Empirical and deterministic approach for the optimization of wideband RF power amplifiers' behavior modeling and predistortion structure (original) (raw)
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RF-Power Amplifier Modeling and Predistortion Based on a Modular Approach
Microwave Integrated Circuit Conference European, 2006
This paper presents the black-box modelling of a microwave Power Amplifier (PA) in the nonlinear operation region and the performance of a modular predistortion model designed for this PA. A rectangle 16-QAM has been used as input signal. The nonlinearities caused by the amplifier in low IBO operating conditions (close to compression) can change the output constellation and lead to difficulties in finding the correct model parameters, as the black-box identification procedure is based on measured input/output signals. A segment of the input/output measurement data is processed to generate an initial model. Then Pseudo-Inverse Techniques are used to find a parsimonious Wiener model, that is cross-validated with the entire measurement data. The presented modelling approach results in a model intended to be numerically robust and having a high identification percentage based on the figure of merit normalized mean squared error (NMSE). Then, once having obtained a PA model, a Hammerstein based predistorter is estimated by means of the indirect learning approach (PA input-output measured data). In order to evaluate the overall performance, simulation results of the resulting predistorted output signal are provided and error vector magnitude (EVM) are shown. Experimental results of this output signal will be provided if the paper is accepted.
IEEE Transactions on Industrial Electronics, 2000
This paper introduces a new, accurate, and complexity-reduced three-nonlinear-box model that is suitable for the behavioral modeling and digital predistortion (DPD) of power amplifiers (PAs) exhibiting memory effects. This model is composed of a look-up table (LUT), a memory polynomial (MP), and an envelope MP (EMP), which are all connected in parallel, and it is termed as Parallel-LUT-MP-EMP (PLUME). The PLUME model's performance is experimentally assessed using a highly nonlinear Doherty PA driven by a multicarrier wideband code division multiple access signal. A comparison is held between the PLUME model and different state-of-the-art models reported in the literature, such as the MP model, the parallel twin nonlinear two-box model, and the generalized MP (GMP) model. The experimental results, in both behavioral modeling and DPD applications, demonstrate that the proposed PLUME model outperforms the first two models. However, it shows the same accuracy as the GMP model but with an approximately 45% reduction in the number of coefficients. This significant decrease in coefficients considerably reduces the model computational complexity. Another comparison of the resources utilized for field programmable gate array implementation of the PLUME model and the GMP model is performed, which reveals that the PLUME model uses much fewer resources than the other model. Index Terms-Behavioral modeling, digital predistortion (DPD), distortions, field programmable gate arrays (FPGA), linearity, memory effects, nonlinearity, power amplifier (PA).
2006
This paper investigates the robustness of the digital predistortion function synthesis process applied to linearize a highly non linear RF power amplifier. For this purpose, a 100-watts peak power amplifier designed for UMTS applications biased in deep class AB is used. Two approaches have been compared: the polynomial curve fitting of the measured AM/AM and AM/PM characteristics and the look-up tables synthesis using the smoothed versions of these same non linear curves. The polynomial based fitting presents badly conditioned matrices that make this approach unpractical for the considered non linearity shape particularly for DSP implementation of the synthesis procedure. The accuracy of both approaches was assessed by measuring the adjacent channel power ratio at the output of the power amplifier under a 2carriers W-CDMA signal. The look-up tables approach based on the averaging technique showed better correction capabilities than the polynomial based fitting.
Microwave , Asia-Pacific Conference, 2006
In this work two different black-box modeling strategies are combined in order to achieve improved RF Power Amplifier (PA) models based on measured input/output signals. The model validation is here done within the low input back-off (IBO) region of the power amplifier, thus showing significant nonlinear operation. The Figure of Merit (FoM) applied is the Normalized Mean Square Error (NMSE). A rectangle constellation modulation, 16-QAM, is used as input signal, and the nonlinearities caused by the low IBO operating conditions of the PA distort the output constellation.
Comparison of modeling techniques for power amplifiers
2013 23rd International Conference Radioelektronika (RADIOELEKTRONIKA), 2013
ABSTRACT Power amplifier is an essential component in communication systems. Digital baseband predistortion is a cost effective approach to linearize a power amplifiers. To study nonlinear characteristics and to construct a predistorter, accurate models of power amplifiers are necessary. In general there exist other research areas where power amplifiers models play key role. In the article several methods are described and compared. The generalized memory polynomials derived from Volterra series has proved to be simple enough with suitable results.
Behavioral Modeling and Digital Predistortion of Radio Frequency Power Amplifiers
The radio frequency power amplifier (RF-PA) within a digital wireless transmitter is a critical component regarding both the energy consumption and the signal quality. Especially due to today's broadband multicarrier modulation methods that generate signals with high peak-to-average power ratio, it is very hard to construct RF-PAs that achieve good energy efficiency and fulfill the strict linearity requirements imposed by the standard. Because of this, the digital predistortion (DPD) of RF-PAs has become a key technique for implementing energy efficient, high data rate wireless transmitters. This thesis investigates theoretical foundations and practical methods for the behavioral modeling and DPD of RF-PAs. The main contributions are a semi-physical model of the joint linearity-efficiency characteristics of RF-PAs, a detailed analysis of polynomial baseband models of RF-PAs focusing on the often neglected even-order terms in baseband, and a collection of practical methods for the dual-band DPD of RF-PAs. The trade-off between the linearity and efficiency of RF-PAs is investigated based on the semi-physical RF-PA model. For this purpose, linearity and efficiency quantification methods are introduced and applied to the model. Furthermore, an overview on highly efficient RF-PA operation modes and efficiency enhancement methods is given. A central result regarding polynomial baseband models is the first formal justification of even-order terms in baseband. This is achieved by deriving explicit passband-baseband pairs for the quasi-memoryless polynomial and the Volterra series, which show that even-order terms in baseband correspond to modified basis functionals in passband. Another central result of the presented analysis of polynomial baseband models is the formulation and proof of the phase homogeneity requirement, which represents a necessary symmetry of all complex baseband models of time-invariant passband systems. The practical methods for the dual-band DPD of RF-PAs include a method for dual-band crest factor reduction by clipping and error-filtering, a dual-band DPD model based on a vector-switched generalized memory polynomial, and a dual-band DPD training algorithm based on the indirect and direct learning architectures. These methods were implemented in MATLAB and validated at the 2017 DPD competition at the IEEE International Microwave Symposium, reaching the first place within the competition.
