“RF and Microwave System Design for A/D and Commercial Wireless applications”

Agilent EEsof EDA - European Microwave Week 2011 Workshop Series

Presenters: Stephen Slater, EEsof Application Engineer Jake Sanderson, MPO Application Engineer

Group/Presentation Title

Month ##, 200X Page 2

• A Systems Modeling Approach • Communications Applications • Aerospace Defense Applications

• System Demonstration • Digital PreDistortion Overview • Wideband DPD Demonstration

Agenda

PHY Architecture Research Analysis

Partitioning Verification

Instrument Links

MIMO/Channel Fading

Jamming Noise

Interference Arrays/Steering

A Systems Modeling Approach Focused on improving system-level design for Defense & Communications

Baseband DSP Modeling Algorithms

Code-Generation Fixed Point/HDL

Verification

RF System Architecture

Behavioral/Noise X-parameters

Links from ADS/GG

PHY Reference IP Wireless Standards

Interoperability Virtual H/W

Coded Test Vectors EDA/Test integration

Target Applications

AEROSPACE / DEFENSE EMERGING COMMS PHY

SDR MILCOM

SATCOM EW ELINT

BROADCAST

3G/4G MOBILITY

NETWORKING

CONNECTIVITY

RADAR

• Superior RF-Baseband architectures • Accelerated real-world design maturity • Lower verification costs

GIGABIT SerDes

Superior BB RF co-design • Allows aggressive Baseband/RF partitioning • Reduces design margins • Lowers risk where BB+RF matters: - wide bandwidth - high linearity/dynamic range - high data throughput - high spectral efficiency/occupancy - high PHY complexity - dynamic behaviors, and quasi-MAC interaction

Value of System Modeling RF-DSP cross-verification bridges the “A/D Converter Gap”

Typical Design Organization

ARCHITECTURE

IMPLEMENTATION

Unified architecture, verification for Layer 1 Comms Augments general purpose tools, or, stands on its own

PHY system integration and verification

Cross-domain PHY modeling framework, for Model-Based Design

Complete a working PHY using combinations of Software, RF/BB Hardware, Simulation, and Measurements

Baseband Algorithms Dataflow Simulation

RF Sys Architecture RF Simulators

Agilent SystemVue

PHY IP

TEST RF Hardware Flows RFIC / MMIC

Hardware SiP / Board Hardware

Baseband Hardware Flows

GPP/ARM Software

DSP/ASSP Software

FPGA/ASIC/SoC Hardware

SystemVue improves top-down PHY System Design with 4 key strengths

Easily assemble Virtual PHYs

Quickly move Ideas to proven, real-world Hardware WiMAX

DVB-S2 ZigBee OFDM

DPD RADAR MIMO Channel mmWave WPAN

HARDWARE & MEASUREMENT CONNECTIVITY

INDUSTRY-LEADING REFERENCE IP

and APPS

POLYMORPHIC BASEBAND

ALGORITHMS & IP

ACCURATE RF & CHANNEL

EFFECTS

.bit Files

FPGA Synthesis

Handwritten HDL

Custom IP

Integrated, tops-down Comms ESL flow Cross-domain model-based design: RF, Comms, and C++/HDL

FPGA Target

REAL HARDWARE

HDL Simulator(s)

SIMULATED H/W

Dataflow Simulation

.m/C++ ALGORITHM

Algorithms C++, .m

Target-neutral HDL Generation

System design RF Architecture

Baseband design PHY Reference

MEASUREMENT, ANALYSIS

VSA software FlexDCA software

DIGITAL BITS, or MODULATED CARRIERS

MXG / ESG

Infiniium Scope

Logic Analyzer

MXA / PXA

Wideband arbs RF sensor

Communications Applications – Partitioning Design Requirements

Phase Noise ADC Jitter

RF Transmitter/ PA Nonlinarities

Baseband Fixed-Point Mixed-Signal

Receiver

Tx Rx Coding Algorithms

D/A

Bits In Decoding Algorithms

Bits Out

RF Channel A/D

Coding/ Decoding

Algorithms

If we take LTE as an example with high performance targets, every part of the transmit and receive chain becomes critical to the link budget

So how to decide the optimum balance, without over-designing?

How are design requirements impacted going from QPSK to 16QAM to 64QAM?

