Wireless Networking by hedongchenchen


									Wireless networking technology

      By Abbas Izadpanah

               January 2007
 The components of Wires-WLAN
   ► Wireless stations
   ► Access points
   ► Ad hoc mode
   ► Infrastructures mode
   ► Roaming
 ► How wireless LANs work
   ► ISM band
   ► FHSS
   ► DSSS
   ► HR/DSSS
   ► COFDM
   ► Some other physical layers
   ► MIMO
Wireless Local Area Network
  A local area network that use
   wireless technology to
   connected computers in the
   network is called a wireless
   local area network (WLANs).
The components of Wires-WLAN

WLAN Stations-It Takes Two
  Wireless networking requires at least
  two radios. Each computer or device
  containing a radio that transmits and/or
  receives data over the wireless network
  is called a station. And station can be
  client or a server.
 The components of Wires-WLAN
►Access points
  – Wireless access point (APs), also called
    wireless stations, have become a crucial
    component for any wireless network that goes
    beyond simple ad hoc status.
  – There are two kinds of access points:
    Software Access Points
    hardware access points
       Software Access Points
• Software Access Points which run on a computer
  equipped with a wireless network interface card as used
  in an ad-hoc or peer-to-peer wireless network.
      Hardware Access Point
• Dedicated hardware access points (HAP) such as
  Lucent's WaveLAN, Apple's Airport Base Station or
  WebGear's AviatorPRO.
  Hardware Access Point cont…
• Access points come in many shapes, size, and
  configuration. However, no matter how else they
  might differ, all APs share the following
  •   Antenna
  •   Ethernet Port
  •   LED Indicators
  •   Reset Button
  •   Power cord
• Note
  • Both wireless adapters and access
    points must be the same brand.
        Extension point
• Some manufacturers produce
  extension points, which act as
  wireless relays, extending the
  range of a single access point.
  Multiple extension points can be
  strung together to provide wireless
  access to far away locations from
  the central access point.
An ad-hoc, or peer-to-peer wireless network

    • An ad-hoc, or peer-to-peer
      wireless network consists of
      a number of computers each
      equipped with a wireless
      networking interface card.
      Each computer can
      communicate directly with all
      of the other wireless enabled
Wireles   BSS 1
                  B   BSS 2

Infrastructures Wireless Network
 • Infrastructures mode refer to a
   wireless network controlled
   through their wireless network
   access point that generate the
   signal for individual devices to read
   through their wireless network

        PC         PC

             DS                   PC


   BSS 2

• A wireless computer can "roam" from one
  access point to another, with the software
  and hardware maintaining a steady
  network connection by monitoring the
  signal strength from in range access
  points and locking on to the one with the
  best quality.

A user can move from Area 1 to Area 2
transparently. The Wireless networking
hardware automatically swaps to the
Access Point with the best signal.
     How wireless LANs work
• The IEEE 802.11 wireless networking
  standard define five ways that data can be
  transmitted between two wireless devices.
  These transmission method are called
  physical layers. Each physical layer is
  independent of other physical layers. Each
  pair of 802.11 complain radios uses of
  these physical layers to communicate.
            The ISM Band
• In 1985 the Federal Communication
  commission (FCC) made change radios
  the radio spectrum regulation and
  assigned three bands designated as the
  industrial, scientific, and medical (ISM).
  These frequency bands are :
   ♦ 902 MHz-928 MHz, a 26 MHz bandwidth
   ♦ 2.4 GHz-2.4835 GHZ , a 83.5 MHz
   ♦   5.725 GHz-5.850 GHz, a 125 MHz
Frequency Hopping Spread Spectrum

 • The Frequency Hopping
   Spread Spectrum
   physical layer is one of
   five available physical
   layers in 802.11.
Direct sequence Spread Spectrum

   Direct-sequence spread-
     spectrum (DSSS) is another
     technique include in the IEEE
     802.11 physical layer that
     uses DSSS can also transmit
     data at up to two Mbps.
     It operates in the 2.4 MHz ISM
High Rate Direct Sequence Spectrum

 • The High Rate Direct Sequence
   Spectrum physical layer is the most
   widely used 802.11 IEEE physical
   layer (1999).
 • This layer specified by IEEE 802.11b
   supplement to the initial standard, uses
   an extension of IEEE 802.11 DSSS
 • It operates in the 2.4 MHz ISM band.
Coded Orthogonal Frequency Division Multiplexing

      • Coded Orthogonal Frequency
        Division Multiplexing
        (COFDM) layer, specified in
        802.11a supplement to the
        802.11 standard. It operates
        in the 5 GHz ISM band.
Some other physical layers

  • The IEEE 802.11 group is
    defining a physical layer that
    use OFDM in 2.4 GHz band.
    This allows 802.11a data rate
    (up to 54 Mbps) in the band
    used by 802.11b.
• (Multiple Input Multiple Output) Pronounced “
  my-mo," it is the use of multiple transmitters
  and receivers (multiple antennas) on wireless
  devices for improved performance. When two
  transmitters and two or more receivers are
  used, two simultaneous data streams can be
  sent, which double the data rate. Multiple
  receivers alone allow greater distances
  between devices. The upcoming IEEE 802.11n
  wireless standard uses MIMO to, at a minimum,
  double the 54 Mbps speed of 802.11a and
  802.11g to 108 Mbps.
         Thank you

Tanks from
Hooman Reisi
Amin mahdavian

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