| 1. |
- Amin, Shoaib, et al.
(författare)
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Behavioral modeling and linearization of crosstalk and memory effects in RF MIMO transmitters
- 2014
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Ingår i: IEEE transactions on microwave theory and techniques. - 0018-9480 .- 1557-9670. ; 62:4, s. 810-823
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
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| 3. |
- Amin, Shoaib, 1985-, et al.
(författare)
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Noise Impact on the Identification of Digital Predistorter Parameters in the Indirect Learning Architecture
- 2012
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Ingår i: 2012 Swedish Communication Technologies Workshop (Swe-CTW). - : IEEE conference proceedings. - 9781467347631 ; , s. 36-39
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Konferensbidrag (refereegranskat)abstract
- The indirect learning architecture (ILA) is the mostused methodology for the identification of Digital Pre-distorter (DPD) functions for nonlinear systems, particularly for high power amplifiers. The ILA principle works in black box modeling relying on the inversion of input and output signals of the nonlinear system, such that the inverse is estimated. This paper presents the impact of disturbances, such as noise in the DPD identification. Experiments were performed with a state-of-art Doherty power amplifier intended for base station operation in current telecommunication wireless networks. As expected, a degradation in the performance of the DPD (measured innormalized mean square error (NMSE)) is found in our experiments. However, adjacent channel power ratio (ACPR) can be a misleading figure of merit showing improvement in the performance for wrongly estimated DPD functions.
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| 4. |
- Björsell, Niclas, et al.
(författare)
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Kautz-Volterra modelling of analogue-to-digital converters
- 2010
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Ingår i: Computer Standards & Interfaces. - : Elsevier BV. - 0920-5489 .- 1872-7018. ; 32:3, s. 126-129
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Tidskriftsartikel (refereegranskat)abstract
- In many test and measurement applications, the analogue-to-digital converter (ADC) is the limiting component. Using post-correction methods can improve the performance of the component as well as the over all measurement system. In this paper an ADC is characterised by a Kautz-Volterra (KV) model, which utilises a model-based post-correction of the ADC with general properties and a reasonable number of parameters. It is also shown that the inverse model has the same dynamic properties as the direct KV model. Results that are based on measurements on a high-speed 12-bit ADC, shows good results for a third order model.
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| 5. |
- Johansson, Anders, et al.
(författare)
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An analysis of Kautz-Volterra models for modeling block structure nonlinear systems
- 2010
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Kautz-Volterra (KV) models of some nonlinear systems were analyzed. The relationsbetween the true pole of the analyzed systems and the optimal pole of the KV modelswere analyzed. The properties of nonlinear systems depend on the order of thesubsystems, since nonlinear operators do not commute. Wiener (H-N) andHammerstein (N-H) systems were analyzed.
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| 6. |
- Landin, Per Niklas, 1983-, et al.
(författare)
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Odd and Odd-Even Memory Polynomial Representations
- 2013
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- It is shown that the absolute value of a complex-valued function can be expressed as a polynomial in the square of the absolute value of the function. A series expansion is given and related to the Volterra-series. The results find application in explaining and improving the understanding of the “even” order memory polynomial models.
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| 7. |
- Nader, Charles, 1982-, et al.
