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Characterization and Linearization of Multi-channel RF Power Amplifiers
KTH, School of Electrical Engineering (EES), Signal Processing. University of Gävle, Sweden.ORCID iD: 0000-0003-1183-6666
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The demands for high data rates and broadband wireless access require the development of wireless systems that can support wide and multi-band signals. To deploy these signals, new radio frequency (RF) front-ends are required which impose new challenges in terms of power consumption efficiency and sources of distortion e.g., nonlinearity. These challenges are more pronounced in power amplifiers (PAs) that degrade the overall performance of the RF transmitter. Since it is difficult to optimize the linearity and efficiency characteristics of a PA simultaneously, a trade-off is needed. At high input power, a PA exhibits high efficiency at the expense of linearity. On the other hand, at low input power, a PA is linear at the expense of the efficiency. To achieve linearity and efficiency at the same time, digital pre-distortion (DPD) is often used to compensate for the PA nonlinearity at high input power. In case of multi-channel PAs, input and output signals of different channels interact with each other due to cross-talk. Therefore, these PAs exhibit different nonlinear behavior than the single-input single-output (SISO) PAs. The DPD techniques developed for SISO PAs do not result in adequate performance when used for multi-channel PAs. Hence, an accurate behavioral modeling is essential for the development of DPD for multi-channel RF PAs. In this thesis, we propose three novel behavioral models and DPD schemes for nonlinear multiple-input multiple-output (MIMO) transmitters in presence of cross-talk. A study of the source of cross-talk in MIMO transmitters have 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 that with partially non-coherent signal generation, the performance of the DPD degrades compared to coherent signal generation. In context of multi-channel RF transmitters, PA behavioral models and DPD schemes suffer from a large number of model parameters with the increase in nonlinear order and memory depth. This growth leads to high complexity model identification and implementation. We have designed a DPD scheme for MIMO PAs using a sparse estimation technique for reducing model complexity. This technique also increases the numerical stability when linear least square estimation model identification is used. A method to characterize the memory effects in a nonlinear concurrent dual-band PAs is also presented. Compared to the SISO PAs, concurrent dual-band PAs are not only affected by intermodulation distortions but also by cross-modulation distortions. The characterization of memory effects inconcurrent dual-band transmitter is performed by injecting a two-tone test signal in each input channel of the transmitter. Asymmetric energy surfaces are introduced for the intermodulation and cross-modulation products, which can be used to identify the power and frequency regions where the memory effects are dominant.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. , vii, 45 p.
Series
TRITA-EE, ISSN 1653-5146 ; 2015:001
National Category
Signal Processing
Research subject
Electrical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-157154ISBN: 978-91-7595-388-5 (print)OAI: oai:DiVA.org:kth-157154DiVA: diva2:769426
Presentation
2015-01-23, 99132, Kungsbäcksvägen 47, Gävle, 10:00 (English)
Opponent
Supervisors
Note

QC 20141217

Available from: 2014-12-17 Created: 2014-12-08 Last updated: 2016-11-30Bibliographically approved
List of papers
1. Behavioral modeling and linearization of crosstalk and memory effects in RF MIMO transmitters
Open this publication in new window or tab >>Behavioral modeling and linearization of crosstalk and memory effects in RF MIMO transmitters
2014 (English)In: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 62, no 4, 810-823 p.Article in journal (Refereed) Published
Abstract [en]

This paper proposes three novel models for behavioral modeling and digital pre-distortion (DPD) of nonlinear 2 x 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 x 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 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.

Keyword
Behavioral modeling, digital pre-distortion (DPD), multiple-input multiple-output (MIMO), nonlinear and linear crosstalk, power amplifiers (PAs), RF
National Category
Signal Processing
Identifiers
urn:nbn:se:kth:diva-142568 (URN)10.1109/TMTT.2014.2309932 (DOI)000334525600010 ()2-s2.0-84898403156 (Scopus ID)
Note

QC 20140505

Available from: 2014-03-13 Created: 2014-03-07 Last updated: 2017-12-05Bibliographically approved
2. Combating the Dimensionality of Nonlinear MIMOAmplifier Predistortion by Basis Pursuit
Open this publication in new window or tab >>Combating the Dimensionality of Nonlinear MIMOAmplifier Predistortion by Basis Pursuit
2014 (English)In: Proceedings of the 44th European Microwave Conference, 2014, 833-836 p.Conference paper, Published paper (Refereed)
Abstract [en]

