318 research outputs found
Modeling Based on Elman Wavelet Neural Network for Class-D Power Amplifiers
In Class-D Power Amplifiers (CDPAs), the power supply noise can intermodulate
with the input signal, manifesting into power-supply induced intermodulation
distortion (PS-IMD) and due to the memory effects of the system, there exist
asymmetries in the PS-IMDs. In this paper, a new behavioral modeling based on
the Elman Wavelet Neural Network (EWNN) is proposed to study the nonlinear
distortion of the CDPAs. In EWNN model, the Morlet wavelet functions are
employed as the activation function and there is a normalized operation in the
hidden layer, the modification of the scale factor and translation factor in
the wavelet functions are ignored to avoid the fluctuations of the error
curves. When there are 30 neurons in the hidden layer, to achieve the same
square sum error (SSE) , EWNN needs 31 iteration steps,
while the basic Elman neural network (BENN) model needs 86 steps. The
Volterra-Laguerre model has 605 parameters to be estimated but still can't
achieve the same magnitude accuracy of EWNN. Simulation results show that the
proposed approach of EWNN model has fewer parameters and higher accuracy than
the Volterra-Laguerre model and its convergence rate is much faster than the
BENN model
A Digital Predistortion Scheme Exploiting Degrees-of-Freedom for Massive MIMO Systems
The primary source of nonlinear distortion in wireless transmitters is the
power amplifier (PA). Conventional digital predistortion (DPD) schemes use
high-order polynomials to accurately approximate and compensate for the
nonlinearity of the PA. This is not practical for scaling to tens or hundreds
of PAs in massive multiple-input multiple-output (MIMO) systems. There is more
than one candidate precoding matrix in a massive MIMO system because of the
excess degrees-of-freedom (DoFs), and each precoding matrix requires a
different DPD polynomial order to compensate for the PA nonlinearity. This
paper proposes a low-order DPD method achieved by exploiting massive DoFs of
next-generation front ends. We propose a novel indirect learning structure
which adapts the channel and PA distortion iteratively by cascading adaptive
zero forcing precoding and DPD. Our solution uses a 3rd order polynomial to
achieve the same performance as the conventional DPD using an 11th order
polynomial for a 100x10 massive MIMO configuration. Experimental results show a
70% reduction in computational complexity, enabling ultra-low latency
communications.Comment: IEEE International Conference on Communications 201
A Comparative Analysis of the Complexity/Accuracy Tradeoff in Power Amplifier Behavioral Models
A comparative study of state-of-the-art behavioral models for microwave power amplifiers (PAs) is presented in this paper. After establishing a proper definition for accuracy and complexity for PA behavioral models, a short description on various behavioral models is presented. The main focus of this paper is on the modeling accuracy as a function of computational complexity.
Data is collected from measurements on two PAs—a general-purpose amplifier and a Doherty PA designed for WiMAX—for different output power levels. The models are characterized in terms of accuracy and complexity for both in-band and out-of-band error. The results show that, among the models studied, the generalized memory polynomial behavioral model has the best tradeoff for accuracy versus complexity for both PAs, and can obtain high performance at half of the computational cost of all other models analyzed
Metodologia Per la Caratterizzazione di amplificatori a basso rumore per UMTS
In questo lavoro si presenta una metodologia di
progettazione elettronica a livello di sistema,
affrontando il problema della caratterizzazione dello spazio di progetto dell' amplificatore a basso rumore costituente il primo stadio di un front end a conversione diretta per UMTS realizzato in tecnologia CMOS con lunghezza di canale .18u. La metodologia è sviluppata al fine di valutare in modo quantititativo le specifiche ottime di sistema per il front-end stesso e si basa sul concetto di Piattaforma Analogica, che prevede la costruzione di un modello di prestazioni per il blocco analogico basato su
campionamento statistico di indici di prestazioni del blocco stesso, misurati tramite simulazione di dimensionamenti dei componenti attivi e passivi soddisfacenti un set di equazioni specifico della topologia circuitale. Gli indici di prestazioni vengono successivamente ulizzati per parametrizzare modelli comportamentali utilizzati nelle fasi di ottimizzazione a livello di sistema. Modelli comportamentali atti a rappresentare i sistemi RF sono stati pertanto studiati per ottimizzare la scelta delle metriche di prestazioni. L'ottimizzazione dei set di
equazioni atti a selezionare le configurazione di
interesse per il campionamento ha al tempo stesso richiesto l'approfondimento dei modelli di dispositivi attivi validi in tutte le regioni di funzionamento, e lo studio dettagliato della progettazione degli amplificatori a basso rumore basati su degenerazione induttiva. Inoltre,
il problema della modellizzazione a livello di sistema degli effetti della comunicazione tra LNA e Mixer è stato affrontato proponendo e analizzando diverse soluzioni. Il lavoro ha permesso di condurre un'ottimizzazione del front-end UMTS, giungendo a specifiche ottime a livello di sistema per l'amplificatore stesso
Digital predistortion of RF amplifiers using baseband injection for mobile broadband communications
Radio frequency (RF) power amplifiers (PAs) represent the most challenging
design parts of wireless transmitters. In order to be more energy efficient, PAs should operate in nonlinear region where they produce distortion that significantly degrades the quality of signal at transmitter’s output. With the aim of reducing this distortion and improve signal quality, digital predistortion (DPD) techniques are widely used. This work focuses on improving the performances of DPDs in modern, next-generation
wireless transmitters. A new adaptive DPD based on an iterative injection approach is developed and experimentally verified using a 4G signal. The signal performances at transmitter output are notably improved, while the proposed DPD does not require large digital signal processing memory resources and computational complexity. Moreover, the injection-based DPD theory is extended to be applicable in concurrent dual-band wireless transmitters. A cross-modulation problem specific to concurrent dual-band transmitters is investigated in detail and novel DPD based on simultaneous injection of intermodulation and cross-modulation distortion products is proposed. In order to mitigate distortion compensation limit phenomena and memory effects in highly
