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New Opportunities in New Opportunities in Wireless CommunicationsWireless Communications
Ali M NiknejadAli M NiknejadRobert W BrodersenRobert W Brodersen
Understanding and Increasing Mesh CapacityUnderstanding and Increasing Mesh Capacity
MSR Mesh Networking SummitMSR Mesh Networking Summit
Berkeley Wireless Research CenterBerkeley Wireless Research Center
PresentationPresentation Outline Outline
60 GHz CMOS Radio Research Cognitive Radio at BWRC Overview of COGUR Project
60 GHz CMOS Radios60 GHz CMOS Radios
Chinh Doan, Sohrab Emami, David SobelChinh Doan, Sohrab Emami, David Sobel
Mounir Bohsali, Sayf AlalusiMounir Bohsali, Sayf Alalusi
Why is operation at 60 GHz Why is operation at 60 GHz interesting?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 dBm
40 dBm
Applications of 60 GHz WLANApplications of 60 GHz WLAN
60 GHz Challenges60 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 area
Silicon 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 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 60 GHz CMOS Wireless LAN System System
10-100 m
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 ArrayAdvantages of Antenna Array
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
Less power per PA (~10 mW) Simpler PA architecture Automatic power control
Multi-Stage ConversionMulti-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).
VGS = 0.65 V
VDS = 1.2 V
IDS = 30 mA
W/L = 100x1u/0.13u
130-nm CMOS Maximum Gain130-nm CMOS Maximum Gain
Microstrip shields EM fields from substrate
CPW can realize higher Q inductors needed for tuning out device capacitance
Use CPW
CPW
Microstrip
Co-planar (CPW) and Microstrip T-Co-planar (CPW) and Microstrip T-LinesLines
First Ever 60 GHz CMOS First Ever 60 GHz CMOS Amplifier!Amplifier!
11.5-dB Gain@ 60 GHz
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 MixerModeling of 60-GHz CMOS Mixer
Conversion-loss is better than 2 dB for PLO=0 dBm
IF=2GHz 6 GHz of bandwidth
System Design ConsiderationsSystem Design Considerations
60 GHz CMOS PA will have limited P1dB point Tx power constraint while targeting 1Gbps Must use low PAR signal for efficient PA utilization
60 GHz CMOS VCOs have poor phase noise -85dBc/Hz @ 1MHz offset typical (ISSCC 2004) Modulation must be insensitive to phase noise
PA
LOTX
From IFTX
Vin
Vout
LNA
LORX
To IFRX
SLO(f)
ffc
ModulationOFDM-QPSK
High-order modulation (16-
QAM)
Single-carrier QPSK
Constant Envelope (MSK)
SNRreq (BER=10-3) 7dB 12dB 7dB 7dB
PARTX ~10dB ~5.5dB ~3dB 0dB
PA linearity req’t High High Moderate Low
Sensitivity to Phase Noise
High (ICI)
High (Symbol Jitter)
Moderate Low
Complexity of Multipath Mitigation Techniques
Moderate (FFT)
High
(Equalizer)
High
(Equalizer)
High
(Equalizer)
Modulation Scheme ComparisonModulation Scheme Comparison
Beamforming to combat multipath.Simple modulation (MSK) for feasible CMOS RF
circuits.
The Hybrid-Analog ArchitectureThe Hybrid-Analog Architecture
RFIF
LOIF
BBI
BBQ
BB’I
BB’Q
Clk
Timing, DFE Carrier Phase,
Estimators
VGA
Clock Rec
ComplexDFE
Analog
Digital
Condition the signal prior to quantization Phase and timing recovery, equalization in analog domain Greatly simplifies requirements on the ADC/VGA circuitry
Synchronization estimators in the digital domain Can still use robust digital algorithms for synchronization
ej
Proposed Baseband Architecture
60 GHz Conclusions60 GHz Conclusions 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* RadiosCognitive* Radios
Danijela CabricDanijela Cabric
* Adapting behavior based on external factors
Window of OpportunityWindow of Opportunity
Time (min)
Fre
quen
cy (
Hz)
Existing spectrum policy forces spectrum to behave like a fragmented
disk Bandwidth is expensive and good
frequencies are taken
Unlicensed bands – biggest innovations in spectrum efficiency
Recent 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 SharingSpectrum Sharing Existing techniques for spectrum sharing:
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
Drawbacks of existing techniques: 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
Cognitive Radio Technology
What is a Cognitive Radio?What is a Cognitive Radio?
