266 research outputs found
Finding Structural Information of RF Power Amplifiers using an Orthogonal Non-Parametric Kernel Smoothing Estimator
A non-parametric technique for modeling the behavior of power amplifiers is
presented. The proposed technique relies on the principles of density
estimation using the kernel method and is suited for use in power amplifier
modeling. The proposed methodology transforms the input domain into an
orthogonal memory domain. In this domain, non-parametric static functions are
discovered using the kernel estimator. These orthogonal, non-parametric
functions can be fitted with any desired mathematical structure, thus
facilitating its implementation. Furthermore, due to the orthogonality, the
non-parametric functions can be analyzed and discarded individually, which
simplifies pruning basis functions and provides a tradeoff between complexity
and performance. The results show that the methodology can be employed to model
power amplifiers, therein yielding error performance similar to
state-of-the-art parametric models. Furthermore, a parameter-efficient model
structure with 6 coefficients was derived for a Doherty power amplifier,
therein significantly reducing the deployment's computational complexity.
Finally, the methodology can also be well exploited in digital linearization
techniques.Comment: Matlab sample code (15 MB):
https://dl.dropboxusercontent.com/u/106958743/SampleMatlabKernel.zi
A Stochastic Conjugate Gradient Method for Approximation of Functions
A stochastic conjugate gradient method for approximation of a function is
proposed. The proposed method avoids computing and storing the covariance
matrix in the normal equations for the least squares solution. In addition, the
method performs the conjugate gradient steps by using an inner product that is
based stochastic sampling. Theoretical analysis shows that the method is
convergent in probability. The method has applications in such fields as
predistortion for the linearization of power amplifiers.Comment: 21 pages, 5 figure
Iterative pre-distortion of the non-linear satellite channel
Digital Video Broadcasting - Satellite - Second Generation (DVB-S2) is the
current European standard for satellite broadcast and broadband communications.
It relies on high order modulations up to 32-amplitude/phase-shift-keying
(APSK) in order to increase the system spectral efficiency. Unfortunately, as
the modulation order increases, the receiver becomes more sensitive to physical
layer impairments, and notably to the distortions induced by the power
amplifier and the channelizing filters aboard the satellite. Pre-distortion of
the non-linear satellite channel has been studied for many years. However, the
performance of existing pre-distortion algorithms generally becomes poor when
high-order modulations are used on a non-linear channel with a long memory. In
this paper, we investigate a new iterative method that pre-distorts blocks of
transmitted symbols so as to minimize the Euclidian distance between the
transmitted and received symbols. We also propose approximations to relax the
pre-distorter complexity while keeping its performance acceptable
Linearization of RF Power Amplifiers Using Adaptive Kalman Filtering Algorithm
International audienceIn this paper, a new linearization algorithm of Power Amplifier, based on Kalman filtering theory is proposed for obtaining fast convergence of the adaptive digital predistortion. The proposed method uses the real-time digital processing of baseband signals to compensate the nonlinearities and memory effects in radio-frequency Power Amplifier. To reduce the complexity of computing in classical Kalman Filtering, a sliding time-window has been inserted which combines off-line measurement and on-line parameter estimation with high sampling time to track the changes in the PA characteristics. We evaluated the performance of the proposed linearization scheme through simulation and experiments. Using digital signal processing, experimental results with commercial power amplifier are presented for multicarrier signals to demonstrate the effectiveness of this new approach
A General Approach to Fully Linearize the Power Amplifiers in mMIMO with Less Complexity
A radio frequency (RF) power amplifier (PA) plays an important role to
amplify the message signal at higher power to transmit it to a distant
receiver. Due to a typical nonlinear behavior of the PA at high power
transmission, a digital predistortion (DPD), exploiting the preinversion of the
nonlinearity, is used to linearize the PA. However, in a massive MIMO (mMIMO)
transmitter, a single DPD is not sufficient to fully linearize the hundreds of
PAs. Further, for the full linearization, assigning a separate DPD to each PA
is complex and not economical. In this work, we address these challenges via
the proposed low-complexity DPD (LC-DPD) scheme. Initially, we describe the
fully-featured DPD (FF-DPD) scheme to linearize the multiple PAs and examine
its complexity. Thereafter, using it, we derive the LC-DPD scheme that can
adaptively linearize the PAs as per the requirement. The coefficients in the
two schemes are learned using the algorithms that adopt indirect learning
architecture based recursive prediction error method (ILA-RPEM) due to its
adaptive and free from matrix inversion operations. Furthermore, for the LC-DPD
structure, we have proposed three algorithms based on correlation of its common
coefficients with the distinct coefficients. Lastly, the performance of the
algorithms are quantified using the obtained numerical results
High Linearity Millimeter Wave Power Amplifiers with Novel Linearizer Techniques
Millimeter-wave communications have experienced phenomenal growth in recent
years when limited frequency spectrum is occupied by the ever-developing communication
services. The power amplifier, as the key component in the transmitter/receiver module
of communication systems, affects performance of the whole system directly and receives
much attention.
For minimized distortion and optimum system performance, the non-constant en-
velope modulation schemes used in communication systems have challenging requirements
on linearity. As linearity is related to communication quality directly, several linearization
techniques, such as predistortion and feedforward, are applied to power amplifier design.
Predistortion method has the advantages over other techniques in relatively simple struc-
ture and reasonable linearity improvement. But current predistortion circuits have quite
limited performance improvement and relatively large insertion loss, which indicate the
need for further research. In most of millimeter-wave amplifier design, great effort has
been spent on output power or gain, while linearity is often ignored. As almost all the
predistortion circuits operate at the RF frequencies, the linearized millimeter-wave com-
munication circuit is still relatively immature and very challenging.
