4Why is operation at 60 GHz interesting? 57 dBm40 dBmLots of Bandwidth!!!7 GHz of unlicensed bandwidth in the U.S. and JapanSame amount of bandwidth is available in the 3-10 UWB band, but the allowed transmit power level is 104 times higher !
660 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
760 GHz CMOS Wireless LAN System 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.
8Advantages of Antenna Array Antenna 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
9Multi-Stage Conversion 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).
10130-nm CMOS Maximum Gain VGS = 0.65 V VDS = 1.2 V IDS = 30 mA W/L = 100x1u/0.13u
11Co-planar (CPW) and Microstrip T-Lines Microstrip shields EM fields from substrateCPW can realize higher Q inductors needed for tuning out device capacitanceUse CPW
12First Ever 60 GHz CMOS Amplifier! 11.5-dB Gain@ 60 GHzGain > 11 dB ; Return loss > 15 dBDesign methodology is incredibly accurate!Reference: “Millimeter-Wave CMOS Design”, to appear in JSSCChinh H. Doan, Sohrab Emami, Ali M. Niknejad, and Robert W. Brodersen
13Modeling of 60-GHz CMOS Mixer Conversion-loss is better than 2 dB for PLO=0 dBmIF=2GHz6 GHz of bandwidth
14System Design Considerations 60 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 noise1MHz offset typical (ISSCC 2004)Modulation must be insensitive to phase noisePALOTXFrom IFTXVinVoutLNALORXTo IFRXSLO(f)ffc
15Modulation Scheme Comparison OFDM-QPSKHigh-order modulation (16-QAM)Single-carrier QPSKConstant Envelope (MSK)SNRreq (BER=10-3)7dB12dBPARTX~10dB~5.5dB~3dB0dBPA linearity req’tHighModerateLowSensitivity to Phase NoiseHigh (ICI)High (Symbol Jitter)Complexity of Multipath Mitigation TechniquesModerate (FFT)(Equalizer)Beamforming to combat multipath.Simple modulation (MSK) for feasible CMOS RF circuits.
16The Hybrid-Analog Architecture Proposed Baseband ArchitectureClkClock RecBB’ITiming, DFE Carrier Phase,EstimatorsBBIRFVGAIFejqComplexDFEBB’QBBQLOIFAnalogDigitalCondition 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 synchronization
1760 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
18* Adapting behavior based on external factors Cognitive* RadiosDanijela Cabric* Adapting behavior based on external factors
19Window of OpportunityExisting spectrum policy forces spectrum to behave like a fragmented diskBandwidth 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 utilizedTime scale of the spectrum occupancy varies from msecs to hoursFrequency (Hz)Time (min)
20Spectrum Sharing Existing techniques for spectrum sharing: Unlicensed bands (WiFi 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
21What is a Cognitive Radio? Cognitive radio requirementsco-exists with legacy wireless systemsuses their spectrum resourcesdoes not interfere with themCognitive radio propertiesRF technology that "listens" to huge swaths of spectrumKnowledge 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
22Application Scenarios Third party access in licensed networksLicensed networkCellular, PCS bandImproved spectrum efficiencyImproved capacityTV bands ( MHz)Non-voluntary third party accessLicensee sets a protection thresholdSecondary marketsUnlicensed networkPublic safety bandVoluntary agreements between licensees and third partyLimited QoSISM, UNII, Ad-hocAutomatic frequency coordinationInteroperabilityCo-existence
23FCC Announcement 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.”
24Channel and Interference Model Measurement of the spectrum usage in frequency, time, and spaceWideband channelCommon with UWBSpatial channel modelClustering approachInterference correlationDerive statistical traffic model of primary usersPower levelBandwidthTime of usageInactive periods302106024090270120300150330180Angular domainFrequency (Hz)Time (min)
25Cognitive Radio Functions Sensing RadioWideband Antenna, PA and LNAHigh speed A/D & D/A, moderate resolutionSimultaneous Tx & RxScalable for MIMOPhysical LayerOFDM transmissionSpectrum monitoringDynamic frequency selection, modulation, power controlAnalog impairments compensationMAC LayerOptimize transmission parametersAdapt rates through feedbackNegotiate or opportunistically use resourcesIFFTFFTADAPTIVELOADINGINTERFERENCEMEAS/CANCELMAE/POWER CTRLCHANNELSEL/ESTTIME, FREQ,SPACE SELLEARNENVIRONMENTQoS vs.RATEFEEDBACKTO CRsPAD/ALNAA/DRF/Analog Front-endDigital BasebandMAC Layer
26Sensing Radio A/D converter: High resolution Speed depends on the applicationLow power ~ 100mWsRF front-end:Wideband antenna and filtersLinear in large dynamic rangeGood sensitivityInterference temperature:Protection threshold for licenseesFCC: MHz band is empty if:Need to determine length of measurementsSpectrum usage in (0, 2.5) GHz0.511.522.5x 109-90-85-80-75-70-65-60-55-50-45-40Frequency (Hz)Signal Strength (dB)TV bandsCellPCSMeasurement taken at BWRC
27Cognitive Radio Baseband Processing PHYMACIFFTFFTADAPTIVELOADINGINTERFERENCEMEAS/CANCELMAE/POWER CTRLCHANNELSEL/ESTTIME, FREQ,SPACE SELLEARNENVIRONMENTQoS vs.RATEFEEDBACKTO CRsMCMA processingOFDM SystemAgile, efficient FFTSpatial processing:Exploits clustered modelScalable with # of antennasPHY – adaptive, parametrizableMAC – intelligent, optimization algo’sPHY+MAC can be implemented on:Software Defined RadiosReconfigurable Radios
28From 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, rateFixed per packetAdaptive bit loadingPacket length, preambleFixedMore flexiblePower levelAdaptive controlInterference mitigationSpatial processingSome (802.11n)Lots…QoS, rate, latencyLimitedSophisticated
29Test Scenario at 2.4 GHz, Indoor Unlicensed band 80 MHz bandwidthOFDM system (like a/g)Multiple antennas for interference avoidance and range extensionCentralized approach through APCR1Microwave ovenAPb/gBluetoothFrequency SelectionDynamicCR2CR3Cordless phone
30Testbed for Wireless Experimentation BWRC infrastructure:BEE Processing Units (4)2.4 GHz RF Front-ends (32)Scalable multiple antenna transmission system
31Research Agenda Derive system specification from measurements Analog front-end specification and designDevelop and implement algorithms for:Sensing environmentDynamic frequency selection and adaptive modulationTransmit power control and spatial processingInterference cancellation in spatial domainSpectrum rental strategiesTest algorithms in realistic wireless scenariosDesign an architecture for a Cognitive Radio
32COGUR Cognizant Universal Radio Axel BernyGang LiuZhiming DengNuntachai Poobuapheun
33COGUR Design Goals An 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
34Dynamic Operation: Near-Far Problem High 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. Don’t be pessimistic!A dynamic transceiver can schedule gain/power of the front-end for optimal performance
35COGUR Transceiver Broadband dynamic LNA/mixer Wide tuning agile frequency synthesizerDual-mode broadband PA with integrated power combining and controlLinear VGA or attenuatorHigh-speed background calibrated ADC/DAC
36Acknowledgements BWRC Member Companies DARPA TEAM Project STMicroelectronics and IBM for wafer processing and design supportAgilent Technologies (measurement support)National SemiconductorQualcommAnalog Devices