Michel Allegue-Martínez

Behavioral Modeling and Predistortion of Power Amplifiers Under Sparsity Hypothesis

A simple and flexible technique for improving the modeling and predistortion of power amplifiers is presented. The technique, which relies on the sparsity assumption for the kernel coefficients of the full Volterra (FV) behavioral model, combines a greedy algorithm for the selection of the active coefficients, a maximum likelihood method for their estimation and an information criterion for determining the best model. The approach has been applied to the design of reduced-parameters FV-based digital predistorters for three power amplifiers driven with orthogonal frequency division multiplexing signals, following the LTE and DVB-T2 standards, and a multichannel wideband code-division multiple access signal. Results show that the proposed linearizers meet the spectral masks and error vector magnitude constraints of the referred standards and provide a reduction better than 45% in the number of parameters, compared to the FV predistorters.

Bandwidth‐constrained digital pre‐compensation technique for multi‐carrier satellite communications

Summary A wide variety of imperfections impact end-to-end performance in multiple-carrier per transponder transparent satellite links. Analysis of the link architecture leads to the identification of the sources and characteristics of distortion experienced by a typical multi-carrier signal. This paper introduces a new remote pre-compensation technique that takes this analysis into account to compensate for the specific distortion that occurs in the satellite channel. The proposed technique succeeds in compensating both linear and nonlinear channel distortions while overcoming the numerous challenges associated with remote waveform predistortion. Excellent linearisation performance has been observed across a wide range of link scenarios, even for high power amplifiers already linearised in the analogue domain. In addition, through an extensive end-to-end simulation campaign and a field programmable gate array implementation of the new algorithms, feasibility of the technique has been verified. Copyright

Output-Controllable Partial Inverse Digital Predistortion for RF Power Amplifiers

In this paper, an output-controllable digital predistortion (DPD) technique is proposed to partially inverse the nonlinear behavior of RF power amplifiers (PAs). Compared to the existing DPD, the proposed method changes the goal that the PA output must be exactly the same as the original input to a new one that the PA output can be arbitrarily controlled according to users demand. The proposed approach largely expands the capability of DPD and thus provides more flexibility for system designers to effectively use DPD to manipulate the PA output in order to handle more application scenarios and objectively conduct further system optimization. Various application cases have been tested. The experimental results demonstrate that the proposed approach has great potential in future wireless communication system design.

Linearization and EVM enhancement of an efficient class J amplifier for 3G and 4G mobile communication signals

This paper presents the synergistic combination of an efficient power amplifier design with a novel approach for the digital predistortion that, in addition to reducing spectral regrowth, is optimized to deal with the in-band distortion. The proposed linearization is based on a pre-processing filter followed by a memoryless nonlinear block, and is easily inserted in an OFDM system. The experimental validation has been accomplished with 3GDPP WCDMA and LTE signals in a class J amplifier based on a 15 W GaN device. Measurements show improvements over 10 dB in ACPR and one-point reduction of EVM compared to other widely-used approaches.

A closed-form equation approach to multi-port/multi-zone behavioral modeling of GaN FET Amplifiers

In this paper, a systematic method for the simulation of weakly and mildly nonlinear GaN FET amplifiers is reported. The core of the proposal is a third-order Volterra-based behavioral model with multi-spectral and multi-node capabilities that is formally derived from a circuit-level representation. Starting with the equivalent circuit of a typical FET device with thermal power feedback and fading memory, described in terms of its large-signal functions, closed-form expressions for the kernels at the gate, drain and thermal nodes are developed up to the third order. The use of these kernels allows the calculation of the responses in the dc, first-, second- and third-harmonic zones, which are shown to be dependent on the frequency response of the amplifier circuit terminating impedances and thermal filter. The simulation approach has been applied to calculate the nonlinear response of a typical power amplifier circuit, showing the ability of the proposed approach to provide an accurate prediction of multi-spectral, multi-node, multi-bias characteristics, including AM/AM-AM/PM conversion, spectral regrowth, intermodulation, and temperature rise, under diverse input signal waveforms and bandwidths. These results have been successfully compared with commercial CAD tools based on harmonic balance or envelope simulation. Copyright

Frequency component controllable digital predistortion of RF power amplifiers

In this paper, a novel frequency component controllable digital predistortion (DPD) for radio frequency (RF) power amplifiers (PAs) is proposed. The detailed analysis and experimental results demonstrate that the target band or frequency component to be linearized can be arbitrarily chosen according to users demand by employing the proposed approach, which makes digital predistortion much more flexible in future wireless communication systems.

A Volterra-Based Procedure for Multi-Port and Multi-Zone GaN FET Amplifier CAD Simulation

This paper reports a systematic method for the computer-aided-design (CAD) simulation of GaN FET power amplifiers (PAs). The core of the proposal is a Volterra-based behavioral model (BM) with multi-spectral and multi-node capabilities, which black-box structure is formally derived from a circuit-level representation of the PA and accounts for both short and long-term memory effects. Starting with the equivalent circuit of a typical FET device with thermal power feedback, the structures of the kernels for the gate, drain and thermal nodes are developed and are shown to be dependent on the frequency response of the PA terminating impedances and thermal filter. The model has been applied to simulate the nonlinear response of a typical PA circuit, showing the ability of the proposed model to provide an accurate prediction of multi-spectral, multi-node characteristics, including AM/AM-AM/PM conversion, spectral regrowth, intermodulation, and temperature rise, under diverse input signal waveforms and bandwidths. These results have been successfully compared with commercial CAD tools based on harmonic balance or envelope simulation.

Bandwidth Constrained Digital Predistortion for Multicarrier Transparent Satellite Payloads

Non-linear distortion in the transparent satellite channel has a severe impact on system efficiency and performance, particularly when multiple carriers access a single transponder. Digital predistortion is a technique that offers improved system performance in the face of such distortion and has seen considerable success in terrestrial applications. However, given the unique characteristics of the transparent satellite channel, use of the technique has been primarily limited to simple data predistortion algorithms for satellite communications. In this paper we present a solution to allow implementation of effective terrestrial waveform predistortion algorithms in the bandwidth-constrained environment of the transparent satellite channel. Through detailed simulations we show that the proposed technique is capable of excellent linearisation across the transponder bandwidth whilst respecting the uplink and downlink spectrum specifications.

Asymmetry and memory effects in quadrature modulators

In this study, an experimental nonlinear characterization of a quadrature modulator for communications following a standard approach based on a two-tone test is investigated. A simple nonlinear model is adopted according to experimental observations. Measurements are presented showing the behavior of the intermodulation (IM) products versus power, and suggesting that distortion is dependent on the baseband rates of the complex envelope input signals. An asymmetry observed at the second-order intermodulation (IM2) products takes especial importance and is theoretically explained. Simulations of the asymmetrical behavior of IM2 based on the proposed model are presented showing good agreement with measurements. The analysis is focused on the 1dB/dB slope characteristic versus the carrier power observed at IM2, a matter that suggests that nonlinear effects can be attributed to baseband nonlinear blocks.