Welcome. Jake Sanderson Application Engineer Modular Product Operation. Daren McClearnon Product Planning Manager Electronic System-Level EDA

Transcription

1 Welcome Jake Sanderson Application Engineer Modular Product Operation Daren McClearnon Product Planning Manager Electronic System-Level EDA 1

2 Agenda About Digital Pre-Distortion (DPD) DPD challenges for 4G/wideband systems Wideband modeling approaches Hardware modeling demonstration Beyond Hardware Q&A 2

3 Problem Statement High DC-RF Efficiency Increase Drive levels High Crest Factor Causes high distortion levels High Spectral Efficiency Back off the drive levels Conflicting requirements How to handle signals with high Crest Factor, while driving the PA to operate with high PAE, while also having low signal distortion? 3

4 Solution Approach High DC-RF Efficiency Increase Drive levels CFR High Crest Factor Causes high distortion levels DPD High Spectral Efficiency Higher Throughput rates for subscribers CFR DPD 4

5 Digital Pre-distortion principles compressing PA OUTPUT POWER Psat Pdesired Pactual LINEAR GAIN PA, WITH GAIN COMPRESSION Pin Pin needed to achieve Pdesired INPUT POWER 5

6 Digital Pre-distortion principles pre-expansion OUTPUT POWER Psat DPD GAIN EXPANSION LINEAR GAIN PA, WITH GAIN COMPRESSION + LINEAR REGION DPD REGION Maximum correctable power INPUT POWER 6

7 Digital Pre-distortion principles linearized result OUTPUT POWER Psat DPD GAIN EXPANSION LINEARIZED DPD + PA PA, WITH GAIN COMPRESSION + = LINEAR REGION DPD REGION Maximum correctable power INPUT POWER 7

8 Linear Operation with time-varying envelope OUTPUT POWER LINEAR GAIN Psat INPUT POWER Peak Average time Peak-to-Avg Power Ratio COMPLEX ENVELOPE 8

9 Nonlinear Operation peaks are compressed OUTPUT POWER LINEAR GAIN Psat (compressed peaks) INPUT POWER CCDF (LTE) 9

10 +19 dbm output, for a Handset PA LTE signal, PA operating at ~1.5 db overall gain compression 10

11 DPD Pre-Expansion peaks are exaggerated OUTPUT POWER Psat LINEAR GAIN (expanded peaks) INPUT POWER Further Improvements: Compensate for artificially higher avg. signal power Condition signal w/crest Factor Reduction (CFR) 11

12 DPD Net Result: Linear gain of complex-valued RF carrier envelope over a specific range of power levels Baseband Digital Pre-Distortion RF Power Amplification OUTPUT POWER LINEAR DPD pre-expanded peaks LINEAR PA compresses peaks INPUT POWER INPUT POWER 12

13 AM-AM Effects (Change in Gain vs. Power level) Pre-Distorter AM-to-AM Power Amp AM-to-AM DPD + PA AM-to-AM Linearized PA 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 13

14 Additional issues: Memory Effects Output is dependent on previous history; path dependence PA without memory AM-to-AM PA with memory AM-to-AM Output waveform has an instantaneous 1:1 correspondence in time with input waveform Output waveform depends on previous values 14

15 What does a DPD look like? (Volterra Model) 15 = = K k z k n n z 1 ) ( ) ( = = = = Q m Q m k l l k k k k m n y m m h n z ) ( ),, ( ) ( = = = = Q m Q m Q m m n y m n y m m h m n y m h h n z ) ( ) ( ), ( ) ( ) ( ) ( 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

16 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 , you can now add your own model, extraction algorithm, and even create your own GUI. z( n) = K Q k = 1 q= 0 a kq y( n q) y( n q) k 1 Where K is Nonlinearity order Q is Memory length MORE INFO: 4G for Everyone webcast 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

17 Agenda About Digital Pre-Distortion (DPD) DPD challenges for 4G/wideband systems Wideband modeling approaches Hardware modeling demonstration Beyond Hardware Q&A 17

