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AY4434 Occupancy Analysis of the 2.4GHz ISM Band

AY4434 Occupancy Analysis of the 2.4GHz ISM Band. February – May 2003. Mike Biggs, mbiggs@mass.co.uk Simon Day , swd@phasor-design.uk.com. Presentation Contents. Introduction to MASS 2.4GHz Monitoring Exercise Scenario Objectives Equipment Measurement and Analysis Techniques Surveys

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AY4434 Occupancy Analysis of the 2.4GHz ISM Band

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  1. AY4434Occupancy Analysis of the 2.4GHz ISM Band February – May 2003 Mike Biggs, mbiggs@mass.co.uk Simon Day , swd@phasor-design.uk.com

  2. Presentation Contents • Introduction to MASS • 2.4GHz Monitoring Exercise • Scenario • Objectives • Equipment • Measurement and Analysis Techniques • Surveys • Results • Conclusions • Questions

  3. Mass Consultants – Who Are We? • Systems House • 3 Divisions • Systems Engineering • Real-Time Systems • Managed Services • Vital Statistics • 100 people strong • Turnover ~ £12M • >90% defence • Based in St Neots

  4. Eurofighter in the Electronic Warfare Test Facility • Experts in the measurement and analysis of jamming signals

  5. MASS and RA • RA concerned with the effects of radio interference • Jamming is intentional RF interference • Applied EW expertise to commercial radiocomms • 3 projects for RA • AY4119 - Man-Made Noise Measurement Programme • AY4364 - EMC Implications of Software Radio • AY4434 - 2.4GHz Monitoring Exercise

  6. 2.4GHz Monitoring Exercise- Scenario • 2,400MHz to 2,483.5MHz ISM band • Many uncoordinated services • Microwave oven leakage • Broadcasting services • RF identification devices • Licensed FWA systems • BlueTooth • WLAN / WiFi / IEEE802.11b • Danger of band congestion

  7. Objectives • Assess band occupancy • Time-varying nature of usage • Spatial distribution of users • Investigate anecdotal evidence of WLAN congestion • Many instances reported to RA • Is there any evidence of congestion? • If so, why is it occurring?

  8. Equipment • Omni antenna • Spectrum analyser • Laptop PC • Bespoke data logging software • Reasonably portable • Capable of running for 7 days continuously

  9. Measurement Process • Continuously scan band of interest • Include 30MHz ‘guard bands’ to check for out-of-band activity • Use 1 MHz bandwidth • Data collected in 10-minute blocks • > 10,000 samples • Good statistical set • Tangible period of time

  10. Activity Percentile Plot • Percentiles • Blue, 50% • Red, 10% • Green, 1% • Magenta, 0.1% • Black, 0.01% Lower band edge Upper band edge Sub-band

  11. Reference Study (1) Microwave Oven BlueTooth (carrying speech)

  12. Reference Study (2) Video Transmitter WLAN (Internet browsing)

  13. Surveys • Private Sector Duration • Internet café 1½ hrs • Hub of broadband wireless provider 24 hrs • Roving exercise around Cambridge 1 day • Public Sector • Primary school school hrs • Secondary school school hrs • Cambridge hospital 24 hrs • Heathrow airport 2 hrs • City centre • London 7 days • Glasgow 7 days

  14. Cambridge Internet Café • Provides wireless internet service to customers • Limited take up of service • Proportion of time with any activity only 5% • Clear WLAN activity • 3 channels • Strong continuous signal • In sub-band • Underlying µwave oven activity • catering

  15. Secondary School • 50 WLAN access points supporting > 1,000 laptops • Internet access (capped at 2MB/s) • File storage • Proportion of time with activity up to 30% • Highest of sites surveyed • Clear WLAN activity • 4 channels • Reputedly very effective • Recorded activity fluctuates according to school timetable

  16. Secondary School – WLAN Interference • Report of WLAN interference • Initial period of problem-free operation • Then interference experienced on some channels • Microwave burglar alarm sensors suspected • Strong sensor signal in central sub-band • WLAN and burglar alarm installed correctly by professionals • Radiation limits not exceeded • But Interference experienced • Work-around is to avoid channels close to sub-band

  17. Central London (1) • Located on roof of IEE building • Energy evenly distributed across band • Band limits adhered to • Large number of emitters • Difficult to identify individual sources • Several continuous signals

  18. Central London (2) • 7-day activity • Repeated daily pattern • Peak activity at lunchtime (microwave ovens) • Occupancy level 5-10%

  19. Conclusions • Recorded levels of activity low in terms of • Signal strength • Proportion of time on • Microwave oven leakage appears to be main source • Microwave movement detectors commonplace • Generally low signal strenths • 1 case where microwave movement detectors were found to be causing interference to WLAN • BlueTooth emissions not observed • But not surprising, as low power, low duty cycle devices • Evidence of widespread usage of WiFi observed • No cases of congestion (due to traffic density) observed

  20. Summary • Introduction to MASS • 2.4GHz Monitoring Exercise • Scenario • Objectives • Equipment • Measurement and Analysis Techniques • Surveys • Results • Conclusions

  21. Further Reading • Study Report on RA website • http://www.radio.gov.uk/topics/research/topics.htm • Article in LPRA News • Published September 2003 • Article in Electronics Weekly • Published 12 November 2003 • Article submitted to IEE Proceedings, Communications, special issue on WLANs • Due for publication in 2004

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