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Characterization and Linearization of Multi-channel RF Power Amplifiers
Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för elektronik, matematik och naturvetenskap, Elektronik.ORCID-id: 0000-0003-1183-6666
2015 (Engelska)Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

The demands for high data rates and broadband wireless access requirethe development of wireless systems that can support wide and multi-bandsignals. To deploy these signals, new radio frequency (RF) front-ends are requiredwhich impose new challenges in terms of power consumption efficiencyand sources of distortion e.g., nonlinearity. These challenges are more pronouncedin power amplifiers (PAs) that degrade the overall performance ofthe RF transmitter.Since it is difficult to optimize the linearity and efficiency characteristicsof a PA simultaneously, a trade-off is needed. At high input power, a PAexhibits high efficiency at the expense of linearity. On the other hand, atlow input power, a PA is linear at the expense of the efficiency. To achievelinearity and efficiency at the same time, digital pre-distortion (DPD) is oftenused to compensate for the PA nonlinearity at high input power. In case ofmulti-channel PAs, input and output signals of different channels interactwith each other due to cross-talk. Therefore, these PAs exhibit differentnonlinear behavior than the single-input single-output (SISO) PAs. The DPDtechniques developed for SISO PAs do not result in adequate performancewhen used for multi-channel PAs. Hence, an accurate behavioral modeling isessential for the development of DPD for multi-channel RF PAs.In this thesis, we propose three novel behavioral models and DPD schemesfor nonlinear multiple-input multiple-output (MIMO) transmitters in presenceof cross-talk. A study of the source of cross-talk in MIMO transmittershave been investigated to derive simple and powerful modeling schemes.These models are extensions of a SISO generalized memory polynomial model.A comparative study with a previously published MIMO model is also presented.The effect of coherent and partially non-coherent signal generationon DPD performance is also highlighted. It is shown experimentally thatwith partially non-coherent signal generation, the performance of the DPDdegrades compared to coherent signal generation.In context of multi-channel RF transmitters, PA behavioral models andDPD schemes suffer from a large number of model parameters with the increasein nonlinear order and memory depth. This growth leads to highcomplexity model identification and implementation. We have designed aDPD scheme for MIMO PAs using a sparse estimation technique for reducingmodel complexity. This technique also increases the numerical stability whenlinear least square estimation model identification is used.A method to characterize the memory effects in a nonlinear concurrentdual-band PAs is also presented. Compared to the SISO PAs, concurrentdual-band PAs are not only affected by intermodulation distortions but alsoby cross-modulation distortions. The characterization of memory effects inconcurrent dual-band transmitter is performed by injecting a two-tone testsignal in each input channel of the transmitter. Asymmetric energy surfacesare introduced for the intermodulation and cross-modulation products, whichcan be used to identify the power and frequency regions where the memory effects are dominant.

Ort, förlag, år, upplaga, sidor
Stockholm: KTH Royal Institute of Technology , 2015. , s. 45
Serie
TRITA-EE, ISSN 1653-5146 ; 2015:001
Nationell ämneskategori
Signalbehandling
Identifikatorer
URN: urn:nbn:se:hig:diva-18848OAI: oai:DiVA.org:hig-18848DiVA, id: diva2:783324
Presentation
2015-01-23, 99132, Kungsbäcksvägen 47, Gävle, 10:00 (Engelska)
Opponent
Handledare
Tillgänglig från: 2015-01-27 Skapad: 2015-01-26 Senast uppdaterad: 2018-03-13Bibliografiskt granskad
Delarbeten
1. Behavioral Modeling and Linearization of Crosstalk and Memory Effects in RF MIMO Transmitters
Öppna denna publikation i ny flik eller fönster >>Behavioral Modeling and Linearization of Crosstalk and Memory Effects in RF MIMO Transmitters
2014 (Engelska)Ingår i: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 62, nr 4, s. 810-823Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

This paper proposes three novel models for behavioral modeling and digital pre-distortion (DPD) of nonlinear 2$,times,$ 2 multiple-input multiple-output (MIMO) transmitters in the presence of crosstalk. The proposed models are extensions of the single-input single-output generalized memory polynomial model. Three types of crosstalk effects were studied and characterized as linear, nonlinear, and nonlinear & linear crosstalk. A comparative study was performed with previously published models for the linearization of crosstalk in a nonlinear 2 $,times,$2 MIMO transmitter. The experiments indicate that, depending on the type of crosstalk, the selection of the correct model in the transmitter is necessary for behavioral modeling and sufficient DPD performance. The effects of coherent and partially noncoherent signal generation on the performance of DPD were also studied. For crosstalk levels of ${-}{hbox{30}}$ dB, the difference in the normalized mean square error and adjacent channel power ratio was found to be 3–4 dB between coherent and partially noncoherent signal generation.

