26-11-2012, 11:42 AM
Introduction to Wireless Technology
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Wireless Data Network Drivers
• Information access
• PDAs
• Network computers
• Alpha paging,
information
distribution
• Web
• Audio and video
What Is the Interest in Wireless?
• Look ma, no more cables…
• Mobility
• Increased productivity
• Competition
• Flexibility
• Many others
Some Wireless Data Solutions
• Field service—dispatch, parts/order,
electronic signature, package tracking
• Public safety—parking enforcement,
ambulance-hospital links, anti-theft
• Financial—news, brokerage, pricing
• Telemetry—Health care, vending
machines, alarm systems, energy
• Identification—inventory in warehouse
and stores, anti-theft
But Wait, More Wireless
Data to Come
• Bluetooth to hit 448 million
enabled in 2004
• Internet mobile will hit 61.5 million
in 2003, probably more
• Some analyst indicate “More people
will access the Internet via wireless
than wired connections.” (ISP Planet,
Feb 2000)
Regulation of Wireless
• Radio Frequency (RF) is a scarce
and shared resource
Each country governs the use of radio
spectrum
In the U.S. the F.C.C. allocates spectrum
for use and resolves conflict disputes
Internationally coordinated through
the ITU
Transmitting a Signal
• The goal of sending data over RF is to
get information across with as much
data as possible, sending it as far as
possible and as fast as possible.
• More data can be placed on a signal in
one of two ways:
More frequency used or
Complex modulation
Radio Modulation
• High speed modem compress the
data to use the same line as an old
300 baud modem. This means the
same bandwidth is available.
• 56Kmodems require a better
(quieter) phone line to
communicate at the higher speed
• If there is noise on the line, the
modem will drop down in speed to
connect.
• Mode noise, less speed
• Complex modulation requires
better signal strength, therefore
less coverage is available
Antenna Gain
• In life you never get ‘something for
nothing’, the same is true in antenna gain
• If the gain of an antenna goes up, the
coverage area or angle goes down
• Coverage areas or radiation patterns are
measured in degrees
• These angles are referred to as
beamwidth, and have a horizontal and
vertical measurement
Theory—Dipole
• To obtain omnidirectional
gain from an isotropic
antenna, the energy lobes
are ‘pushed in’ from the
top and bottom, and
forced out in a doughnut
type pattern.
• The higher the gain
smaller the vertical
beamwidth, and the more
horizontal lobe area
• This is the typical dipole
pattern. Gain of a dipole is
2.14dBi (0dBd)
The LOS Solution
• VOFDM (Vector
Orthogonal Frequency
Division Multiplexing)
technology employs
both frequency and
spatial diversity to
create a robust
processing technique
for multipath fading
and narrow band
interference
• VOFDM enables
greater coverage and
substantially reduces
LOS limitations