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On Radio Frequency Behavioral Modeling: Measurement Techniques, Devices and Validation Aspects
KTH, School of Electrical Engineering (EES), Signal Processing.
2009 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [sv]

Effektförstärkare för radiofrekvensapplikationer utgör fortfarande ett av de största problemen i trådlösa kommunikationssystem. Detta beror på att dessa förstärkare är ickelinjära, har låg energieffektivitet och ger mycket distortioner. Bättre verktyg för att förstå och korrigera dessa beteenden är nödvändiga. Ett sådant verktyg är beteendemodellering. En beteendemodell kan ses som en svart låda med insignal(er) och utsignal(er). In detta fall är dessa signaler samplade basbandssignaler och den svarta lådan är en matematisk relation mellan en insignal och en utsignal.

Avhandlingen behandlar några krav för beteendemodellering av nämnda system genom att presentera metoder för utvärdering och förbättring av modellernas prestanda. Detta åstadkoms genom att betrakta ett frekvensviktat felkriterium. Ett högpresterande mätsystem är också nödvändigt för experimenten. Prestandan hos det tillgängliga systemet jämförs med prestandan hos ett allmänt erkänt mätsystem, en s.k. storsignalsnätverksanalysator, genom att betrakta prestandan hos beteendemodellerna som extraheras och valideras med data från respektive mätsystem. Resultatet visar att det existerande mätsystemet har god prestanda.

Ett stort problem vid beteendemodellering är att kunna sampla med tillräckligt hög hastighet. Genom att använda Zhu-Franks generaliserade samplingsteorem vid beteendemodellering kan en del av detta problem undvikas. Teoremet medför att man kan sampla med en väsentligt lägre samlingsfrekvens än vad Nyquistteoremet säger. Modeller extraheras och prestandan utvärderas genom att använda kriteriet normalized mean square error (NMSE).

För stabil prediktion och korrektion av utsignalen måste robustheten hos de använda modellerna verifieras. En sådan studie som berör robustheten mot variationer i lastimpedansen har genomförts. Prestandan på direkta modeller försämras med 7 dB mätt som adjacent channel error power ratio (ACEPR). Prestanda på inversmodellen, implementerad som digital predistortion, försämras med upp till 13 dB mätt som adjacent channel power ratio (ACPR).

Abstract [en]

Radio frequency (RF) power amplifiers (PA) are still the most troublesomepart of a wireless system due to their inherent nonlinearity, low powerefficiency and high distortions. Better tools are needed to understand and correct the undesirable behavior. Some of these tools are behavioral models. A behavioral model is often thought of as a black box with some inputs andsome outputs. In the case here these inputs are sampled signals which meansthat the modeling amounts to finding a mathematical relationship betweenthe input signal(s) and the output signal(s).

This thesis considers some requirements for behavioral modeling of said systems by presenting methods for general performance evaluation and improvement by considering a frequency weighted error criterion.

A high performance measurement system is also needed. The performance of the available system is compared to the performance of a well recognized system, the largesignal network analyzer (LSNA). The results show that the existing measurementsystem can extract behavioral models with the same performance as the LSNA and can give lower performance validation errors.

Still the need for higher bandwidths drives the measurement systems to the limits, especially the digital parts. By utilizing the so called Zhu-Frank generalized sampling theorem, behavioral modeling of a PA is done by using data acquired at a sampling rate lower than the Nyquist rate. Models of a PA are extracted and the performance is evaluated using the normalized meansquare error (NMSE) criterion. For prediction and correction of the output signals the stability of the models regarding changes must be investigated. One such study considering controlled variations on the output load of the PA is done and both the predictive and corrective capabilities of the models are evaluated. The predictive capability gets up to 7 dB worse measured as adjacent channel error powerratio (ACEPR) and the corrective, as digital predistortion, gets up to 13 dB worse measured as adjacent channel power ratio (ACPR).

Place, publisher, year, edition, pages
Stockholm: KTH , 2009. , vi, 65 p.
Series
Trita-EE, ISSN 1653-5146 ; 2009:056
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-11678ISBN: 978-91-7415-526-6 (print)OAI: oai:DiVA.org:kth-11678DiVA: diva2:279216
Presentation
2009-12-10, Hörsal 99131, Högskolan i Gävle, Kungsbäcksvägen 47, Gävle, 10:00 (English)
Opponent
Supervisors
Available from: 2009-12-09 Created: 2009-12-02 Last updated: 2010-10-15Bibliographically approved
List of papers
1. Comparison of Evaluation Criteria for Power Amplifier Behavioral Modeling
Open this publication in new window or tab >>Comparison of Evaluation Criteria for Power Amplifier Behavioral Modeling
2008 (English)In: 2008 IEEE MTT-S INTERNATIONAL MICROWAVE SYMPOSIUM DIGEST, New York: IEEE , 2008, 1441-1444 p.Conference paper, Published paper (Refereed)
Abstract [en]

In this paper different evaluation criteria for power amplifier behavioral modeling are studied and evaluated using measuremed data. The figure-of-merits are calculated from complex-envelope data of a sampled power amplifier intended for 3G. Both time- and frequency domain methods are included in the study. It is found that a model evaluation criterion should have ability to capture both the linear and nonlinear distortion as well as the memory effects in the power amplifier. The normalized mean square error (NMSE) and the weighted error-to-signal power ratio (WESPR) are found to be the strongest candidates for capturing the in-band and the out-of-band errors, respectively. Both are also independent of power amplifier technology and stimuli input.

