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This paper reports a new measurement method for wideband radiofrequency power amplifier (PA) characterization and digital predistortion. The proposed measurement procedure significantly relaxes the sampling rate requirement on the analog-to-digital converters of the feedback path. Successful PA linearizations were achieved in the presence of 20, 40, and 60-MHz LTE-A signals using a vector signal analyzer with sampling speeds equal to only 24, 40.96, and 61.44 Ms/s, respectively. Despite these very low sampling rates, a quasiperfect cancellation of the PA distortions was achieved (more than 50 dBc in terms of ACLR), in all tests, over bandwidths including up to fifth-order intermodulation distortions. Such a correction bandwidth is much wider than the observation bandwidths associated with the receiver sampling rates. [ABSTRACT FROM PUBLISHER]

In this paper, a novel weighted memory polynomial (WMP)-based model is proposed for wireless transmitters and radio-frequency power amplifiers' (PAs) behavioral modeling and predistortion. The new model introduces an instantaneous-power-dependent weight function on the static and dynamic terms of the conventional memory polynomial (MP) model. Experimental validation in both modeling and predistortion contexts was performed on a PA prototype driven by a 20-MHz Long Term Evolution signal. The proposed model was assessed against the standard MP model. The experimental results demonstrate the superiority of the proposed polynomial in behavioral modeling applications as it results in up to 50% (3-dB) improvement in the normalized mean square error for the same number of coefficients. The model robustness was then validated by using a second test signal applied to two Doherty PAs using different transistor technologies. Furthermore, when applied for digital predistortion, the proposed WMP function achieves the same performance as the state-of-art MP while requiring approximately 50% less coefficients. [ABSTRACT FROM PUBLISHER]

This paper investigates the effects of crest factor reduction and digital predistortion on the performances of communication and broadcasting systems. The overdrive of digitally predistorted power amplifiers is proposed for power efficient linear amplification of amplitude modulated signals having high peak to average power ratio. This is achieved by adding, at the input of the digital predistortion system, a clipping function to allow for an overdrive of the linearized power amplifier while meeting spectrum emission mask linearity requirements. The proposed technique is experimentally validated using a GaN Doherty power amplifier driven by long-term evolution (LTE) signals. Measurement results show that the overdriven power amplifier can deliver up to 2.5 dB extra output power, up to 80% enhancement in the power utilization factor, and up to 20% relative increase in the power efficiency while being compliant with the linearity requirements of the LTE standard. [ABSTRACT FROM PUBLISHER]

This paper reports an envelope tracking (ET) transmitter architecture for multi-band/widely-spaced carrier signals. Due to the bandwidth limitations of the envelope modulator, the dynamic supply voltage is controlled by combining the low frequency envelopes of the multi-inputs rather than the true composite envelope of the input signals. The ET transmitter is tested for dual-band and tri-band power amplifiers (PAs) operating in concurrent mode using various bandwidth carrier aggregated long term evolution (LTE) signals. The transmitter is linearized using a phase-aligned Volterra digital predistortion that considers the inter-modulation distortion (IMD) products around the carrier frequencies as well as the third-order IMD products in the tri-band case. Experimental results are shown to validate the proposed techniques for linearization and efficiency enhancement of the multi-band ET transmitter and compared to the case of fixed supply biasing of the PA. [ABSTRACT FROM AUTHOR]

This letter presents a linearization algorithm designed for envelope tracking transmitters with an optimal highly efficient envelope shaping function. Targeting high efficiency at all power regions of the PA results in a severe nonlinear input-output response, and broadening of the PA output spectrum compared with a fixed voltage, or other envelope shaping functions. A two-box modeling approach is used, where a static nonlinearity function focuses on reducing the nonlinearity of the transmitter, and a memory polynomial model is used in cascade to reduce remaining distortions. The results show a definite improvement over traditional one-box models, and is suitable for PAs exhibiting unique nonlinear responses, especially for ET applications. [ABSTRACT FROM PUBLISHER]

Power amplifiers are widely used in RF broadcasting applications. However, they tend to exhibit nonlinear behavior that distorts the input signals both in the time and frequency domains, consequently motivating the development of techniques, such as digital predistortion, which can counteract this behavior. Among the challenges facing the identification of an amplifier's digital predistorter and behavioral model is finding the correct model dimensions, as this requires a priori knowledge of multiple parameters. In this paper, a predistorter based on a cluster-based implementation particle swarm optimization technique with embedded model-size estimation capability is presented. The validation of the proposed technique on a Doherty power amplifier prototype demonstrates its ability to efficiently find the dimensions of a memory polynomial based digital predistorter, while accurately estimating its coefficients. [ABSTRACT FROM PUBLISHER]

In this paper, a bandwidth and power scalable digital predistortion architecture is proposed for the linearization of power amplifiers (PA) exhibiting memory effects. The proposed digital predistorter allows for low complexity update following changes in the signal's bandwidth and/or power level. Experimental validation carried on a 300-W Doherty PA shows that the scalable predistorter architecture achieves similar performance as its conventional counterpart. However, the proposed predistorter requires the update of up to 50% less coefficients than the conventional predistorter. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This work proposes a novel two-box dual-input single-output digital predistorter (labeled as the LUT MISO predistorter) suitable for linearizing dynamic nonlinear envelope tracking power amplifiers. The LUT MISO predistorter is built by cascading a single-input memoryless nonlinear function with a two-input polynomial model with memory. The predistorted signal is synthesized as a function of the baseband complex waveform as well as the corresponding envelope-shaped signal. The LUT MISO predistorter is experimentally benchmarked against its single-box dual-input counterpart. It is shown that for the same number of coefficients, reduced spectrum regrowth and better adjacent channel power ratio were obtained with the LUT MISO predistorter. Moreover, the proposed predistorter was found to pass the ACPR requirements of the LTE standard while its conventional counterpart fails. [ABSTRACT FROM PUBLISHER]