4,202 research outputs found
Digital Predistortion in Large-Array Digital Beamforming Transmitters
In this article, we propose a novel digital predistortion (DPD) solution that
allows to considerably reduce the complexity resulting from linearizing a set
of power amplifiers (PAs) in single-user large-scale digital beamforming
transmitters. In contrast to current state-of-the art solutions that assume a
dedicated DPD per power amplifier, which is unfeasible in the context of large
antenna arrays, the proposed solution only requires a single DPD in order to
linearize an arbitrary number of power amplifiers. To this end, the proposed
DPD predistorts the signal at the input of the digital precoder based on
minimizing the nonlinear distortion of the combined signal at the intended
receiver direction. This is a desirable feature, since the resulting emissions
in other directions get partially diluted due to less coherent superposition.
With this approach, only a single DPD is required, yielding great complexity
and energy savings.Comment: 8 pages, Accepted for publication in Asilomar Conference on Signals,
Systems, and Computer
Sum-Rate Maximization in Two-Way AF MIMO Relaying: Polynomial Time Solutions to a Class of DC Programming Problems
Sum-rate maximization in two-way amplify-and-forward (AF) multiple-input
multiple-output (MIMO) relaying belongs to the class of difference-of-convex
functions (DC) programming problems. DC programming problems occur as well in
other signal processing applications and are typically solved using different
modifications of the branch-and-bound method. This method, however, does not
have any polynomial time complexity guarantees. In this paper, we show that a
class of DC programming problems, to which the sum-rate maximization in two-way
MIMO relaying belongs, can be solved very efficiently in polynomial time, and
develop two algorithms. The objective function of the problem is represented as
a product of quadratic ratios and parameterized so that its convex part (versus
the concave part) contains only one (or two) optimization variables. One of the
algorithms is called POlynomial-Time DC (POTDC) and is based on semi-definite
programming (SDP) relaxation, linearization, and an iterative search over a
single parameter. The other algorithm is called RAte-maximization via
Generalized EigenvectorS (RAGES) and is based on the generalized eigenvectors
method and an iterative search over two (or one, in its approximate version)
optimization variables. We also derive an upper-bound for the optimal values of
the corresponding optimization problem and show by simulations that this
upper-bound can be achieved by both algorithms. The proposed methods for
maximizing the sum-rate in the two-way AF MIMO relaying system are shown to be
superior to other state-of-the-art algorithms.Comment: 35 pages, 10 figures, Submitted to the IEEE Trans. Signal Processing
in Nov. 201
One-log call iterative solution of the Colebrook equation for flow friction based on Pade polynomials
The 80 year-old empirical Colebrook function zeta, widely used as an informal standard for hydraulic resistance, relates implicitly the unknown flow friction factor lambda, with the known Reynolds number Re and the known relative roughness of a pipe inner surface epsilon* ; lambda = zeta(Re, epsilon* ,lambda). It is based on logarithmic law in the form that captures the unknown flow friction factor l in a way that it cannot be extracted analytically. As an alternative to the explicit approximations or to the iterative procedures that require at least a few evaluations of computationally expensive logarithmic function or non-integer powers, this paper offers an accurate and computationally cheap iterative algorithm based on Pade polynomials with only one log-call in total for the whole procedure (expensive log-calls are substituted with Pade polynomials in each iteration with the exception of the first). The proposed modification is computationally less demanding compared with the standard approaches of engineering practice, but does not influence the accuracy or the number of iterations required to reach the final balanced solution.Web of Science117art. no. 182
Computing the common zeros of two bivariate functions via Bezout resultants
The common zeros of two bivariate functions can be computed by finding the common zeros of their polynomial interpolants expressed in a tensor Chebyshev basis. From here we develop a bivariate rootfinding algorithm based on the hidden variable resultant method and B�ezout matrices with polynomial entries. Using techniques including domain subdivision, B�ezoutian regularization and local refinement we are able to reliably and accurately compute the simple common zeros of two smooth functions with polynomial interpolants of very high degree (� 1000). We analyze the resultant method and its conditioning by noting that the B�ezout matrices are matrix polynomials. Our robust algorithm is implemented in the roots command in Chebfun2, a software package written in object-oriented MATLAB for computing with bivariate functions
Low-Complexity Sub-band Digital Predistortion for Spurious Emission Suppression in Noncontiguous Spectrum Access
Noncontiguous transmission schemes combined with high power-efficiency
requirements pose big challenges for radio transmitter and power amplifier (PA)
design and implementation. Due to the nonlinear nature of the PA, severe
unwanted emissions can occur, which can potentially interfere with neighboring
channel signals or even desensitize the own receiver in frequency division
duplexing (FDD) transceivers. In this article, to suppress such unwanted
emissions, a low-complexity sub-band DPD solution, specifically tailored for
spectrally noncontiguous transmission schemes in low-cost devices, is proposed.
The proposed technique aims at mitigating only the selected spurious
intermodulation distortion components at the PA output, hence allowing for
substantially reduced processing complexity compared to classical linearization
solutions. Furthermore, novel decorrelation based parameter learning solutions
are also proposed and formulated, which offer reduced computing complexity in
parameter estimation as well as the ability to track time-varying features
adaptively. Comprehensive simulation and RF measurement results are provided,
using a commercial LTE-Advanced mobile PA, to evaluate and validate the
effectiveness of the proposed solution in real world scenarios. The obtained
results demonstrate that highly efficient spurious component suppression can be
obtained using the proposed solutions
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