“Wi-Fi Technology”
Abstract
In the past decade, wireless has grown from an
obscure and expensive curiosity into a
practical
and
affordable
networking
technology. Today’s most common wireless
standard is 802.11b Ethernet, also called
Wi-Fi (Wireless Fidelity). The 802.11b
standard is fast enough to be practical and
affordable enough for home networks. You
can buy the components to set up a wireless
network in nearly any store that sells
computers.
The convenience of wireless is appealing—
you don’t have to deal with running cable, and
you can move computers anywhere you want
and still be connected to the network. Wireless
is especially suited for use with laptop or
notebook computers, offering users great
freedom of movement. But enthusiasm for this
new technology sometimes leads to the
installation of a wireless network where a
wired network would be more effective,
economical, and secure. Wireless has
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.
In infrastructure mode, network traffic
passes through a wireless access point.
The Concept:
Wi-Fi is short for Wireless Fidelity and is
meant to be used generically when referring to
any type of 802.11 network, whether 802.11b,
802.11a, 802.11g, dual-band, etc.
Wi-fi is a wireless technology that uses radio
frequency to transmit data through the air.
An Access Point is a separate wireless unit,
which has the ability to extend from the router
to maximize wireless reception. Up to 16
users can connect to one access point .It
allows several wireless clients to connect to a
single device.
Wi-fi hot spot is defined as any location in
which wireless technology both exists and is
available for use to consumers.
Wi-fi was intended to be used for wireless
devices and LANS, but is now often used for
internet access.
WI-FI Specification:

Wi-Fi is a wireless technology that uses
radio frequency to transmit data through the
air.








Quick/easy temp network access
Staff access to corporate network
Patron internet access (hotspot)
Interconnecting two networks
Mobility
Flexibility
Savings
 Expandability
Advantages:




Setup Cost – Reduced cabling
required
Flexibility – Quick and easy to setup
in temporary or permanent space.
Scaleable – Can be expanded with
growth
Freedom – You can work from any
location that you can get a signal
Lower total cost of ownership –
Because of affordability and low
install cost additionally
Mobile Users – Can access the
Corporate network from any public
hotspot using VPN
Range and Performance:
Performance decreases as distance increases.

802.11a (Wireless Ethernet)



Indoor
40-300 feet
Outdoor 100 - 1000 feet
802.11b (Wireless Ethernet Refined)


Indoor
100-300 feet
Outdoor 400 – 1500 feet
Interference - doors, walls, furniture,
ceiling 253 maximum number of client per
AP, but 15-20 recommended.
Differences in wireless standards
Wireless
Wi-Fi
Standards (802.11)
Maximum
54 Mbps
Speed
WiMax
(802.16)
Coverage
300 feet
50 Miles
Licences
Mobile
Option
No
Both
Several
Miles
Yes
No
Yes
Yes
Pros
Speed,
Price
Cons
Short
Range
10 to 100
Mbps
Speed,
Range,
Versatile
Interface
Issues
Mobile-Fi
(802.20)
16 Mbps
Speed,
Mobility
 Coexistence: “wireless systems can be
collocated without significantly
impacting the performance of either”
Bluetooth



High Price
Applications:
1. Wi-Fi with Bluetooth Technology
In this section, we will be discussing
how our Wi-Fi Technology works together
with Bluetooth.
 Two prominent wireless technologies:
1. WPAN: Wireless Personal Area
Networking
 Supports a short range (10m),
implemented in Bluetooth
 Applications such as wireless
headsets, PDAs, keyboards,
mice, etc.
2. WLAN: Wireless Local Area
Networking
 Supports wider range (100m),
designed in Wi-Fi (802.11b)
 Applications such as wireless
routers, wireless cards,
wireless printers, etc.
 WPAN & WLAN are complementary
 Collocation of Wi-Fi and Bluetooth
become increasingly significant.