(författare)
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Peak-power controlling technique for enhancing digital pre-distortion of RF power amplifiers
- 2012
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Ingår i: IEEE transactions on microwave theory and techniques. - 0018-9480 .- 1557-9670. ; 60:11, s. 3571-3581
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we present a method to limit the generation of signal peak power at the output of a digital pre-distorter that is applied to a RF power amplifier (PA) operating in strong compression. The method can be considered as a joint crest-factor reduction and digital pre-distortion (DPD). A challenging characteristic of DPD when applied to a PA in strong compression is the generation of relatively high peaks due to the DPD expansion behavior. Such high peaks generation, which may be physically unrealistic, can easily damage the amplification system. Such a phenomenon, referred in this study as DPD-avalanche, is more noticed when the signal exciting the PA is compressed due to crest-factor reduction. The suggested method for controlling such DPD-avalanche is based on shaping the input signal to the DPD in such a way to keep the pre-distorted signal peak power below or near the maximum allowed peak power of the PA. The suggested method is tested experimentally on a Class-AB and a Doherty PA when excited with a wideband orthogonal frequency-division multiplexing (OFDM) signal. Scenarios for an OFDM signal with and without crest-factor reduction are evaluated. Measurement results when using the proposed DPD-avalanche controller show smooth deterioration of the in-band and out-of-band linearity compared to steep deterioration when no controller is used. In addition, the suggested controller offers a higher operating power range of the DPD while fulfilling out-of-band distortion requirements and preserving low in-band error.
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| 8. |
- Piazza, Roberto, et al.
(författare)
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Multicarrier Digital Pre-distortion/ EqualizationTechniques for Non-linear Satellite Channels
- 2012
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Ingår i: Proc. 30th AIAA Intern.Commun. Satellite Syst. Conference. - Reston, Virigina : American Institute of Aeronautics and Astronautics. ; , s. 1-5
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Konferensbidrag (refereegranskat)abstract
- Two key advances are envisaged for future missions: (a) spectrally efficienttransmission to meet the increasing demand and (b) sharing of satellite capacityamong different links to meet power/mass requirements. Joint amplification ofmultiple-carrier DVB-S2 signals using a single High-Power Amplifier (HPA) is aparticular application of satellite resource sharing. However, effects specific to sucha scenario that degrade power and spectral efficiencies include (a) an increasedAdjacent Channel Interference caused by non-linear characteristic of the HPA and(b) increased peak to average power ratio. The paper studies signal processingtechniques – digital pre-distortion (DPD) at the gateway and equalization (EQ) atthe User Terminal – to mitigate the non-linear effects and improve power as well asspectral efficiencies. While the algorithms for DPD and EQ are described inliterature, their use in multi-carrier scenario is novel and poses new challenges thatare investigated in the paper.
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| 9. |
- Piazza, Roberto, et al.
(författare)
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Sensitivity Analysis of Multicarrier Digital Pre-distortion/ Equalization Techniques for Non-linear Satellite Channels
- 2013
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Ingår i: 31st AIAA International Communications Satellite Systems Conference, ICSSC 2013. - Reston, Virginia : American Institute of Aeronautics and Astronautics. - 9781624102448
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Konferensbidrag (refereegranskat)abstract
- In order to mitigate the nonlinear distortion appearing in multicarrier satellite operation a significant back off is required, leading to power efficiency loss. This motivates the need to study techniques to improve power and spectral efficiencies. These techniques – digital pre-distortion (DPD) at the gateway and equalization (EQ) at the User Terminal– have been well documented in literature for single carrier per HPA 2-7and only a few results are available for multicarrier case8-10. This paper builds on our initial work in Ref.1 that performed a survey on the adaptability of various compensation techniques to the considered scenario and short-listed the most favourable ones. Preliminary performance analysis of these techniques was undertaken with Signal to Interference Ratio (SINR) as the figure of merit. The contribution of this work over Ref. 1 is twofold : (a) a full DVB-S2 chain is simulated with the chosen techniques with Total Degradation (TD) as the figure of merit and (b) a sensitivity analysis is performed to study the dependence of the pre-distortion/ equalization performance ( measured as TD) on the channel parameters. This study will provide insights into the commercial viability of using single on-board HPA along with the on-ground compensation techniques. Of particular interest would be the analysis of the performance provided by the on ground processing techniques with respect to the amplifier technology (linearized/non-linearized TWTAs). In the paper we describe: the scenario supporting multiple carriers per HPA, the non-linear channel model and its implications to multiple carrier transmissions in Section II, Enhancement techniques DPD and EQ in Section III and their simulation results in Section IV. Conclusions are drawn in Section V.
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| 10. |
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