Cognitive radio requirements co-exists with legacy wireless systems uses their spectrum resources does not interfere with them
Cognitive radio properties 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 ScenariosApplication Scenarios
Licensed network
Secondary markets
Third party access in licensed networks
Unlicensed network
Cellular, PCS band
Improved spectrum efficiency
Improved capacity
Public safety band
Voluntary agreements between licensees and third party
Limited QoS
TV bands (400-800 MHz)
Non-voluntary third party access
Licensee sets a protection threshold
Automatic frequency coordination
Interoperability
Co-existence
ISM, UNII, Ad-hoc
FCC AnnouncementFCC 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.”
Channel and Interference ModelChannel and Interference Model Measurement of the spectrum
usage in frequency, time, and space
Wideband channel Common with UWB
Spatial channel model Clustering approach Interference correlation
Derive statistical traffic model of primary users
Power level Bandwidth Time of usage Inactive periods
30
210
60
240
90
270
120
300
150
330
180 0
Time (min)
Fre
quen
cy
(Hz)
Angular domain
Cognitive Radio FunctionsCognitive Radio Functions
D/APA
LNA A/D
IFFT
FFT
ADAPTIVELOADING
INTERFERENCEMEAS/CANCEL
MAE/POWER CTRL
CHANNELSEL/EST
TIME, FREQ,SPACE SEL
LEARN ENVIRONMENT
QoS vs.RATE
FEEDBACKTO CRs
Sensing Radio Wideband Antenna, PA
and LNA High speed A/D & D/A,
moderate resolution Simultaneous Tx & Rx Scalable for MIMO
Physical Layer OFDM transmission
Spectrum monitoring
Dynamic frequency selection, modulation, power control
Analog impairments compensation
MAC Layer Optimize transmission
parameters
Adapt rates through feedback
Negotiate or opportunistically use resources
RF/Analog Front-end Digital Baseband MAC Layer
Sensing RadioSensing Radio A/D converter:
High resolution Speed depends on the application Low power ~ 100mWs
RF front-end: Wideband antenna and filters Linear in large dynamic range Good sensitivity
Interference temperature: Protection threshold for licensees FCC: 2400-2483.5 MHz band is
empty if:
Need to determine length of measurements
MHzB
dBdwNIN25.1
030)( 0 0.5 1 1.5 2 2.5
x 109
-90
-85
-80
-75
-70
-65
-60
-55
-50
-45
-40
Frequency (Hz)
Sig
na
l S
tre
ng
th (
dB
)
TV bands
Cell
PCS
Spectrum usage in (0, 2.5) GHz
Measurement taken at BWRC
Cognitive Radio Baseband Processing Cognitive Radio Baseband Processing
IFFT
FFT
ADAPTIVELOADING
INTERFERENCEMEAS/CANCEL
MAE/POWER CTRL
CHANNELSEL/EST
TIME, FREQ,SPACE SEL
LEARN ENVIRONMENT
QoS vs.RATE
FEEDBACKTO CRs
MCMA processing
• OFDM System
Agile, efficient FFT
• Spatial processing:
Exploits clustered model
Scalable with # of antennas
PHY MAC
PHY – adaptive, parametrizable
MAC – intelligent, optimization algo’s
PHY+MAC can be implemented on:
•Software Defined Radios
•Reconfigurable Radios
From WiFi to Cognitive RadiosFrom WiFi to Cognitive Radios
Functionality WiFi Cognitive Radio
Multiple channels for agility27 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, IndoorTest Scenario at 2.4 GHz, Indoor
Bluetooth
802.11 b/g
Microwave oven
Cordless phone
CR2
CR1
AP
CR3
Dynam
ic
Frequency Selection
Unlicensed band 80 MHz bandwidth OFDM system (like 802.11a/g) Multiple antennas for interference
avoidance and range extension Centralized approach through AP
Testbed for Wireless ExperimentationTestbed for Wireless Experimentation
BWRC infrastructure: BEE Processing Units (4) 2.4 GHz RF Front-ends (32) Scalable multiple antenna
transmission system
Research AgendaResearch Agenda Derive system specification from measurements Analog front-end specification and design Develop and implement algorithms for:
Sensing environment Dynamic frequency selection and adaptive modulation Transmit power control and spatial processing Interference cancellation in spatial domain Spectrum rental strategies
Test algorithms in realistic wireless scenarios Design an architecture for a Cognitive Radio
COGURCOGUR
CogCognizant nizant UUniversal niversal
RRadioadioAxel Berny
Gang Liu
Zhiming Deng
Nuntachai Poobuapheun
COGUR Design GoalsCOGUR Design Goals 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 Dynamic Operation: Near-Far ProblemProblem
High power consumption due to simultaneous requirement of high linearity in RF front-end 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 TransceiverCOGUR Transceiver
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
AcknowledgementsAcknowledgements
BWRC Member Companies DARPA TEAM Project STMicroelectronics and IBM for wafer processing and
design support Agilent Technologies (measurement support) National Semiconductor Qualcomm Analog Devices
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