�Wi-Fi Technology�

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					                            “Wi-Fi Technology”
Abstract                                          In infrastructure mode, network traffic
                                                  passes through a wireless access point.
In the past decade, wireless has grown from an
obscure and expensive curiosity into a            The Concept:
practical     and    affordable     networking
technology. Today’s most common wireless          Wi-Fi is short for Wireless Fidelity and is
standard is 802.11b Ethernet, also called         meant to be used generically when referring to
Wi-Fi (Wireless Fidelity). The 802.11b            any type of 802.11 network, whether 802.11b,
standard is fast enough to be practical and       802.11a, 802.11g, dual-band, etc.
affordable enough for home networks. You          Wi-fi is a wireless technology that uses radio
can buy the components to set up a wireless       frequency to transmit data through the air.
network in nearly any store that sells
computers.                                        An Access Point is a separate wireless unit,
                                                  which has the ability to extend from the router
The convenience of wireless is appealing—         to maximize wireless reception. Up to 16
you don’t have to deal with running cable, and    users can connect to one access point .It
you can move computers anywhere you want          allows several wireless clients to connect to a
and still be connected to the network. Wireless   single device.
is especially suited for use with laptop or       Wi-fi hot spot is defined as any location in
notebook computers, offering users great          which wireless technology both exists and is
freedom of movement. But enthusiasm for this      available for use to consumers.
new technology sometimes leads to the
installation of a wireless network where a        Wi-fi was intended to be used for wireless
wired network would be more effective,            devices and LANS, but is now often used for
economical, and secure. Wireless has              internet access.
shortcomings that make it ill suited for many
networks. Yet its popularity and ongoing
efforts to improve the technology make it a
promising option in the future.

The common usage of Wi-fi technology is for
laptop users to gain Internet access in
locations such as coffee shops, airports and so
on.

Types of Wireless LANs:
A WI-FI network can operate in two
modes:
     Ad-hoc mode
     Infrastructure mode
In ad-hoc mode, your computers talk directly
to each other and do not need an access point.
WI-FI Specification:                                 Lower total cost of ownership –
                                                      Because of affordability and low
Wi-Fi is a wireless technology that uses              install cost additionally
radio frequency to transmit data through the         Mobile Users – Can access the
air.                                                  Corporate network from any public
                                                      hotspot using VPN
    Quick/easy temp network access
    Staff access to corporate network         Range and Performance:
    Patron internet access (hotspot)
    Interconnecting two networks              Performance decreases as distance increases.
    Mobility
    Flexibility
                                                     802.11a (Wireless Ethernet)
    Savings                                                 Indoor  40-300 feet
    Expandability                                           Outdoor 100 - 1000 feet

Advantages:                                          802.11b (Wireless Ethernet Refined)

      Setup Cost – Reduced cabling                          Indoor  100-300 feet
       required                                              Outdoor 400 – 1500 feet
      Flexibility – Quick and easy to setup
       in temporary or permanent space.        Interference - doors, walls, furniture,
      Scaleable – Can be expanded with        ceiling 253 maximum number of client per
       growth                                  AP, but 15-20 recommended.
      Freedom – You can work from any
       location that you can get a signal
Differences in wireless standards                Coexistence: “wireless systems can be
                                                  collocated without significantly
Wireless  Wi-Fi        WiMax       Mobile-Fi      impacting the performance of either”
Standards (802.11)     (802.16)    (802.20)
Maximum                10 to 100                Bluetooth
          54 Mbps                  16 Mbps
Speed                  Mbps
                                   Several            A cable replacement radio frequency
Coverage    300 feet   50 Miles
                                   Miles               technology: low cost, modest
Licences    No         Both        Yes                 transfer rate, and short range.
Mobile
            No         Yes         Yes                Supports Pico nets of up to eight
Option                                                 active devices with three
                       Speed,                          synchronous connection-oriented
            Speed,                 Speed,
Pros                   Range,                          links asynchronous connectionless.
            Price                  Mobility
                       Versatile
            Short      Interface
                                                      Pico net: an ad-hoc computer
Cons                               High Price          network
            Range      Issues
                                                      It uses Frequency-Hop-Ping Spread
                                                       Spectrum (FHSS) at 1600hops/s
Applications:                                          Data transfer rate 11Mb/s or higher