18 DPD challenges for 4G/wideband systems Wider Bandwidth Higher Crest Factor Rapidly changing environment LTE-Advanced (100MHz) and ac (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 18

19 Oversampling increases the Measurement BW 1x oversampling Measures: In-band EVM, Throughput Most Effective DPD Region 3x-5x oversampling Measures: Out-of-band Spectral Masks 19

20 DPD challenges for 4G/wideband systems Wider Bandwidth Higher Crest Factor Rapidly changing environment 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? CCDF 20

21 The Effect of Carrier Aggregation on PAPR CA Scenario 1 FDD DL CA Scenario 4 FDD DL CA Scenario 4 FDD UL CA Scenario 2 TDD DL 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 db Scenario 4 FDD DL 2x20+2x20MHz 8.38 db 9.58 db FDD UL MHz 5.79 db 6.86 db 21

22 DPD challenges for 4G/wideband systems Wider Bandwidth Higher Crest Factor Rapidly changing environment LTE-Advanced, ac, 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 22

23 Agenda About Digital Pre-Distortion (DPD) DPD challenges for 4G/wideband systems Wideband modeling approaches Hardware modeling demonstration Beyond Hardware Q&A 23

24 Wideband modeling platform N5182A MXG, E8267D PSG (as external modulator) or Device Under Test Baseband I,Q M9330A AWG W1461 SystemVue W1716 DPD 89600B VSA M9392A PXI VSA 24

25 How is this wideband modeling platform used? Early R&D Scenarios Architectures Algorithms System-level Validation Vendor Qualification Component Design.m, C++, VHDL Test Vectors Standards reference DPD, CFR WIDEBAND RF SOURCE WIDEBAND RF ANALYZER WIDEBAND MODELING PLATFORM Deployment Scenarios COMMS PHY BASEBAND FPGA / DSP REALIZATION IF/RF UPCONVERSION COMMS PHY BASEBAND.. DPD IF/RF UPCONVERSION Wireless SoC DPD 25

26 Wideband modeling software Flexible modeling environment, integrates.m, C++, VHDL, along with instrument drivers, simulators, scripting DPD modeling & extraction algorithms W1461 SystemVue W1716 DPD 89600B VSA 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 26

27 SystemVue for unified architecture, verification Agilent SystemVue Cross-domain PHY modeling framework, for Model-Based Design Baseband Algorithms Dataflow Simulation PHY IP RF Sys Architecture RF Simulators Baseband Hardware Flows GPP/ARM Software DSP/ASSP Software FPGA/ASIC/SoC Hardware TEST RF Hardware Flows RFIC / MMIC Hardware SiP / Board Hardware PHY system integration and verification Complete a working PHY using combinations of Software, RF/BB Hardware, Simulation, and Measurements 27

28 Wideband platform PXI modular instruments Stimulus M9330A AWG N5182A MXG, or E8267D PSG (as external modulator) M9392A PXI VSA 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. 28

29 Agenda About Digital Pre-Distortion (DPD) DPD challenges for 4G/wideband systems Wideband modeling approaches Hardware modeling demonstration Beyond Hardware Q&A 29

30 Wideband platform TODAY S DEMONSTRATION Jake Sanderson Application Engineer, Agilent Modular Products 30

31 Wideband platform TODAY S DEMONSTRATION SystemVue with modular PXI instruments (bandwidth ~250MHz) ~10 db improvement in spectral leakage (1 st iteration) 31

32 Wideband platform TODAY S DEMONSTRATION SystemVue with modular PXI instruments (bandwidth ~250MHz) 1. Instrument setup to capture PA input signal MXG as external modulator M9392A PXI VSA External Trigger M9330A AWG 2. Instrument setup to capture PA output signal MXG as external modulator External Trigger M9392A PXI VSA M9330A AWG Attenuator 32

33 SystemVue DPD Hardware Flow for LTE/LTE-A 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 The download power and length of the waveform can also be set. 33

34 SystemVue DPD Hardware Flow for LTE/LTE-A 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. 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. 34

