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  • 1. Andersen, O.
    et al.
    Wisell, David
    KTH, School of Electrical Engineering (EES), Signal Processing. University of Gävle, Sweden.
    Keskitalo, N.
    Stenvard, P.
    Cost effective high performance modular instrumentation, signal generation and signal analysis for future mobile communication systems2007In: 2007 IEEE Autotestcon, IEEE , 2007, p. 660-668Conference paper (Refereed)
    Abstract [en]

    A decrease in life cycle cost is a key issue for testing of mobile communication systems. The rapid development and edge technology requires high performance instruments and state of the art measurement technology. It is desired to use virtual/synthetic instruments and put the measurement technology in software independent of hardware, i.e. software driven measurements. Increased flexibility and modularization, both in hardware and software, are requirements to support the cost decrease. The hardware basis is signal generation and signal analysis. In this paper state of the art signal generation and signal analysis capabilities are demonstrated in a modular and flexible architecture. A direct IF synthesis is used to generate 1 WideBand Code-Division Multiple Access (WCDMA) carrier with more than 72 dB Adjacent Carrier Leakage Ratio (ACLR) 2 carrier with more than 68 dBc ACLR over a total bandwidth of 100 MHz. The signal analysis capabilities, ACLR performance, for a WCDMA carrier is better than -70 dBc and for a continuous wave better than -85 dBc over a bandwidth of 42.5 MHz. The critical down converter in the set up doesn't degrade the performance.

  • 2.
    Isaksson, Magnus
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. University of Gävle, Sweden .
    Wisell, David
    KTH, School of Electrical Engineering (EES), Signal Processing. University of Gävle, Sweden .
    Eng, A.
    Rönnow, D.
    A study of a variable-capacitance drain network's influence on dynamic behavioral modeling of an RF power amplifier2007In: 69th ARFTG Microwave Measurements Conference - Addressing Metrology Needs for Future High-Speed Information and Communications Systems, 2007, p. 5456336-Conference paper (Refereed)
    Abstract [en]

    An investigation of the complex-valued parameters of two different dynamic behavioral models due to changes in the drain decoupling network of a PA has been performed. The study is based on complex-envelope measurements on a real PA. The complex coefficients of the parallel Hammerstein (PH) and the optimal pole placements of the Kautz-Volterra (KV) models are analyzed. It is concluded that the parameters follow smooth, predictable functions and that the KV poles give a robust description of the PA's memory effects compared with the PH model.

  • 3.
    Isaksson, Magnus
    et al.
    University of Gävle.
    Wisell, David
    University of Gävle.
    Rönnow, Daniel
    University of Gävle.
    A Comparative Analysis of Behavioral Models for RF Power Amplifiers2006In: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 54, no 1, p. 348-359Article in journal (Refereed)
    Abstract [en]

    A comparative study of nonlinear behavioral models with memory for radio-frequency power amplifier (PAs) is presented. The models are static polynomial, parallel Hammerstein (PH), Volterra, and radial basis-function neural network (RBFNN). Two PAs were investigated: one was designed for the third-generation (3G) mobile telecommunication systems and one was designed for the second-generation (2G). The RBFNN reduced the total model error slightly more than the PH, but the error out of band was significantly lower for the PH. The Volterra was found to give a lower model error than did a PH of the same nonlinear order and memory depth. The PH could give a lower model error than the best Volterra, since the former could be identified with a higher nonlinear order and memory depth. The qualitative conclusions are the same for the 2G and 3G PAs, but the model errors are smaller for the latter. For the 3G PA, a static polynomial gave a low model error as low as the best PH and lower than the RBFNN for the hardest cross validation. The models with memory, PH, and RBFNN, showed better cross-validation performance, in terms of lower model errors, than a static polynomial for the hardest cross validation of the 2G PA.