Coding/ Decoding

Algorithms Algorithm Test Vectors for FPGA Development

Baseband Affects RF? Baseband Fixed-Point

Transmitter Design System-Level Trade-Offs

Transmitter Design

RF Transmitter/ PA Nonlinarities

Evaluating BER Performance vs Swept Eb/No and Phase Noise

Specify Phase Noise (e.g. -80 dBc/Hz @ 10kHz offset) Phase Noise

ADC Jitter

Mixed-Signal Receiver

Simulation Results for QPSK, 16QAM, 64QAM vs. Swept Phase Noise at 10 kHz Frequency Offset

-60 dBc/Hz

-70 dBc/Hz

-80 dBc/Hz

RF System Architecture – “Spectrasys” continuous spectrum simulation

Full continuous spectrum at every node (unique RF simulator)

Track origin and propagation of spurs, noise, mismatch, leakage paths

Easily plot Budget & Spectral info

Create and refine RF System Architectures, then use them in System-level Dataflow

A base-station user says . . .“After briefly using SPECTRASYS on a 'must work right the first time' RF design, I identified several issues that were undetected in our spreadsheets and current simulation tools. I'm absolutely positive that it has saved us at least one board spin! ”

RFLINK – “Virtualizes the RF” to enable concurrency

Drag & Drop Dataflow modeling “on the fly”

Automated model-based link captures RF effects: - power/frequency-dependence - broadband noise spectral densities - spectral inversion from up/downconversion

Fast, convenient, enables BB-RF concurrent design Enjoy superior RF results with less detailed

RF knowledge, and less RF flow integration

Using X-Parameters in dataflow with “RF Link”

X-parameter physical effects – contribute to the overall RF System performance – therefore affect link-level Dataflow performance also

Baseband and System-level users – can also enjoy convenient access to RF implementation accuracy,

without understanding the RF design, or learning/maintain the RF tools

LTE-Advanced baseband verification library Industry’s first design support for 3GPP Release 10

Carrier Aggregation: Enhanced Multi-Antenna Technologies:

A/D Applications - Radar Model Library New features for digital array, beamforming

Tx Waveform Tx / Rx Components Measurement

Pulse Generator • LFM • NLFM • BarkerCode • FrankCode • ZCCode Coherent Signal Generator for Multiple Channel (future)

• Tx Front-end • Rx Front-end • DUC • DDC • DAC • ADC • PA • Filter • DDS? • LNA?

Environment Radar Signal Processing

• Detection Prob. • False alarm rate

• Target • RCS • Clutter • Jammer • Interference

• Digital Pulse Compression (PC) • Moving Target Indication (MTI) • Moving Target Detection (MTD) • Pulse Doppler Processing (PD) • Constant False Alarm Rate (CFAR)

• Digital Beam-forming (future) • Space-Time Adaptive Processing (STAP) (future)

Antenna (future)

• Antenna Models • T/R Antenna Array • Antenna Propagation

SystemVue “integrated test solutions for A/D” Continue model-based verification from S/W into the real world

RF Signal Analyzers Logic Analyzers, Oscilloscopes VSA software

OPTIONAL: UPLOAD BACK TO SystemVue TO TEST YOUR SOFTWARE RECEIVER IP

Standards Based IP Reference Models

Fading, noise, and Interference

BB Pattern Generator BB Arb. Waveform Gen Agilent wideband Arb’s RF Signal Generator

DOWNLOAD FROM

SystemVue SystemVue Radar Library

RF Transmitter RF Receiver

BB DSP/FPGA

MEASURE HARDWARE DEVICE UNDER TEST

STEP 1

STEP 2

Perform earlier physical layer Fcn verification LTE FDD UL Throughput Test (TS 36.141), or BER/BLER

Filter X

~

Filter A/D 1 2 3 4

DU Gain DPD Filter X

~

A/D

RU DU

C P R I

Signal Generator

Signal Analyzer

SystemVue – Generates signal, then closes the loop

VSA 89600 waveform recording SystemVue – LTE decode

Customer Hardware eNodeB receiver

STEP 1

STEP 2

SystemVue closed a loop to help measure LTE throughput

APP NOTE 5990-6202EN

MIMO and Multi-channel/Beamforming apps Using SystemVue to virtualize multiple signals, RF channels

1,2,4,8 MIMO

Additional support for hardware verification Leverage SystemVue for apps that “fall between” other products

