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Wireless “ESP”: Using Sensors to Develop Better Network Protocols

Wireless “ESP”: Using Sensors to Develop Better Network Protocols. Lenin Ravindranath Calvin Newport, Hari Balakrishnan, Sam Madden. Massachusetts Institute of Technology. Big Changes in Access Devices. 172M smartphones sold worldwide in 2009 25% of US phone market; 50% in two years

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Wireless “ESP”: Using Sensors to Develop Better Network Protocols

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  1. Wireless “ESP”: Using Sensors to Develop Better Network Protocols Lenin Ravindranath Calvin Newport, Hari Balakrishnan, Sam Madden Massachusetts Institute of Technology

  2. Big Changes in Access Devices • 172M smartphones sold worldwide in 2009 • 25% of US phone market; 50% in two years • Smartphones and tablets will exceed PC sales by 2011 • Mobile Internet growing at a tremendous pace

  3. Big Changes in Access Devices Dominant mode of data access in the future

  4. “Truly Mobile” Devices • Often switch between static and mobile • Exhibit a variety of mobility modes • Move through different environments

  5. The Problem • Protocols need to adapt to different settings • Mobility mode impacts wireless performance • Most protocols optimized for static settings • They perform poorly during mobility • Protocols that compensate for mobility are not optimal in static settings

  6. Static vs. Mobile • Channel constantly changing • Channel assessments quickly outdated • Protocols should not maintain long histories • Channel relatively stable • Protocols can average estimates • Ignore short-term variations

  7. Static vs. Mobile • Topology changing rapidly • Probe for links more often • Compute routes over shorter time scales • Topology is hardly changing • Probe for links less frequently • Compute routes over long time scales

  8. Current Wireless Protocols • Do not differentiate between mobility modes • Attempt to adapt to both settings implicitly using measurements of packet loss, SNR, BER • Leading to suboptimal performance • Lack of explicit knowledge about prevalent mobility mode • Can we do better?

  9. Proximity Sensor Camera Accelerometer Compass Gyro GPS Ambient Light Sensor Microphone

  10. Proximity Sensor Camera Accelerometer Compass Gyro GPS Ambient Light Sensor Many, many, applications… Microphone

  11. Proximity Sensor Camera Accelerometer Ignored by Protocols! Compass Gyro GPS Ambient Light Sensor Microphone

  12. Proximity Sensor Camera Wireless Protocol Stack Application Transport Accelerometer Network Ignored by Protocols! Compass MAC Gyro PHY GPS Wireless Radio Ambient Light Sensor Microphone

  13. Wireless Protocol Stack Application Transport Accelerometer Network Compass MAC Gyro PHY GPS Wireless Radio

  14. Wireless Protocol Stack Application GPS Transport Compass Hints Network Accl MAC Gyro PHY Wireless Radio

  15. Wireless Protocol Stack • Movement • Direction • Speed Application GPS Transport Compass Hints Network Accl MAC Use hints to adapt to different mobility modes differently Gyro PHY Wireless Radio Adapt to hints from neighbors Hints Protocol

  16. Wireless Protocol Stack Application Speed GPS Vehicular Routing Transport Compass Heading Network AP Association Accl Walking MAC Rate Adaptation Movement Gyro PHY Wireless Radio

  17. Wireless Protocol Stack Network Monitoring Application Speed GPS Vehicular Routing Location Transport Compass Disassociation Heading Network AP Association Accl Walking MAC Rate Adaptation Movement Gyro PHY Packet Scheduling Speed Preamble Wireless Radio Power Saving

  18. Wireless Protocol Stack Application Speed GPS Vehicular Routing Transport Compass Heading Network AP Association Accl Walking MAC Rate Adaptation Movement Gyro PHY Wireless Radio

  19. Wireless Protocol Stack Application GPS Transport Compass Network Accl MAC Rate Adaptation Movement Gyro PHY Wireless Radio

  20. Accl Movement Reliably detect movement within 100ms

  21. Wireless Protocol Stack Application GPS Transport Compass Network Accl MAC Rate Adaptation Movement Gyro PHY Wireless Radio

  22. Rate Adaptation in Wireless Networks 802.11a/g bit rates 6 Mbps 9 Mbps 12 Mbps 18 Mbps 24 Mbps 36 Mbps 48 Mbps 54 Mbps Packet encoded at a particular bit rate Rate Adaptation: Finding the best bit rate to transmit a packet

  23. Static vs. Mobile Performance • Static and walkingtraces • Cycle through bit rates • 4 different environments • 80 traces, 20 seconds long • Trace-driven simulation • TCP throughput Compare to optimal throughput

