2,161 research outputs found
Reduced-Rank Space-Time Interference Suppression with Joint Iterative Least Squares Algorithms for Spread Spectrum Systems
This paper presents novel adaptive space-time reduced-rank interference
suppression least squares algorithms based on joint iterative optimization of
parameter vectors. The proposed space-time reduced-rank scheme consists of a
joint iterative optimization of a projection matrix that performs
dimensionality reduction and an adaptive reduced-rank parameter vector that
yields the symbol estimates. The proposed techniques do not require singular
value decomposition (SVD) and automatically find the best set of basis for
reduced-rank processing. We present least squares (LS) expressions for the
design of the projection matrix and the reduced-rank parameter vector and we
conduct an analysis of the convergence properties of the LS algorithms. We then
develop recursive least squares (RLS) adaptive algorithms for their
computationally efficient estimation and an algorithm for automatically
adjusting the rank of the proposed scheme. A convexity analysis of the LS
algorithms is carried out along with the development of a proof of convergence
for the proposed algorithms. Simulations for a space-time interference
suppression application with a DS-CDMA system show that the proposed scheme
outperforms in convergence and tracking the state-of-the-art reduced-rank
schemes at a comparable complexity.Comment: 8 figure
Low-Rank Signal Processing: Design, Algorithms for Dimensionality Reduction and Applications
We present a tutorial on reduced-rank signal processing, design methods and
algorithms for dimensionality reduction, and cover a number of important
applications. A general framework based on linear algebra and linear estimation
is employed to introduce the reader to the fundamentals of reduced-rank signal
processing and to describe how dimensionality reduction is performed on an
observed discrete-time signal. A unified treatment of dimensionality reduction
algorithms is presented with the aid of least squares optimization techniques,
in which several techniques for designing the transformation matrix that
performs dimensionality reduction are reviewed. Among the dimensionality
reduction techniques are those based on the eigen-decomposition of the observed
data vector covariance matrix, Krylov subspace methods, joint and iterative
optimization (JIO) algorithms and JIO with simplified structures and switching
(JIOS) techniques. A number of applications are then considered using a unified
treatment, which includes wireless communications, sensor and array signal
processing, and speech, audio, image and video processing. This tutorial
concludes with a discussion of future research directions and emerging topics.Comment: 23 pages, 6 figure
Coordinate Tomlinson-Harashima Precoding Design for Overloaded Multi-user MIMO Systems
Tomlinson-Harashima precoding (THP) is a nonlinear processing technique
employed at the transmit side to implement the concept of dirty paper coding
(DPC). The perform of THP, however, is restricted by the dimensionality
constraint that the number of transmit antennas has to be greater or equal to
the total number of receive antennas. In this paper, we propose an iterative
coordinate THP algorithm for the scenarios in which the total number of receive
antennas is larger than the number of transmit antennas. The proposed algorithm
is implemented on two types of THP structures, the decentralized THP (dTHP)
with diagonal weighted filters at the receivers of the users, and the
centralized THP (cTHP) with diagonal weighted filter at the transmitter.
Simulation results show that a much better bit error rate (BER) and sum-rate
performances can be achieved by the proposed iterative coordinate THP compared
to the previous linear art.Comment: 3 figures, 6 pages, ISWCS 2014. arXiv admin note: text overlap with
arXiv:1401.475
Joint Power Adjustment and Interference Mitigation Techniques for Cooperative Spread Spectrum Systems
This paper presents joint power allocation and interference mitigation
techniques for the downlink of spread spectrum systems which employ multiple
relays and the amplify and forward cooperation strategy. We propose a joint
constrained optimization framework that considers the allocation of power
levels across the relays subject to an individual power constraint and the
design of linear receivers for interference suppression. We derive constrained
minimum mean-squared error (MMSE) expressions for the parameter vectors that
determine the optimal power levels across the relays and the linear receivers.
