signal processing in future radio systems

Berkeley Wireless Research Center

Signal Processing in Future Radio Systems

Bob BrodersenBob BrodersenDept. of EECSDept. of EECSUniv. of Calif.Univ. of Calif.

Berkeley Berkeley

http://bwrc.eecs.berkeley.edu


Who really does the work…

I would like to acknowledge my fellow researchers

UWBTransceiversIan O’DonnellMike ChenStanley WangFrank Wang

Cognitive Radios Danijela CabicMubaraq MishraJing YangAdam WoliszDaniel Wilcomm

60 GHzCMOSChinh DoanSohrab EmamiDavid SobelSayf AlalusiAli Niknejad


FCC - Unlicensed SpectraUltra WidebandUWB

ISM U-NII U-NIIU-NII

ISM

MillimeterWave Band

UPCSISM UPCS

UltraWideband

(2002)

Cognitive Radio

(2005?)

Out of Band Emission

Antenna Gain

Power Spectral Density

Total Transmit Power

Modulation

Link Control

Millimeter Wave(1998)

U-NII(1997)

UPCS(1994)

ISM(1986)

➼➼ ➼ ➼

➼➼ ➼

➼

More Sharing

➼➼

➼➼➼➼➼

➼

960

0

Frequency

1060

0

5900

0

3100

2390

2400

2484

5250

5350

5725

5825

5850

1910

1930

5150

6400

0

902

928

(MHz)

➼


17 GHz of New Unlicensed Bandwidth!

! The UWB bands have some use restrictions, but FCC requirements will allow a wide variety of new applications

! The 59-64 GHz band can transmit up to .5 Watt with little else constrained

! Cognitive Radio allocations in the regulatory process (400-800MHz band to start with)

! How can we use these new resources?

MmWaveBand

60 GHzComm

20 30Vehicular

UWB UWBUWB

10Comm

40 500ID


UWB, 60 GHz and Cognitive radios extend therange of application of radio technology

Carrier Frequency (GHz)

Pea

k D

ata

Rat

e (b

ps)

1 M

100 k

10 k

HDTV motion picture,Pt.-to-Pt. links

NTSC video;rapid file transfer

MPEG video;PC file transfer

Voice,Data

Cellular

3G

802.11b

60 GHzPt.-to-Pt.

60 GHzWLAN

Bluetooth

0.1 1 10 100

802.11a

ZigBee

UWB

UWB

CognitiveRadios

1 G

100 M

10 M


Lets start with UWB…

According to the FCC:

“Ultrawideband radio systems typically employ pulse modulation where extremely narrow (short) bursts of RF energy are modulated and emitted to convey information. … the emission bandwidths … often exceed one gigahertz. In some cases “impulse” transmitters are employed where the pulses do not modulate a carrier.”

-- Federal Communications Commission, ET Docket 98-153, First Report and Order, Feb. 2002


Two basically different signaling approaches

Sinusoidal, Narrowband

FrequencyTime

Impulse, Ultra-Wideband

FrequencyTime


First Major Application Area

High Speed, Inexpensive Short Range Communications (3.1-10.6 GHz)» FCC limit of -41dBm/Mhz at 10 feet severely

limits range – Power level roughly 1 mW– For short range communications this may be OK –

e.g. line of sight from 10 feet for connecting a camcorder to a set-top box, “wireless Firewire”

» Advantage is that it should be less expensive and lower power than a WLAN solution (since 802.11a > 100 Mbits/sec for short range)


Status of High Rate, Short Range UWB

Major standards battle in IEEE 802.15.3Two competing approaches» OFDM

– Exploits the wide bandwidth to provide higher rates with lower precision hardware (e.g. reduced A/D accuracy, linearity requirements)

– Uses a well understood technique (802.11a/g)» Impulse radios

– New approach, so somewhat unknown ultimate performance and efficiency

I’ll talk about some example new interesting signal processing possibilities using the impulse approach


High Rate Impulse Communications

0 2 4 6 8 10 12

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Time (nS)

Mag

nitu

de (V

)

“1” “0”Biphase signalling

! Basically pulsed rate data transmission – sort of optical fiber without the fiber…

! Key design problem, as in wireline transmission, is synchronization


Integrated Analog Front End

UWB attenna

BpLNA

ADC

DigitalBackend

! Mostly Digital Radio Architecture:- Wideband antenna- Wideband amplifier / matching network- RF bandpass filtering (low Q filter)- High bandwidth sample and track- High-speed and low resolution ADC- Sampling Clock generator- DSP


Receive match filterPN0 PN1

Nripple<= 64 ns

Trep10ns ~ 100ns

! Basic approach is to create a match filter for the above received pulse shape

! This collects all the energy associated with the waveform


Sampling Offset Effects! Unfortunately a small timing offset results in a very

different waveform so the match filter output is very dependent on the timing

150 160 170 180 190 200-1

0

1x 10-4 0Ts

150 160 170 180 190 200-1

0

1x 10-4 0.125Ts

150 160 170 180 190 200-1

0

1x 10-4 0.25Ts

150 160 170 180 190 200-1

0

1x 10-4 0.375Ts

150 160 170 180 190 200-1

0

1x 10-4 0.5Ts

150 160 170 180 190 200-1

0

1x 10-4 0.625Ts

150 160 170 180 190 200-1

0

1x 10-4 0.75Ts

150 160 170 180 190 200-1

0

1x 10-4 0.875Ts


A solution to this… (Mike Chen)

ADC

AnalyticMFHilbert

ShapeEst

Ave Det

Imag

RealPulse

in (real)

! Convert the single baseband pulse into an analytic signal (real and imaginary parts) via a Hilbert transformation.

