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Anatomy of Radio LAN Onno W. Purbo

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Presentation on theme: "Anatomy of Radio LAN Onno W. Purbo"— Presentation transcript:

1 Anatomy of Radio LAN Onno W. Purbo

2 Reference Tourrilhes/Linux/Linux.Wireless.wlan.ht ml

3 Functional Diagram

4 Spread Spectrum Techniques Direct Sequence Frequency Hopping

5 Direct Sequence

6 Frequency Hopping

7

8 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 …

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

10 Antenna Directional Antenna Sectoral Antenna Beam forming Antenna

11 Range Issues Propagation Attenuation Reflection Fading

12 Transmitter Power Higher power: Drain battery quickly Frequency reuse drawback

13 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.

14 Attenuation: Propagation & Range

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

16 Modulation

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

18 2FSK B = base frequency d = deviation symbol 0 B + d 1 B – d

19 Frequency Modulation 2FSK

20 4FSK B = base frequency d = deviation Symbol 00 B+ 1/2d 01 B – 1/2d 10 B + 3/2d 11 B – 3/2d

21 IEEE (11Mbps) CCK – Complementary Code Keying 11 Mbps 5.5Mbps

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

23 Interference & Noise

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

25 Multipath & Delay Spread


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