  • 4.
    Isaksson, Magnus
    et al.
    University of Gävle.
    Wisell, David
    Ericsson AB, Gävle.
    Rönnow, Daniel
    University of Gävle.
    Wide-band dynamic modeling of power amplifiers using radial-basis function neural networks2005In: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 53, no 11, p. 3422-3428Article in journal (Refereed)
    Abstract [en]

    A radial-basis function neural network (RBFNN) has been used for modeling the dynamic nonlinear behavior of an RF power amplifier for third generation. In the model, the signal's envelope is used. The model requires less training than a model using IQ data. Sampled input and output signals were used for identification and validation. Noise-like signals with bandwidths of 4 and 20 MHz were used. The RBFNN is compared to a parallel Hammerstein (PH) model. The two model types have similar performance when no memory is used. For the 4-MHz signal, the RBFNN has better in-band performance, whereas the PH is better out-of-band, when memory is used. For the 20-MHz; signal, the models have similar performance in- and out-of-band. Used as a digital-predistortion algorithm, the best RBFNN with memory suppressed the lower (upper) adjacent channel power 7 dB (4 dB) compared to a memoryless nonlinear predistorter and 11. dB (13 dB) compared to the case of no predistortion for the same output power for a 4-MHz-wide signal.

  • 5.
    Landin, Per Niklas
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Nader, Charles
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Björsell, Niclas
    Center for RF Measurement Technology, Univeristy of Gävle.
    Isaksson, Magnus
    Wisell, David
    Ericsson AB, Stockholm.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Andersen, Olav
    Ericsson AB, Gävle.
    Keskitalo, Niclas
    Center for RF Measurement Technology, University of Gävle.
    Wideband Characterization of Power Amplifiers Using Undersampling2009In: 2009 IEEE MTT-S International Microwave Symposium Digest, 2009, p. 1365-1368Conference 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.

  • 6.
    Rönnow, Daniel
    et al.
    WesternGeco AS, Oslo.
    Wisell, David
    Ericsson AB, Gävle.
    Isaksson, Magnus
    Department of Electronics, University of Gävle.
    Three-Tone Characterization of Nonlinear Memory Effects in Radio Frequency Power Amplifier2007In: IEEE Transactions on Instrumentation and Measurement, ISSN 0018-9456, E-ISSN 1557-9662, Vol. 56, no 6, p. 2646-2657Article in journal (Refereed)
    Abstract [en]

    A stepped three-tone measurement technique based on digitally modulated baseband signals is used in characterizing radio-frequency power amplifiers (PAs). The bandwidths of the stepped measurement were 8.8 MHz for the input signal and 26.4 MHz for the output signal. A PA designed for third-generation mobile telecommunication system was analyzed. The amplitude and phase of the third-order Volterra kernel were determined from the identified intermodulation products. The properties of the Volterra kernel along certain paths in the 3-D frequency space were analyzed and compared to some box models for non-linear systems. The main symmetry of the third-order Volterra kernel of this PA was found to be of the type given by the cascaded quadratic nonlinearities with a linear filter in between (a Hammerstein-Wiener system), and frequency dependence, i.e., memory effects, was found to be due to the effects at the baseband.

  • 7.
    Wisell, David
    Department of Technology, Ericsson AB, University of Gävle.
    A Baseband Time Domain Measurement System for Dynamic Characterisation of Power Amplifiers with High Dynamic Range over Large Bandwidths2003In: Conference Record - IEEE Instrumentation and Measurement Technology Conference, 2003, p. 1177-1180Conference paper (Refereed)
    Abstract [en]

    This paper describes, and discusses in some detail, a measurement system for dynamic characterisation of power amplifiers. The system uses data that are generated and collected at baseband to accurately calculate AM/AM and AM/PM distortion as well as memory effects in the amplifiers. The limitations of the system in terms of dynamic range and bandwidth are discussed as well as techniques to overcome them.