FILL HOLES

OFDM, MIMO LTE-Advanced

WNW, Defense

Jamming, Interfere Clutter, Targets RF, Phase Noise Cognitive environments

Throughput Coded BER

DPD

MULTI-BOX COORDINATION Digital vs. RF interfaces

Missing test coverage Missing user hardware

NON-STD WAVEFORMS

FADING, IMPAIRMENTS

How SystemVue connects to instrumentation

MATLAB .m modeling

Signal Studio

(licensed)

VSA visualization, connectivity

TCP/IP SCPI

FlexDCA visualization

(free with SV)

MATLAB™ scripting plotting

Agilent I/O Lib Connectivity

(free with SV)

PSA/PXA/MXA Infiniuum/DCA PXI/Modular Simulation

Any test H/W Customer equipment Customer Virtual Plat Simulators and Apps

File I/O

ESG MXG PSG Arbs

Modeling Interfaces Scripting Reference IP

PNA-X X-parameters

Group/Presentation Title

Month ##, 200X Page 25

• A Systems Modeling Approach • Communications Applications • Aerospace Defense Applications

• System Demonstration • Digital PreDistortion Overview • Wideband DPD Demonstration

Agenda

Group/Presentation Title

Month ##, 200X Page 26

• A Systems Modeling Approach • Communications Applications • Aerospace Defense Applications

• System Demonstration • Digital PreDistortion Overview • Wideband DPD Demonstration

Agenda

Conflicting requirements

Problem Statement

27

How to handle signals with high Crest Factor, while driving the PA to operate with high PAE, while also having low signal distortion?

High DC-RF Efficiency

High Crest Factor

High Spectral

Efficiency

Increase Drive levels

Causes high distortion

levels

“Back off” the drive

levels

Solution Approach

28

High DC-RF Efficiency High

Crest Factor

High Spectral

Efficiency

Increase Drive levels

Causes high distortion

levels

Higher Throughput

rates for subscribers

CFR

DPD

CFR

DPD

29

Psat

Pin

LINEAR GAIN

INPUT POWER

OUTPUT POWER

Pdesired

Pactual

Pin needed to achieve Pdesired

PA, WITH GAIN COMPRESSION

Digital Pre-distortion principles – compressing PA

30

Digital Pre-distortion principles – pre-expansion

Maximum correctable power

Psat

LINEAR GAIN

INPUT POWER

OUTPUT POWER

LINEAR REGION

DPD REGION

PA, WITH GAIN COMPRESSION

DPD GAIN EXPANSION

+

31

Maximum correctable power

Psat

INPUT POWER

OUTPUT POWER

LINEAR REGION

DPD REGION

LINEARIZED DPD + PA

Digital Pre-distortion principles – linearized result

PA, WITH GAIN COMPRESSION

DPD GAIN EXPANSION

+ =

Linear Operation with time-varying envelope

32

Psat

LINEAR GAIN

INPUT POWER

OUTPUT POWER

Peak-to-Avg Power Ratio

COMPLEX ENVELOPE

time

Peak Average

Nonlinear Operation – peaks are compressed

33

Psat

LINEAR GAIN

INPUT POWER

OUTPUT POWER

(compressed peaks)

CCDF (LTE)

+19 dBm output, for a Handset PA LTE signal, PA operating at ~1.5 dB overall gain compression

DPD Pre-Expansion – peaks are exaggerated

35

Psat

LINEAR GAIN

INPUT POWER

OUTPUT POWER

Further Improvements: • Compensate for artificially higher avg. signal power • Condition signal w/Crest Factor Reduction (CFR)

(expanded peaks)

DPD Net Result: Linear gain of complex-valued RF carrier envelope over a specific range of power levels

36

LINEAR

INPUT POWER

OUTPUT POWER

DPD pre-expanded peaks

INPUT POWER

PA compresses peaks LINEAR

Baseband Digital Pre-Distortion

RF Power Amplification

AM-AM Effects (Change in Gain vs. Power level)

Pre-Distorter AM-to-AM

DPD + PA AM-to-AM

Linearized PA

Power Amp AM-to-AM

Definitions • AM-AM : Change in Gain vs. Power level, compared to small-signal (dB(S21)) • AM-PM : Change in Transmission Phase, compared to small-signal (phase(S21)) • CCDF: Percentage of time a particular amplitude level spends above avg power