In order to solve the proposed optimization problem efficiently, we develop
joint adaptive power allocation and interference suppression algorithms that
can be implemented in a distributed fashion. The proposed stochastic gradient
(SG) and recursive least squares (RLS) algorithms mitigate the interference by
adjusting the power levels across the relays and estimating the parameters of
the linear receiver. SG and RLS channel estimation algorithms are also derived
to determine the coefficients of the channels across the base station, the
relays and the destination terminal. The results of simulations show that the
proposed techniques obtain significant gains in performance and capacity over
non-cooperative systems and cooperative schemes with equal power allocation.Comment: 6 figures. arXiv admin note: text overlap with arXiv:1301.009
Multi-User Flexible Coordinated Beamforming using Lattice Reduction for Massive MIMO Systems
The application of precoding algorithms in multi-user massive multiple-input
multiple-output (MU-Massive-MIMO) systems is restricted by the dimensionality
constraint that the number of transmit antennas has to be greater than or equal
to the total number of receive antennas. In this paper, a lattice reduction
(LR)-aided flexible coordinated beamforming (LR-FlexCoBF) algorithm is proposed
to overcome the dimensionality constraint in overloaded MU-Massive-MIMO
systems. A random user selection scheme is integrated with the proposed
LR-FlexCoBF to extend its application to MU-Massive-MIMO systems with arbitary
overloading levels. Simulation results show that significant improvements in
terms of bit error rate (BER) and sum-rate performances can be achieved by the
proposed LR-FlexCoBF precoding algorithm.Comment: 5 figures, Eusipc
Adaptive Reduced-Rank RLS Algorithms based on Joint Iterative Optimization of Filters for Space-Time Interference Suppression
This paper presents novel adaptive reduced-rank filtering algorithms based on
joint iterative optimization of adaptive filters. The novel scheme consists of
a joint iterative optimization of a bank of full-rank adaptive filters that
constitute the projection matrix and an adaptive reduced-rank filter that
operates at the output of the bank of filters. We describe least squares (LS)
expressions for the design of the projection matrix and the reduced-rank filter
and recursive least squares (RLS) adaptive algorithms for its computationally
efficient implementation. Simulations for a space-time interference suppression
in a CDMA system application show that the proposed scheme outperforms in
convergence and tracking the state-of-the-art reduced-rank schemes at about the
same complexity.Comment: 3 figures. arXiv admin note: substantial text overlap with
arXiv:1205.4390, arXiv:1301.269
Study of BEM-Type Channel Estimation Techniques for 5G Multicarrier Systems
In this paper, we investigate channel estimation techniques for 5G
multicarrier systems. Due to the characteristics of the 5G application
scenarios, channel estimation techniques have been tested in Orthogonal
Frequency Division Multiplexing (OFDM) and Generalized Frequency Division
Multiplexing (GFDM) systems. The orthogonality between subcarriers in OFDM
systems permits inserting and extracting pilots without interference. However,
due to pulse shaping, subcarriers in GFDM are no longer orthogonal and
interfere with each other. Due to such interference, the channel estimation for
GFDM is not trivial. A robust and low-complexity channel estimator can be
obtained by combining a minimum mean-square error (MMSE) regularization and the
basis expansion model (BEM) approach. In this work, we develop a BEM-type
channel estimator along with a strategy to obtain the covariance matrix of the
BEM coefficients. Simulations show that the BEM-type channel estimation shows
performance close to that of the linear MMSE (LMMSE), even though there is no
need to know the channel power delay profile, and its complexity is low.Comment: 2 figures, 7 page
Study of Set-Membership Kernel Adaptive Algorithms and Applications
Adaptive algorithms based on kernel structures have been a topic of
significant research over the past few years. The main advantage is that they
form a family of universal approximators, offering an elegant solution to
problems with nonlinearities. Nevertheless these methods deal with kernel
expansions, creating a growing structure also known as dictionary, whose size
depends on the number of new inputs. In this paper we derive the set-membership
kernel-based normalized least-mean square (SM-NKLMS) algorithm, which is
capable of limiting the size of the dictionary created in stationary
environments. We also derive as an extension the set-membership kernelized
affine projection (SM-KAP) algorithm. Finally several experiments are presented
to compare the proposed SM-NKLMS and SM-KAP algorithms to the existing methods.Comment: 4 figures, 6 page
Low-Complexity Robust Data-Adaptive Dimensionality Reduction Based on Joint Iterative Optimization of Parameters
This paper presents a low-complexity robust data-dependent dimensionality
reduction based on a modified joint iterative optimization (MJIO) algorithm for
reduced-rank beamforming and steering vector estimation. The proposed robust
optimization procedure jointly adjusts the parameters of a rank-reduction
matrix and an adaptive beamformer. The optimized rank-reduction matrix projects
the received signal vector onto a subspace with lower dimension. The
beamformer/steering vector optimization is then performed in a
reduced-dimension subspace. We devise efficient stochastic gradient and
recursive least-squares algorithms for implementing the proposed robust MJIO
design. The proposed robust MJIO beamforming algorithms result in a faster
convergence speed and an improved performance. Simulation results show that the
proposed MJIO algorithms outperform some existing full-rank and reduced-rank
algorithms with a comparable complexity.Comment: 5 pages, 3 figures. CAMSAP 201
Adaptive Reduced-Rank Processing Using a Projection Operator Based on Joint Iterative Optimization of Adaptive Filters For CDMA Interference Suppression
This paper proposes a novel adaptive reduced-rank filtering scheme based on
the joint iterative optimization of adaptive filters. The proposed scheme
consists of a joint iterative optimization of a bank of full-rank adaptive
filters that constitutes the projection matrix and an adaptive reduced-rank
filter that operates at the output of the bank of filters. We describe minimum
mean-squared error (MMSE) expressions for the design of the projection matrix
and the reduced-rank filter and simple least-mean squares (LMS) adaptive
algorithms for its computationally efficient implementation. Simulation results
for a CDMA interference suppression application reveals that the proposed
scheme significantly outperforms the state-of-the-art reduced-rank schemes,
while requiring a significantly lower computational complexity.Comment: 4 figures. Published in SSP 2010. arXiv admin note: substantial text
overlap with arXiv:1205.4390, arXiv:1304.754
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