1. Wireless LAN
第一組
電機四 林長寬 B
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2. Outline What is “wireless”? Challenges of wireless networks
Introduction to various standards
Comparison
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3. “Wireless” means?
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4. Popular Dominant Wireless Systems
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5. Architecture
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6. Challenges for wireless network (1)
Interference from other sources
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7. Solution Candidates Simple but inefficient when users are idle.
The total number of users is limited.
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8. Random Access Protocol
Carrier Sense Multiple Access (CSMA)
Every user has the opportunity to access to the media.
Listen before you speak!
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9. Challenges for wireless network (2)
When a common media is shared for each host in the same BSS…
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10. Solutions to Multiple Access
CSMA / CA (Carrier Sense Multiple Access / Collision Avoidance)
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11. Other Transmission Techniques
Interference & Jamming
DSSS (Direct Sequence Spread Spectrum)
FHSS (Frequency Hopping Spread Spectrum)
Bandwidth Efficiency
OFDM (orthogonal frequency division multiplexing)
Please refer to the Communication System course.
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12. Wireless Standards
IrDA
802.11a/b/g
HomeRF
HiperLAN/2
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13. IrDA Infrared Data Association (IrDA) <Applications>
Remote Controller, transmission between consuming electronic gadgets.
<Features>
Line of sight transmission only
Connection between 2 devices only
Low security level
Low price
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14. 802.11a/b/g (cont’) Standardized by IEEE, also known as Wi-Fi.
<Applications>
WLAN interface card, AP, etc.
<Features>
The most popular wireless
standards.
Use CSMA/CA and identical
frame structure.
Both infrastructure mode and
ad hoc are allowed.
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15. 802.11a/b/g (cont’) 802.11a 802.11b 802.11g Standard Operating Freq.
Data Rate
Distance
Modulation Scheme
802.11a
5.1 ~ 5.8 GHz
54 Mbps
30 m
OFDM
802.11b
2.4 ~ GHz
11 Mbps
100m (indoor)
400m (outdoor)
DSSS with CCK
802.11g
20Mbps↑:OFDM
20Mbps↓:DSSS
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16. HomeRF Based on Share Wireless Access protocol (SWAP)
<Applications>
Intended for use in homes, for communication between PCS, or other consumer devices.
<Features>
Integrate both data and
voice signal transmission.
Relatively inexpensive to
set up and maintain.
Responds well to interference
because of frequency-hopping modulation.
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17. HiperLAN/2
Standardized by the European Telecommunication Standardization Institution (ETSI)
<Applications>
WLAN devices
<Features>
Only in Europe.
Theoretical maximum speed of 54 Mbps.
Bandwidth guaranteed.
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18. Comparison IrDA 802.11b HomeRF HiperLAN/2 Standard Operating Freq.
Data Rate
Distance
Modulation Scheme
IrDA
Wavelength:
820 nm
4/16 Mbps
~ 5 m
802.11b
2.4 ~ GHz
11 Mbps
100m (indoor)
400m (outdoor)
DSSS with CCK
HomeRF
2.4 GHz
10 Mbps
50 m
FHSS
HiperLAN/2
5 GHz
54 Mbps
30m (indoor)
150m (outdoor)
OFDM
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19. Reference
Computer networking A Top-Down Approach Featuring the Internet 3rd by James F.Kurose & Keith W. Ross
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20. Thank you for your listening!
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