Optimizing Wideband Software Radio Performance · Optimizing Wideband Software Radio Performance...

Optimizing Wideband SoftwareRadio Performance

1998 INTERNATIONAL SYMPOSIUM ONADVANCED RADIO TECHNOLOGIES

Boulder, Colorado

9-11 September 1998

8/7/98 15:04 Copyright 1998 Donald H. SteinbrecherAll rights reserved.

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Optimizing Wideband SoftwareRadio Performance

Dr. Donald H. SteinbrecherSubmarine Electromagnetic Systems Department

Bldg.1319, Room 356, Code 34111176 Howell Street

Newport, RI [email protected]

Tel:401.832.5656 Fax:401.832.7345 DSN: 920.5656


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Wide-band RF DigitalConversion

• Essential to a seamless air-glass interface

• High Spurious-free Dynamic Range is Key

• Frequency Translator and A/D Converter

are the Cornerstones of Performance


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Wide-band RF/Digital Conversion Is Essentialto a seamless air-glass interface

• Air-Side Signals are modulated on to analogRF carriers (eg 900 MHz)

• Glass-side signals are digital and are

modulated onto digital carriers(ATM over

SONET)


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High Spurious-free Dynamic Rangeis Key

• A typical 12-MHz Cellular Band Needs 70-dB for Signal Dynamic Range plus 30-dBfor A/D Converter Headroom

• 70+30 = 100-dB SFDR for continuous full-band operation. (about 16-bits/sample)

• …Unless, of course, you power control

48-Tone Test, 10-MHz Band

99-dBSFDR


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Intercepts

PowerOut

PowerIn

fundam

enta

l

dist

ortio

n

Intercept

Gain

0input

intercept

outputintercept


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Third-Order Intercept

Noise Level

Two-Tone Level

Dynamic Range


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Third-Order Intercept

Noise Level

Two-Tone Level

Inter-ModulationRatio(Db)

Third-Order InterceptIMR/2

IMR


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Spurious-Free Dynamic Range

• SFDR is defined as a power ratio...

• The numerator is the power in each tone of a two-tone.....

• The denominator is the noise power in a specifiedbandwidth, usually one Hertz...

• The ratio is taken when the power of the largestdistortion product produced by system non linearity isjust equal to the noise power in the specified band.


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PP

IkT Fthird

tt

third

= =3

2 0

SFDR

P(two tone)

kT0F


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SFDR

P(two tone)

kT0F

( )SFDR =

P

kTtt

0 F

kT F I

kT Fthird= 0

1 3 2 3

0

/ /


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SFDR

P(two tone)

kT0F

SFDR =I

kTinputthird

0 F

2 3/


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Spurious-Free Signals,30-KHz Band

100-dBSFDR


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The A/D Aperture Constraint

fNyquist fsample

Full Scale Input to theA/D Converter

S(t)

S t f tNNyquist( ) sin( )= −2 21 π


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The A/D Aperture ConstraintS(t)

1 2 21= −NNyquist aperturef tsin( )π

1

taperture

ω πt N= 2


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The A/D Aperture ConstraintS(t)

1 2= NNyquist aperturef tπ

1

taperture

ω πt N= 2


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( )N N Log fA Nyquist= − 2

Nt

A N

apertureeff

=1

2 π


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Nt

A N

apertureeff

=1

2 π


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Optimum Design

Log2(fNyquist)

Neff

Aperture Constraint

NA

Slope = -1



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1-LSB Occurs in1-LSB Occurs in

3.24 x103.24 x10-13-13 Second Second

The Speed of Light...The Speed of Light...

Light Travels AboutLight Travels About

100 microns100 microns

16-Bit Quantizer, 15-MHz Sinusoid


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RF TranslatorRF Translator

Intermediate-Frequency

Analog Processor

Intermediate-Frequency

Analog Processor

AntennaElement

AntennaElement

Analog-to-Digital

Converter

Analog-to-Digital

ConverterDigital Object

FormatterDigital Object

Formatter

Atmosphere

Network Fibersphere


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Atmosphere FibersphereAnalog RF A/D ConversionR

elat

ive

Ban

dwid

th


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Atmosphere FibersphereAnalog RF A/D ConversionR

elat

ive

SFD

R


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Wide-Band Software RadioDesign is Driven by the

Properties of the Chosen A/DConverter


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f=0

f=fNyquist

N02 N01N03N04NikFrequency AxisIncreasing

Nyquist zones of a periodically driven A/Dconverter. The zone most often used as the

signal band is N01


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Intermediate-Freq.

Processor

Frequency

Translator

A/D

Converter

Translation

ImageAlias

Frequency Axis

f=0

f=fN/2

The basic analog elements of asoftware radio.


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Translation

ImageAlias

SFDR

Anti-aliasFilter

Requirement

Signal Band

Frequency Axis

f=fN/2

f=0

f=fIF

Alias Band Image Band

Nyquist Band

Figure 3. The anti-aliasing filer requirement isdetermined by the properties of the A/D converter.


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SFDR

Signal BandAlias Band Image Band

Nyquist Band

RippleBand

Anti-aliasFilter

Requirement

The anti-aliasing filer requirement is determined bythe properties of the A/D converter.


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Partition Band

SFDR

Transition BandTransition Band

Signal BandSignal Band

The digital filter characteristics of the signal bandpartitioner.

Frequency Axis


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A/D

Converter

Digital

Filter

Digital

Filter

Digital

Filter

Digital

FilterCommutator

CH 01

CH 02

CH 03

CH nn

A digital partitioner separates the Nyquist band intonn equal sub bands.

Dis

cret

e or

der-

nn F

ouri

er T

rans

form

01

02

03

nn


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ATM PacketFormatter

ATM PacketFormatter

CH ik

Network Fibersphere

Address ControlAddress Control


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Summary

• A/D Converter drives design of SoftwareRadio.

• Opportunity for developing a core radiocomponent suitable for all software radiosusing a particular A/D Converter.

• Opportunity for developing a networkinterface device suitable for a wide varietyof software radio applications.

Optimizing Wideband Software Radio Performance · Optimizing Wideband Software Radio Performance...

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