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Ultra-Wideband
- John Burnette -
What is UWB?

Know since 60’s
“Zero carrier” or “carrier free”
 Transmit short bursts

Fraction of typical RF carrier wave
 Thus utlra wide band
 Difficult to determine carrier frequency

What is UWB? Cont’d
Ultrawideband
Communication
Narrowband
Communication
Time-domain behavior

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0
1
0
Frequency-domain behavior
1
Frequency
Modulation
2.4
1
Impulse
Modulation
0
GHz
1
time
3
frequency
10 GHz
(FCC Min=500Mhz)
Communication that occupies more than 500 MHz of spectrum
Communication with fractional bandwidth of more than 0.2
UWB Spectrum
FCC allows spectrum overlap for UWB
Bluetooth,
802.11b
Cordless Phones
Microwave Ovens
PCS
Emitted
Signal
Power
GPS

802.11a
“Part 15 Limit”
-41 dBm/Mhz
UWB
Spectrum
1.6 1.9
2.4
3.1
5
Frequency (Ghz)

10.6
UWB can operate between 3.1 and 10 GHz as
long as it stays below -41dBm
Good things about UWB

7.5 GHz of “free spectrum” in the US.



The spectrum allocation for UWB overlays existing spectrum but the
FCC power limitations are set to minimize interference with existing
systems.
High Data rates – under current regulations 500 Mbps at 10
feet.[1] Due to the short-pulse waveform of an UWB signal, they
can be used to provide extremely high data rate performance in
multi-user network applications. Also, when used for radar,
these pulses provide a very fine range resolution and position
measurement.
Can function on simple CMOS transmitters so:



Low cost – maybe whole radio can be digital with integrated antenna
Ideal for battery powered devices
“Moores Law Radio” – The data rate scales with the shorter pulse widths
which are made increasingly faster by CMOS circuits
Good things cont’d



When used for radar, these pulses provide a very
fine range resolution and position measurement
See through walls
Imaging
And more…

waves are relatively immune to multi-path cancellation
When a strong reflected wave arrives partially or totally out
of phase with the direct path signal thus canceling part of the
signal—reduced amplitude at the receiver end.
 Therefore ideal for high-speed networked, mobile wireless
applications.
 The signals are multiplexed in the time domain so protocols
like TDMA can be used to implement this.
UWB system is frequency adaptive. In other words, it can be
positioned anywhere in the RF spectrum and still use its full
bandwidth.


Good things about UWB cont’d
Low Energy Density

Because of the short pulse duration, the signal can span
the RF spectrum, and that at a low energy density.


This makes the signal harder to detect by “unfriendly”
receivers
But Drawback


Localization



A drawback of the LPD is that it may produce a “minimal
interference to proximity systems and minimal RF health hazards
Sub-centimeter resolution using pulse leading edge detection
passes through building blocks, walls, etc. (LOS not required)
Difficult to intercept in traditional ways


Low interference
Very low spectral energy density
Early Implementation

Take a wideband microwave antenna and use fast risetime pulse excitations to generate the antennas
“impulse” response (it is actually the antenna’s step
response that is produced and radiated).


Problem: generates a lot of unwanted, out-of-band radiation
which can cause interference with other systems.
Modern techniques create a UWB waveform through
pulse shaping prior to actual transmission.

This gives control to the engineers to prevent radiation into
restricted bands, thus preserving safely and life systems.
Safety Concerns

Safety-of-flight systems
UWB not perfect

Since this is an RF technology it still has some
of the same limitations that are inherent in RF
systems.


In designing a UWB system, address tradeoffs like
signal-to-noise ratio versus bandwidth, range versus
power levels.
This technology isn’t the answer to everything.

For example, high capacity optical fiber or optical
wireless systems can still provide higher data rates,
although these systems are much more expensive in
both component cost and installation.
References
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
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http://www.timedomain.com
http://www.palowireless.com/uwb/tutorials.asp
Technical Issues in Ultra-Wideband Radar Systems
Harold F. Engler, Jr.
Chapter Two, Introduction to Ultra-Wideband Radar Systems, edited
by James D. Taylor, CRC Press, 1995
http://www.aetherwire.com/CDROM/General/papers.html