuck Lee, Kwan Hong Lee Power Saving in Wireless VoIP

Introduction Approaches Experiments/Results Conclusions

Power Save Comparison Experiment

Measurement tool: ACPI(Advanced Configuration andPower Interface) battery information, KismetWLAN cards: Intel PRO/Wireless 2200 NetworkConnection/Mad-WiFi(Atheros)

Wei Wu, Sung Hyuck Lee, Kwan Hong Lee Power Saving in Wireless VoIP

Introduction Approaches Experiments/Results Conclusions

PSM Power Consumption

Setting Total (mW/min) ∆ powerNIC off (base) 202NIC on, no traffic, PSM off 236 34NIC on, no traffic, PSM on 218 16NIC on, VoIP traffic, PSM off 244 42NIC on, VoIP traffic, PSM on, level 1 243 41NIC on, VoIP traffic, PSM on, level 3 242 40NIC on, VoIP traffic, PSM on, level 5 238 36

Intel card. PSM level 1: timeout 350ms, period 400msIntel card. PSM level 3: timeout 75ms, period 1000msIntel card. PSM level 5: timeout 25ms, period 1000ms

Wei Wu, Sung Hyuck Lee, Kwan Hong Lee Power Saving in Wireless VoIP

Introduction Approaches Experiments/Results Conclusions

PSM Experiment Conclusion

ConclusionLegacy PSM does not help much because of bidirectional(every 20 ms) traffic.UPSD is beneficial for VoWiFi

Wei Wu, Sung Hyuck Lee, Kwan Hong Lee Power Saving in Wireless VoIP

Introduction Approaches Experiments/Results Conclusions

Codec Comparison

Figure: http://www.oreillynet.com/lpt/a/6373

Wei Wu, Sung Hyuck Lee, Kwan Hong Lee Power Saving in Wireless VoIP

Introduction Approaches Experiments/Results Conclusions

Codec Complexity

Figure: Krishna, Signal Processing for Packet Voice Telephony

Wei Wu, Sung Hyuck Lee, Kwan Hong Lee Power Saving in Wireless VoIP

Introduction Approaches Experiments/Results Conclusions

Codec Power Consumption Setup

Measurement tool: ACPI(Advanced Configuration andPower Interface) battery information, KismetWLAN cards: Intel PRO/Wireless 2200 NetworkConnection/Mad-WiFi (Atheros)

Wei Wu, Sung Hyuck Lee, Kwan Hong Lee Power Saving in Wireless VoIP

Introduction Approaches Experiments/Results Conclusions

Codec Power Consumption

Codecs

ConclusionComputation does not matter because of CPU on laptop,packet size dominates.

Wei Wu, Sung Hyuck Lee, Kwan Hong Lee Power Saving in Wireless VoIP

Introduction Approaches Experiments/Results Conclusions

Guidelines for Power Savings on WiFi VoIP

Our design principles for Power SavingsTalk less (Send Less)

codecs, MAC protocol (11g), header compression, sliencedetection

Be lazy (Sleep More)codecs, PSM(timeout/period) < UPSD, slience detection

Wei Wu, Sung Hyuck Lee, Kwan Hong Lee Power Saving in Wireless VoIP

Introduction Approaches Experiments/Results Conclusions

Lessons Learned

Very difficult to measure power.

Figure: Raghunathan, Experience with a low power wireless mobilecomputing platform

Wei Wu, Sung Hyuck Lee, Kwan Hong Lee Power Saving in Wireless VoIP

Introduction Approaches Experiments/Results Conclusions

Lessons Learned

iwconfig power save mode does not work. Don’t use it!use iwpriv, iwlist

Please use 802.11e (QoS) enabled access points.Further study: Transmit Power, AP topologies

Wei Wu, Sung Hyuck Lee, Kwan Hong Lee Power Saving in Wireless VoIP

Introduction Approaches Experiments/Results Conclusions

Thank You

Please Applaud!

Wei Wu, Sung Hyuck Lee, Kwan Hong Lee Power Saving in Wireless VoIP