35 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 DPD AM-to-AM Characteristic 35

36 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 36

37 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 37

38 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 38

39 DPD of LTE-Advanced, using M9330A/M9392A 4x20MHz contiguous CA, (80MHz signal BW) Source = M9330A AWG Vector Analyzer= M9392A - 12bits ADC - up to 250MHz bandwidth PA output Spectrum (Blue) PA+DPD Spectrum (Red) PA input Spectrum (Green) 39

40 DPD of LTE-Advanced, using M9330A/M9392A 2x20MHz + 20MHz non-contiguous CCs, (80MHz signal BW) Source = M9330A AWG Vector Analyzer= M9392A - 12bits ADC - up to 250MHz bandwidth PA output Spectrum (Blue) PA+DPD Spectrum (Red) PA input Spectrum (Green) 40

41 DPD of ac, using M9330A/M9392A (80MHz Option) Source = M9330A AWG Vector Analyzer= M9392A - 12bits ADC - up to 250MHz bandwidth PA output Spectrum (Blue) PA+DPD Spectrum (Red) PA input Spectrum (Green) 41

42 Agenda About Digital Pre-Distortion (DPD) DPD challenges for 4G/wideband systems Wideband modeling approaches Hardware modeling demonstration Beyond Hardware Q&A 42

43 Simulation vs. Measurement DPD Extraction SIMULATION-BASED DPD (predictive) ADS CO-SIM, MODELS GG ADS & GoldenGate Circuits as simulated RF DUTs - Complex loading, memory FX, dynamic behaviors NVNA X-parameter measurement model, - Great for smaller solid-state devices CO-SIM, MODELS X-parameters MODEL N5241,2 PNA-X RF DUT MEASUREMENT-BASED DPD M9392A PXI VSA (>140MHz) or N9030A PXA (<140 MHz) VSA External Trigger I,Q RF M9330A AWG if > 100 MHz N5182 MXG or E8257D PSG as external modulator RF DUT Attenuator 43

44 Simulation-based, predictive DPD SystemVue STIMULUS CO-SIM ADS Ptolemy (circuit-system cosimulation) CO-SIM SystemVue RESPONSE Full, nonlinear RF Time-varying behaviors & memory effects Envelope Tracking Complex loadings No H/W limitations ADS circuitlevel PA (circuit envelope simulation) Applications: Early assessment, early validation, cross-domain troubleshooting 44

45 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 45

46 Further information About Wideband DPD Watch a demo: Read an app note: About Agilent Products

47 Agenda About Digital Pre-Distortion (DPD) DPD challenges for 4G/wideband systems Wideband modeling approaches Hardware modeling demonstration Looking ahead Q&A 47

48 Q&A 48

49 Selected DPD References 1. Lei Ding, Zhou G.T., Morgan D.R., Zhengxiang Ma, Kenney J.S., Jaehyeong Kim, Giardina C.R., A robust digital baseband predistorterconstructed using memory polynomials, Communications, IEEE Transactions on, Jan. 2004, Volume: 52, Issue:1, page Lei Ding, Digital Predistortion of Power Amplifiers for Wireless Applications, PhD Thesis, March Roland Sperlich, Adaptive Power Amplifier Linearization by Digital Pre-Distortion with Narrowband Feedback using Genetic Algorithms, PhD Thesis, 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 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 , July 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 Page(s): Olli Vaananen, Digital Modulators with Crest Factor Reduction Techniques, PhD Thesis, 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 Boumaiza, Slim, Advanced Memory Polynomial Linearization Techniques, IMS2009 Workshop WMC (Boston, MA), June

50 Recent DPD resources from Agilent App Notes (Wideband DPD) (3G/4G) (algorithms used) Demonstration Videos (Wideband DPD) Previous Webcasts 4G For Everyone: Extended RF Performance with DPD (June 2010) 50

51 You are invited Dr. Yi Cao Digital Hardware Designer, RIM (Research In Motion) You can find more webcasts Hee-Soo Lee 3D EM Applications Specialist, Agilent EEsof EDA 51