Wireless LAN

							            Wireless LAN
                 第一組
              電機四 林長寬
               B9090193

2012/5/27                  1
                 Outline
   What is “wireless”?
   Challenges of wireless networks
   Introduction to various standards
   Comparison




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            “Wireless” means?




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            Popular Dominant Wireless
                     Systems




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            Architecture




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Challenges for wireless network (1)
   Interference from other sources




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            Solution Candidates
   Simple but inefficient when users are idle.
   The total number of users is limited.




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            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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Challenges for wireless network (2)
   When a common media is shared for each
    host in the same BSS…




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       Solutions to Multiple Access
   CSMA / CA    (Carrier Sense Multiple Access / Collision
    Avoidance)




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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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            Wireless Standards
   IrDA
   802.11a/b/g
   HomeRF
   HiperLAN/2




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                          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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              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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            802.11a/b/g (cont’)
            Operating                                Modulatio
Standard              Data Rate      Distance
              Freq.                                  n Scheme


             5.1 ~ 5.8
802.11a         GHz
                          54 Mbps       30 m           OFDM



            2.4 ~ 2.485             100m (indoor)    DSSS with
802.11b         GHz
                          11 Mbps
                                    400m (outdoor)     CCK

                                                     20Mbps↑:OFD
            2.4 ~ 2.485             100m (indoor)         M
802.11g         GHz
                          54 Mbps
                                    400m (outdoor)   20Mbps↓:DSS
                                                          S
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                      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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                   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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                  Comparison
            Operating                                  Modulation
 Standard                 Data Rate    Distance
              Freq.                                     Scheme

            Wavelength:
    IrDA     820 nm
                          4/16 Mbps      ~5m


            2.4 ~ 2.485               100m (indoor)    DSSS with
802.11b         GHz
                           11 Mbps
                                      400m (outdoor)     CCK


HomeRF       2.4 GHz       10 Mbps        50 m           FHSS


 HiperLA                               30m (indoor)
              5 GHz        54 Mbps                       OFDM
   N/2                                150m (outdoor)
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                         Reference
   Computer networking                A Top-Down Approach
    Featuring the Internet 3rd by James F.Kurose & Keith W. Ross
   http://www.hi-pda.com/drupal/
   http://www.ibm.com/tw/
   http://www.purplesky.com.tw/2k.htm
   http://www.dlink.com.tw/home.asp
   http://cobra.ee.ntu.edu.tw/~oops/HTML6/01_html/Oral_presentation.htm
   http://www.webopedia.com/quick_ref/WLANStandards.asp




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  Thank you for your listening!



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