Nyckelord
Behavioral modeling; digital pre-distortion (DPD); multiple-input multiple-output (MIMO); nonlinear and linear crosstalk; power amplifiers (PAs); RF
Nationell ämneskategori
Signalbehandling
Identifikatorer
urn:nbn:se:hig:diva-16413 (URN)10.1109/TMTT.2014.2309932 (DOI)000334525600010 ()2-s2.0-84898403156 (Scopus ID)
Tillgänglig från: 2014-03-13 Skapad: 2014-03-13 Senast uppdaterad: 2018-11-26Bibliografiskt granskad
2. Combating the Dimensionality of Nonlinear MIMO Amplifier Predistortion by Basis Pursuit
Öppna denna publikation i ny flik eller fönster >>Combating the Dimensionality of Nonlinear MIMO Amplifier Predistortion by Basis Pursuit
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2014 (Engelska)Ingår i: Proceedings of the 44th European Microwave Conference, 2014, s. 833-836Konferensbidrag, Publicerat paper (Refereegranskat)
Abstract [en]

A general description of nonlinear dynamic MIMO systems, given by Volterra series, has significantly larger complexity than SISO systems. Modeling and predistortion of MIMO amplifiers consequently become unfeasible due to the large number of basis functions. We have designed digital predistorters for a MIMO amplifier using a basis pursuit method for reducing model complexity. This method reduces the numerical problems that appear in MIMO Volterra predistorters due to the large number of basis functions. The number of basis functions was reduced from 1402 to 220 in a 2x2 MIMO amplifier and from 127 to 13 in the corresponding SISO case. Reducing the number of basis functions caused an increase of approximately 1 dB of model error and adjacent channel power ratio.

Nyckelord
Digital pre distortion (DPD), MIMO power ampli fiers, LASSO, basis pursuit, power amplifier linearization
Nationell ämneskategori
Kommunikationssystem Signalbehandling
Identifikatorer
urn:nbn:se:hig:diva-17716 (URN)000392912200209 ()2-s2.0-84922721597 (Scopus ID)
Konferens
The 44th European Microwave Conference (EuMC 2014), Roma, Italy, October 5-10, 2014
Tillgänglig från: 2014-10-23 Skapad: 2014-10-23 Senast uppdaterad: 2018-03-13Bibliografiskt granskad
3. Characterization of concurrent dual-band power amplifiers using a dual two-tone excitation signal
Öppna denna publikation i ny flik eller fönster >>Characterization of concurrent dual-band power amplifiers using a dual two-tone excitation signal
2015 (Engelska)Ingår i: IEEE Transactions on Instrumentation and Measurement, ISSN 0018-9456, E-ISSN 1557-9662, Vol. 64, nr 10, s. 2781-2791, artikel-id 7104121Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

A method to characterize the memory effects in a nonlinear concurrent dual-band transmitter is presented. It is an extension of the conventional two tone test for power amplifiers to concurrent dual band transmitters. The output signal of a concurrent dual-band transmitter is affected not only by intermodulation products but also by cross-modulation products. In one frequency band, the transmitter is excited by a two tone signal which frequency separation is swept. In the second band the transmitter is concurrently excited by an other two tone signal with slightly wider frequency separation. The frequency difference of the two signals is fixed during the frequency sweep. The two tone test is made at different power levels. The upper and lower third-order inter- and cross-modulation products are measured. The asymmetry between the upper and lower third-order inter- and cross-modulation products are measures of the transmitter's memory effects. The measurement results show that the memory effects are more dominant in the third-order intermodulation products than in the cross modulation products. An error analysis and system calibration was performed and measurement results for two different devices are presented.

Ort, förlag, år, upplaga, sidor
IEEE Press, 2015
Nyckelord
Concurrent dual-band, power amplifier, characterization, linearization, nonlinear distortion, MIMO, DPD
Nationell ämneskategori
Signalbehandling
Identifikatorer
urn:nbn:se:hig:diva-18854 (URN)10.1109/TIM.2015.2427731 (DOI)000361487500019 ()2-s2.0-84959505984 (Scopus ID)
Tillgänglig från: 2014-12-17 Skapad: 2015-01-27 Senast uppdaterad: 2018-03-13Bibliografiskt granskad

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