Characterization and Linearization of Multi-channel RF Power Amplifiers
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
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.
Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology , 2015. , 45 p.
, TRITA-EE, ISSN 1653-5146 ; 2015:001
IdentifiersURN: urn:nbn:se:hig:diva-18848OAI: oai:DiVA.org:hig-18848DiVA: diva2:783324
2015-01-23, 99132, Kungsbäcksvägen 47, Gävle, 10:00 (English)
Gustavsson, Ulf, PhD
Rönnow, DanielHändel, Peter
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