1. Copyright 1999, S.D. Personick. All Rights Reserved. Telecommunications Networking II Lecture 23 Wireless LAN Technology Layer 1&2

2. Copyright 1999, S.D. Personick. All Rights Reserved. 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

3. Copyright 1999, S.D. Personick. All Rights Reserved. A Picture is Worth 1000 Words? Printer PC PDA TV Set Top HUB Remote Lighting & Security Network Infrared RF Cu TBD

4. Copyright 1999, S.D. Personick. All Rights Reserved. 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

5. Copyright 1999, S.D. Personick. All Rights Reserved. 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 => 90 ns of delay

6. Copyright 1999, S.D. Personick. All Rights Reserved. Delay Spreading Receiver Walls with metal studs

7. Copyright 1999, S.D. Personick. All Rights Reserved. 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 data rate to ~5 Mbps per carrier

8. Copyright 1999, S.D. Personick. All Rights Reserved. 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 5 GHz standard under development

9. Copyright 1999, S.D. Personick. All Rights Reserved. NW660 InstantWave Access Point Specifications Standards Frequency Hopping Spread Spectrum IEEE 802.11 Compatible Ethernet LAN and Bridge Radio Product Type: Small RF Output Radio Station for Data Transmission Emission Type: Frequency Hopping Spread Spectrum Communication Method: Simplex RF Frequency Range: 2.4000 GHz ~ 2.4835GHz - North America

10. Copyright 1999, S.D. Personick. All Rights Reserved. Data Modulation Type: 2GFSK for 1Mbps and 4GFSK for 2Mbps Transmitter Power: 20dBm Frequency Stability: Within ± 25 ppm Diversity: Rx diversity Receiving Sensitivity: -80dBm for 1 Mbps and -70dBm for 2 Mbps at room temperature ( BER 10E-5) Range: 1Mbps: 100m (indoor applications) 2Mbps: 60m (indoor applications)

11. Copyright 1999, S.D. Personick. All Rights Reserved. A quick calculation 1 Mbps IEEE 802.11; 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

12. Copyright 1999, S.D. Personick. All Rights Reserved. Infrared links LED Detector + Rcvr

13. Copyright 1999, S.D. Personick. All Rights Reserved. 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

14. Copyright 1999, S.D. Personick. All Rights Reserved. Infrared Link LED Background light: shot noise=(PT/hf)**0.5; where T=1/bit rate Detector + Receiver (Thermal Noise~ 1000-5000 photons)