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International Symposium on Low Power Electronics and Design
A case for leveraging 802.11p for direct phonetophone
communications
1Pilsoon Choi, 1Jason Gao, 2Nadesh Ramanathan, 2Mengda Mao,
2Shipeng Xu, 2Chirn-Chye Boon,
2Suhaib Fahmy, and 1Li-Shiuan Peh
1Massachusetts Institute of Technology2Nanyang Technological
University
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Introduction Device-to-Device (D2D) communications
Vehicular-to-Vehicular (V2V) communications Low Energy Electronic
Systems (LEES) process
System prototyping Application S/W Digital logic RF circuit
System evaluation Summary
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Outline
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Base-station or Access-point based communications E.g. WiFi
Direct, LTE Direct, Not suitable for highly mobile networks with
rapidly
changing topologies Whos the group owner?
Also Short range Slow response time
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Current D2D Technologies
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V2V is basically for car safety and congestion control But, in
essence, a form of D2D With longer range and fast response time
Dedicated Short Range Communications (DSRC) IEEE 802.11p
standard (vs. 802.11a)
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Burgeoning V2V Communications
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5
DSRC on a smartphone?
Bottleneck of
small form-factor &
power consumption
H/W breakdown for communication systems
From iFixit iPhone 4 teardown
Better power density &
efficiency than CMOS
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Integrated CMOS + III-V on a single die
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LEES Process
802.11p
MAC/BB
DAC / ADC
5GHz RF
TRX
28.8dBm PA
Android App.
CMOS
III-V
S/W
Schematic cross-section view of the monolithically
integrated GaN HEMT with Si CMOS
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Making use of an existing WiFi solution on a smartphone,
combined with 802.11p front-end circuit
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System Prototyping
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Sonar packet transmission & reception
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Android Application - Sonar
Sonar app.
https://www.youtube.com/watch?v=6oQ0fg8uSrg&feature=youtu.behttps://www.youtube.com/watch?v=6oQ0fg8uSrg&feature=youtu.be
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FPGA Sub-system
802.11p OFDM output @ DAC (Freq. domain vs. Time domain)
1) 802.11p Airblue baseband (originally designed for
802.11a)
2) Android phone-to-PHY interface for packet Tx/Rx
3) RF interface for Tx power control
w/o filter w/ filter
vs.
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RF Circuit in CMOS
5.9GHz wireless transmitter Using 0.18um CMOS technology
Adopting a digital calibration algorithm for balancing RF
quadrature signals SSB rejection: -52dBc EVM: -36.5dB
Fabricated die microphotograph (1.4mm2)
BBA
LO for Tx
Receiver for calibration
LO for Rx
Up-mixer
Driver amplifier
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RF Circuit in GaN
GaN PA @ 5.9GHz
(1.28 mm2)
CPA,Decouple CLNA,Decouple
Class-AB
Class-C
TXSW
RXSWLNA
ANT
PA
IN
LN
AO
UT
5.825 5.875 5.925Freq. (GHz)
0
Sp
ect
rum
(d
B)
-20
-40
1
Q 0
-1
-1 0 1I
27.8dBm
EVM=25.3dB
10%
20%
30%
20dBm
(100mW)
30dBm
(1W)
Drain efficiency
Pout
Advantage on system level power saving:
> 22% efficiency over one decade power change
GaN Front-end @ 5.9GHz
(2 mm2)
evolving
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Prototyping System Integration
Android application (on a smart phone) => USB-Ethernet
interface =>
Baseband (in FPGA) => DAC => CMOS RF Tx => GaN power
amplifier
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System Evaluation (1/2)
Deployment area in Cambridge
Average power
consumption of
RoadRunner V2V
token exchanges
(w/ & w/o adaptive
power control)
RoadRunner In-vehicle Android app for
road congestion control Assigning tokens to vehicles
for specific road segment Permit tokens distributed to
vehicles over LTE or DSRC
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System Evaluation (2/2)
Deployment route in Cambridge
Average power
consumption of
SignalGuru UDP
broadcasts
(w/ & w/o adaptive
power control)
SignalGuru Vehicular traffic light detection
iPhone app (via the camera) Data sharing among multiple
phones to collaboratively learn traffic signal transition
patterns
UDP packets over WiFi or DSRC
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Summary
Feasibility of a 802.11p front-end at the stringent power and
area budget of a smart phone
LEES process & circuit Novel GaN+CMOS monolithic process GaN
HEMT for high-power 802.11p power amplifier CMOS MOSFET for 5GHz
transmitter
Prototype system integration & evaluation
Android application on a phone + digital baseband on an FPGA +
RF circuits on Si/GaN
System level power saving by adaptive power control
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