UWB Radars: Possibilities and Problems

1
UWB Radars Possibilities and Problems

• Dr. Amit Kumar Mishra
• Department of ECE
• IIT Guwahati

2
Signposts!

• Plan of presentation
• UWB radars an introduction
• UWB radars types
• UWB radars usages
• Problems and challenges
• Talk timing 20min (talk) 10min (QA)

3
UWB A brief introduction

• Ultra wide band
• BW gt 20 of central frequency, OR
• BW gt 500 MHz
• Three types
• Impulse UWB radar
• LFM UWB radar
• Noise UWB radar
• Recent FCC regulation

4
UWB Spectrum

• FCC ruling permits UWB spectrum overlay

Bluetooth, 802.11b Cordless Phones Microwave Ovens
802.11a
Emitted Signal Power
PCS
Part 15 Limit
-41 dBm/Mhz
UWB Spectrum
1.6
1.9
2.4
3.1
5
10.6
Frequency (Ghz)

• FCC ruling issued 2/14/2002 after 4 years of
  study public debate
• FCC believes current ruling is conservative

5
Summary of the FCC Rules

• Significant protection for sensitive systems
• GPS, Federal aviation systems, etc.
• Lowest Limits Ever by FCC
• Incorporates NTIA recommendations
• Allows UWB technology to coexist with existing
  radio services without causing interference
• The RO rules are designed to ensure that
  existing and planned radio services, particularly
  safety services, are protected.

6
Some typical advantages of UWB

• Multipath immunity
• Ease of signal generation and processing
  architectures (!)
• Radar
• Inherent high precision
  sub-centimeter ranging
• Wideband excitation for detection of
  complex, low RCS targets
• Geolocation/Positioning
• Sub-centimeter resolution using pulse
  leading edge detection
• passes through building blocks, walls,
  etc. (LOS not required)
• Low Cost
• Nearly all-digital architecture
• ideal for microminiaturization into a
  chipset
• Frequency diversity with minimal hardware
  modifications

7
UWB Radar types

• LFM UWB radars Not much different from any other
  radar system
• Noise Radar UWB feature from the BW of noise
• Impulse Radar Time frequency uncertainty!

8
LFM UWB Radar

• Tx signal is a simple chirp with UWB properties
• e.g. VHF radar image
• 20-90 MHz (but BW gt 25 of fc)
• In use since long
• Problems
• target modeling!
• too much information!

Courtesy SDMS
9
Noise UWB Radar

• The question is how you model noise!
• Advantages
• Frequency diversity
• Immunity to detection, jamming etc.
• Spectral efficiency (little cross-interference
  between 2 noise radars)
• Many proofs of concept available

10
Impulse UWB radar

• Non-sinusoidal waveforms
• Fav. Shape Gaussian waveforms
• Autocorrelation is Gaussian shape!
• FT is also Gaussian shape!
• Major advantages obtained from time domain
  analysis
• Impulse waveform 1ns
• Depth of pulse 30cm
• Finer resolution

11
Possibilities of impulse radar

• Resolution
• Target identification
• Low elevation performance (time of arrival is
  different!)
• Antenna pattern depend on signal characteristics
• Both range and X-range resolution improved by
  higher BW
• Immunity to interference and noise
• Decreased dead-zone
• MTI without using Doppler
• Theoretically no side-lobes!

12
Ranging and Imaging Capabilities

• Many early applications of modern UWB technology
  were in radar systems
• Sub-nanosecond time resolution leads to precision
  ranging and imaging capabilities
• Capabilities result from the large relative and
  coherent bandwidth

13
Bio-medical sensing using UWB radar imaging

• the required power for a UWB to image human body
  is much lower than the permitted maximum level of
  electro-magnetic (EM) energy
• One of the major uses of UWB radar imaging for
  biomedical purpose has been to get information
  about the heart beat of a person. Termed as heart
  rate variability (HRV), this diagnosed
  information has been shown to be of immense
  utility

14
Imaging through obstacles

• Foliage penetration (FOPEN) has been an active
  research area for the military radar community
• With UWB techniques, systems can have both good
  resolution as well as FOEN capabilities

15
Problems and challenges

• Impulse radar
• Shape change during propagation
• Time domain analysis yet to achieve all the
  promises
• Noise radar
• Yet to fully prove its capacities
• Energy control is difficult
• LFM radar
• Not suitable for FCC based utilities
• Difficult and costly to generate UWB using LFM

16
Related Standards

• IEEE 802.15 Wireless Personal Area Network
  (WPAN)
• IEEE 802.15.1 Bluetooth, 1Mbps
• IEEE 802.15.3 WPAN/high rate, 50Mbps
• IEEE 802.15.3a WPAN/Higher rate, 200Mbps, UWB
• IEEE 802.15.4 WPAN/low-rate, low-power, mW
  level, 200kbps

17
FCC UWB Device Classifications

• RO authorizes 5 classes of devices Different
  limits for each
• Imaging Systems
• Ground penetrating radars, wall imaging, medical
  imaging
• Thru-wall Imaging Surveillance Systems
• Communication and Measurement Systems
• Indoor Systems
• Outdoor Hand-held Systems
• Vehicular Radar Systems
• collision avoidance, improved airbag activation,
  suspension systems, etc.

18
Summary of Preliminary RO Limits

• Indoor and outdoor communications devices have
  different out-of-band emission limits

19
UWB Emission Limit for Indoor Systems
3.1
10.6
1.99
GPS Band
0.96
1.61
20
UWB Emission Limit for Outdoor Hand-held Systems
3.1
10.6
1.99
GPS Band
0.96
1.61
21
UWB Emission Limits for GPRs, Wall Imaging,
Medical Imaging Systems
3.1
10.6
1.99
GPS Band
1.61
0.96
Operation is limited to law enforcement, fire and
rescue organizations, scientific research
institutions, commercial mining companies, and
construction companies.
22
UWB Emission Limits for Thru-wall Imaging
Surveillance Systems
GPS Band
1.99
10.6
0.96
1.61
Operation is limited to law enforcement, fire and
rescue organizations. Surveillance systems may
also be operated by public utilities and
industrial entities.