ULTRAWIDEBAND WIRELESS DIGITAL COMMUNICATIONS USING

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ULTRAWIDEBAND WIRELESS DIGITAL COMMUNICATIONS
USING PHOTOCONDUCTIVE SAMPLING

Eric E. Funk
Joint Program for Advanced Electronic Materials,
Department of Electrical Engineering,
and
Laboratory for Atomic, Molecular, and Optical
Science and Engineering,
University of Maryland,

College Park, MD 20742

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Outline
Research Background
Wideband wireless system architecture

Photoconductive sampling as enabling technology
Demonstration of impulse radio receiver
Ultra-wideband beamsteering
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Research Background
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Research Background

• Microwave Optoelectronics
• Generation, transmission, processing of
  RF/microwave signals
• Applications Wireless, CATV, Radar
• My research
• Wideband wireless receivers
• RF-to-digital conversion
• Impulse radio
• Steerable/ smart antenna systems
• Ultra-wideband beamsteering

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Wideband Wireless
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More Bandwidth
Shannon
C W log
(1 S/N)
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Higher throughput

Wireless access to high-speed digital networks.


Spread-spectrum techniques

GHz bandwidths?

Signal security
- LPI, LPD
Multiple access -
CDMA, TDMA

Interference rejection
- AJ, Part 15
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More Flexibility

• Re-configurable
• Adaptable

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Photoconductive Sampling, Enabling Technology
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Direct RF to digital conversion
Photoconductive Samplers
High speed (ns to ps)
High dynamic range ( 30 dBm compression)
Large bandwidth (gt GHz) Low jitter- sub ps
1.075 GHz sideband (10 dB/div)
C
onnectorized photoconductive sampler
Dynamic range of
photoconductive sampler
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1 Gs/s A/D converter design
Work to be proposed in response to DoD BAAs
ANT
1
00 MHz
clock
pulsed
laser

Nyquist filter
N
1
100 Ms/s

Capacitor

To DSP
PC Gate
12 bit
ADC
Hold
72 dB DR
t
N
10
100 Ms/s
wideband

Capacitor

PC Gate
12 bit
ADC
filter
Hold
72 dB DR
Photoconductive sample/hold digital front-end
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Technology comparison
Only photoconductive switch offers
Low transients
High dynamic range
High speed
Large bandwidth
Schottky (1)
GaAs (2)
PIN (3)
High (4)
Photocond.
Diode
FET
Diode
DR
Switch
Switch
Switch
Switch
Mixer
GaAs
Transition time (ns)
3
3
80
gt1
lt1
Switching speed (ns)
9
25
280
gt1
lt1
Isolation (dB)
63
32
72
30
30
Transients (mV)
26
12
780
gt6
2
1 dB comp. (dBm)
gt12
17
gt24
23
24
Bandwidth (MHz)
5-400
DC-2000
10-2000
10-1000
DC-gt10 GHz
12 (2 nJ/pulse)
Insert. loss (dB) (1 GHz)
1.1
0.4
0.6
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1 (25 nJ/pulse)
(1) Daico DS0950
(2) Daico DS0850
(3) Daico DS0052
(4) Watkins Johnson High DR mixer HDM1001
-
our estimates of performance as a switch
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Photoconductive switch geometry
Undoped GaAs substrate
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Impulse Radio Demonstration
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Impulse Radio Introduction
New wideband radio system architecture using
short ( 1 ns) 1-3 cycle carrierless RF pulses.
Combines time-hopping (TH) and code division
multiple access (CDMA).
FCC Notice of inquiry for licensing now open.
Commercial vendor in place.
G
10 log (1/Duty Factor)
p
v
t
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Spread-spectrum processing gain from TH in
impulse radio
Time
hopped
spread-spectrum
P
pk
P
G
p
P
ave
t
Jammer
P
t
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Impulse radio demonstration
1 ns

digital OOK impulse radio sequence
1 GHz narrowband interferer

Synchronized

ANT
Mode-locked

CORRELATION RECEIVER
Laser
BERT
LNA
D
TTL Message
38 Mb/s
Threshold detector
(single bit A/D)
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Excellent bit error rate performance against
strong
narrowband interference
1E-01
1E-02
Signal power -35 dBm
Jammer power -27 dBm

1E-03
1E-04
Bit Error Rate
1E-05
Data Rate 38 Mbps
Signal BW 750 MHz
Signal fc 1 GHz
1E-06
CW Interferer at 1 GHz
1E-07
1E-08
-9.0
-8.5
-8.0
-7.5
-7.0
-6.5
-6.0
-5.5
-5.0
Signal to Interferer ratio (dB)
Note Strong interference. This is NOT the
sensitivity limit.
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Signal and Noise model for ultra-wideband receiver
Thermal Noise
k
T
B
P
J
ant
,
ant
Front-end

Photoconductive

Gain
Filter,
filter
sampler
Bandwidth
B
P
J
P
J
P
J
N
in ,
in
s
,
s
d
,
d,
d
Signal at input to sampler
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Transmitter/Receiver synchronization Delay-locked
loop or early-late correlation
Mode-locked
laser
ANT
A
loop filter
LNA
Data out
D
Threshold

detector
(or A/D)
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Laboratory Demonstration
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Ultra-wideband Beamsteering
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• Optical true-time delay
• Wideband squint-free beamsteering
• Coherent addition of power as n2

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Ultra-wideband beamsteering array setup
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Ultrawideband Beamsteering Demonstration
1.0
T
0 ps
0.8
0.6
Normalized peak E-field
0.4
0.2
0.0
80
60
40
20
0

Azimuth angle (degrees)
Azimuth angle (degrees)
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Received signal at various azimuth angles
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Conclusion
Photoconductive sampling enables digital
front-end.
High dynamic range/bandwidth performance.
receiver.
Demonstration impulse radio correlation
Anti-jam/interference resistance performance
demonstrated.
High data rate 38 Mb/s demonstrated.
Wireless receiver clock synchronization
capability demonstrated.