  • 8.
    Wisell, David
    KTH, School of Electrical Engineering (EES), Signal Processing. Ericsson AB, Gävle, Sweden .
    Exploring the sampling rate requirements for behavioural amplifier modelling2006In: 18th IMEKO World Congress 2006: Metrology for a Sustainable Development, 2006Conference paper (Refereed)
    Abstract [en]

    In this paper it is shown that for the purpose ofnonlinear power amplifier behavioural modelling, thesampling rate can be set to the Nyquist rate of the inputsignal, rather than to the Nyquist rate of the output signal bymaking use of Zhu’s generalized sampling theorem. Thisclaim is supported by measurements on a basestation poweramplifier. The findings are that the model error obtainedwhen the output signal is sampled at the Nyquist rate of theinput signal is approximately 1.5 dB higher than when thesampling rate is set to the Nyquist rate of the output signal.However, if a sampling rate of twice the Nyquist rate of theinput signal is used, which is still typically, much lower thanthe Nyquist rate of the output signal, the degradation is only0.2 dB. These are important findings that will substantiallyease the requirements on ADCs used in measurement setupsused for amplifier modelling.

  • 9.
    Wisell, David
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Measurement Techniques for Characterization of Power Amplifiers2007Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    In this thesis a sampling time domain measurement system primarily intended for measurements on radio frequency power amplifiers is discussed. The need for such a measurement system is established. Impairments due to non-ideal measurement instruments are discussed as well as methods to compensate for these impairments. Techniques to improve upon the raw measurement performance of the measurement instruments with regard to bandwidth, dynamic range, linear and nonlinear distortion are discussed.

    | A method to simultaneously find the phase and amplitude ripple of a vector signal generator and a vector signal analyzer is presented. The method is verified with extensive measurements.

    Two techniques, frequency stitching and Zhu’s generalized sampling theorem, to extend the effective measurement bandwidth of the measurement system is discussed and evaluated with measurements. They are both found to be able to extend the effective bandwidth for measurements of output signals of nonlinear power amplifiers with more than five times.

    The measurement system is used for sampled input – output measurements of power amplifiers and the obtained data are fitted to different behavioral power amplifier models including memory. Some different behavioral models are evaluated and compared for different kinds of power amplifiers. A neural network model and extensions to the well-known parallel Hammerstein model are specifically discussed. The parallel Hammerstein model are also used together with frequency stitching and Zhu’s generalized sampling theorem.

    A general hardware and software structure of a versatile measurement system based on virtual instruments for measurements on power amplifiers is discussed in some detail. Special attention is given to the software architecture and to the concepts of hardware and software reusability.

    An automated, fast, accurate and production-friendly method for two-tone power and frequency sweep measurements, including measurement of the phase of the intermodulation products in addition to the amplitude, is also presented.

  • 10.
    Wisell, David
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Implementation Considerations on the Use of Zhu's General Sampling Theorem for Characterization of Power Amplifiers2007In: Conference Record - IEEE Instrumentation and Measurement Technology Conference, 2007, p. 612-615Conference paper (Refereed)
    Abstract [en]

    In this paper Zhu's generalized sampling theorem for sampling of the output signal of a nonlinear system is applied to the case of radio frequency power amplifier modeling. The paper deals in some detail with hardware implementational issues in order to optimize the hardware design in order to make full use of the benefits given by Zhu's generalized sampling theorem. It is shown that some design changes have to be done compared to more traditional receiver designs, such as removing the anti-aliasing filters. It is also shown that the behavioral ampler models that are extracted using data taken using Zhu's generalized sampling theorem have equal or better performance with regard to out-of-band spectral emissions than when the models are extracted using data taken using Nyquist sampling of the output signal of the amplifier.

  • 11.
    Wisell, David
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Simultaneous Measurement of Transmitter and Receiver Magnitude and Phase Ripple2009Report (Other academic)
    Abstract [en]

    This paper describes a method to simultaneously measure the amplitude and phase ripple of two band pass linear systems in cascade by changing the center frequency for one of the systems. Extensive measurements are presented to support the theory.

    The method has a wide applicability for measurements on RF power amplifiers, transmitters, receivers, etc. The accuracy of the method is in the order of a few hundredths of a dB and one degree for most realistic measurement set-ups.

