Unit-3: Mobile computing lecture notes (Wireless LANs)

Unit-3: Mobile computing lecture notes (Wireless LANs) in Mobile computing uploaded at P.R.Engineering college

Unit-3: Mobile computing lecture notes (Wireless LANs) in Mobile computing at P.R.Engineering college uploaded by P.R.Engineering college Staff in lecturenotes.net

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WLAN
WIRELESS LANs
The increased demands for mobility and flexibility in our daily life are demands that lead 
the development from wired LANs to wireless LANs (WLANs).
WLANs use electromagnetic radio waves to transport data between computers in a Local 
Area Network(LAN),without the limitations set by “ hard wired network cable or phone wire 
connection”, Whilst simple optical links are commercially available, radio is presently more 
useful since it is not strictly restricted to line of sight paths.
Radio waves are often called radio carriers when they are used to carry information. The 
data to be transported is superimposed on the radio carrier by various modulation techniques
which allow the data to be faithfully reconstructed at the receiving end.-Once data is
superimposed (modulated)onto the radio carrier, this combined “radio signal” now occupies
more than a single frequency components or spectra of the modulating data add frequency to 
the basic carrier ( in direct proportion to its information content or bit rate).
The frequency range which is needed to accommodate a radio signal with any given 
modulation bandwidth is called a channel. Radio receiver techniques can select one radio 
channel while efficiently rejecting signals on other frequencies. Many radio signals to and 
from many users can thereby co-exist in the same place and time without interfering with 
each other if the radio waves are transmitted at minimum necessary power within different 
radio channels.
3.1 ADVANTAGES OF WLAN OVER WIRED LAN
(1) Flexibility: With in radio coverage nodes can communicate without further restriction.
(2) Planning: Wireless ad hoc network allow communication without planning whereas
wired network needs wiring plans.
(3)Design: Wireless Network can survive disaster. If the wireless devices survive people can 
communicate.
(4) Cost: Adding additional users to a wireless network will be increase the cost. But where 
as with fixed network addition of an user will lead into unplugging and plugging. Wireless
connections do not wear out.IT1403-MOBILE COMPUTING IV YEAR / VIII SEM
DEPARTMENT OF CSE 115 PREC
Disadvantages:
(1) QOS:
Wireless offers lower quality than that of wired .The reasons are: 
The Lower bandwidth due to limitations in radio transmission. 
High error rate due to interference.
Higher delay due to error correction and detection mechanisms. 
(2) Proprietary Solution:
Many companies have comeup with proprietary solutions offering standardized 
functionality.
This is due to slow standardization procedures. 
(3) Restriction:
The wireless products need to comply with national regulations.
WLAN are limited to low power senders and certain license free frequency hand 
which are not same world wide.
(4) Safety and security:
The radio waves are used for data transmission. They will interface with other
equipment. Precautions have to be taken to prevent safety hazards.
As it is via radio transmission eaves dropping is possible.
Design Goals: TO Ensure Commercial Success
(1) Global Operation:
While the product is being sold in all the countries, national and international 
frequency regulation should be considered.
(2) Low Power:
Devices communicating via WLAN are also wireless devices. These Devices run on 
battery power- While designing a WLAN these aspects should also be considered 
(i.e) Power saving modes and power management functions to be considered
` (3) License Free Operation:
The equipment must operate in a license free band such as 2.4 GHz ISM Band.
(4) Robust Transmission Technology:
WLAN operate under difficult conditions. As they are radio transmission many 
other electrical devices can interfere with them.
(5) Simplified Spontaneous Co-Operation:
WLAN should not require complicated startup routines, but should run 
spontaneously after power up.
(6) Easy to Use:
WLAN‟s are made for simple use. They should be like plug and play. 
(7) Production of Investment:
For transition from wired to wireless, simple bridging should be enough to 
interoperate.
(i.e.) Wireless LAN should support the same data types and services as that of wired

Title:
Unit-3: Mobile computing lecture notes (Wireless LANs)

Subject:
Mobile computing

Institute:
P.R.Engineering college

Unit-3: Mobile computing lecture notes (Wireless LANs)

Unit-3: Mobile computing lecture notes (Wireless LANs) in Mobile computing uploaded at P.R.Engineering college

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