A general description of nonlinear dynamic MIMOsystems, given by Volterra series, has significantly larger complex-ity than SISO systems. Modeling and predistortion of MIMOamplifiers consequently become unfeasible due to the largenumber of basis functions. We have designed digital predistortersfor a MIMO amplifier using a basis pursuit method for reducingmodel complexity. This method reduces the numerical problemsthat appear in MIMO Volterra predistorters due to the largenumber of basis functions. The number of basis functions wasreduced from 1402 to 220 in a 2x2 MIMO amplifier and from127 to 13 in the corresponding SISO case. Reducing the numberof basis functions caused an increase of approximately 1 dB ofmodel error and adjacent channel power ratio.

Keyword
Digital pre distortion (DPD), MIMO power ampli- fiers, LASSO, basis pursuit, power amplifier linearization.
National Category
Electrical Engineering, Electronic Engineering, Information Engineering Communication Systems
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-154563 (URN)
Conference
44th European Microwave Conference,Roma, Italy on October 5-10, 2014
Note

QC 20141117

Available from: 2014-10-23 Created: 2014-10-23 Last updated: 2016-11-30Bibliographically approved
3. Characterization of a Concurrent dual-band Power Amplifier using a dual-tone excitation signals
Open this publication in new window or tab >>Characterization of a Concurrent dual-band Power Amplifier using a dual-tone excitation signals
2014 (English)In: IEEE Transactions on Instrumentation and Measurement, ISSN 0018-9456, E-ISSN 1557-9662Article in journal (Other academic) Submitted
National Category
Signal Processing
Identifiers
urn:nbn:se:kth:diva-157862 (URN)
Note

QC 20141217

Available from: 2014-12-17 Created: 2014-12-17 Last updated: 2017-12-05Bibliographically approved
In thesis
1. Characterization and Linearization of Multi-band Multi-channel RF Power Amplifiers
Open this publication in new window or tab >>Characterization and Linearization of Multi-band Multi-channel RF Power Amplifiers
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The World today is deeply transformed by the advancement in wireless technology. The envision of a smart society where interactions between physical and virtual dimensions of life are intertwined and where human interaction is mediated by machines, e.g., smart phones, demands increasingly more data traffic. This continual increase in data traffic requires re-designing of the wireless technologies for increased system capacity and flexibility. In this thesis, aspects related to behavioral modeling, characterization, and linearization of multi-channel/band power amplifiers (PAs) are discussed.

When building a model of any system, it is advantageous to take into account the knowledge of the physics of the system and include into the model. This approach could help to improve the model performance. In this context, three novel behavioral models and DPD schemes for nonlinear MIMO transmitters are proposed.

To model and compensate distortions in GaN based RF PAs in presence of long-term memory effects, novel models for SISO and concurrent dual-band PAs are proposed. These models are based on a fixed pole expansion technique and have infinite impulse response. They show substantial performance improvement. A behavioral model based on the physical knowledge of the concurrent dual-band PA is derived, and its performance is investigated both for behavioral modeling and compensation of nonlinear distortions.

Two-tone characterization is a fingerprint method for the characterization of memory effects in dynamic nonlinear systems. In this context, two novel techniques are proposed. The first technique is a dual two-tone characterization technique to characterize the memory effects of self- and cross-modulation products in concurrent dual-band transmitter. The second technique is for the characterization and analysis of self- and cross-Volterra kernels of nonlinear 3x3 MIMO systems using three-tone signals.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2017. 59 p.
Series
TRITA-EE, ISSN 1653-5146 ; 2016:185
National Category
Signal Processing
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-197266 (URN)978-91-7729-198-5 (ISBN)
Public defence
2017-02-24, 99133, Kungsbäcksvägen 47, Gävle, 10:15 (English)
Opponent
Supervisors
Note

QC 20161205

Available from: 2016-12-05 Created: 2016-11-30 Last updated: 2016-12-05Bibliographically approved

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