  • 12.
    Wisell, David
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. University of Gavle, Sweden.
    Isaksson, Magnus
    KTH, School of Electrical Engineering (EES), Signal Processing. University of Gavle, Sweden.
    Keskitalo, N.
    A general evaluation criteria for behavioral power amplifier modeling2007In: 69th ARFTG Microwave Measurements Conference - Addressing Metrology Needs for Future High-Speed Information and Communications Systems, 2007, p. 5456311-Conference paper (Refereed)
    Abstract [en]

    In this paper a new goodness measure for behavioral complex envelope power amplifier models is defined in the frequency domain. The measure can be calculated for any input signal using the same formulas, which makes it general and easy to use. The results will however be dependent on the input signal. The total model error, or normalized mean-square error, for power amplifier models are normally dominated by the in-band error, often mainly caused by the linear distortion. The new measure is aimed at capturing the nonlinear modeling performance of the amplifier model. This is of interest since it is most often the nonlinear, rather than the linear, distortion that causes most harm in real-life power amplifier applications.

  • 13.
    Wisell, David
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Isaksson, Magnus
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Keskitalo, N.
    University of Gävle, Dept. of Electronics.
    Rönnow, D.
    University of Gävle, Dept. of Electronics.
    Wideband Characterization of a Doherty Amplifier Using Behavioral Modeling2007In: 2006 67th ARFTG Microwave Measurements Conference: Measurements and Design of High Power Devices and Systems, 2007Conference paper (Refereed)
    Abstract [en]

    A Doherty amplifier was investigated using behavioral amplifier modeling techniques. A measurement system for simultaneous wide bandwidth (>100 MHz) and large dynamic range (similar to 70 dBc ACLR) sampled measurements that are needed for the behavioral modeling is presented. Both the measurement system and the performance of the Doherty amplifier are described. The findings are that the well known and widely used parallel Hammerstein model, also denoted the memory polynomial model, is well suitable also for modeling and predistortion of Doherty amplifiers, and that a Doherty amplifier can be designed with only minor memory effects. This is seen in the modeling error, which is reduced by 13 dB, compared with a constant gain, using a memoryless polynomial model and only 6 dB further by adding memory to the model.

  • 14. Wisell, David
    et al.
    Jaldén, Joakim
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Behavioral Power Amplifier Modeling Using the LASSO2008In: 2008 IEEE INSTRUMENTATION AND MEASUREMENT TECHNOLOGY CONFERENCE, 2008, p. 1864-1867Conference paper (Refereed)
    Abstract [en]

    In this paper we use regularization; in the form of the LASSO, as identification procedure in order to find the parameters of the parallel Hammerstein model for behavioral power amplifier modeling. It is shown that the LASSO chooses a subset of the parameters of the parallel Hammerstein model in a systematic way and thereby reduces the number of model parameters while maintaining the performance. The values of the parameters are also smaller than when the ordinary least-squares algorithm is used for the parameter extraction since the LASSO imposes a limit on the L1-norm of the parameters Thus, the problem with larger and sometimes very large, parameters that is often encountered in behavioral power amplifier modeling is avoided Experimental results from measurements on a power amplifier intended for the 3G WCDMA system is provided to support the theory.

  • 15.
    Wisell, David
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Keskitalo, N.
    A Behavioral Power Amplifier Model that Includes the Average Power Level2006In: ARFTG 68, Boulder, CO.Article in journal (Refereed)
  • 16.
    Wisell, David
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. University of Gävle, Dept. of Electronics, Gävle, SE-80176, Sweden; Ericsson AB, Box 6206, Gävle, SE-80006, Sweden.
    Keskitalo, N.
    A behavioral power amplifier model that includes the average power level2018In: 2006 68th ARFTG Conference on Measurement for Emerging Technologies, ARFTG 2006, Institute of Electrical and Electronics Engineers (IEEE), 2018Conference paper (Refereed)
    Abstract [en]

    In this paper a behavioral power amplifier model that incorporates the average input power level is proposed. The result is a model that can accurately predict the output signal of the amplifier for all input power levels. The model is validated using measurements on a radio base station power amplifier and it is found that it does indeed has improved generalization capabilities with regard to input power level compared to previous models.

