New Opportunities in
Wireless Communications
Ali M Niknejad
Robert W Brodersen
Understanding and Increasing Mesh Capacity
MSR Mesh Networking Summit
Berkeley Wireless Research Center
Presentation Outline
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60 GHz CMOS Radio Research
Cognitive Radio at BWRC
Overview of COGUR Project
60 GHz CMOS Radios
Chinh Doan, Sohrab Emami, David Sobel
Mounir Bohsali, Sayf Alalusi
Why is operation at 60 GHz interesting?
57 dBm
40 dBm
Lots of Bandwidth!!!
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7 GHz of unlicensed bandwidth in the U.S. and Japan
Same amount of bandwidth is available in the 3-10 UWB band, but the
allowed transmit power level is 104 times higher !
Applications of 60 GHz WLAN
60 GHz Challenges
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High path loss at 60 GHz (relative to 5 GHz)
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Silicon substrate is lossy – high Q passive elements difficult
to realize?
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Antenna array results in better performance at higher frequency
because more antennas can be integrated in fixed area
No, the Q factor is even better at high frequencies with T-lines, MIM
caps, and loop inductors (Q > 20)
CMOS device performance at mm-wave frequencies
CMOS building blocks at 60 GHz
Design methodology for CMOS mm-wave
Low power baseband architecture for Gbps communication
60 GHz CMOS Wireless LAN System
10-100 m
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A fully-integrated low-cost Gb/s data communication using 60
GHz band.
Employ emerging standard CMOS technology for the radio
building blocks. Exploit electronically steer-able antenna
array for improved gain and resilience to multi-path.
Advantages of Antenna Array
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Antenna array is dynamic and
can point in any direction to
maximized the received signal
Enhanced receiver/transmitter
antenna gain (reduced PA
power, LNA gain)
Improved diversity
Reduced multi-path fading
Null interfering signals
Capacity enhancement through
spatial coding
Spatial power combining means
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Less power per PA (~10 mW)
Simpler PA architecture
Automatic power control
Multi-Stage Conversion
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9 GHz VCO is locked to reference. Power consumption of
frequency dividers is greatly reduced.
A frequency tripler generates a 27 GHz LO.
Gain comes from RF at 60 GHz, at IF of 33 GHz, and
through a passband VGA at 6 GHz (easier than a
broadband DC solution).
130-nm CMOS Maximum Gain
VGS = 0.65 V
VDS = 1.2 V
IDS = 30 mA
W/L = 100x1u/0.13u
Co-planar (CPW) and Microstrip T-Lines
CPW
Microstrip
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Microstrip shields EM fields from
substrate
CPW can realize higher Q inductors
needed for tuning out device
capacitance
Use CPW
First Ever 60 GHz CMOS Amplifier!
11.5-dB Gain
@ 60 GHz
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Gain > 11 dB ; Return loss > 15 dB
Design methodology is incredibly accurate!
Reference: “Millimeter-Wave CMOS Design”, to appear in JSSC
Chinh H. Doan, Sohrab Emami, Ali M. Niknejad, and Robert W. Brodersen
Modeling of 60-GHz CMOS Mixer
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Conversion-loss is better than 2 dB
for PLO=0 dBm
IF=2GHz
6 GHz of bandwidth
System Design Considerations
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60 GHz CMOS PA will have limited P1dB point
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Tx power constraint while targeting 1Gbps
Must use low PAR signal for efficient PA utilization
60 GHz CMOS VCOs have poor phase noise
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-85dBc/Hz @ 1MHz offset typical (ISSCC 2004)
Modulation must be insensitive to phase noise
From IFTX
LOTX
PA
LNA
To IFRX
SLO(f)
Vout
LORX
Vin
fc
f
Modulation Scheme Comparison
OFDMQPSK
High-order
modulation (16QAM)
Singlecarrier
QPSK
Constant
Envelope
(MSK)
7dB
12dB
7dB
7dB
~10dB
~5.5dB
~3dB
0dB
PA linearity req’t
High
High
Moderate
Low
Sensitivity to Phase
Noise
High
(ICI)
High
(Symbol Jitter)
Moderate
Low
Moderate
(FFT)
High
(Equalizer)
High
(Equalizer)
High
(Equalizer)
Modulation
SNRreq (BER=10-3)
PARTX
Complexity of Multipath
Mitigation Techniques
Beamforming to combat multipath.
Simple modulation (MSK) for feasible CMOS RF circuits.
