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