Copyright 2002, S.D. Personick. All Rights Reserved.1 Telecommunications Networking II Topic 12 Wireless LAN Technology (Layer 1&2) Dr. Stewart D. Personick Drexel University

Copyright 2002, S.D. Personick. All Rights Reserved.2 What are we trying to do? We are trying to use wireless technologies to physically interconnect devices of various kinds (computers, hubs, printers, personal digital assistants, sensors, entertainment system components, household appliances….) We would like the cost of the wireless components to be << than the cost of the device(s) they are associated with We would like this to be simple to configure

Copyright 2002, S.D. Personick. All Rights Reserved.3 COTS Residential LAN Lighting & Security Network PC hub/gateway PDA TV set top box printer Infrared RF Cu TBD remote DVD

Copyright 2002, S.D. Personick. All Rights Reserved.4 Possibilities UHF 300 MHz - 3 GHz SHF 3GHz - 30 GHz Optical 300,000 GHz 1000 MHz => 0.3 meters: transmitted/re- radiated 10 GHz =>3cm: transmitted/re-radiated/reflected Optical => ~1 micrometer: absorbed/reflected/scattered

Copyright 2002, S.D. Personick. All Rights Reserved.5 Something to Consider Delay spreading: Inside a building, re-radiation of r.f. from metallic objects (metal studs, steel building skeleton, file cabinets….) leads to delay spreading of the received signals. 30 meters (~98 ft) of path length => 100 ns of delay

Copyright 2002, S.D. Personick. All Rights Reserved.6 Delay Spreading Receiver Walls with metal studs

Copyright 2002, S.D. Personick. All Rights Reserved.7 Delay Spreading Delay spreading inside large office buildings and shopping malls can be as large as several hundred nanoseconds. Delay spreading in smaller buildings may be as large as 100 nanoseconds ~100 nanoseconds of delay spreading limits the achievable symbol rate to ~5M baud per carrier

Copyright 2002, S.D. Personick. All Rights Reserved.8 IEEE (standard) Uses r.f. frequency hopping or direct sequence spread spectrum (>10 x spreading ratio) or infrared (light). R.f. nominal frequency (U.S.) is 2.4 GHz (~12.5 cm wavelength) 1-2 Mbps (802.11); up to 11 Mbps (802.11b) 5 GHz standard under development

Copyright 2002, S.D. Personick. All Rights Reserved.9

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Copyright 2002, S.D. Personick. All Rights Reserved.11

Copyright 2002, S.D. Personick. All Rights Reserved.12 A quick calculation 1 Mbps IEEE ; required power at the receiver (assume 26 dB SNR, thermal noise limited operation): kT x 10**6 x 400 ~ 1.6 x 10**-9 mW NW 660 transmitter : +20 dBm= 100 mW Link loss budget: (if thermal noise limited) ~110 dB

Copyright 2002, S.D. Personick. All Rights Reserved.13 Bluetooth spectrogram Time  (41.63 seconds)  GHz +/- 18 MHz 

Copyright 2002, S.D. Personick. All Rights Reserved.14 Infrared links LED Detector + Receiver

Copyright 2002, S.D. Personick. All Rights Reserved.15 Infrared links LED Detector + Receiver

Copyright 2002, S.D. Personick. All Rights Reserved.16 Infrared Link LED emits ~ 1-10 mW Receiver requires ~12,000-60,000 photons per received (on-off modulated) pulse Photon energy ~ 2 x 10**-19 Joules Example: 1Mbps > 1.2 x 10**-6 mW Allowable loss ~60 dB (maybe less) Background light adds “shot” noise

Copyright 2002, S.D. Personick. All Rights Reserved.17 Infrared Link LED Background light: shot noise=(PT/hf)**0.5; where T=1/bit rate Detector + Receiver (Thermal Noise ~ photons)