nonlinear RF PAs, this DPD is further extended and complete generalised DPD system for concurrent dual-band transmitters is developed. It is clearly proved in experiments that the proposed predistorter remarkably improves the in-band and out-of-band
performances of both signals. Furthermore, it does not depend on frequency separation between frequency bands and has significantly lower complexity in comparison with previously reported concurrent dual-band DPDs
Comparative Analysis of Greedy Pursuits for the Order Reduction of Wideband Digital Predistorters
This paper provides a review of greedy pursuits for optimizing Volterra-based behavioral models structure and estimating its parameters. An experimental comparison of the digital predistortion (DPD) linearization performance achieved by these approaches for model-order reduction, such as compressive sampling matching pursuit (CoSaMP), subspace pursuit (SP), orthogonal matching pursuit (OMP), and the novel doubly OMP (DOMP), is presented. A benchmark of the techniques in the DPD of a commercial class AB power amplifier (PA) and a class J PA operating over a 15-MHz Long-Term Evolution (LTE) signal is presented, giving a clear overview of their pruning characteristics in terms of linearization indicators and regressor selection capabilities. In addition, the benchmark is run in a cross-validation scheme by identifying the DPD with a 30-MHz 5G-new radio (NR) signal and validating with the same signal and a 20-MHz multicarrier wideband code division multiple access (WCDMA) signal. The DOMP is shown to be a promising technique since it achieves an enhanced model-order reduction for a similar linearization performance and precision
Improved Nonlinear Model Implementation for VCSEL Behavioral Modeling in Radio-Over-Fiber links
Open Access provided by `Alma Mater Studiorum - Università di Bologna' within the CRUI CARE AgreementInternational audienc
Linear Operation of Switch-Mode Outphasing Power Amplifiers
Radio transceivers are playing an increasingly important role in modern society. The
”connected” lifestyle has been enabled by modern wireless communications. The demand
that has been placed on current wireless and cellular infrastructure requires increased spectral
efficiency however this has come at the cost of power efficiency. This work investigates
methods of improving wireless transceiver efficiency by enabling more efficient power
amplifier architectures, specifically examining the role of switch-mode power amplifiers in
macro cell scenarios. Our research focuses on the mechanisms within outphasing power
amplifiers which prevent linear amplification. From the analysis it was clear that high power
non-linear effects are correctable with currently available techniques however non-linear effects
around the zero crossing point are not. As a result signal processing techniques for suppressing
and avoiding non-linear operation in low power regions are explored. A novel method of digital
pre-distortion is presented, and conventional techniques for linearisation are adapted for the
particular needs of the outphasing power amplifier. More unconventional signal processing
techniques are presented to aid linearisation of the outphasing power amplifier, both zero
crossing and bandwidth expansion reduction methods are designed to avoid operation in nonlinear
regions of the amplifiers. In combination with digital pre-distortion the techniques
will improve linearisation efforts on outphasing systems with dynamic range and bandwidth
constraints respectively.
Our collaboration with NXP provided access to a digital outphasing power amplifier,
enabling empirical analysis of non-linear behaviour and comparative analysis of behavioural
modelling and linearisation efforts. The collaboration resulted in a bench mark for linear
wideband operation of a digital outphasing power amplifier. The complimentary linearisation
techniques, bandwidth expansion reduction and zero crossing reduction have been evaluated in
both simulated and practical outphasing test benches. Initial results are promising and indicate
that the benefits they provide are not limited to the outphasing amplifier architecture alone.
Overall this thesis presents innovative analysis of the distortion mechanisms of the
outphasing power amplifier, highlighting the sensitivity of the system to environmental effects.
Practical and novel linearisation techniques are presented, with a focus on enabling wide band
operation for modern communications standards
CAD identification and validation of a non-linear dynamic model for performance analysis of large-signal amplifiers
We describe the CAD identification and software implementation of a Volterra-like integral series expansion for the behavioral-level simulation of communication amplifiers. The model represents an improvement with respect to the classical AM-AM AM-PM memoryless approach. The performance of the model is compared with both the AM-AM AM-PM approach and circuit-level CAD simulatio
Compact Digital Predistortion for Multi-band and Wide-band RF Transmitters
This thesis is focusing on developing a compact digital predistortion (DPD) system
which costs less DPD added power consumptions. It explores a new theory
and techniques to relieve the requirement of the number of training samples and
the sampling-rate of feedback ADCs in DPD systems. A new theory about the
information carried by training samples is introduced. It connects the generalized
error of the DPD estimation algorithm with the statistical properties of
modulated signals. Secondly, based on the proposed theory, this work introduces
a compressed sample selection method to reduce the number of training samples
by only selecting the minimal samples which satisfy the foreknown probability
information. The number of training samples and complex multiplication operations
required for coefficients estimation can be reduced by more than ten
times without additional calculation resource. Thirdly, based on the proposed
theory, this thesis proves that theoretically a DPD system using memory polynomial
based behavioural modes and least-square (LS) based algorithms can be
performed with any sampling-rate of feedback samples. The principle, implementation
and practical concerns of the undersampling DPD which uses lower
sampling-rate ADC are then introduced. Finally, the observation bandwidth of
DPD systems can be extended by the proposed multi-rate track-and-hold circuits
with the associated algorithm. By addressing several parameters of ADC
and corresponding DPD algorithm, multi-GHz observation bandwidth using only
a 61.44MHz ADC is achieved, and demonstrated the satisfactory linearization
performance of multi-band and continued wideband RF transmitter applications
via extensive experimental tests
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