Spring 2006

EE 548

Ultra Wideband Radio:

Ranging

Spring 2006

Spring 2006

Approaches to ranging(IEEE 802.15 TG4)

The ranging subcommittee has identified 5 different techniques or doing ranging. •Time of Arrival Ranging•Angle of Arrival Ranging•Time Difference of Arrival Ranging•Signal Strength Ranging•Near Field EM Ranging

Spring 2006

Ranging: time of arrival

Node

L

2/

/2

cLR

cL

Spring 2006

Ranging: critical issues

• Detecting the peak of the received signal

• Correlating the received signal with the transmitted signal

• Mitigation of the effects of noise and jitter

Spring 2006

Ranging: why use UWB?

• Wide bandwidth and short pulse duration provide– More target information– Improve range accuracy– Improve resilience to passive scatterers (clutter)– Mitigate destructive multipath effects from

ground reflection– Enable a narrow antenna beam pattern

Spring 2006

Ranging use short duration pulses:traditional RADAR approach

processing signal special nowith

meters 015.02/)1010010 x (3 R

100psec~ duration pulse

7.5GHz, ofbandwidth a with pulse aFor

resolutionR

widthpulse

light of speedc

2/

128

xx

cR

Spring 2006

Errors in time of arrival ranging:Cramer-Rao lower bound (CRLB)

arrival of in time iancevar

density noise

frequency

)()2(2

2

0

22

02

N

f

dffPf

N

Spring 2006

CRLB for square pulses

otherwise 0,,for )( 0

2

HL fffGfP

)(238 33

02

02

LH ffG

N

Spring 2006

CRLB for square pulses (II)

))((238 22

02

02

LHLHLH ffffffG

N

20

202

28

of valueslargefor

BfG

N

ff

f

ffB

LH

LH

Spring 2006

CRLB for square pulses: example

• Assume UWB,

• B=10.6-3.1 = 7.5GHz

• PSD = FCC max

• 2G0=9.86x10-24 joules/Hz

• N0=2x10-20 W/Hz, at room temp and 7dB noise figure

mxc

x6

292

1044.2 error estimation distance

1063.6

Spring 2006

Improving the accuracy in TOA ranging

• Need to accurately compare received pulse with transmitted pulse to determine time delay

• Use correlation techniques– Slide correlation window in time– Look for maximum

Spring 2006

Correlation technique for TOA based ranging

T

Rectangular pulse of duration T

s(t)

Spring 2006

Output of matched filter for square wave pulse

2T0

RS(

T

Spring 2006

Early-late gate synchronizer

• Exploits correlator output– Measures output at symmetric points in time

relative to expected peak value

– Then evaluates the difference

)()( TRTRR ss

When the samples are made at points that aresymmetric about the peak, R=0

When there is an unknown delay , R is not zero

Spring 2006

Effect of unknown delay on the output of early-late gate

synchronizer

2T0

RS(

T

R

Measurement of R enables calculation of

Spring 2006

Lower bound on ranging errors

Use multiple, repetitive pulses to average out jitter and noiseto increase accuracy, at the expense of processing time

Spring 2006

Time integrating correlator (TIC)

• Received signal s(t) stored• Reference code moved past the analog input signal• Product of received signal and code are summed

in a bank of parallel analog integrators• Each correlator uses same code, but shifted in time• When received signal is aligned with proper code,

the integrator output reaches as maximum

Spring 2006

Pulse pair, offset spreading sequences, and TIC output

Spring 2006

UWB ranging is relatively immune to multipath

Spring 2006

In-building multipath measurements

Spring 2006

Through-wall sensing: RadarVision• Specifications

• Size:56 cm x 35.5 cm x 20.3 cmWeight: <4.5 kgEnclosure: High Impact PlasticColor: BlackPower: Removeable/rechargeable lithium ion batteryOperating Time/Charge: >3 HoursRechargeable Time: <4 HoursRange Accuracy: +/- 1 meter (+/- 0.5m typical)Horizontal Field of View: > +/- 60 degreeVertical Field of View: > +/- 45 degreeLine of Sight: 20 meter through Wood, Brick, Gypsum Wall & 20 cm Solid ConcreteShock/Vibration: Drop tested at 2 metersHumidity: 0% to >90% (non-condensing) Liquid: Water resistant (not submersible)Operating Temperature: -10 degree C to +50 degree CStore Temperature: -20 degree C to 60 degree CEmission Type: Coded ultra wideband pulsesPulse Rate: 10 Million pulses per second Transmit Power: 1.5 mWBandwidth: 1-3.5 GHz

http://www.radarvision.com/RadarVision2/Rv2.htm

Spring 2006

Example locator systemMicro Air Vehicle Collision

Avoidance System

Weight Less than 50g

Size Small

Resolution +/- 1 foot

Range 50 feet

Span 360 degrees

Update rate 1000 times/sec