Wireless LANs
By
Armaghan Khan
Fakhruddin Mahmood
Sadiq Hasan
Agenda
1.
2.
3.
4.
5.
6.
Introduction
How Wireless LANs Work?
Technologies Involved
Standards
Advantages/Disadvantages
Summary
How WLANs Work
WLANs Consist of 3 Components:
1) Wired Network
2) Access Point
translates between wired LAN and wireless LAN
3) Wireless-LAN Adapters like PC cards
Used by end users to access the WLAN
How WLANs Work (Cont)
How WLANs Work (Cont)
Different Access Points
Wireless LANs Technology
There are 3 different types of wireless
technologies



Infrared Wireless LANs
Spread Spectrum LANs
Narrowband Microwave LANs
Infrared LANs
There are 3 types of Infrared
transmission techniques
1.
2.
3.
Directed Beam Infrared
Omnidirectional
Diffused
Infrared LANs
Directed Beam
1.
2.
3.
Directed IR beams are used to
create point to point links.
A focussed IR beam can have a
range of several kilometers.
Can be used for cross building
interconnection or for indoor
interconnection of LANs
Infrared LANs
Omnidirectional




A single base station which is within the
line of sight of all wireless stations on the
LAN.
Mounted on the ceiling
It acts as a multiple repeater and
broadcasts a omnidirectional beam.
The wireless stations transmit a directional
beam aimed at the ceiling base unit
Infrared LANs
Diffused


All the IR transmitters are focussed
at a point on the reflecting ceiling.
IR radiations striking the ceiling is
reradaited omnidirectionally and
picked up by all the receivers in the
area.
Infrared LANs
Advantages
1.
2.
3.
4.
5.
6.
Virtually unlimited bandwidth.
Unregulated Spectrum.
IR light is diffusely reflected by light-colored
objects. Can use this property to provide
coverage in presence of obstacles.
Does not penetrate walls or other opaque objects.
Easy to secure
Separate networks can operate without
interference
Infrared LANs
Disadvantages
1.
2.
3.
4.
Interference from background radiation
from sunlight.
Power restrictions due to eye safety.
Ambient radiation appears as noise in an
infrared receiver.
Transmitters of higher power required.
Spread Spectrum LANs
1.
2.
3.
Spread data transmission across the
available frequency band in excess of
minimum bandwidth required to send
information.
Makes it resistant to noise, interference,
eavesdropping.
Used with wireless LANs and other
personal digital communication devices
such as digital cellular phones.
Spread Spectrum LANs
Two of the most popular types of
transmission using Spread Spectrum
Analysis are:
1. Direct Sequence Spread Spectrum
(DSSS)
2. Frequency Hopping Spread Spectrum
(FSSS)
Spread Spectrum LANs
Direct Sequence Spread
Spectrum(DSSS):
1.
2.
3.
4.
5.
Most widely recognized form of Spread Spectrum.
Converts an incoming data bit stream into a
symbol stream.
Each symbol represents a group of one or more
bits.
Using QPKS techniques it multiplies each symbol
with a noise like code called pseudorandom noise
sequence.
Multiplication artificially increases used bandwidth
based on the length of the chip sequence.
Spread Spectrum LANs
Frequency Hopping Spread
Spectrum(FHSS)
1.
2.
3.
Hops from narrow band to narrow band within a
wide band.
The hopping pattern or sequence appears
random but is actually a periodic sequence
tracked by sender and receiver.
Can be susceptible to noise during any one hop
but can achieve transmissions during other hops
within the wideband.
Spread Spectrum LANs
Advantages
1.
2.
3.
4.
Has the ability to eliminate or alleviate the effect
of multipath interference.
Can share the same frequency band (overlay)
with other users.
Provides privacy due to unknown random codes.
Involves low power spectral density since signal is
spread over a large frequency band.
Spread Spectrum LANs
Disadvantages
1.
The bandwidth is inefficient
2. The implementation of the
Spread Spectrum LANs is
somewhat complex.
Narrowband Microwave
LANs
There are basically two types of
Narrowband Microwave LANs


Licensed Narrowband RF
Unlicensed Narrowband RF
Narrowband Microwave
LANs
Licensed Narrowband RF
1.
2.



Licensed within specific geographic areas
to avoid potential interference.
Motorola - 600 licenses in 18-GHz range
Covers all metropolitan areas
Due to licensing, independent LANs in
nearby locations don’t interfere
Encrypted transmissions prevent eavesdropping
Guarantees interference free communication
Narrowband Microwave
LANs
Unlicensed Narrowband RF
1. RadioLAN introduced narrowband
wireless LAN in 1995.
2. Uses unlicensed ISM spectrum
3. Operates at 10 Mbps in the 5.8-GHz
band
4. Range = 50 m to 100 m
WLAN Standards: The
IEEE 802.11


Original IEEE 802.11
Ammendments
– 802.11a
– 802.11b
– 802.11g
– 802.11n

802.11 Architecture
Original IEEE 802.11
(WiFi)




Formed in 1990
Operates in 2.4 GHz band
Data rates of 1 & 2 Mbps
3 different technologies
– Frequency Hopping Spread Spectrum
(FHSS)
– Direct Sequence Spread Spectrum (DSSS)
– Infrared
IEEE 802.11
Ammendments: 802.11a





Ratified in 1999
uses Orthogonal Frequency Division
Multiplexing (OFDM)
Data rates of up to 54 Mbps
Operates in 5 GHz band [free of
interference]
Reduced indoor range from 50 to 30m
IEEE 802.11
Ammendments: 802.11b




Ratified in 1999
Extension of original 802.11
uses a technique called
Complementary Code Keying (CCK)
Improved data rate of 11 Mbps
IEEE 802.11
Ammendments: 802.11g




Ratified in 2003
Operates in 2.4 GHz band
Uses Orthogonal Frequency Division
Multiplexing (OFDM) like 802.11a
Data rates of up to 54 Mbps
IEEE 802.11
Ammendments: 802.11n




Announced in 2004
Expected in 2007
Will use Multiple-Input Multiple-Output
(MIMO) technology
Proposed data rate of 540 Mbps!!!
IEEE 802.11 Architecture
Components
– Basic Service Set (BSS)
– Access Point (AP)
– Distribution System (DS)
– Extended Service Set (ESS)
– Portal
IEEE 802.11 Architecture
PORTAL
LAN
Other standards





HiperLAN developed by European
Telecommunications Standards
Institute (ETSI)
Also HiperLAN II
OpenAir
Developed by
HomeRF
private corporations
SWAP
Advantages of WLANs
1) Long-Term Cost Savings
a) Eliminating the direct costs of cabling
b) Effects of reorganization
2) Reduced Installation Time
a) Eliminating the time needed for cabling
b) reach places that cannot be reached by wires
Advantages of WLANs (Cont)
3) Mobility
- users can physically move while using the LAN
- Examples: healthcare workers, policemen
4) Scalability
a) Designed at any size, then can be expanded
b) connect several buildings
Advantages of WLANs (Cont)
5) Easy access to the Internet in
public places
-Examples: conference rooms ,hotels.
Disadvantages of WLANs
1)Interference
Same bandwidth like mobiles & microwave ovens.
2) Speed
much less speed than that offered with wired LAN
3) Health
Same health concerns as cell phones
4) Security
any neighbor may be able to access to internal
resources
network