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New Opportunities in Wireless CommunicationsAli M NiknejadRobert
W Brodersen
Understanding and Increasing Mesh CapacityMSR Mesh Networking
Summit
Berkeley Wireless Research Center
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Presentation Outline
60 GHz CMOS Radio ResearchCognitive Radio at BWRCOverview of
COGUR Project
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60 GHz CMOS RadiosChinh Doan, Sohrab Emami, David SobelMounir
Bohsali, Sayf Alalusi
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Why is operation at 60 GHz interesting?Lots of Bandwidth!!!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 !57 dBm40 dBm
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Applications of 60 GHz WLAN
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60 GHz Challenges
High path loss at 60 GHz (relative to 5 GHz)Antenna array
results in better performance at higher frequency because more
antennas can be integrated in fixed areaSilicon substrate is lossy
high Q passive elements difficult to realize?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
frequenciesCMOS building blocks at 60 GHzDesign methodology for
CMOS mm-waveLow power baseband architecture for Gbps
communication
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60 GHz CMOS Wireless LAN System 10-100 mA 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.
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Advantages of Antenna ArrayAntenna array is dynamic and can
point in any direction to maximized the received signalEnhanced
receiver/transmitter antenna gain (reduced PA power, LNA gain)
Improved diversityReduced multi-path fadingNull interfering
signalsCapacity enhancement through spatial codingSpatial power
combining meansLess power per PA (~10 mW)Simpler PA
architectureAutomatic power control
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Multi-Stage Conversion9 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).
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VGS = 0.65 VVDS = 1.2 VIDS = 30 mAW/L = 100x1u/0.13u130-nm CMOS
Maximum Gain
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Microstrip shields EM fields from substrateCPW can realize
higher Q inductors needed for tuning out device capacitanceUse
CPWCo-planar (CPW) and Microstrip T-Lines
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First Ever 60 GHz CMOS Amplifier!Gain > 11 dB ; Return loss
> 15 dB Design methodology is incredibly accurate!Reference:
Millimeter-Wave CMOS Design, to appear in JSSCChinh H. Doan, Sohrab
Emami, Ali M. Niknejad, and Robert W. Brodersen
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Modeling of 60-GHz CMOS Mixer Conversion-loss is better than 2
dB for PLO=0 dBmIF=2GHz6 GHz of bandwidth
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System Design Considerations60 GHz CMOS PA will have limited
P1dB pointTx power constraint while targeting 1GbpsMust use low PAR
signal for efficient PA utilization60 GHz CMOS VCOs have poor phase
noise-85dBc/Hz @ 1MHz offset typical (ISSCC 2004)Modulation must be
insensitive to phase noise
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Modulation Scheme ComparisonBeamforming to combat
multipath.Simple modulation (MSK) for feasible CMOS RF
circuits.
ModulationOFDM-QPSKHigh-order modulation (16-QAM)Single-carrier
QPSKConstant Envelope (MSK)SNRreq
(BER=10-3)7dB12dB7dB7dBPARTX~10dB~5.5dB~3dB0dBPA linearity
reqtHighHighModerateLowSensitivity to Phase NoiseHigh (ICI)High
(Symbol Jitter)ModerateLowComplexity of Multipath Mitigation
TechniquesModerate
(FFT)High(Equalizer)High(Equalizer)High(Equalizer)
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The Hybrid-Analog ArchitectureIFLOIFBBIBBQBBIBBQClk
Timing, DFE Carrier Phase,Estimators
Clock RecComplexDFECondition the signal prior to
quantizationPhase and timing recovery, equalization in analog
domainGreatly simplifies requirements on the ADC/VGA
circuitrySynchronization estimators in the digital domainCan still
use robust digital algorithms for synchronizationejqProposed
Baseband Architecture
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60 GHz ConclusionsAt 130 nm, mainstream digital CMOS is able to
exploit the unlicensed 60-GHz bandAccurate device modeling is
possible by extending RF frequency methodologiesA
transmission-line-based circuit strategy provides predictable and
repeatable low-loss impedance matching and filteringAnalog
equalization with digital domain estimation and calibration will
enable low-power Gb/s baseband
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Cognitive* RadiosDanijela Cabric
* Adapting behavior based on external factors
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Window of OpportunityTime (min)Frequency (Hz)Existing spectrum
policy forces spectrum to behave like a fragmented disk Bandwidth
is expensive and good frequencies are takenUnlicensed bands biggest
innovations in spectrum efficiencyRecent measurements by the FCC in
the US show 70% of the allocated spectrum is not utilized Time
scale of the spectrum occupancy varies from msecs to hours
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Spectrum SharingExisting techniques for spectrum
sharing:Unlicensed bands (WiFi 802.11 a/b/g)Underlay licensed bands
(UWB)Opportunistic sharingRecycling (exploit the SINR margin of
legacy systems) Spatial Multiplexing and BeamformingDrawbacks of
existing techniques:No knowledge or sense of spectrum
availabilityLimited adaptability to spectral environmentFixed
parameters: BW, Fc, packet lengths, synchronization, coding,
protocols, New radio design philosophy: all parameters are
adaptiveCognitive Radio Technology
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What is a Cognitive Radio?Cognitive radio requirements co-exists
with legacy wireless systems uses their spectrum resources does not
interfere with themCognitive radio propertiesRF technology that
"listens" to huge swaths of spectrum Knowledge of primary users
spectrum usage as a function of location and timeRules of sharing
the available resources (time, frequency, space)Embedded
intelligence to determine optimal transmission (bandwidth, latency,
QoS) based on primary users behavior
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Application ScenariosLicensed network Secondary marketsThird
party access in licensed networksUnlicensed networkCellular, PCS
bandImproved spectrum efficiencyImproved capacityPublic safety
bandVoluntary agreements between licensees and third partyLimited
QoSTV bands (400-800 MHz)Non-voluntary third party access Licensee
sets a protection thresholdAutomatic frequency coordination
InteroperabilityCo-existenceISM, UNII, Ad-hoc
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FCC AnnouncementReleased 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.