This project is dedicated to solve the linearity problem faced by millimeter-wave
power amplifier in communication systems, which lacks of e®ective techniques in this field.
Linearity improvement with the predistortion method will be the key issue in this project
and some original ideas for predistortion circuit design will be applied to millimeter-wave
amplifiers.
In this thesis, several predistortion circuits with novel structure were proposed,
which provide a new approach for linearity improvement for millimeter-wave power am-
plifier. A millimeter-wave power ampli¯er for LMDS applications built on GaAs pHEMT
technology was developed to a high engineering standard, which works as the test bench
for linearization. Actual operation and parasitic elements at tens of gigahertz have been
taken into consideration during the design.
Firstly, two novel predistorter structures based on the amplifier were proposed, one
is based on an amplifier with a fixed bias circuit and the other is based on an amplifier with
a nonlinear signal dependant bias circuit. These novel structures can improve the linearity
while improving other metrics simultaneously, which can effectively solve the problem of
insertion loss faced by the conventional structures. Besides this, an original predistortion
circuit design methodology derived from frequency to signal amplitude transformation was
proposed. Based on this methodology, several transfer functions were proposed and related
predistortion circuits were built to linearize the power amplifier. As this methodology is
quite different from the traditional approach, it can improve the linearity signifficantly
while other metrics are affected slightly and has a broad prospect for application
High Linearity Millimeter Wave Power Amplifiers with Novel Linearizer Techniques
Millimeter-wave communications have experienced phenomenal growth in recent
years when limited frequency spectrum is occupied by the ever-developing communication
services. The power amplifier, as the key component in the transmitter/receiver module
of communication systems, affects performance of the whole system directly and receives
much attention.
For minimized distortion and optimum system performance, the non-constant en-
velope modulation schemes used in communication systems have challenging requirements
on linearity. As linearity is related to communication quality directly, several linearization
techniques, such as predistortion and feedforward, are applied to power amplifier design.
Predistortion method has the advantages over other techniques in relatively simple struc-
ture and reasonable linearity improvement. But current predistortion circuits have quite
limited performance improvement and relatively large insertion loss, which indicate the
need for further research. In most of millimeter-wave amplifier design, great effort has
been spent on output power or gain, while linearity is often ignored. As almost all the
predistortion circuits operate at the RF frequencies, the linearized millimeter-wave com-
munication circuit is still relatively immature and very challenging.
This project is dedicated to solve the linearity problem faced by millimeter-wave
power amplifier in communication systems, which lacks of e®ective techniques in this field.
Linearity improvement with the predistortion method will be the key issue in this project
and some original ideas for predistortion circuit design will be applied to millimeter-wave
amplifiers.
In this thesis, several predistortion circuits with novel structure were proposed,
which provide a new approach for linearity improvement for millimeter-wave power am-
plifier. A millimeter-wave power ampli¯er for LMDS applications built on GaAs pHEMT
technology was developed to a high engineering standard, which works as the test bench
for linearization. Actual operation and parasitic elements at tens of gigahertz have been
taken into consideration during the design.
Firstly, two novel predistorter structures based on the amplifier were proposed, one
is based on an amplifier with a fixed bias circuit and the other is based on an amplifier with
a nonlinear signal dependant bias circuit. These novel structures can improve the linearity
while improving other metrics simultaneously, which can effectively solve the problem of
insertion loss faced by the conventional structures. Besides this, an original predistortion
circuit design methodology derived from frequency to signal amplitude transformation was
proposed. Based on this methodology, several transfer functions were proposed and related
predistortion circuits were built to linearize the power amplifier. As this methodology is
quite different from the traditional approach, it can improve the linearity signifficantly
while other metrics are affected slightly and has a broad prospect for application
Advanced transceivers for spectrally-efficient communications
In this thesis, we will consider techniques to improve the spectral
efficiency of digital communication systems, operating on the whole transceiver
scheme. First, we will focus on receiver schemes having detection algorithms
with a complexity constraint. We will optimize the parameters of the reduced
detector with the aim of maximizing the achievable information rate. Namely, we
will adopt the channel shortening technique. Then, we will focus on a technique
that is getting very popular in the last years (although presented for the
first time in 1975): faster-than-Nyquist signaling, and its extension which is
time packing. Time packing is a very simple technique that consists in
introducing intersymbol interference on purpose with the aim of increasing the
spectral efficiency of finite order constellations. Finally, in the last
chapters we will combine all the presented techniques, and we will consider
their application to satellite channels.Comment: PhD Thesi
Adaptive digital predistortion for linearization of power amplifier
Ankara : The Department of Electrical and electronics Engineering and the Institute of Engineering and Science of Bilkent University, 2009.Thesis (Master's) -- Bilkent University, 2009.Includes bibliographical references leaves 55.In most communication systems, power amplifiers are used to obtain high output
power. The nonlinear characteristics of the power amplifier leads to the distortion
of the output signal. This distortion affects the efficiency of the power amplifier.
The way to reduce this effect is to linearize the power amplifier near the saturation
region where it is nonlinear. The widely used technique for the linearization
of power amplifiers is predistortion. The proposed technique for predistortion
uses a LUT(look-up-table), a complex multiplier, an address calculator, delay
elements and an adaptation logic. A new adaptation logic to update the LUT
coefficients, is used. The predistorter is simulated in Matlab software using a
baseband model for the power amplifier. 16-QAM baseband modulation is used
to simulate the predistorter. In order to see the performance of the proposed
predistorter, hardware logic is implemented in FPGA and experimental setup
with RF circuits and RF power amplifier is used. For different LUT sizes, the
algorithm is tested and for the LUT size of 64, nearly 15 dB improvement in
power spectrum is observed. The LUT size of 64 is observed to be the optimal
LUT size in the experiments.Şekerlisoy, BurakM.S
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