Place, publisher, year, edition, pages
New York: IEEE, 2008
Series
IEEE MTT-S INTERNATIONAL MICROWAVE SYMPOSIUM DIGEST, ISSN 0149-645X ; 1-4
Keyword
Memories, Modeling, Nonlinear systems, Power amplifiers, Radio transmitters
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-11676 (URN)10.1109/MWSYM.2008.4633050 (DOI)000262480000363 ()2-s2.0-57349143458 (Scopus ID)978-1-4244-1780-3 (ISBN)
Conference
2008 IEEE MTT-S International Microwave Symposium Digest, Atlanta, GA, JUN 15-20, 2008, IEEE
Note
QC 20101015Available from: 2009-12-02 Created: 2009-12-02 Last updated: 2010-10-15Bibliographically approved
2. Parameter Extraction and Performance Evaluation Method for Increased Performance in RF Power Amplifier Behavioral Modeling
Open this publication in new window or tab >>Parameter Extraction and Performance Evaluation Method for Increased Performance in RF Power Amplifier Behavioral Modeling
2010 (English)In: International Journal of RF and Microwave Computer-Aided Engineering, ISSN 1096-4290, E-ISSN 1099-047X, Vol. 20, no 2, 200-208 p.Article in journal (Refereed) Published
Abstract [en]

A frequency-weighted parameter extraction method based on the performance evaluation criterion weighted error spectral power ratio (WESPR) is proposed. Performance of models extracted using the normalized mean square error (NMSE) are compared to the performances of models extracted using the WESPR. The results show an increase in performance with a decrease in model complexity.

Keyword
Behavioral modeling, Digital predistortion, Model validation, Out-of-band properties, Radio frequency power amplifiers
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-11671 (URN)10.1002/mmce.20422 (DOI)000275767300009 ()2-s2.0-77649209140 (Scopus ID)
Note
QC 20100927. Uppdaterad från Accepted till Published (20100927).Available from: 2009-12-02 Created: 2009-12-02 Last updated: 2017-12-12Bibliographically approved
3. Power Amplifier Behavioral Modeling Performance Comparison of the LSNA and the Modulation-Domain System
Open this publication in new window or tab >>Power Amplifier Behavioral Modeling Performance Comparison of the LSNA and the Modulation-Domain System
2008 (English)In:  72ND ARFTG MICROWAVE MEASUREMENT SYMPOSIUM - TIME DOMAIN AND FREQUENCY DOMAIN MEASUREMENT     , New York: IEEE , 2008, 73-78 p.Conference paper, Published paper (Refereed)
Abstract [en]

The performance of power amplifier behavioral models depends strongly on the performance of the system used to measure the amplifiers. In this study two different systems with nonlinear measurement capability are used to model a commercially available PA. One system is a large-signal network analyzer (LSNA) and the second system is a modulation-domain system (MDS) consisting of a vector signal generator and a vector signal analyzer.

The PA was tested with multitone and WCDMA signals and behavioral models were extracted from the measured data. The evaluation criteria normalized mean square error and weighted error spectral power ratio or adjacent channel error power ratio were then computed to compare the performance of the models from the two systems. Cross-validation between the systems, using data from one system to obtain the model and validating its performance with data from the other system, shows that the model performance is mainly affected by the used validation data. Validating the performance of models from the LSNA with data from the MDS indicates that the identified models have almost the same performance as the MDS-identified models, i.e. it does not matter which system is used to identify the models. Cross-validation using a WCDMA-signal and multitone signal from the different systems shows that the normalized mean square error is mainly affected by modeling imperfections introduced by using another signal type. WESPR and ACEPR show a certain difference in performance with somewhat lower values for the MDS. The behavior of the two systems can be explained by different noise levels.

