1. Ultra-Wideband
- John Burnette -

2. 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

3. Frequency-domain behavior
What is UWB? Cont’d
Frequency
Modulation
2.4
GHz
Narrowband
Communication 1
Time-domain behavior
Frequency-domain behavior
Impulse
Modulation 3 10
GHz
frequency
Ultrawideband
Communication
time 1
(FCC Min=500Mhz)
Communication that occupies more than 500 MHz of spectrum
Communication with fractional bandwidth of more than 0.2

4. UWB Spectrum FCC allows spectrum overlap for UWB
1.6
1.9
2.4
Bluetooth,
802.11b
Cordless Phones
Microwave Ovens
GPS
PCS 5
802.11a
-41 dBm/Mhz
“Part 15 Limit”
UWB
Spectrum
Frequency (Ghz)
Emitted
Signal
Power
10.6
3.1
UWB can operate between 3.1 and 10 GHz as long as it stays below -41dBm

5. 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

6. Good things cont’d
When used for radar, these pulses provide a very fine range resolution and position measurement
See through walls
Imaging

7. 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.

8. Good things about UWB cont’d

9. 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
A drawback of the LPD is that it may produce a “minimal interference to proximity systems and minimal RF health hazards
Localization
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

10. Early Implementation
Take a wideband microwave antenna and use fast rise-time 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.

11. Safety Concerns
Safety-of-flight systems

12. 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.

13. References http://www.timedomain.com
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