  • 17.
    Wisell, David
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Ronnow, Daniel
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    A bandwidth extension technique for dynamic characterization of power amplifiers2006In: 2006 IEEE Instrumentation and Measurement Technology Conference Proceedings, 2006, p. 1972-1976Conference paper (Refereed)
    Abstract [en]

    In this paper a method for increasing the bandwidth of a test-bed for dynamic characterization of power amplifiers is described. The technique is readily implemented using commercially available instruments which makes it suitable for e.g. production testing The bandwidth extension technique is combined with coherent averaging of the measurements in order to simultaneously increase the bandwidth and dynamic range of the test-bed. In addition the errors in the obtained wideband signal are estimated. The method is evaluated experimentally on a basestation power amplifier for the 3G WCDAM system.

  • 18.
    Wisell, David
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Rudlund, Björn
    Racomna AB, Uppsala.
    Rönnow, Daniel
    Department of Electronics, University of Gävle.
    Characterization of memory effects in power amplifiers using digital two-tone measurements2007In: IEEE Transactions on Instrumentation and Measurement, ISSN 0018-9456, E-ISSN 1557-9662, Vol. 56, no 6, p. 2757-2766Article in journal (Refereed)
    Abstract [en]

    In this paper, a novel method to measure the amplitude and phase of two-tone third-order intermodulation products generated in a high-power amplifier is presented. The method is based on the sampled input and output signals of the amplifier. The presented measurement setup and the associated algorithms for the calculation of the amplitudes and phases are considerably faster and simpler than the current methods. By making use of the sampled input and output signals of the amplifier and the signal processing techniques, the need for a nonlinear reference, a tunable attenuator, and a phase shifter in the existing measurement setups is eliminated, which makes it simple and easy to use. Hence, this is a substantial simplification of the measurement setup compared to what has been reported earlier. The proposed measurement setup is also suitable for fast automated measurements, which is of interest for many applications that are both laboratory and production oriented. In addition, a method to increase the bandwidth of the measured signal is used to overcome the bandwidth limitation set by the Nyquist criteria for sampled systems. Measurements are done on two base-station high-power amplifiers and are found to be in agreement with theory and reference measurements.

  • 19.
    Wisell, David
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Rönnow, Daniel
    Department of Electronics, University of Gävle.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    A technique to extend the bandwidth of an RF power amplifier test bed2007In: IEEE Transactions on Instrumentation and Measurement, ISSN 0018-9456, E-ISSN 1557-9662, Vol. 56, no 4, p. 1488-1494Article in journal (Refereed)
    Abstract [en]

    In this paper, a method for increasing the bandwidth of a test bed for dynamic characterization of power amplifiers (PAs) is described. The technique is readily implemented using commercially available instruments, which makes it suitable for, e.g., production testing. The bandwidth extension technique is combined with coherent averaging of the measurements in order to simultaneously increase the bandwidth and dynamic range of the test bed. The errors in the obtained wideband signal are also estimated. The method is evaluated experimentally on a base station PA for the third-generation wideband code division multiple access system and on a Doherty amplifier. A tenfold increase in bandwidth to a total of 144 MHz and a more than 10-dB increase in dynamic range to 78 dB were obtained in practice. In addition, the obtained wideband signal is used for behavioral amplifier modeling.

  • 20.
    Wisell, David
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. University of Gävle, Sweden.
    Stenvard, Patrik
    Ericsson AB, Stockholm.
    Hansebacke, Anders
    Ericsson AB, Stockholm.
    Keskitalo, Niclas
    Ericsson AB, Stockholm.
    Considerations when Designing and Using Virtual Instruments as Building Blocks in Flexible Measurement System Solution2007In: 2007 IEEE Instrumentation and Measurement Technology Conference, IEEE , 2007, p. 382-386Conference paper (Refereed)
    Abstract [en]

    In this paper the software and hardware structure of a virtual instrument measurement system is discussed. The focus is on flexibility, modularity, generality and hardware independence. A software architecture that meets these requirements is proposed and discussed in some detail. The proposed software architecture has a layered structure that makes it suitable for implementation of versatile measurement systems. The measurement functionality is encapsulated in its own, hardware independent layer and communicates with its environment, e.g. physical hardware, through intermediary software components. Finally a measurement system for characterization of power amplifiers that is designed following the proposed software architecture, with software driven measurements, is implemented.

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