Place, publisher, year, edition, pages
New York: IEEE, 2008
Keyword
Block codes, Electric network analysis, Heterojunction bipolar transistors, Mean square error, Power amplifiers, Signal generators
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-11675 (URN)10.1109/ARFTG.2008.4804282 (DOI)000270442000013 ()978-1-4244-2299-9 (ISBN)
Conference
72nd ARFTG Microwave Measurement Conference, Portland, OR, DEC 09-12, 2008 ARFTG; MTT S; IEEE
Note
QC 20101015Available from: 2009-12-02 Created: 2009-12-02 Last updated: 2010-10-15Bibliographically approved
4. A Study of memory effects of RF power LDMOS before and after digital predistortion
Open this publication in new window or tab >>A Study of memory effects of RF power LDMOS before and after digital predistortion
2009 (English)In:  2009 IEEE 10TH ANNUAL WIRELESS AND MICROWAVE TECHNOLOGY CONFERENCE    , New York: IEEE , 2009, 103-107 p.Conference paper, Published paper (Refereed)
Abstract [en]

Sideband asymmetries in distortion products are created due to electrical and thermal memory effects and this can be difficult to correct for in a digital predistortion algorithm. In this study, sideband asymmetries in third-order intermodulation distortion products before and after digital predistortion were investigated using 2-tone and 2-carrier WCDMA signals. The parallel Hammerstein (PH) model was used in the digital predistortion algorithm. The sign of the asymmetries before correction were found to depend on power level. Memoryless correction lead to an increase in asymmetries for some power ranges whereas using a PH model of order 13 with only one order of memory length lead to good correction over a large power range.

Place, publisher, year, edition, pages
New York: IEEE, 2009
Keyword
Microwave devices, Microwaves, Parallel algorithms
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-11673 (URN)10.1109/WAMICON.2009.5207289 (DOI)000272995600024 ()2-s2.0-70449346137 (Scopus ID)978-1-4244-4564-6 (ISBN)
Conference
10th Annual IEEE Wireless and Microwave Technology Conference Clearwater, FL, APR 20-21, 2009 IEEE
Note
QC 20101015Available from: 2009-12-02 Created: 2009-12-02 Last updated: 2010-10-15Bibliographically approved
5. Wideband Characterization of Power Amplifiers Using Undersampling
Open this publication in new window or tab >>Wideband Characterization of Power Amplifiers Using Undersampling
Show others...
2009 (English)In: 2009 IEEE MTT-S International Microwave Symposium Digest, 2009, 1365-1368 p.Conference paper, Published paper (Refereed)
Abstract [en]

In this paper a radio frequency power amplifier is measured and characterized by the use of undersampling based on the generalized Zhu-Frank sampling theorem. A test system has been designed allowing the bandwidth of the stimuli signal to be 100 MHz in the characterization process. That would not be possible with any vector signal analyzer on the market. One of the more challenging problem within the proposed concept is the model validation process. Here, two different techniques for model validation are proposed, the multitone and the spectrum scan validation methods.

Series
IEEE MTT-S International Microwave Symposium, ISSN 0149-645X ; Vols 1-3
Keyword
Communication system performance, modeling, nonlinear systems, power amplifiers, radio transmitters
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-11674 (URN)10.1109/MWSYM.2009.5165959 (DOI)000273507400343 ()2-s2.0-70450273349 (Scopus ID)978-1-4244-2803-8 (ISBN)
Conference
2009 IEEE MTT-S International Microwave Symposium, IMS 2009; Boston, MA; United States; 7 June 2009 through 12 June 2009
Note

QC 20150713

Available from: 2009-12-02 Created: 2009-12-02 Last updated: 2015-07-13Bibliographically approved
6. Power Amplifier Behavioural Model Mismatch Sensitivity and the Impact on Digital Predistortion Performance
Open this publication in new window or tab >>Power Amplifier Behavioural Model Mismatch Sensitivity and the Impact on Digital Predistortion Performance
2009 (English)In: 2009 EUROPEAN MICROWAVE CONFERENCE, VOLS 1-3, New York: IEEE , 2009, 338-341 p.Conference paper, Published paper (Refereed)
Abstract [en]

This paper presents an investigation of poweramplifier behavioural model performance sensitivity to in-bandreflections. The measurement system and model extractionprocess is presented together with the results and an analysis ofthe effect of parameter variations in a digitally predistortedsystem. A load-pull system is used together with a digitalbaseband model extraction system to identify the impact onmodelling performance. The results show that the modelperformance varies greatly with in-band reflection magnitudeand phase on the amplifier output. It is also shown that a digitalpredistortion based on a model extracted at matched conditions,where it gives an excellent improvement of 20 dB in adjacentchannel leakage ratio (ACLR), gives a poor improvement of 7 dBfor miss-matched conditions with as low reflections as Γ=0.2(return loss 14 dB). This indicates that in-band reflections needto be considered and adaptive predistortion used also for lowVSWR system like base-stations for telecommunication.

Place, publisher, year, edition, pages
New York: IEEE, 2009
Keyword
Microwaves, Power amplifiers
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-11672 (URN)000275097800086 ()978-1-4244-4748-0 (ISBN)
Conference
37th European Microwave Conference, Rome, ITALY, SEP 29-OCT 01, 2009
Note

QC 20101015

Available from: 2009-12-02 Created: 2009-12-02 Last updated: 2017-04-28Bibliographically approved

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CiteExportLink to record
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