Additional issues: Memory Effects Output is dependent on previous history; “path dependence”

PA with memory AM-to-AM

PA without memory AM-to-AM

Output waveform has an instantaneous 1:1 correspondence in time with input waveform

Output waveform depends on previous values

What does a DPD look like? (Volterra Model)

39

∑=

=K

kk nznz

1)()( ∑ ∑ ∏

= = =

−=Q

m

Q

m

k

llkkk

k

mnymmhnz0 0 1

11

)(),,()(

∑∑∑= ==

+−−+−+=Q

m

Q

m

Q

mmnymnymmhmnymhhnz

0 021212

01110

1 21

)()(),()()()(

Volterra series pre-distorter can be described by

where

Which is a 2-dimensional summation of power series & past time envelope responses

A full Volterra produces a huge computational load. People usually simplify it into • Wiener model • Hammerstein model • Wiener-Hammerstein model • Memory polynomial model

DPD principles – Memory Polynomial Model

If only diagonal terms are kept, Volterra reduces to “Memory polynomial” model.

Agilent uses an indirect learning algorithm to extract MP coefficients.

As of SystemVue 2011.10, you can now add your own model, extraction algorithm, and even create your own GUI.

40

L. Ding, G. T. Zhou, D. R. Morgan, Z. Ma, J. S. Kenney, J. Kim, and C. R. Giardina, “Memory polynomial predistorter based on the indirect learning architecture,” in Proc. of GLOBECOM, Taipei, Taiwan, 2002, vol. 1, pp. 967–971.

∑∑= =

−−−=K

k

Q

q

kkq qnyqnyanz

1 0

1)()()(

Where • K is Nonlinearity order • Q is Memory length

DPD challenges for 4G/wideband systems

• LTE-Advanced (100MHz) and 802.11ac (160MHz) are physically 5x-8x wider than previous generation

• Oversampling increases this bandwidth an additional 3x-5x

• Drives wider ADC/DAC, data rates, test equipment, & more

• Requires powerful embedded processors : DSP/FPGA/ASIC

Wider Bandwidth

Higher Crest Factor

Rapidly changing environment

Oversampling increases the Measurement BW

1x

3x-5x

oversampling

oversampling

Measures: In-band EVM, Throughput

Measures: Out-of-band Spectral Masks

Most Effective DPD Region

DPD challenges for 4G/wideband systems

• Carrier aggregation increases PAPR (drives Efficiency down)

• Highly-configurable signals (time-varying RBs) can lead to worst-case RF scenarios

• People apply Crest Factor Reduction differently…. ….how to estimate the effect of CFR on your PA if someone else is doing the DSP?

Wider Bandwidth

Higher Crest Factor

Rapidly changing environment

CCDF

The Effect of Carrier Aggregation on PAPR

Carrier Agg.

Scenario

Link Type

Configuration PAPR of single CC, before aggregation

PAPR with CCs, after aggregation

Scenario 1 FDD DL 4x20 MHz CCs 8.45 dB 9.98 dB

Scenario 2 TDD DL 5x20 MHz CCs 9.17 dB 11.71 dB

Scenario 4 FDD DL 2x20+2x20MHz 8.38 dB 9.58 dB

FDD UL 20 + 20MHz 5.79 dB 6.86 dB

CA Scenario 1 FDD DL

CA Scenario 2 TDD DL

CA Scenario 4 FDD DL CA Scenario 4 FDD UL

DPD challenges for 4G/wideband systems

• LTE-Advanced, 802.11ac, and other Standards still changing

• IP issues: interoperability of signals, algorithms, channels, coded performance

• Closed DPD IP (no control) • Availability of commercial DPD

solutions • Ecosystem & vendor

re-alignments • BB/RF hardware platform

neutrality for local spectral variations, vendors, standards

Wider Bandwidth

Higher Crest Factor

Rapidly changing environment

Wideband modeling platform

N5182A MXG, or E8267D PSG (as external modulator)

W1461 SystemVue W1716 DPD 89600B VSA

M9330A AWG

M9392A PXI VSA

Device Under Test

Baseband I,Q

How is this wideband modeling platform used?