1. Wi-Fi with Bluetooth Technology              Overview of Wi-Fi and Bluetooth
       In this section, we will be discussing   Characteristics
how our Wi-Fi Technology works together
with Bluetooth.                                  Wi-Fi (802.11b)
                                                   Supports multipoint networking
 Two prominent wireless technologies:             Data types as broadcast, multicast,
                                                     unicast
   1. WPAN: Wireless Personal Area
                                                   MAC address built-in, allowing
      Networking
                                                     unlimited number of devices to be
          Supports a short range (10m),
                                                     active
            implemented in Bluetooth
          Applications such as wireless           It uses direct-sequence spread
            headsets, PDAs, keyboards,               spectrum
            mice, etc.                           Both Wi-Fi and Bluetooth share the
                                                  same frequency band, 2.4Ghz
   2. WLAN: Wireless Local Area
      Networking
          Supports wider range (100m),         Issues of Coexistence
            designed in Wi-Fi (802.11b)
          Applications such as wireless         Both Wi-Fi & Bluetooth operate at the
            routers, wireless cards,              same time within the same frequency
            wireless printers, etc.               band, they will interfere with each other,
                                                  creating in-band colored noise.
 WPAN & WLAN are complementary                  The inference is called noise
 Collocation of Wi-Fi and Bluetooth
  become increasingly significant.
 Noise: in-band noise & out-of-band             Important milestone and enabler in the
  noise                                           growth of Wi-Fi beyond the PC market
   In-band noise: the transmitter uses           into
     the undesired energy in frequencies            – Wi-Fi Cellular Convergence
     to transmit the desired signal.                products
   Out-band noise: the transmitter does            – Voice over Wi-Fi applications
     not use.                                       – Consumer Electronics
   White noise: interference from
     multiple sources without their            Features and Benefits of WMM
     coordination.                             Power Save
   Colored         noise:      interference
     transmitted by two intentional                      Feature                  Benefit
     radiators, behave in time &               Individual applications      More finely tuned
     frequency                                 (instead of the device       power save
                                               driver) decide when the      mechanism
 Occurrence of the interference:
                                               client communicates with     that is customized
   An 802.11b receiver senses both            the access point and         to individual
     Bluetooth and 802.11b signals at the      how long it can doze         applications
     same time. The effect happens when
                                                                            More efficient
     Bluetooth signal is within the 22-
                                                                            data transfer than
     MHz wide pass band of the receiver.
                                               Uses fewer packets to        legacy
   A Bluetooth receiver senses both           exchange data                power save =
     802.11b and Bluetooth signals at the                                   lower power
     same time. The inference occurs                                        consumption
     when the 802.11b signal is within the     Coexists with legacy
     Bluetooth receiver.                       power save devices and
 The interference reduces the                 networks
  performance of data transfer rate and        – Legacy APs can             Devices work in
  packet lost.                                   support WMM Power          all Wi-Fi
                                                  Save clients (in legacy   networks,
                                                  mode) & vice versa        including legacy
2. WMM Power Save                                                           power save
   (Wi-Fi Multimedia Power Save)               – Both AP and client         Easily
                                                  must have WMM             upgradeable
  Extends battery life for Wi-Fi devices         Power Save to take
   by increasing efficiency and flexibility       advantage of advanced
   of data transmission                          features
     - Data indicates improvements
         ranging from 15 – 40%
  Uses mechanisms included in IEEE
   802.11e standard
CONCLUSION:                                       References:
In this paper, we have presented a new            [1] Akshaya: A Kerala state initiative for
technology called Wi-Fi, its standards,               Creating powerful social and economic
specifications, ranges and even its                   e-networks.http://www.akshaya.net/.
performance. Along with these we presented
how this Wi-Fi works together with other          [2] IEEE P802.11, The Working Group for
technologies like Bluetooth and Multimedia.          Wireless LANs.
To our knowledge, Our main conclusion is             http://grouper.ieee.org/groups/802/11/.
that long-distance links can be planned well
for predictable performance using Wi-fi.          [3] Radio laboratory handbook.
How-ever, any interference within the                http://wireless.ictp.trieste.it
network can cause drastic reductions in                         /handbook/index.html,
performance. Interference can occur
between adjacent links even in the so-called      [4] Pravin Bhagwat, Bhaskaran Raman,
non-interfering channels. This means that it          and Dheeraj Sanghi. Turning 802.11
is important to develop the knowledge-base            Inside-Out. In HotNets-II, Nov 2003.
for deployment planning.
Wi-Fi-based community networks have               [5] Sanjit Biswas and Robert Morris.
received a lot of attention in the recent past.       Opportunistic Routing in Multi-Hop
The same is necessary for long-distance               Wireless Networks.
Wi-Fi deployments too, especially given its
potential to provide truly pervasive              [6] Mobile Computing / Netwoking by
networking.     We      believe     that   our        Ashoke .K Talukder & Roopa .R
measurement study is a significant step in            Yavagal
this re-guard, and hope that the results will
be useful in future de-ployments and
protocol studies.

Acknowledgment

We thank everyone who helped us at various
levels

				
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posted:9/17/2012
language:Latin
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