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Telecommunications Networking II Topic 12 Wireless LAN Technology (Layer 1&2) Dr. Stewart D. Personick 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. 1

What are we trying to do? • We are trying to use wireless technologies 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. 2

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

Possibilities • • UHF 300 MHz - 3 GHz SHF 3 GHz - 30 Possibilities • • UHF 300 MHz - 3 GHz SHF 3 GHz - 30 GHz Optical 300, 000 GHz 1000 MHz => 0. 3 meters: transmitted/re-radiated 10 GHz =>3 cm: transmitted/re-radiated/reflected Optical => ~1 micrometer: absorbed/reflected/scattered Copyright 2002, S. D. Personick. All Rights Reserved. 4

Something to Consider • Delay spreading: Inside a building, re-radiation of r. f. from 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. 5

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

Delay Spreading • Delay spreading inside large office buildings and shopping malls can be 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 ~5 M baud per carrier Copyright 2002, S. D. Personick. All Rights Reserved. 7

IEEE 802. 11 (standard) • Uses r. f. frequency hopping or direct sequence spread IEEE 802. 11 (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. 11 b) • 5 GHz standard under development Copyright 2002, S. D. Personick. All Rights Reserved. 8

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

Copyright 2002, S. D. Personick. All Rights Reserved. 10 Copyright 2002, S. D. Personick. All Rights Reserved. 10

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

A quick calculation • 1 Mbps IEEE 802. 11; required power at the receiver A quick calculation • 1 Mbps IEEE 802. 11; required power at the receiver (assume 26 d. B SNR, thermal noise limited operation): k. T x 10**6 x 400 ~ 1. 6 x 10**-9 m. W • NW 660 transmitter : +20 d. Bm= 100 m. W • Link loss budget: (if thermal noise limited) ~110 d. B Copyright 2002, S. D. Personick. All Rights Reserved. 12

seconds) Time (41. 63 Bluetooth spectrogram Copyright 2002, S. D. Personick. All Rights Reserved. seconds) Time (41. 63 Bluetooth spectrogram Copyright 2002, S. D. Personick. All Rights Reserved. 2. 4256 GHz +/- 18 MHz 13

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

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

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

Infrared Link Detector + Receiver (Thermal Noise ~ 1000 -5000 photons) LED Background light: Infrared Link Detector + Receiver (Thermal Noise ~ 1000 -5000 photons) LED Background light: shot noise=(PT/hf)**0. 5; where T=1/bit rate Copyright 2002, S. D. Personick. All Rights Reserved. 17