! The analogy is the use of the I and Q channel for sinusoidal systems

Extract the hidden information and becomeinsensitive to timing!


Matched filter detection of the analytic impulse signal

-0.01 -0.005 0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04-0.01

-0.005

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035sampling offset =0Ts

-0.01 -0.005 0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04-0.01

-0.005

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035sampling offset =0.05Ts

-0.01 -0.005 0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04-0.01

-0.005

0

0.005

0.01

0.015

0.02

0.025

0.03


-0.01 -0.005 0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04-0.01

-0.005

0

0.005

0.01

0.015

0.02

0.025

0.03


0Ts 0.05Ts

0.15Ts 0.1TsReal

Imag

signal+noisenoise

0

0

Without creating the imaginary part, the signal is real and some phase shifts can’t be differentiated from the noise


UWB impulse signal processing

Research into the signal processing for impulse detection is just beginning – so lots of opportunities for new ideas!

Analytic impulse signal processing also achieves a timing resolution below the sampling period, what can this be used for?


Second Major Application Area

Low Data Rate, Short Range Communications with Locationing (< 960 MHz)» Round trip time for pulse provides range

information – multiple range estimates provides location

» Used for asset tracking – a sophisticated RFID tag that provides location

» Can be used to track people (children, firemen in buildings)

» Sensor networks


Location Determination Using UWB

! UWB provides» Indoor measurements» Relative location » Insensitivity to multipath» Material penetration (0-1 GHz band)

Time of flight

! Transmit short discrete pulses instead of Transmit short discrete pulses instead of modulating code onto carrier signalmodulating code onto carrier signal–– Pulses last ~1Pulses last ~1--2 ns2 ns–– Resolution of inches Resolution of inches


A UWB locationing transceiver chip(Ian O’Donnell)

A single chip CMOS UWB transceiver at power levels of 1 mW/Mbit for locationing and tracking applications

» Flexible design for a wide range of data rates to investigate UWB transmission characteristics

» For low rate applications, transmission at minimum possible signal level

» Develop limits of locationing accuracy


Chip Architecture

1 GHz bandwidth (2 Gsample/sec , 1 bit)

.

LNA AGCA/D

A/D

A/D

TransientCapture

ParallelA/D’s

....

....

Oscillator

Crystal

Correlation, detection and synchronization

PulserPLL

Detector

Din

Dout

AGCControlTiming &

ProgrammableCorrelators

ECC

Synchronization

Encoder


Processing to detect signals below noise levels

V[31:0]

To Analog

Data Out

• Acquisition: 128-Tap Matched Filter x 128 x 11 PN Phases• Synchronization: Early/On-Time/Late PN Phases


Signal processing for ranging

0 100 200 300 400 500 600 700 800 900-0.1

-0.05

0

0.05

0.1

0 100 200 300 400 500 600 700 800 900-10

-5

0

5

10

The problem is to determine the leading edge of the response

! Simple averaging…

! “Clean” algorithm (iterative best fit of time delayed waveforms)

0 10 20 30 40 50 60 70 80-0.05

0

0.05

0.1

0.15

0 10 20 30 40 50 60 70 800

0.005

0.01

0.015


Summary: Many new problems to solve

! Impulse signal processing (e.g. analytic processing) and timing acquisition

! Detection of signals below noise levels! Range estimation and locationing

calculations


Next lets look at the 60 GHz band…Mm

WaveBand

40 50 60 GHzComm

20 30Vehicular

UWB UWBUWB

10Comm

0ID

Microwave communications


Why is operation at 60 GHz interesting?

57 dBm

40 dBm

Lots of Bandwidth!!!» 7 GHz of unlicensed bandwidth in the U.S. and Japan » Europe CEPT “there is an urgent need to identify and

harmonize civil requirements in the frequency range 54–66GHz.”


Why isn’t 60 GHz in widespread use?

! Misconceptions about path loss and propagation at 60 GHz

! The technology to process signals at 60 GHz is expensive


Path loss of line-of-sight transmission…

" Typical path loss (Friis) formula is a function of antenna gain Gr and Gt:

" But maximum antenna gain increases with frequency for the same antenna area, A

( )22

4 rGG

PP tr

t

r

πλ=

2

4λπ AG =


Using the same effective area then…

22

1r

AAPP tr

t

r

λ=

" There is theoretically 22-dB gain at 60 GHz over 5 GHz with optimal antenna design

" A 16 antenna array (λ/2 pitch) at 60 GHz has 3-dB gain over a 5-GHz system with 1/10th the area


Why isn’t 60 GHz in widespread use?

