WE2F-01
Millimeterwave Imaging Sensor Nets: A
Scalable 60-GHz Wireless Sensor
Network
Munkyo Seo*, B. Ananthasubramaniam,
M. Rodwell and U. Madhow
Electrical and Computer Engineering
University of California, Santa Barbara
CA 93106, USA
1
Outline
• Motivation
(1) A scalable, simplistic approach to the wireless
sensor network
(2) Exploit millimeter-wave frequencies
• Proposed Approach
• Collector System
• 60-GHz Passive sensors
• Indoor Radio Experiment
2
Wireless Sensor Networks (WSN)
• Goal: Distributed data collection & localization to
obtain an information map, D[x,y,z,t]
• Many scientific, industrial and military applications
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Environmental monitoring,
Wildlife research,
Seismic activity detection,
remote sensing,
battle field surveillance,
border policing,
planetary exploration,
Body-area network,
…
3
Current WSN Practice
• Data collection: Multi-hop based communication
– Low-power communication 
– Not very suitable for large-scale networks 
• Localization: Fixed ID code, GPS, acoustics, etc
– Tends to make sensors costly, complex 
From Akyildiz et al, IEEE Comm. Mag., Aug. 2002
4
Simplistic Sensor Approach
Sensor with minimal functionality
Move all complexity to the collector
(1) Collector sweeps a beam
f delta
(2) Sensors receive, modulate and transmit it back.
(3) Collector jointly detects data & location
5
DATA
sensor
Simplistic Approach
• Similarities with optical imaging & radar
• Scalability
– Communication grows linearly as # of sensors
• Built-in Localization
– Range resolution by a wideband range-code
– Angular resolution by a narrow beam
• Simplistic sensors (= low-cost, low-power)
– No communication among sensors
– No localization capability required.
• Concerns
– Need line-of-sight, complex collector signal processing
6
Exploit Millimeter-waves
Narrow
Beamwidth
Wide Bandwidth
D  4
• Motivations:
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–
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–
Ae

41,000


  HPBW
HPBW
Higher angular resolution @ same antenna aperture
Higher range resolution @ same fractional BW
High data rate
Unlicensed band @60GHz (BW>5GHz)
7
2
Signal Processing Principle
•
Localization
– Goal: Find the most likely sensor location.
– How? 3-D matched filtering (M/F)
(1) Range correlation (Tx Range code)
Maximum(2) Azimuth correlation (w/ AGF)
likelihood
(3) Elevation correlation (w/ AGF)
detection
(4) Find a peak!
Accuracy eventually limited by the received SNR
•
Data Demodulation
– Goal: Retrieve the local sensing data (1? 0?)
– How? Track the peak
8
Round-trip Radio Link
6~16dB/km @ 60-GHz band
2R
Pr
e
2
2
 DTX DRX DsensGsens updown 
4
Pt
4R 
60-GHz
Pt
DTX
DRX
Dsens
Gsens
7dBm 23dBi 40dBi 7dBi -3dB
25dBm 40dBi 40dBi 7dBi -3dB
25dBm 40dBi 40dBi 7dBi 80dB
9
60-GHz +/- fdelta
Rmax @10kbps, BER  106
25m (current prototype)
200m (possible ext.)
1,600m (“active” sensor)
60-GHz Collector Block Diagram
Directivity= 40dB (2 deg)
0.4m@R=10m
4.0m@R=100m
Range code: 20-MHz PRBS (26-1)
Single-chip= 7.5m,
Max. field size= 470m
Steerable
(azimuth, elevation)
PRBS
(R=20MHz)
Tx ANT
Waveform
Synthesizer
x3
TX-IF
20.166 GHz
S/G
20.166 GHz
D=23dBi
BPF
P=7dBm
TX-RF
60.5 GHz
Rx ANT
D=40dBi
Oscilloscope
USB port
Computer
I/Q
Demod.
Downconv.
