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Measuring IEEE 802.11 Performance in Airplanes

Measuring IEEE 802.11 Performance in Airplanes. Scott Marston Cabin Systems Tech Center Boeing Commercial Airplanes scott.e.marston@boeing.com. What’s unique about WLAN in airplanes? Types of Airplane WLAN Applications Open - passenger connectivity

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Measuring IEEE 802.11 Performance in Airplanes

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  1. Measuring IEEE 802.11 Performance in Airplanes Scott Marston Cabin Systems Tech Center Boeing Commercial Airplanes scott.e.marston@boeing.com Scott Marston, Boeing

  2. What’s unique about WLAN in airplanes? Types of Airplane WLAN Applications Open - passenger connectivity Closed - crew, entertainment, system monitoring, etc. Problems with today’s measurements Signal Strength, SNR, EVM, don’t correlate to throughput or stability PER does correlate, but only after link has degraded Measurement Requests to 802.11k TG Measurement Access Outline Scott Marston, Boeing

  3. The network moves among different regulatory domains while operating The airplane has its own regulatory requirements (EMI, potential failure modes, etc.) Very high potential client density Multiple NICs in every passenger seat Adjacent Channel Interference Dynamic RF changes have correspondingly high impact Highly reflective physical environment Potential mix of “open” and “closed” systems No IT personnel on board to manage or troubleshoot network problems What’s Unique About WLANs in Airplanes? Scott Marston, Boeing

  4. Closed – Airline controls all radios In Flight Entertainment data distribution to seat-mounted equipment Crew Information Services to mobile crew terminals on board and on ramp System Status / System Health Monitoring Open – Passengers carry on their own radios Internet / Telephone Connectivity Closed vs. Open Onboard WLAN Scott Marston, Boeing

  5. Dynamic Frequency Selection and Transient Power Control are good, in theory Haven’t had the opportunity to test them yet Signal Strength (RSSI), Noise Level No correlation with link performance Not repeatable or linear in controlled conditions Error Vector Magnitude (EVM) Only marginally better quality indicator than RSSI/noise Packet Error Rate Does sometimes seem to correlate to link bit rate, but only after the link has degraded Today’s Standard Measurements Scott Marston, Boeing

  6. 802.11a Performance in an AirplaneTheoretical vs. Measured • Transmitter Power, • Antenna Pattern/Orientation, • Clear/Blocked Line-of-Sight, • Absorbing/Reflecting Materials (e.g., Bodies in Seats), • Co-Channel Interference, • …all impact Signal to Noise (Interference) Ratio and Media Access Coordination Measured Airplane Performance Scott Marston, Boeing

  7. RSSI Variation with NIC and Orientation • Anechoic Chamber • 3 meters distance • Three Identical Client Cards -48 dBm -60 dBm -52 dBm -64 dBm -55 dBm -62 dBm 12 dB variation under identical conditions -62 dBm -68 dBm Scott Marston, Boeing

  8. Single NIC – RSSI vs. Distance Theoretically expect 6 dB power delta with twice the distance Scott Marston, Boeing

  9. 802.11b RSSI in a 747 • RF Signal & Noise strength measured two ways: • -Airmagnet site survey tool • -Client software on individual laptops Airmagnet Signal Client Signal Client Noise Airmagnet Noise Scott Marston, Boeing

  10. High Client Density Implies Adjacent Channels in Close Proximity 802.11a Adjacent Channel Performance can be marginal… Scott Marston, Boeing

  11. Coverage Area vs. Interference Area Co-Channel Interference Boundary Co-Channel Interference Area Desired Coverage Area Scott Marston, Boeing

  12. Airplane Channel Fading Channel Fade of 10 dB or more is common in airplanes 36 40 44 48 52 56 60 64 Scott Marston, Boeing

  13. EVM vs. Link Performance According to Vector Signal Analyzer, EVM for this burst was -14.056 dB, which corresponds to 18 Mb/sec link. But burst was transmitted and received successfully at 54 Mb/sec. Scott Marston, Boeing

  14. Network Regulatory Domain Awareness Local Spectrum Usage Limits Local Human Exposure Limits What would it take to add “Commercial Airplane” to the list of country codes? Adjacent Channel Interference Indication Meaningful Signal Strength (instantaneous and over time) Meaningful Signal Quality (instantaneous and over time) Why was current link rate selected? (e.g., 36 Mb vs. 54) Which diversity antenna was used to Transmit or Receive a given frame? Measurement Wish List Scott Marston, Boeing

  15. Ideally, there would be a way to tell clients that are not Associated in the Service Set to stay out of certain channels, and/or turn power down How about specifying some channel models, including a narrowbody and widebody airplane! Measurement Wish List (cont’d) Scott Marston, Boeing

  16. Most onboard network management is either completely local or completely remote: Local: Maintenance personnel solve problems on ground between flights Remote: NOC accesses airplane via satellite or gatelink Aviation Industry already working on network MIB access protocols (SNMP/RMON, etc.) through Airlines Electronic Engineering Committee (AEEC) ARINC standards http://www.arinc.com/aeec/ Measurement Access Scott Marston, Boeing

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