  24. Static vs. Mobile Loss Patterns Probability that packet i+k is lost given packet i is lost 10 ms k Losses are more bursty when a node is mobilethan when a node is static

  25. RapidSample • 1. After a single loss • Reduce rate 6 Mbps 9 Mbps 12 Mbps 18 Mbps 24 Mbps 36 Mbps 48 Mbps 54 Mbps 6 Mbps 9 Mbps 12 Mbps 18 Mbps 24 Mbps 36 Mbps 48 Mbps 54 Mbps 6 Mbps 9 Mbps 12 Mbps 18 Mbps 24 Mbps 36 Mbps 48 Mbps 54 Mbps • 2. History - 10 ms • Don’t retry a failed rate • Or any higher rate [failed – within last 10ms] • 3. Channel not degrading, probably improving • After few successes, sample higher rate not failed • If wrong, come back to the original rate [failed – within last 10ms]

  26. RapidSample, when device is moving • Trace driven (ns3) • 30 traces • 20 seconds long • TCP throughput Up to 75% better throughput than SampleRate 25% better than other protocols

  27. But when static… • Trace driven (ns3) • 30 traces • 20 seconds long • TCP throughput Up to 30% lower throughput than other schemes

  28. Hint-Aware Rate Adaptation Wireless Protocol Stack • RapidSample when movement • SampleRate when static Application GPS Transport Compass Network Accl Rate Adaptation Movement Gyro PHY Wireless Radio Movement

  29. Hint-Aware Rate Adaptation • Trace driven (ns3) • 10 traces • 20 seconds long • Static + Moving • TCP throughput 40-50% better than other schemes

  30. Wireless Protocol Stack Application Speed GPS Vehicular Routing Transport Compass Heading Network AP Association Accl Walking MAC Rate Adaptation Movement Gyro PHY Wireless Radio

  31. Wireless Protocol Stack Application GPS Transport Compass Heading Network AP Association Accl Walking MAC Gyro PHY Wireless Radio

  32. AP Association Scan Scan Scan Infrequent scans

  33. AP Association Static Suboptimal Association

  34. Movement-Aware Association 1. Static – Stop Scanning 2. Moving – Scan Periodically 3. Moving to Static – Scan once

  35. Movement-Aware Association • Android implementation • 30 traces • Static + Moving • Throughput On median, 40% more throughput

  36. Heading-Aware Association Minimize Handoff Heading Training based approach

  37. Heading-Aware Association • Android implementation • Training (30 traces) • 30 traces • # Handoffs 40% median reduction in handoffs

  38. Wireless Protocol Stack Application Speed GPS Vehicular Routing Transport Compass Heading Network AP Association Accl Walking MAC Rate Adaptation Movement Gyro PHY Wireless Radio

  39. Wireless Protocol Stack Application Speed GPS Vehicular Routing Transport Compass Heading Network Accl MAC Gyro PHY Wireless Radio

  40. Routing in Vehicular Mesh Networks “V2V”

  41. Routing in Vehicular Mesh Networks • Longevity of links useful – avoids expensive repairs • Link between nodes heading in the same direction tend to last longer Connection Time Estimate (CTE) • Use heading,speed and position to predict connection duration

  42. Routing in Vehicular Mesh Networks • Empirical evaluation on taxi traces • 15 networks, 100 vehicles each Links with similar heading lasted 4 to 5 times longer than the median duration over all links

  43. Wireless Protocol Stack Application Speed GPS Vehicular Routing Transport Compass Heading Network AP Association Accl Walking MAC Rate Adaptation Movement Gyro PHY Wireless Radio

  44. Wireless Protocol Stack Network Monitoring Application Speed GPS Vehicular Routing Location Transport Compass Disassociation Heading Network AP Association Accl Walking MAC Rate Adaptation Movement Gyro PHY Packet Scheduling Speed Preamble Wireless Radio Power Saving

  45. Related Work • Wireless power saving • WakeOnWireless, Cell2Notify, Blue-Fi • Vehicular networking – use GPS • AP association • Mobisteer, Breadcrumbs • Rate adaptation • CARS: Adapt rate based on speed and heading • Very recent work • Accelerometer-assisted rate adaptation

  46. Take-Away Message • Truly mobile devices will soon be dominant • Variety of mobility modes poses problems for wireless protocols • Sensors on these devices give us a new opportunity to develop network protocols • Protocol architecture using sensor hints can significantly improve MAC, link, network layers

  47. Backup

  48. Probing • Delivery Probability • ETX, ETT Probes How frequently should nodes probe?

  49. Infrequent Probing Inaccurate link estimation leads to poor throughput

  50. Frequent Probing Probing wastes bandwidth

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