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Anatomy of Radio LAN

Anatomy of Radio LAN. Onno W. Purbo Onno@indo.net.id. Reference. http://www.hpl.hp.com/personal/Jean_Tourrilhes/Linux/Linux.Wireless.wlan.html. Functional Diagram. Spread Spectrum Techniques. Direct Sequence Frequency Hopping. Direct Sequence. Frequency Hopping. Comparisons.

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Anatomy of Radio LAN

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  1. Anatomy of Radio LAN Onno W. Purbo Onno@indo.net.id

  2. Reference • http://www.hpl.hp.com/personal/Jean_Tourrilhes/Linux/Linux.Wireless.wlan.html

  3. Functional Diagram

  4. Spread Spectrum Techniques • Direct Sequence • Frequency Hopping

  5. Direct Sequence

  6. Frequency Hopping

  7. Comparisons • DS modem more complicated, MAC in DS much simpler. • FH appears to be cheaper. • BW sharing, DS tends to have lower overhead on the air. • DS vs. FH = religion war  …

  8. Diversity • Diversity • Redudancy in the system to overcome noise and to increase the reliability of the system. • Antenna Diversity

  9. Antenna • Directional Antenna • Sectoral Antenna • Beam forming Antenna

  10. Range Issues • Propagation • Attenuation • Reflection • Fading

  11. Transmitter Power • Higher power: • Drain battery quickly • Frequency reuse drawback

  12. Sensitivity • Defined as • Point at 3% packet loss (400 byte packet in Gaussian channel). • 7 dB worse if we use Raleigh channel + antenna diversity. • Normally –80 dBm, better –90 dBm.

  13. Attenuation:Propagation & Range

  14. SNR • Signal-to-Noise Ratio • Difference of power in the receiver between a valid signal and noise.

  15. Modulation

  16. Multi-rate system • Better throughput more bandwidth. • The higher the signalling rate, the shorter the distance.

  17. 2FSK • B = base frequency • d = deviation • symbol • 0 B + d • 1 B – d

  18. Frequency Modulation 2FSK

  19. 4FSK • B = base frequency • d = deviation • Symbol • 00 B+ 1/2d • 01 B – 1/2d • 10 B + 3/2d • 11 B – 3/2d

  20. IEEE 802.11 (11Mbps) • CCK – Complementary Code Keying • 11 Mbps • 5.5Mbps

  21. IEEE 802.11a (OFDM) • Orthogonal Frequency Division Multiplex (OFDM). • Using equalization in post processing, overcome delay spread. • OFDM is pre-processing technique. • Use in 5Ghz UNII Band.

  22. Interference & Noise

  23. Interference & Noise • Fading • Variation in time. • Microwave oven & other interferer. • Forward Error Correction (FEC) • Not effective, better retransmit the packet. • Delay Spread

  24. Multipath & Delay Spread

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