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Wireless Communication: Overview of basic concepts

Wireless Communication: Overview of basic concepts. Narayan Mandayam. Wired Vs. Wireless Communication. Each cable is a different channel. One media (cable) shared by all. High signal attenuation. Signal attenuation is low. High interference

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Wireless Communication: Overview of basic concepts

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  1. Wireless Communication: Overview of basic concepts Narayan Mandayam

  2. Wired Vs. Wireless Communication Each cable is a different channel One media (cable) shared by all Highsignal attenuation Signal attenuation is low High interference noise; co-channel interference; adjacent channel interference No interference

  3. Why go wireless ? Advantages • Sometimes it is impractical to lay cables • User mobility • Cost Limitations • Bandwidth • Fidelity • Power • (In)security

  4. EM Spectrum ISM band 902 – 928 Mhz 2.4 – 2.4835 Ghz FM radio S/W radio TV TV AM radio cellular 5.725 – 5.785 Ghz VHF UHF SHF EHF LF MF HF  300MHz 30MHz 30GHz 300GHz 3GHz 3MHz 30kHz 300kHz  100mm 10cm 10m 1cm 1m 100m 10km 1km X rays Gamma rays visible UV infrared  1 MHz 1 GHz 1 kHz 1 THz 1 EHz 1 PHz Propagation characteristics are different in each frequency band

  5. Unlicensed Radio Spectrum  12cm 5cm 33cm 26 Mhz 83.5 Mhz 125 Mhz 902 Mhz 2.4 Ghz 5.725 Ghz 2.4835 Ghz 5.850 Ghz 928 Mhz 802.11a 802.11b Bluetooth Microwave oven cordless phones baby monitors WaveLan

  6. Understanding wireless communication Tx Rx • How does signal propagate ? • How much attenuation take place ? • How does signal look like at the receiver ?

  7. Radio Propagation Three basic propagation mechanisms Scattering λ >> D Diffraction λ  D Reflection λ << D • Propagation effects depend on not only on the specific portion of spectrum used for transmission, but also on the bandwidth (or spectral occupancy) of the signal being transmitted • Spatial separation of Tx-Rx

  8. Propagation in the “Real World” EE a wave can be absorbed penetrate reflect bend

  9. Propagation EE And, the higher frequencies will usually encounter more “loss” in “real world” situations (again, smaller cells?; more base stations?)

  10. The Cluttered World of Radio Waves hills girders rain hallways windows vehicles trees walls

  11. Evaluating Frequencies • 50 MHz- Good for range outdoors (antenna size, bending and penetrating), no foliage problems. “Sees” metallic building structures, doesn’t pass through windows or down corridors, needs large antenna (2 meter). TV? • 450 MHz to 2 GHz - Good compromise for cellular-type systems. Antenna small, but big enough for outdoor range. Minor foliage effects. OK for windows walls and corridors. (450 might be best, but ...) (Range issue for 2 GHz systems- more bases) • 5-20 GHz- Antenna too small for range. Foliage and rain effects. Indoor microcells? Point-to-point? Satellites to ground stations?

  12. Path loss in dB 10 W P1 dB = 10 log (----) P2 101 Power 1 mW 10-3 10,000 times 1,000 times 1 W 40 dB 30 dB 10-6 d1 source d2 Path loss from source to d2 = 70dB

  13. dBm ( absolute measure of power) 10 W P1 dBm = 10 log (-------) 1mW 101 Power 1 mW 10-3 1 W 10-6 d1 source d2 = 40 dBm + 10,000 times = 0 dBm - 1,000 times = -30 dBm

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