The Hybrid-Analog Architecture
Proposed Baseband
Architecture
RF
IF
Clock Rec
BB’I
BBI
VGA
BBQ
Clk
ejq
Complex
DFE
BB’Q
Timing, DFE
Carrier Phase,
Estimators
LOIF
Analog
Digital
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Condition the signal prior to quantization
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Phase and timing recovery, equalization in analog domain
Greatly simplifies requirements on the ADC/VGA circuitry
Synchronization estimators in the digital domain
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Can still use robust digital algorithms for synchronization
60 GHz Conclusions
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At 130 nm, mainstream digital CMOS is able to exploit the
unlicensed 60-GHz band
Accurate device modeling is possible by extending RF
frequency methodologies
A transmission-line-based circuit strategy provides
predictable and repeatable low-loss impedance matching
and filtering
Analog equalization with digital domain estimation and
calibration will enable low-power Gb/s baseband
Cognitive* Radios
Danijela Cabric
* Adapting behavior based on external factors
Window of Opportunity
 Recent measurements by the
FCC in the US show 70% of the
allocated spectrum is not utilized
 Bandwidth is expensive and good
frequencies are taken
 Time scale of the spectrum
occupancy varies from msecs to
hours
 Unlicensed bands – biggest
innovations in spectrum efficiency
Frequency (Hz)
 Existing spectrum policy forces
spectrum to behave like a fragmented
disk
Time (min)
Spectrum Sharing
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Existing techniques for spectrum sharing:
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Drawbacks of existing techniques:
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Unlicensed bands (WiFi 802.11 a/b/g)
Underlay licensed bands (UWB)
Opportunistic sharing
Recycling (exploit the SINR margin of legacy systems)
Spatial Multiplexing and Beamforming
No knowledge or sense of spectrum availability
Limited adaptability to spectral environment
Fixed parameters: BW, Fc, packet lengths, synchronization,
coding, protocols, …
New radio design philosophy: all parameters are adaptive
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Cognitive Radio Technology
What is a Cognitive Radio?
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Cognitive radio requirements
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co-exists with legacy wireless systems
uses their spectrum resources
does not interfere with them
Cognitive radio properties
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RF technology that "listens" to huge swaths of spectrum
Knowledge of primary users’ spectrum usage as a function of
location and time
Rules of sharing the available resources (time, frequency, space)
Embedded intelligence to determine optimal transmission
(bandwidth, latency, QoS) based on primary users’ behavior
Application Scenarios
Licensed network
Third party access in
licensed networks
Cellular, PCS band
TV bands (400-800 MHz)
Improved spectrum
efficiency
Non-voluntary third party
access
Improved capacity
Licensee sets a protection
threshold
Secondary markets
Unlicensed network
Public safety band
ISM, UNII, Ad-hoc
Voluntary agreements
between licensees
and third party
Automatic frequency
coordination
Limited QoS
Co-existence
Interoperability
FCC Announcement
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Released on Dec 30th 2003, (ET Docket No. 03-108)
Facilitating Opportunities for Flexible, Efficient, and Reliable Spectrum
Use Employing Cognitive Radio Technologies
“We recognize the importance of new cognitive radio technologies,
which are likely to become more prevalent over the next few years and
which hold tremendous promise in helping to facilitate more effective
and efficient access to spectrum”
“We seek to ensure that our rules and policies do not inadvertently
hinder development and deployment of such technologies, but instead
enable a full realization of their potential benefits.”
Channel and Interference Model
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Measurement of the spectrum
usage in frequency, time, and
space
Wideband channel
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30
0
210
330
240
Clustering approach
Interference correlation
Power level
Bandwidth
Time of usage
Inactive periods
60
180
Common with UWB
Derive statistical traffic model of
primary users
90
150
Spatial channel model
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120
270
300
Angular domain
Frequency (Hz)
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Time (min)
Cognitive Radio Functions
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Sensing Radio
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 Physical Layer
 MAC Layer
Wideband Antenna, PA
and LNA
High speed A/D & D/A,
moderate resolution
Simultaneous Tx & Rx
Scalable for MIMO
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OFDM transmission
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Spectrum monitoring
Optimize transmission
parameters
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Dynamic frequency
selection, modulation,
power control
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Adapt rates through
feedback
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Negotiate or
opportunistically use
resources
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Analog impairments
compensation
PA
D/A
IFFT
LNA
A/D
FFT
RF/Analog Front-end
MAE/
POWER CTRL
CHANNEL
SEL/EST
ADAPTIVE
LOADING
INTERFERENCE
MEAS/CANCEL
Digital Baseband
TIME, FREQ,
SPACE SEL
QoS vs.
