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Tutorial
 Wireless
LAN Technology and Network Implementation
Rick
Gallaher is course
director for CCI,
President of Telecommunications Technical Services Inc., and author of Rick
Gallaher's MPLS Training Guide
March 10, 2003
An
early convert, I am not – but I finally broke down and
installed a wireless network into my home. I have a two-story
home, with the ground floor being dedicated to office space
and the top floor containing my family's living space.
Some days, I just do not want to go down into the
office; I want to work from the back deck, or from the kitchen
table. Extending
connectivity meant that I could either run wires to the second
floor (i.e., tear up the house) or go wireless.
This article will explore basic wireless theory,
existing differences in standards for wireless technology,
wireless compatibility, security, and results of wireless
tests for 802.11b.
Vocabulary
- Access
point
- Main station, router, or device that provides interfaces
with wired and wireless
devices
- AM
- Amplitude
Modulation (a modulation method)
- BPSK
- Binary
Phase Shift Keying (a modulation method)
- CCK
- Complementary
Code Keying
- CSMA/CD
- Carrier
Sense Multiple Access with Collision Detection
- DSS
- Direct
Spread Spectrum
- DSSS
- Digital
Sequence Spread Spectrum
- FHSS
- Frequency
Hopping Spread Spectrum
- FM
- Frequency
Modulation (a modulation method)
- OFDM
- Orthogonal
Frequency Division Multiplexing
- PBCC
- Packet
Binary Convolutional Coding
- PCMCIA
- Personal
Computer Memory Card International Association
- QPSK
- Quadrature
Phase Shift Keying
- Wi-Fi
- Wireless
Fidelity. Also, a certification standard for 802.11
compliant products managed by the Wi-Fi
Alliance.
The
first portion of this article examines the theory of wireless
communication, defining modulation, carriers, signal-to-noise
ratios, and antenna propagation.
Modulation
Data
rates of a few bits per minute (bpm), all the way to 100 Mbps,
do not have radio characteristics that are sufficient to allow
them free movement through the air.
To make data move through the air, it must be mixed
with a frequency that has good free-air transmission
characteristics. The frequency that can carry the data is
called the carrier frequency.
In
Figure 1, we see a block diagram of a simple transmitter.
Note that, as the data enters on the left of the
figure, it is mixed with the carrier frequency in a functional
box called a modulator. A
generator produces the carrier frequency. When the
intelligence is mixed with that frequency, it creates an
output signal that may resemble the output shown in the
antenna.
The
mixing, or modulating, of intelligence with the carrier
frequency comes in various forms. Common methods are AM, CCK,
PBCC, FM, BPSK, and QPSK.
Figure
1: Block Diagram of Simple Transmitter
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