New Opportunities in Wireless CommunicationsAli M NiknejadRobert W Brodersen

Understanding and Increasing Mesh CapacityMSR Mesh Networking Summit

Berkeley Wireless Research Center

Presentation Outline

60 GHz CMOS Radio ResearchCognitive Radio at BWRCOverview of COGUR Project

60 GHz CMOS RadiosChinh Doan, Sohrab Emami, David SobelMounir Bohsali, Sayf Alalusi

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

Applications of 60 GHz WLAN

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

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.

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

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).

VGS = 0.65 VVDS = 1.2 VIDS = 30 mAW/L = 100x1u/0.13u130-nm CMOS Maximum Gain

Microstrip shields EM fields from substrateCPW can realize higher Q inductors needed for tuning out device capacitanceUse CPWCo-planar (CPW) and Microstrip T-Lines

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

Modeling of 60-GHz CMOS Mixer Conversion-loss is better than 2 dB for PLO=0 dBmIF=2GHz6 GHz of bandwidth

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

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)

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

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

Cognitive* RadiosDanijela Cabric

* Adapting behavior based on external factors

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

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

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

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

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.

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

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

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

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

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

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

Testbed for Wireless ExperimentationBWRC infrastructure:BEE Processing Units (4)2.4 GHz RF Front-ends (32)Scalable multiple antenna transmission system

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

COGUR Cognizant Universal RadioAxel Berny Gang LiuZhiming Deng Nuntachai Poobuapheun

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

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

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

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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