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AY4434 Occupancy Analysis of the 2.4GHz ISM Band Mike Biggs, Simon Day, February – May 2003.

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Presentation on theme: "AY4434 Occupancy Analysis of the 2.4GHz ISM Band Mike Biggs, Simon Day, February – May 2003."— Presentation transcript:

1 AY4434 Occupancy Analysis of the 2.4GHz ISM Band Mike Biggs, Simon Day, February – May 2003

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 –AY Man-Made Noise Measurement Programme –AY EMC Implications of Software Radio –AY GHz 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% Sub-band Lower band edgeUpper band edge

11 Reference Study (1) Microwave OvenBlueTooth ( carrying speech )

12 Reference Study (2) Video TransmitterWLAN ( Internet browsing )

13 Surveys Private SectorDuration –Internet café1½ hrs –Hub of broadband wireless provider24 hrs –Roving exercise around Cambridge1 day Public Sector –Primary schoolschool hrs –Secondary schoolschool hrs –Cambridge hospital24 hrs –Heathrow airport2 hrs City centre –London7 days –Glasgow7 days

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

15 Secondary School –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 50 WLAN access points supporting > 1,000 laptops –Internet access (capped at 2MB/s) –File storage

16 Secondary School – WLAN Interference –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 Report of WLAN interference –Initial period of problem-free operation –Then interference experienced on some channels Microwave burglar alarm sensors suspected

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

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.htmhttp://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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