RX-IF2
900MHz
S/G
900MHz
BPF
RX-IF1
4.25GHz
10
RX-RF
60.5 GHz +50MHz
S/G
18.766 GHz
60-GHz Collector Transceiver
Rx Antenna (40dB)
Tx Antenna (23dB)
Remote-controlled
Positioner (Az, El)
Transceiver board
11
60-GHz Collector System
• Transceiver with all
required instruments.
• Mounted on a mobile
cart.
12
Measured Antenna Gain Function (AGF)
Magnitude
AGF = (TX ANT) (RX ANT)
= (23dB Horn) (40dB Cassegrain)
1
0.5
0
-4
-3
-2
-1
0
1
2
3
Azimuth, Elevation (degree)
13
4
60-GHz Passive Sensor: Block Diagram
• Receive, modulate and re-radiate the beam
• Simplicity, low cost, robustness, etc
Baseband
fdelta= 50MHz
XTAL
16-bit
Local
data
BPSK Modulator Open-slot Antenna
¼λ
MS-to-SL
transition
¼λ
PIN diode (MA-COM)
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60-GHz Passive Sensor: Considerations
• Antenna
– Patch type?
– Slot-type?
– Open-slot type?
• Substrate: RO4003C
– 0.2mm, Er=3.38
– Loss= 0.07dB/mm, Q=20
• Standard low-cost PC-board
manufacturing
– Min. line width/spacing =
PIN diode
5mil (125um)
(flip-chip)
– This favors high Z0
(=90ohm)
Size: 15mm x 10mm
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Modulator Impedance
a
b
60GHz
b  mod Vmod a
65GHz
a : indident w ave
b : reflected wave
Bias ON
(7mA)
55GHz
• Switches between two
impedance states.
55GHz
Bias OFF
60GHz
• ~180 degree relative
phase shift
65GHz
• BPSK Modulation
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Linearly-Tapered Open-Slot Antenna
HFSS
Beam Pattern (7dBi)
0dB
Input Match
`
dB(S(1,1))
-10dB
0
-10
-20
-30
50
55
60
65
Freq (GHz)
HPBW= 50 deg
17
70
CMOS Passive Sensor (under fab.)
For low-power operation, CMOS integration
is necessary
Layout (1mm2)
• 3-channel sensor (90-nm CMOS)
• dc power = 0.5~3uW
• Contains a BPSK modulator and
low-power, voltage-controlled
ring-oscillator
• Flip-chip interface to ANT.
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Indoor Radio Experiment
sensor
19
Received Power (dBm)
Received Power vs Range
Measured
Calculated
-80
-90
-100
-110
-120
100
1R
Range (m)
20
101
4
Received Spectrum (RX-IF2)
Sensor ON (~3m)
Power (dBm)
Sensor OFF
0
-10
-20
-30
-40
-50
0
-10
-20
-30
-40
-50
0.85 0.90 0.95 1.00 1.05
0.85 0.90 0.95 1.00 1.05
Freq. (GHz)
Freq. (GHz)
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2-D Localization (M/F output)
Sweep 15.6 deg
Step= 0.6 deg
collector
azimuth
Single sensor
radial
Two sensors
collector
Field size: 12x0.6 m2
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3-D Localization (M/F output)
1.5 deg
1.0 deg
0.5 deg
Elevation
0 deg
-0.5 deg
-1.0 deg
-1.5 deg
23
Data Demodulation
0.05
Reference PRBS
0
-0.05
0.2
Received signal (I)
Cross-correlation
0
-0.2
4
2
0
1111 0001 001 0 111 00
Demodulated Data
(10kbps)
0.2
0
-0.2
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Summary
• Millimeter-wave wireless sensor network
– Large-scale network w/ simplistic sensors
• 60-GHz prototype
– Collector
– PIN-diode based passive sensor
– CMOS sensor (dc power: uW level)
• Indoor radio experiment (<12m)
– Data demodulation, 3D localization
• Next
– uW CMOS sensor module
– Large-scale radio experiment
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Thank you.
Questions?
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