A cable replacement radio frequency
technology: low cost, modest
transfer rate, and short range.
Supports Pico nets of up to eight
active devices with three
synchronous connection-oriented
links asynchronous connectionless.
Pico net: an ad-hoc computer
network
It uses Frequency-Hop-Ping Spread
Spectrum (FHSS) at 1600hops/s
Data transfer rate 11Mb/s or higher
Overview of Wi-Fi and Bluetooth
Characteristics
 Wi-Fi (802.11b)
 Supports multipoint networking
 Data types as broadcast, multicast,
unicast
 MAC address built-in, allowing
unlimited number of devices to be
active
 It uses direct-sequence spread
spectrum
 Both Wi-Fi and Bluetooth share the
same frequency band, 2.4Ghz
Issues of Coexistence
 Both Wi-Fi & Bluetooth operate at the
same time within the same frequency
band, they will interfere with each other,
creating in-band colored noise.
 The inference is called noise
 Noise: in-band noise & out-of-band
noise
 In-band noise: the transmitter uses
the undesired energy in frequencies
to transmit the desired signal.
 Out-band noise: the transmitter does
not use.
 White noise: interference from
multiple sources without their
coordination.
 Colored
noise:
interference
transmitted by two intentional
radiators, behave in time &
frequency
 Occurrence of the interference:
 An 802.11b receiver senses both
Bluetooth and 802.11b signals at the
same time. The effect happens when
Bluetooth signal is within the 22MHz wide pass band of the receiver.
 A Bluetooth receiver senses both
802.11b and Bluetooth signals at the
same time. The inference occurs
when the 802.11b signal is within the
Bluetooth receiver.
 The interference reduces the
performance of data transfer rate and
packet lost.
2. WMM Power Save
(Wi-Fi Multimedia Power Save)
 Extends battery life for Wi-Fi devices
by increasing efficiency and flexibility
of data transmission
- Data indicates improvements
ranging from 15 – 40%
 Uses mechanisms included in IEEE
802.11e standard
 Important milestone and enabler in the
growth of Wi-Fi beyond the PC market
into
– Wi-Fi Cellular Convergence
products
– Voice over Wi-Fi applications
– Consumer Electronics
Features and Benefits of WMM
Power Save
Feature
Individual applications
(instead of the device
driver) decide when the
client communicates with
the access point and
how long it can doze
Uses fewer packets to
exchange data
Coexists with legacy
power save devices and
networks
– Legacy APs can
support WMM Power
Save clients (in legacy
mode) & vice versa
– Both AP and client
must have WMM
Power Save to take
advantage of advanced
features
Benefit
More finely tuned
power save
mechanism
that is customized
to individual
applications
More efficient
data transfer than
legacy
power save =
lower power
consumption
Devices work in
all Wi-Fi
networks,
including legacy
power save
Easily
upgradeable
CONCLUSION:
References:
In this paper, we have presented a new
technology called Wi-Fi, its standards,
specifications, ranges and even its
performance. Along with these we presented
how this Wi-Fi works together with other
technologies like Bluetooth and Multimedia.
To our knowledge, Our main conclusion is
that long-distance links can be planned well
for predictable performance using Wi-fi.
How-ever, any interference within the
network can cause drastic reductions in
performance. Interference can occur
between adjacent links even in the so-called
non-interfering channels. This means that it
is important to develop the knowledge-base
for deployment planning.
[1] Akshaya: A Kerala state initiative for
Creating powerful social and economic
e-networks.http://www.akshaya.net/.
Wi-Fi-based community networks have
received a lot of attention in the recent past.
The same is necessary for long-distance
Wi-Fi deployments too, especially given its
potential to provide truly pervasive
networking.
We
believe
that
our
measurement study is a significant step in
this re-guard, and hope that the results will
be useful in future de-ployments and
protocol studies.
[5] Sanjit Biswas and Robert Morris.
Opportunistic Routing in Multi-Hop
Wireless Networks.
Acknowledgment
We thank everyone who helped us at various
levels
[2] IEEE P802.11, The Working Group for
Wireless LANs.
http://grouper.ieee.org/groups/802/11/.
[3] Radio laboratory handbook.
http://wireless.ictp.trieste.it
/handbook/index.html,
[4] Pravin Bhagwat, Bhaskaran Raman,
and Dheeraj Sanghi. Turning 802.11
Inside-Out. In HotNets-II, Nov 2003.
[6] Mobile Computing / Netwoking by
Ashoke .K Talukder & Roopa .R
Yavagal