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CoolSpots

CoolSpots. Yuvraj Agarwal, CSE, UCSD Trevor Pering, Intel Research Rajesh Gupta, CSE, UCSD Roy Want, Intel Research. Motivation: Wireless Power Is a Problem!. Depending on the usage model, the power consumption of emerging mobile devices can be easily dominated by the wireless interfaces!.

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CoolSpots

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  1. CoolSpots Yuvraj Agarwal, CSE, UCSD Trevor Pering, Intel Research Rajesh Gupta, CSE, UCSDRoy Want, Intel Research

  2. Motivation: Wireless Power Is a Problem! Depending on the usage model, the power consumption of emerging mobile devices can be easily dominated by the wireless interfaces! Power breakdown for a fullyconnected mobile device in idle mode, with LCD screen and backlight turned off.

  3. Opportunity: Devices With Multiple Radios • Many devices already have multiple wireless interfaces… • PDA’s HP h6300 (GSM/GPRS, BT, 802.11) • Mobile Phones - Motorola CN620 (BT, 802.11, GSM) • Laptops (Wi-Fi, BT, GSM, …) These radios typically function as isolated systems, but what if their operation was coordinated to provide a unified network connection?

  4. Properties of Common Radio Standards Higher throughput radios have a lower energy/bit value … have a higher idle power consumption …and they have different rangecharacteristics!

  5. Low-power Access Within a WiFi Hot-spot Mobile Device(e.g., cell-phone) Wi-Fi HotSpot CoolSpots

  6. Your entire house would be coveredby a WiFi HotSpot… Your TV would be a Bluetooth-enabled CoolSpot!

  7. Inter/Intra Technology Power Management CoolSpots Bluetooth Wi-Fi WiFiActive BTSniff WiFiActive BTActive WiFiActive WiFiPSM WiFiActive 5.8 mW 81 mW 264 mW 990 mW CoolSpots implement inter-technology power management on top of intra-technology techniques to realize better power & performance than any single radio technology.

  8. Switching is transparent: applications always use the IP address of the local subnet. 1 2 3 4 5 Access point changes routing table on “switch” message from mobile device WiFi link is dynamically activated based on switching determination Low-power Bluetooth link(always maintained, when possible) Mobile device monitors channel and implements switching policy IP address onBackbone Subnet CoolSpots Network Architecture Backbone Network Infrastructure Computers CoolSpotAccess PointBTWiFi BTWiFiMobile Device

  9. Switching Overview • Three main components contribute to the behavior of a multi-radio system: where, what, and when • Position: Whereyou are • Need to address the difference in range between Bluetooth and WiFi • Benchmarks: What you are doing • Application traffic patterns greatly affect underlying policies • Policies: When to switch interfaces • A non-intrusive way to tell which interface to use

  10. Where: Position Position 1 Base Station • Bluetooth and WiFi have very different operating ranges! (approx. 10m vs. 100m) • Optimal switching point will depend on exact operating conditions, not just range • Experiments and (effective) policies will measure and take into account a variety of operating conditions Bluetooth channel capacity depends on range, so the further away you are, the sooner you need to switch… Position 2 In some situations, Bluetooth will not be functional and WiFi will be the only alternative Position 3

  11. What: Benchmarks • Baseline: target underlying strengths of wireless technologies • Idle: connected, but no data transfer • Transfer: bulk TCP data transfer • Video: range of streamingbit-rates varying video quality • 128k, 250k, 384k datarates • Streaming data, instant start • WWW: realistic combination of idle and data transfer conditions • Idle: “think time” • Small transfer: basic web-pages • Bulk transfer: documents or media

  12. When: Policies • The switching policy determines how the system will react under different operating conditions Use WiFi Channel wifi CAM (normalization baseline) wifi-fixed (using PSM) kbps < X Z = kbps kbps < Z kbps < X bandwidth-X cap-static-X cap-dynamic kbps > X time > Y time > Y bluetooth-fixed (using sniff mode) Use Bluetooth Channel

  13. Experimental Setup Benchmark suite • Characterize power for WiFi and BT • Multiple Policies • Different locations • Suite of benchmark applications • Stargate research platform • 400Mhz processor, 64MB RAM, Linux • Allows detailed power measurement • Tested using “today’s” wireless: • WiFi is NetGear MA701 CF card • Bluetooth is a CSR BlueCore3 module • Use the geometric mean to combine benchmarks into an aggregate result • Moved devices around on a cart to vary channel characteristics Test Machine(TM) Data Acquisition(DA) ETH mW BT Base Station (BS)RM Mobile Device (MD) SP WiFi Distanceadjustment ETH = Wired Ethernet mW = Power Measurements BT = Bluetooth WiFi = WiFi Wireless RM = Route Management SP = Switching Policy

  14. Wi-Fi Bluetooth Switch : Wi-Fi -> BT Switching Example: MPEG4 streaming • Simple bandwidth policy • Switch from WiFi to BT when application has buffered enough data Demonstrates how switching is transparent to unmodified applications!

  15. Results Overview (Intermediate Location) • blue-fixed does well in terms of energy but at the cost of increased latency • cap-dynamic does well in terms of both energy and increased latency

  16. Impact of Range/Distance Missing data indicates failure of at least one application, and therefore an ineffective policy!

  17. Results across various benchmarks wifi-fixed consumes lowest energy for data transfer, any bluetooth policy for idle Overall, cap-dynamic does well taking into account energy and latency Video benchmarks really highlight problems with wifi-fixedand bandwidth-x

  18. Cap-Dynamic Switching Policy • Switch up based on measured channel capacity (ping time > Y) • Remember last seen Bluetooth bandwidth (Z=kbps) • Switch down based on remembered bandwidth (kbps < Z) cap-dynamic policy time > Y Z = kbps kbps < Z

  19. Switching Policies – Analysis • “Wifi-Fixed” Policy (WiFi in Power Save Mode) • Works best for as-fast-as-you-can data transfer • Higher power consumption, especially idle power • “Blue-Fixed” Policy • Very low idle power consumption • Increases total application latency, fails at longer ranges • “Bandwidth” Policy • Static coded bandwidth thresholds, fails to adapt at longer ranges • Switches too soon (bandwidth-0) or switches too late (bandwidth-50) • “Capacity-Static” Policy • Estimates channel capacity and uses that to switch up • Fails at longer ranges due to incorrect switch-down point • “Capacity-Dynamic” Policy • Dynamic policy, remembers the last seem switch-up bandwidth • Performs well across all benchmarks and location configurations!

  20. Conclusions • A dynamic system can leverage the different underlying radio characteristics to reduce communication energy while still maintaining good performance • Advanced policies can adapt well to changing operating conditions • Application behavior • Radio link quality • Evaluation of CoolSpots policies shows around a 50% reduction in energy consumption over the present power management scheme in WiFi (PSM) across a range of situations

  21. Thank you! • Questions?

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