Brett Kaufman, Aydin Babakhani, and Behnaam Aazhang

Brett Kaufman, Aydin Babakhani, and Behnaam Aazhang

CWC
A Network Perspective of Full-Duplex
Oulu
Brett Kaufman, Aydin Babakhani, and Behnaam Aazhang!
(bkaufman, ab28, aaz)@rice.edu
User 2
User 1
-40
-60
-80
2.395
2.445
FD-VA
FD-LNA
VGain
-20
-40
-60
-80
⇤
VGain
-100
0
0.5
= 0.81 V
1.0
1.5
✴FD Variable Gain Amplifier!
✴Isolation Maximization!
✴Bias Voltage
Phase
Shifter
VShif t
+
Combined
Output Signal
Self-Interference Cancellation (dB)
!
Channel Phase (degrees)
0
Circuitry tunes phase to zero
at desired frequency→
-90
Bandwidth (MHz)
⇤
VShif t
2.437
-40
0
-90
-180
2.415
2.460
2.437
2.460
f (GHz)
40
←Below 60 dB isolation on
average
30
20
Circuitry improves isolation
by 20 to 40 dB→
10
-60
-80
30
20
10
0
-40
-100
-60
-80
-100
Self-Interference Cancellation (dB)
Conclusions
-50
-60
-70
⇤
VShif
t = 0.41 V
0
0.4
0.8
1.2
1.6
!
✴Active Circuitry!
✴Improved Isolation!
✴Improved Bandwidth!
✴Frequency Tuned
-80
-100
Antenna Only
Tuned Circuit
f (GHz)
90
VShif t
VShif t (V)
2.437
2.460
= arg max S21(VShif t )
-60
-120
2.415
←Random phase values at
desired frequency
40
VGain (V)
-40
2.437
f (GHz)
-80
2.0
-100
f (GHz)
Self-Interference Cancellation (dB)
Self-Interference Cancellation (dB)
VGain
Incoming
Desired
Signal
Patch
Antenna
Self-Interference Cancellation (dB)
✴FD Low Noise Amplifier!
✴Phase Shifter!
✴Frequency Tuning!
✴Bias Voltage
Unwanted
Self-Interference
Signal
2.460
90
0
-40
= arg max S21(VGain )
-80
180
-180
2.415
Optimal Isolation Tuning
!
2.437
-60
-120
2.415
180
2.495
✴Measured with an Agilent
high frequency Network
Analyzer!
✴Measured in a low-reflective
“Anechoic Chamber”!
✴Transmission coefficients
S21 are used to measure
self-interference cancellation!
⇤
VGain
Circuitry tunes isolation to!
desired frequency→
-80
-40
f (GHz)
f (GHz)
✴Self-interference cancellation is critical!
✴Provide as much cancellation as possible!
✴Passive Cancellation with patch antenna!
✴Antenna affected by multipath reflections!
✴Active Cancellation with circuitry!
✴Circuitry also provides frequency tuning
-60
-100
2.415
-100
2.345
Problem Statement
←Dynamic channel realizations
Channel Phase (degrees)
Self-Interference Cancellation (dB)
Tx
-40
Self-Interference Cancellation (dB)
✴High Isolation!
✴Wide Bandwidth!
✴Highly Dynamic
Weak Desired!
Signal
Rx
Tx
✴Patch Antenna!
✴Four-layers!
✴Dual-polarized!
Self-Interference Cancellation (dB)
✴Full-duplex communication enables simultaneous
transmission and reception at User 1!
Strong !
Self-Interference
Performance Gains
Experimental Setup
Bandwidth (MHz)
What is Full-Duplex?
2.460
✴The isolation provided by the patch antenna is highly dynamic!!
✴Active circuitry can vastly improve the isolation performance!
✴Increase isolation!
✴Increase bandwidth!
✴Tune maximal isolation to desired frequency
Acknowledgements
✴This work is funded by a NSF grant and by Renesas through a research contract. We
also thank Peiyu Chen from the Babakhani Lab for the helpful discussions.