WIDEBAND MODELING PLATFORM

WIDEBAND RF SOURCE

WIDEBAND RF ANALYZER

.m, C++, VHDL

Test Vectors

Standards reference

DPD, CFR

Early R&D Scenarios

Architectures Algorithms

System-level Validation Vendor Qualification Component Design

Deployment Scenarios

COMMS PHY ….. BASEBAND

IF/RF UPCONVERSION DPD

COMMS PHY BASEBAND

IF/RF UPCONVERSION

FPGA / DSP REALIZATION

Wireless SoC DPD

Wideband modeling – software

Flexible modeling environment, integrates .m, C++, VHDL, along with instrument drivers, simulators, scripting

DPD modeling & extraction algorithms

Instrument control

Wireless Standards libraries, for test vector generation and system-level tests

Connection to VSA software, RF EDA design flows, MATLAB, and other tools

W1461 SystemVue W1716 DPD 89600B VSA

Wideband platform – PXI modular instruments

Stimulus – User-defined (or locally generated) test vectors – Wideband, calibrated AWG – RF/MW signal generator (modulate & upconvert) – Driver pre-amp (optional)

Response – RF/MW downconverter, attenuator, signal conditioning – Wideband baseband digitizer

Integration pieces – DC bias source, cables, connectors, PA output

attenuator, etc.

M9330A AWG

M9392A PXI VSA

N5182A MXG, or E8267D PSG (as external modulator)

Wideband platform Demonstration –

Wideband platform – SystemVue with modular PXI instruments (bandwidth ~250MHz)

~10 dB improvement

in spectral leakage

(1st iteration)

1. Instrument setup to capture PA input signal

2. Instrument setup to capture PA output signal

Wideband platform

External Trigger

M9330A AWG

MXG as external modulator M9392A PXI VSA

M9392A PXI VSA

External Trigger

Attenuator

M9330A AWG

MXG as external modulator

SystemVue DPD Hardware Flow for LTE/LTE-A

The download power and length of the waveform can also be set.

53

Step 1. Create DPD stimulus waveform • LTE parameters such as bandwidth, Resource Block allocation and others

can be set. • Switch LTE or LTE-Advanced waveform

Connect the MXG/AWG directly to the PXA/M9392A and click the “Capture Waveform” button. The captured signal is the input of the PA. Connect the MXG to the PA, connect the PA to the PXA/M9392A, and click the “Capture Waveform” button. The captured signal is the output of the PA DUT. The measured I/Q files are stored and used in following steps.

54

Step 2. Capture PA response • SystemVue interfaces directly to the MXG or M9330A AWG (source) and PXA

or M9392A(analyzer). • Instrument parameters such as number of signal, trace assignment and file

name can be set.

SystemVue DPD Hardware Flow for LTE/LTE-A

DPD AM-to-AM Characteristic

55

SystemVue DPD Hardware Flow for LTE/LTE-A

Step 3. DPD Model Extraction • DPD model parameters such as number

of training samples, memory order and nonlinear order can be set.

PA AM-to-AM Characteristic

56

SystemVue DPD Hardware Flow for LTE/LTE-A

Step 3. DPD Model Extraction (Custom IP) • Provide UI to allow customers to export their

own Matlab code of DPD algorithm (IP) into MathLang to verify their DPD algorithm performance.

Custom DPD Model Extraction

Custom Digital Pre-distorter

57

SystemVue DPD Hardware Flow for LTE/LTE-A Step 4. Capture DPD+PA Response • The signal is predistorted by the DPD model

and downloaded into the MXG or M9330A AWG. DPD+PA output (blue) and original raw signal (red) is displayed

Set the RF power DPD+PA AM-to-AM Characteristic

SystemVue DPD Hardware Flow for LTE/LTE-A

Step 5. Verify DPD+PA response • LTE performance for the DPD model used with the PA hardware is verified.

Spectrum, EVM and ACLR are calculated and plotted automatically

58

Simulation vs. Measurement DPD Extraction

External Trigger

Attenuator N5182 MXG

or E8257D PSG as external modulator M9330A AWG if > 100 MHz

89600 VSA

M9392A PXI VSA (>140MHz) or N9030A PXA (<140 MHz)

I,Q RF

RF DUT

SIMULATION-BASED DPD (predictive)

• ADS & GoldenGate Circuits as simulated RF DUTs - Complex loading, memory FX, dynamic behaviors • NVNA X-parameter measurement model, - Great for smaller solid-state devices