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Channel and Interference ModelMeasurement of the spectrum usage
in frequency, time, and space Wideband channelCommon with
UWBSpatial channel modelClustering approachInterference
correlationDerive statistical traffic model of primary usersPower
levelBandwidthTime of usageInactive periods
Time (min)Frequency (Hz)Angular domain
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Cognitive Radio FunctionsLNAA/DSensing RadioWideband Antenna, PA
and LNA High speed A/D & D/A, moderate resolutionSimultaneous
Tx & RxScalable for MIMOPhysical LayerOFDM transmissionSpectrum
monitoring Dynamic frequency selection, modulation, power
controlAnalog impairments compensationMAC Layer Optimize
transmission parametersAdapt rates through feedbackNegotiate or
opportunistically use resources RF/Analog Front-endDigital
BasebandMAC Layer
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Sensing RadioA/D converter:High resolution Speed depends on the
applicationLow power ~ 100mWsRF front-end:Wideband antenna and
filtersLinear in large dynamic rangeGood sensitivity Interference
temperature: Protection threshold for licensees FCC: 2400-2483.5
MHz band is empty if:
Need to determine length of measurementsSpectrum usage in (0,
2.5) GHzMeasurement taken at BWRC
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Cognitive Radio Baseband Processing
MCMA processingOFDM SystemAgile, efficient FFTSpatial
processing:Exploits clustered modelScalable with # of
antennasPHYMACPHY adaptive, parametrizableMAC intelligent,
optimization algosPHY+MAC can be implemented on:Software Defined
RadiosReconfigurable Radios
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From WiFi to Cognitive Radios
FunctionalityWiFiCognitive RadioMultiple channels for agility27
fixed 20MHz channelsVariable # and BWSensing
collisions/interferenceWiFi interference onlyAny
interferenceSimultaneous spectrum sensing and transmissionNot
possibleNecessaryModulation scheme, rate Fixed per packetAdaptive
bit loadingPacket length, preamble FixedMore flexiblePower
levelFixed per packetAdaptive controlInterference mitigationWiFi
interference onlyAny interferenceSpatial processingSome
(802.11n)LotsQoS, rate, latencyLimited Sophisticated
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Test Scenario at 2.4 GHz, IndoorBluetooth 802.11 b/gMicrowave
ovenCordless phone APDynamicFrequency SelectionUnlicensed band 80
MHz bandwidthOFDM system (like 802.11a/g)Multiple antennas for
interference avoidance and range extensionCentralized approach
through AP
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Testbed for Wireless ExperimentationBWRC infrastructure:BEE
Processing Units (4)2.4 GHz RF Front-ends (32)Scalable multiple
antenna transmission system
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Research AgendaDerive system specification from
measurementsAnalog front-end specification and designDevelop and
implement algorithms for:Sensing environmentDynamic frequency
selection and adaptive modulation Transmit power control and
spatial processingInterference cancellation in spatial
domainSpectrum rental strategies Test algorithms in realistic
wireless scenariosDesign an architecture for a Cognitive Radio
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COGUR Cognizant Universal RadioAxel Berny Gang LiuZhiming Deng
Nuntachai Poobuapheun
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COGUR Design GoalsAn agile dynamic radio cognizant of its
environment Universal operation ensures multi-standard and future
standard compatibilityCognitive behavior allows spectrum re-use,
underlay, and overlayDynamic 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
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Dynamic Operation: Near-Far ProblemHigh power consumption due to
simultaneous requirement of high linearity in RF front-end and low
noise operationThe conflicting requirements occur since the
linearity of the RF front-end is exercised by a strong interferer
while trying to detect a weak signalThe worst case scenario is a
rare event. Dont be pessimistic!A dynamic transceiver can schedule
gain/power of the front-end for optimal performance
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COGUR Transceiver
Broadband dynamic LNA/mixerWide tuning agile frequency
synthesizerDual-mode broadband PA with integrated power combining
and control Linear VGA or attenuatorHigh-speed background
calibrated ADC/DAC
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Acknowledgements
BWRC Member CompaniesDARPA TEAM ProjectSTMicroelectronics and
IBM for wafer processing and design supportAgilent Technologies
(measurement support)National Semiconductor Qualcomm Analog
Devices
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