1. Wireless LAN Technologies and Products
Chapter 4
Wireless LAN Technologies and Products
2019/4/16
Prof. Huei-Wen Ferng

2. A Brief Introduction to Network and Communication Terminology
Preliminary
A Brief Introduction to Network and Communication Terminology
2019/4/16
Prof. Huei-Wen Ferng

3. Wireless Media Microwave Infrared Unlicensed primary: ISM bands
Most wireless networking traffic is carried in microwave frequency bands
Infrared
Infrared is used in short-range wireless communication
Unlicensed primary: ISM bands
Some equipment in the industry, scientific, and medical fields without the intent of communication such as microwave ovens
2019/4/16
Prof. Huei-Wen Ferng

4. Wireless Media Unlicensed Secondary usage: ISM bands
Use the spread spectrum technology
They don’t interfere with the primary user
Why do we want unlicensed bands for WLAN?
Roaming is a problem for a WLAN user
Short-range communication:
Bluetooth and Infrared
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6. Applications Classified by Media
Radio: 100 meters
Conference, campus, universe
Infrared: 10 meters, point-to –point
Office, conference
Bluetooth: 5 meters
Small office small home (SOHO)
2019/4/16
Prof. Huei-Wen Ferng

7. Spread Spectrum Technology
Two major SS technology:
Frequency Hopping SS (FHSS)
Direct Sequence SS (DSSS)
These techniques resides at the physical layer
The responsibility of PHY layer is to transmit bits over the medium
2019/4/16
Prof. Huei-Wen Ferng

8. FHSS It is different with frequency division multiplexing (FDM)
The typical bandwidth of the information signal is 1 MHz
How does FHSS help to not interfere with the primary user?
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14. DSSS
The input data stream is transferred to a chip stream running x times faster
A chip is a zero or a one, just like a bit, it is called a chip to distinguish it from a bit
The frequency spectrum is spread out and the spectral energy is x times lower
It is so low that it does not interfere with the primary user
2019/4/16
Prof. Huei-Wen Ferng

15. DSSS (Cont’d)
The transmitter and receiver use the same coded chip and synchronized
How to transfer each of x chips to 1 bit?
What is the effect of the interference?
The degradation of the FHSS and DSSS in the presence of interference is quite different
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18. Summary of FHSS and DSSS
Can have up to 10 or 15 channels
Each channel can provide 1 or 2 Mbps
Degrades in step of 1.25%
DSSS
Can have up to two or three channels
Degrade in steps of 50%
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20. Hidden Nodes Problem A B C
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21. CSMA/CA A Simple solution for hidden nodes problem
Carrier sense
Sender broadcast RTS (request to send) to receiver
Receiver broadcast CTS (clear to send) to sender
Is CSMA/CD possible in wireless network?
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23. Digital Modulation Techniques
Convert digital stream into the analog signal
The characteristics of this signal has:
Amplitude, frequency, and phase
We can change the three characteristics to formulate the modulation techniques:
Amplitude Shift Keying (ASK)
Frequency Shift Keying (FSK)
Phase Shift Keying (PSK)
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