Optimum design of a predistortion RF power amplifier for multicarrier WCDMA applications
IEEE Transactions on Microwave Theory and Techniques, 2000
This paper provides a design guide for optimum design of an RF power amplifier with a predistortion linearizer. For a two-tone signal, three performance degradation factors, higher order terms, amplitude, and phase mismatches are analyzed quantitatively. The results are implemented to the design of optimized predistortion power amplifier for a WCDMA signal application. For the experiments, a 2.4-GHz class-AB power amplifier is fabricated using an LDMOSFET with a 30-W peak envelope power. A simple third-order predistorter is used to measure the relative phases of the harmonics, as well as to linearize the amplifier. The performance of the optimized predistortion power amplifier is excellent for a IS-95 code-division-multiple-access signal. Finally, a method for reducing the memory effects of the amplifier is devised to get a good cancellation performance for a wide-band signal, and the performance degradation caused by the memory effects is analyzed. For a forward-link four-carrier WCDMA signal, the predistortion power amplifier delivers an adjacent channel leakage ratio of 46 dBc at a 4-W average output power with a cancellation of 13.4 dB.
Frequency-Selective Predistortion Linearization of RF Power Amplifiers
IEEE Transactions on Microwave Theory and Techniques, 2000
This paper presents a frequency-selective RF vector predistortion linearization system for RF multicarrier power amplifiers (PAs) affected by strong differential memory effects. Differential memory effects can be revealed in two-tone experiment by the divergence for increasing tone-spacing of the vector Volterra coefficients associated with the lower and upper intermodulations tones. Using large-signal vector measurement with a large-singal network analyzer, a class-AB LDMOS RF PA is demonstrated to exhibit a strong differential memory effect for modulation bandwidth above 0.3 MHz. New frequency-selective RF and baseband predistortion linearization algorithms are proposed to separately address the linearization requirements of the interband and inband intermodulation products of both the lower and upper sidebands. Theoretical verification of the algorithms are demonstrated with MATLAB simulations using a Volterra/Wiener PA model with memory effects. The baseband linearization algorithm is next implemented in a field-programmable gate array and experimentally investigated for the linearization of the class-AB LDMOS PA for two carrier wideband code-division multiple-access signals. The ability of the algorithm to selectively linearize the two interband and four inband intermodulation products is demonstrated. Adjacent channel leakage ratio of up to 45 dBc for inband and interband are demonstrated experimentally at twice the typical fractional bandwidth.
A Systematic Technique for Designing Wideband RF Power Amplifiers
2006 International RF and Microwave Conference, 2006
The objective of this article is the design and implementation of wideband RF power amplifiers that can be used in different solid-state wireless transmitting systems. A systematic technique has been devised and confirmed. This technique uses the RF power transistor's optimum load and source impedances, obtained from the load-pull procedure, to characterize the RF power device at the required output
Behavioral modeling for concurrent dual-band power amplifiers using 2D hammerstein/wiener models
International Journal of RF and Microwave Computer-Aided Engineering, 2013
Behavioral modeling for the concurrent dual-band power amplifier (PA) is a critical problem in practical applications. The nonlinear distortion in the concurrent dualband PA is quite different from that in the conventional single-band PA. This article analyzes the nonlinearities in the concurrent dual-band PA and reveals that both input signals in the dual bands are important for the behavioral modeling. The 2D Hammerstein model and 2D Wiener model are proposed for the first time for the concurrent dual-band PA. They are extended versions of conventional Hammerstein and Wiener structures used in the single-band PA by including the cross-band intermodulation in the static nonlinearity block. The proposed 2D models require much less coefficients than the original work of the 2D-DPD model. Experiments were carried out for an 880 MHz/1960 MHz concurrent dualband Doherty PA to demonstrate the effectiveness of the proposed models. The results clearly show that less than À40 dB normalized mean square errors (NMSEs) are obtained in the dual bands in the behavioral modeling. V C 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE 23:646-654, 2013. Keywords: power amplifiers (PAs); concurrent dual-band; behavioral model; memory nonlinearity; Hammerstein; Wiener tion (DPD) linearization of PA [5-9]. Furthermore, as modern communication schemes employ higher order modulation signals with wide bandwidth (e.g., 5-20 MHz) and nonconstant envelopes, memory effects become another critical problem in the behavioral modeling of PA. In such a context, various behavioral models have been proposed in the literature. A memory polynomial (MP) model was proposed [2] for DPD purpose for PA. Then, the MP model was further applied in the work [6]. The work by Jebali et al. [5] proposed a Zernike polynomials model for the behavioral modeling of wideband PA. The dynamic deviation reduction-based Volterra (DDR-Volterra) model was proposed in [7] and applied to DPD linearization in [8]. As an extension of the MP model, [9] presented a generalized memory polynomial (GMP) model for PA's DPD linearization. More specifically, two-boxbased model like Hammerstein model or Wiener model is