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  • Leverage these already present multiple radios on commodity devices to provide a similar user experience while saving energy and increasing battery lifetime
  • Add power numbers!
  • Now in order to quantify the benefits of using CoolSpots we wanted to characterize the power for each of the wireless interfaces – namely Bluetooth and WiFi. This had to be done for the multiple policies , at different locations and for each of the benchmark applications. We instrumented the Stargate platform with current sense resistors in order to measure instantaneous power consumption for WiFi and BT ! Mention that for the range experiments we put the device on a cart and moved it around at different locations. Benchmarks suite - idle - 2 - File Transfer traces - 2 - web traffic traces - 3 - media streams at different bit rates
  • This is just an illustration of the switching behaviour of the bandwidth only policy of CoolSpots. We chose an MPEG-4 streaming application which starts off using WiFi and then switches to BT. Note in this case when the application has buffered enough data towards the end the system switches to Bluetooth to maintain the trickle bandwidth ! WiFi in this case would still consume considerable power ! This would be the case even if using WiFi in PSM mode
  • This chart gives an overview of the energy saving benefits of a selction of CoolSpots Policies at an intermediate location across all benchmarks ! All policies do better than Wifi in CAM and the CoolSpot polices do much better than WiFi in PSM mode … Mention the latency – is the increase in total benchmark time Bluetooth -- the increase in application latency leads to reduced user experience … (How can we word this ?) These policies as we show next are also affected by operating distance/range with some of them not performing as well at differnet ranges ..(next slide)
  • In order to evaluate the effects of range we set up three location configurations (1,2 LOS and 3 NLOS) The Bandwidth policies save substantial power, however at longer ranges at least one benchmarks starts to fail … Cap-static does better, but that too starts to fail at Location 3 configuration. Cap-dynamic which dynamically remembers the last seen location B/W does well and does not fail (and thus is relatively robust), while maintaining a low energy bound. As expected bluetooth-only gives lowest energy but benchmarks fail as well as it increases latency as described earlier.
  • This chart illustrates the energy breakdown for the benchmarks for some representative policies. We have chosen an intermediate location where none of the policies fail. Results are normalized to WiFi in Cam mode (100%) Talk about the switching overhead amortizes as seen from transfer-1 and transfer-2.
  • Add about both swith-up and switch down having some hysteresis.
  • In the light of the results present we can now analyze why certain policies do better that the others.
  • Presented detailed experiments and evaluation of various “policies” For multiple applications, at different ranges Implemented the CoolSpots switching framework No change to the application themselves ! Coolspots leverages the good features of these “heterogeneous” radios

Transcript

  • 1. CoolSpots Yuvraj Agarwal, CSE, UCSD Trevor Pering, Intel Research Rajesh Gupta, CSE, UCSD Roy Want, Intel Research
  • 2. Motivation: Wireless Power Is a Problem! Power breakdown for a fully connected mobile device in idle mode, with LCD screen and backlight turned off. Depending on the usage model, the power consumption of emerging mobile devices can be easily dominated by the wireless interfaces!
  • 3.
    • 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, …)
    Opportunity: Devices With Multiple Radios 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 range characteristics!
  • 5. Low-power Access Within a WiFi Hot-spot Wi-Fi HotSpot Mobile Device (e.g., cell-phone) CoolSpots
  • 6. Your entire house would be covered by a WiFi HotSpot… Your TV would be a Bluetooth-enabled CoolSpot!
  • 7. Inter/Intra Technology Power Management WiFi Active CoolSpots implement inter -technology power management on top of intra -technology techniques to realize better power & performance than any single radio technology. WiFi Active WiFi PSM WiFi Active BT Active WiFi Active BT Sniff Bluetooth Wi-Fi CoolSpots 264 mW 990 mW 81 mW 5.8 mW
  • 8. CoolSpots Network Architecture Infrastructure Computers CoolSpot Access Point BT WiFi BT WiFi Mobile Device Backbone Network IP address on Backbone Subnet Low-power Bluetooth link (always maintained, when possible) 1 Mobile device monitors channel and implements switching policy 2 WiFi link is dynamically activated based on switching determination 3 Access point changes routing table on “switch” message from mobile device 4 Switching is transparent: applications always use the IP address of the local subnet. 5
  • 9. Switching Overview
    • Three main components contribute to the behavior of a multi-radio system: where, what, and when
    • Position : Where you 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
    • 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
    Position 1 Position 3 Bluetooth channel capacity depends on range, so the further away you are, the sooner you need to switch… Base Station In some situations, Bluetooth will not be functional and WiFi will be the only alternative Position 2
  • 11. What: Benchmarks
    • Baseline: target underlying strengths of wireless technologies
    • Idle: connected, but no data transfer
    • Transfer: bulk TCP data transfer
    • WWW: realistic combination of idle and data transfer conditions
    • Idle: “think time”
    • Small transfer: basic web-pages
    • Bulk transfer: documents or media
    • Video: range of streaming bit-rates varying video quality
    • 128k, 250k, 384k datarates
    • Streaming data, instant start
  • 12. When: Policies
    • The switching policy determines how the system will react under different operating conditions
    bluetooth-fixed (using sniff mode) wifi CAM (normalization baseline) wifi-fixed (using PSM) bandwidth-X cap-static-X cap-dynamic kbps > X kbps < X kbps < X time > Y time > Y kbps < Z Z = kbps Use WiFi Channel Use Bluetooth Channel
  • 13. Experimental Setup
    • 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) Base Station (BS) RM Mobile Device (MD) SP Data Acquisition (DA) ETH BT WiFi mW Distance adjustment ETH = Wired Ethernet mW = Power Measurements BT = Bluetooth WiFi = WiFi Wireless RM = Route Management SP = Switching Policy Benchmark suite
  • 14. 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! Switch : Wi-Fi -> BT Bluetooth Wi-Fi
  • 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 w ifi-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-fixed and 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 kbps < Z Z = kbps
  • 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?