X-parameters

RF DUT N5241,2 PNA-X

MEASUREMENT-BASED DPD

CO-SIM, MODELS

CO-SIM, MODELS

MODEL

ADS

GG

Simulation-based, predictive DPD

ADS circuit-level PA

(circuit envelope simulation)

ADS Ptolemy (circuit-system co-

simulation)

SystemVue STIMULUS

SystemVue RESPONSE

CO-SIM

• Full, nonlinear RF • Time-varying behaviors

& memory effects • Envelope Tracking • Complex loadings • No H/W limitations

CO-SIM

Applications: Early assessment, early validation, cross-domain troubleshooting

Conclusion

New bandwidth and linearity requirements are driving 4G designers to spec DPD earlier in their system designs

The velocity of the industry is pushing DPD activity in-house, where designers are taking a more active role

The integration of an open Comms EDA environment with versatile wideband instruments enables

– Flexibility for modeling, realization, validation, and troubleshooting – Higher performance – Integration with the baseband DSP you are already doing

Further information

About Wideband DPD – Watch a demo:

http://www.youtube.com/watch?v=bocF6P74T9E – Read an app note:

http://cp.literature.agilent.com/litweb/pdf/5990-8883EN.pdf

About Agilent Products – http://www.agilent.com/find/eesof-systemvue – http://www.agilent.com/find/modular

Contact

– Stephen Slater (stephen_slater@agilent.com)

– Jake Sanderson ( jake_sanderson@agilent.com)

Q&A

1. Lei Ding, Zhou G.T., Morgan D.R., Zhengxiang Ma, Kenney J.S., Jaehyeong Kim, Giardina C.R., “A robust digital baseband predistorter constructed using memory polynomials”, Communications, IEEE Transactions on, Jan. 2004, Volume: 52, Issue:1, page 159-165.

2. Lei Ding, “Digital Predistortion of Power Amplifiers for Wireless Applications”, PhD Thesis, March 2004. 3. Roland Sperlich, “Adaptive Power Amplifier Linearization by Digital Pre-Distortion with Narrowband

Feedback using Genetic Algorithms”, PhD Thesis, 2005. 4. Helaoui, M. Boumaiza, S. Ghazel, A. Ghannouchi, F.M., “Power and efficiency enhancement of 3G

multicarrier amplifiers using digital signal processing with experimental validation”, Microwave Theory and Techniques, IEEE Transactions on, June 2006, Volume: 54, Issue: 4, Part 1, page 1396-1404.

5. H. A.Suraweera, K. R. Panta, M. Feramez and J. Armstrong, “OFDM peak-to-average power reduction scheme with spectral masking,” Proc. Symp. on Communication Systems, Networks and Digital Signal Processing, pp.164-167, July 2004.

6. Zhao, Chunming; Baxley, Robert J.; Zhou, G. Tong; Boppana, Deepak; Kenney, J. Stevenson, “Constrained Clipping for Crest Factor Reduction in Multiple-user OFDM”, Radio and Wireless Symposium, 2007 IEEE Volume , Issue , 9-11 Jan. 2007 Page(s):341- 344.

7. Olli Vaananen, “Digital Modulators with Crest Factor Reduction Techniques”, PhD Thesis, 2006 8. Boumaiza, et a, “On the RF/DSP Design for Efficiency of OFDM Transmitters” , IEEE Transactions on

Microwave Theory and Techniques, Vol. 53, No. 7, July 2005, pp 2355-2361. 9. Boumaiza, Slim, “Advanced Memory Polynomial Linearization Techniques,” IMS2009 Workshop WMC

(Boston, MA), June 2009.

Selected DPD References

Recent DPD resources from Agilent

App Notes http://cp.literature.agilent.com/litweb/pdf/5990-8883EN.pdf (Wideband DPD)

http://cp.literature.agilent.com/litweb/pdf/5990-7818EN.pdf (3G/4G)

http://cp.literature.agilent.com/litweb/pdf/5990-6742EN.pdf

http://cp.literature.agilent.com/litweb/pdf/5990-6534EN.pdf (algorithms used)

Demonstration Videos http://www.youtube.com/watch?v=bocF6P74T9E (Wideband DPD)

Previous Webcasts “4G For Everyone: Extended RF Performance with DPD” (June 2010) http://www.home.agilent.com/agilent/eventDetail.jspx?cc=US&lc=eng&ckey=1842093&nid=-11143.0.00&id=1842093