Mayada Younes

An Accurate Complexity-Reduced “PLUME” Model for Behavioral Modeling and Digital Predistortion of RF Power Amplifiers

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 models 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.

Metrics and Methods for Benchmarking of RF Transmitter Behavioral Models With Application to the Development of a Hybrid Memory Polynomial Model

This paper presents a study of performance evaluation metrics for behavioral models of power amplifiers and transmitters. A novel normalized absolute mean spectrum error criterion is proposed as a performance evaluation metric along with a method for accurate benchmarking of behavioral models and their ability to predict the in-band response, static nonlinearity, and memory effects of the device under test. The proposed metric and method are validated with a study of different memory polynomial based models, focusing on the model accuracy, complexity, and identification robustness. This experimental validation highlights the robustness of the proposed metric and its ability to accurately quantify the performance of several behavioral models in predicting the static nonlinearity and memory effects of the device under test for several test conditions. In addition, the results of the comparative study between the memory polynomial models are used to propose a hybrid memory polynomial model. The superiority of the proposed model is assessed by comparing its performance to that of the studied memory polynomial models.

Linearization of Concurrent Tri-Band Transmitters Using 3-D Phase-Aligned Pruned Volterra Model

This paper reports a novel digital predistortion (DPD) scheme for concurrent tri-band power amplifiers (PAs). The proposed tri-band DPD is based on a pruned Volterra model that takes into account the impact of the phase distortion observed in multi-band PAs as well as the compound amplitude distortion. By taking into account the phase variation effects across a wide frequency band, the proposed 3-D phase-aligned Volterra DPD can effectively compensate for the crosstalk effects between the fundamental frequencies, their harmonics, and intermodulation products due to the nonlinearity the tri-band PA exhibited. The performance of the proposed DPD is validated using a broadband Class-AB PA driven concurrently by three independent carrier-aggregated long-term evolution signals at separation frequencies around 100 MHz. The measurement results validate the accurate performance of the proposed 3-D phase-aligned pruned Volterra DPD in suppressing the in-band and cross-band intermodulation effects, and shows improvement over a basic 3-D tri-band DPD model that neglects phase variation effects across frequency.

On the Modeling and Linearization of a Concurrent Dual-Band Transmitter Exhibiting Nonlinear Distortion and Hardware Impairments

This paper proposes a novel, complexity-reduced, dual-input, two-box model for the modeling and digital predistortion of a dual-band power amplifier (PA) in the presence of in-phase/quadrature (I/Q) modulator imperfections. The model is composed of two cascaded nonlinear blocks. The first block is implemented as a mildly nonlinear dual-input truncated Volterra filter, which includes second-order cross-terms for the mutual characterization of the dynamic mildly nonlinear memory effects exhibited by the dual-band PA and for the compensation of I/Q imperfections. The second block is implemented as a two-dimensional look-up table for the characterization of the static nonlinearity of the dual-band PA. The proposed model was evaluated through the excitation of the dual-band Doherty PA by two concurrent multi-carrier signals, applied at 880 MHz and 1978 GHz, in the presence of I/Q modulator imperfections. The experimental results showed the accurate performance of the proposed model in suppressing the adjacent channel error power, when compared to other state-of-the-art models, the computational complexity of the proposed model was significantly reduced, which economizes the resources utilized by the model for implementation on a digital signal processing/field-programmable gate array platform.

Three-Dimensional digital predistorter for concurrent tri-band power amplifier linearization

This paper reports a novel digital predistortion (DPD) scheme for concurrent tri-band power amplifier (PA). The proposed three-dimensional tri-band DPD is based on the analysis of crosstalk between the fundamental frequencies, their harmonics and intermodulation products due to the nonlinearity exhibited by the tri-band PA. The DPD performance is validated using a broadband PA driven concurrently with LTE, WIMAX, and WCDMA signals centered at 2.14 GHz, 2.425 GHz, and 2.655 GHz, respectively.

Generalised twin-box model for compensation of transmitters radio frequency impairments

A novel generalised twin-box model is proposed for the mutual compensation of modulator imperfections and power amplifier (PA) distortion. It is composed of two cascaded boxes, a dual branch of simplified Volterra filters for the joint characterisation of the mild non-linear dynamic memory effects of the PA and modulator imperfections. The second box is a look-up table for characterising the highly non-linear static distortion exhibited by the PA. Hence, the proposed model has reduced complexity in comparison with the state-of-the-art models, owing to the separate identification of the dynamic and static effects of the PA. The model validation is carried out using a Class AB PA, and the proposed model showed significant improvement in performance as well as reducing the computational complexity of the model.

Performance-Driven Dimension Estimation of Memory Polynomial Behavioral Models for Wireless Transmitters and Power Amplifiers

A novel approach is proposed for automated dimension estimation in memory polynomial based power ampliflers/transmitters behavioral models. This method consists of successively identifying the static nonlinearity order and memory depth of the model in accordance with a predeflned performance criterion. The proposed method is validated using a 3G Doherty power amplifler driven by various WCDMA signals. Experimental results demonstrate the robustness of the proposed successive sweep approach compared to the conventional blind simultaneous sweep approach. The proposed dimension estimation method is an enabling tool for e-cient design optimization of power ampliflers circuits to enhance their linearizability.

Behavioral Modeling of Concurrent Dual-Band Transmitters Based on Radially-Pruned Volterra Model

This paper presents a radially-pruned multi-dimensional Volterra model for the modeling and linearization of concurrent dual-band transmitters. The proposed model accounts for the impact of cross-band intermodulation distortions of the dual-band power amplifier (PA) and also the effect of quadrature modulator (QM) imperfections. The performance of the proposed model is validated using a broadband class AB PA driven concurrently by two independent LTE signals at a separation frequency of around 60 MHz, in the presence of in-phase/quadrature (I/Q) modulator imperfections. The measurement results validate the accurate linearization performance of the proposed model in suppressing the adjacent channel power (ACP) , as well as the QM impairments, as compared to other state-of-the-art models.

Dual-band Predistortion Linearization of an Envelope Modulated Power Amplifier Operated in Concurrent Multi-Standard Mode

This paper reports a dual band predistortion linearization technique for an envelope modulator based transmitter operated in concurrent multi-band, multi-standard mode driven by 20 MHz bandwidth LTE and 4 carrier 20 MHz bandwidth WCDMA signals. To reduce the speed of the composite envelope path, a bandwidth reduced combined envelope signal is used for the dynamic supply of the dual-band PA. Measurement results using the dual-band linearization technique show an increase of over 10 dB in ACPR and 15% in average operating efficiency.

Concurrent Multi-Band Envelope Modulated Power Amplifier Linearized Using Extended Phase-Aligned DPD

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.