! Misconceptions about path loss and propagation at 60 GHz

! The technology to process signals at 60 GHz is expensive


CMOS can do it - 130-nm CMOS has a gain of 7dB at 60 GHz

VGS = 0.65 V

VDS = 1.2 V

IDS = 30 mA

W/L = 100x1u/0.13u


40-GHz and 60-GHz CMOS Amplifiers

18-dB Gain@ 40 GHz

11.5-dB Gain@ 60 GHz

! Design and modeling can be incredibly accurate….! Power consumption: 36 mW (40 GHz), 54 mW (60 GHz)


CMOS Mixers at 60-GHz

! Conversion-loss is better than 2 dB for PLO=0 dBm

! IF=2GHz! 6 GHz of bandwidth


A Leap Forward for CMOS

X Where we are nowwith 130 nm

• CMOS offers two orders of magnitude cost reduction while providing higher integration and reliability

• Each new process generation moves it 20-40% higher


The open questions…! How best to implement a flexible, adaptive

antenna system! What is the best way to use 7 GHz of

bandwidth to implement a high datarate link?» Extremely inefficient modulation but at a very

high rate? (say 2 GHz of bandwidth for 1 Gigabit/sec) – requires analog processing

» Or use an efficient modulation, so lower bandwidth. e.g. OFDM – but needs digital processing and a fast A/D


Adaptive antennas by Using Multiple Antenna Beamformers

a1

b1

a0

b0

a2

b2

PA

PA

PASingle Channel

Transceiver

! Wavelength is 5mm, so in a few square inches a large antenna array can be implemented

! The signal processing challenge is how to determine the coefficients of this beamformer to maximize range while minimizing interference


An analog/digital hybrid 1Gb/s base-band architecture (David Sobel)

RF IF

LOIF

BBI

BBQ

BB’I

BB’Q

Clk

Timing, DFE Carrier Phase,

Estimators

VGA

Clock Rec

ComplexDFE

AnalogDigital

ejq

Proposed Baseband Architecture

! Synchronization in “hybrid-analog” architecture» ESTIMATE parameter error in digital domain» CORRECT for parameter error in analog domain

! Greatly simplifies requirements on power-hungry analog interface ckts (i.e. ADC, VGA) by using digital processing


Last topic – Cognitive Radios

According to the FCC:“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”

- Federal Communications Commission,

ET Docket No. 03-108, Dec 30th 2003


The spectrum shortage….

3 4 5 6 GHz

! All frequency bands up to 60 GHz (and beyond) have FCC allocations for multiple users

! The allocation from 3-6 GHz is typical - seems very crowded….


The reality…

0 1 2 3 4 5 6 GHz

The TV band

! Even though the spectra is allocated it is almost unused ! Cognitive radios would allow unlicensed users to share the

spectrum with primary users! The TV band is interesting, but higher frequencies are

even more attractive


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 database to determine optimal

transmission (bandwidth, latency, QoS) based on primary users’ behavior


Cognitive 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 Radio Function

0 0.5 1 1.5 2 2.5x 10

9

-90

-85

-80

-75

-70

-65

-60

-55

-50

-45

-40

Frequency (Hz)Si

gnal

Str

engt

h (d

B)

TV bands

Cell

PCS

Spectrum usage in (0, 2.5) GHz

! Subdivide the spectrum into sub-channels (say 1 MHz)

! Detect primary user occupancy in each location/direction

! Continually monitor for appearance of primary user

! Provide information to MAC layer


From WiFi to Cognitive Radios

SophisticatedLimited QoS, rate, latency

Lots…Some (802.11n)Spatial processing

Any interferenceWiFi interference onlyInterference mitigation

Adaptive controlFixed per packetPower level

More flexibleFixedPacket length, preamble

Adaptive bit loadingFixed per packetModulation scheme, rate

NecessaryNot possibleSimultaneous spectrum sensing and transmission

Any interferenceWiFi interference onlySensing collisions/interference

Variable # and BW27 fixed 20MHz channelsMultiple channels for agility

Cognitive RadioWiFiFunctionality


Summary! UWB radios provide a new way to utilize the

spectrum and there is a wide variety of unique applications of this technology

However, it takes a completely new kind of radio design…

! At the present state of technology CMOS is able to exploit the unlicensed 60 GHz band

However, it will take a new design and modeling methodology…

! Cognitive radios are the ultimate solution to sharingIt will require an unprecedented level of processing to

sense, avoid interference and flexibly transmit


Conclusion

Lots of New Opportunities for Signal Processing in these Future Radio

Technologies!!

signal processing in future radio systems

Documents