RATE
LEARN
ENVIRONMENT
FEEDBACK
TO CRs
MAC Layer
Sensing Radio
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A/D converter:
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High resolution
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Speed depends on the application
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Low power ~ 100mWs
RF front-end:
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Wideband antenna and filters
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Linear in large dynamic range
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Good sensitivity
Interference temperature:
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Protection threshold for licensees
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FCC: 2400-2483.5 MHz band is
empty if:
Spectrum usage in (0, 2.5) GHz
-40
Cell
-45
Signal Strength (dB)
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-50
-55
PCS
TV bands
-60
-65
-70
-75
-80
-85
 ( N  I  N )dw  30dB
B 1.25 MHz
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0
Need to determine length of
measurements
-90
0
0.5
1
1.5
Frequency (Hz)
2
2.5
9
x 10
Measurement taken at BWRC
Cognitive Radio Baseband Processing
PHY
IFFT
FFT
ADAPTIVE
LOADING
MAE/
POWER CTRL
CHANNEL
SEL/EST
INTERFERENCE
MEAS/CANCEL
MAC
TIME, FREQ,
SPACE SEL
LEARN
ENVIRONMENT
QoS vs.
RATE
FEEDBACK
TO CRs
 MCMA processing
PHY – adaptive, parametrizable
•
MAC – intelligent, optimization algo’s
OFDM System
 Agile, efficient FFT
•
Spatial processing:
 Exploits clustered model
 Scalable with # of antennas
PHY+MAC can be implemented on:
•Software Defined Radios
•Reconfigurable Radios
From WiFi to Cognitive Radios
Functionality
WiFi
Cognitive Radio
Multiple channels for agility
27 fixed 20MHz
channels
Variable # and BW
Sensing collisions/interference
WiFi interference only
Any interference
Simultaneous spectrum sensing
and transmission
Not possible
Necessary
Modulation scheme, rate
Fixed per packet
Adaptive bit loading
Packet length, preamble
Fixed
More flexible
Power level
Fixed per packet
Adaptive control
Interference mitigation
WiFi interference only
Any interference
Spatial processing
Some (802.11n)
Lots…
QoS, rate, latency
Limited
Sophisticated
Test Scenario at 2.4 GHz, Indoor
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CR1
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Unlicensed band 80 MHz bandwidth
OFDM system (like 802.11a/g)
Multiple antennas for interference
avoidance and range extension
Centralized approach through AP
Microwave oven
AP
802.11 b/g
Bluetooth
CR2
CR3
Cordless phone
Testbed for Wireless Experimentation
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BWRC infrastructure:
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BEE Processing Units (4)
2.4 GHz RF Front-ends (32)
Scalable multiple antenna
transmission system
Research Agenda
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Derive system specification from measurements
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Analog front-end specification and design
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Develop and implement algorithms for:
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Sensing environment
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Dynamic frequency selection and adaptive modulation
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Transmit power control and spatial processing
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Interference cancellation in spatial domain
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Spectrum rental strategies
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Test algorithms in realistic wireless scenarios
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Design an architecture for a Cognitive Radio
COGUR
Cognizant Universal Radio
Axel Berny
Gang Liu
Zhiming Deng
Nuntachai Poobuapheun
COGUR Design Goals
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An agile dynamic radio cognizant of its environment
Universal operation ensures multi-standard and future
standard compatibility
Cognitive behavior allows spectrum re-use, underlay, and
overlay
Dynamic operation allows low power (only need linearity
and low-phase noise VCO in a near-far situation)
Multi-mode PA can work in “linear” mode for OFDM and
high PAR modulation schemes. Efficiency is maintained
while varying output power
Dynamic Operation: Near-Far Problem
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High power consumption due
to simultaneous requirement
of high linearity in RF frontend and low noise operation
The conflicting requirements
occur since the linearity of
the RF front-end is exercised
by a strong interferer while
trying to detect a weak signal
 The worst case scenario is a rare event. Don’t be
pessimistic!
 A dynamic transceiver can schedule gain/power of the
front-end for optimal performance
COGUR Transceiver
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Broadband dynamic
LNA/mixer
Wide tuning agile
frequency synthesizer
Dual-mode broadband
PA with integrated
power combining and
control
Linear VGA or
attenuator
High-speed
background calibrated
ADC/DAC
Acknowledgements
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BWRC Member Companies
DARPA TEAM Project
STMicroelectronics and IBM for wafer processing and
design support
Agilent Technologies (measurement support)
National Semiconductor
Qualcomm
Analog Devices