49,316 research outputs found
Deduction of Lorentz Transformation from the existence of absolute rest. Deduction of the speed of light in any frame of reference
We begin by admitting the following: (i) there is a frame of reference where
the speed of light is the same in any direction (that speed is c) (ii) the
average speed of light on a two-way journey is c in every frame of reference.
From this two premises we obtain an expression for the speed of light which
implies the speed of light depends on the motion of the frame of reference.
Also from this two premises solely we deduct Lorentz Transformation.Comment: 6 pages, 0 figure
The Energy-Entropy Principle
In this paper, through a criticism of what we call the paradigmatic view of
thermodynamics, we aim at showing a new perspective attained in this matter.
The generalization of heat as internal energy (generalization of the kinetic
energy concept of heat) permits the generalization of the Kelvin postulate: "It
is impossible, without another effect, to convert internal energy into work"
(no reference to heat or to heat reservoir).Comment: 18 pages, 1 figur
The physical meaning of synchronization and simultaneity in Special Relativity
Based on two previous papers, the physical meaning of synchronization and
simultaneity as is presented in Einstein's Special Relativity paper of 1905 is
reconsidered. We follow Einstein's argumentation to introduce a criterium of
synchronization and for the same arguments we arrive at a different criterium
for synchronization. From that we conclude that simultaneity is absolute.Comment: 11 pages, 0 figure
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
Distributed Low-Rank Adaptive Algorithms Based on Alternating Optimization and Applications
This paper presents a novel distributed low-rank scheme and adaptive
algorithms for distributed estimation over wireless networks. The proposed
distributed scheme is based on a transformation that performs dimensionality
reduction at each agent of the network followed by transmission of a reduced
set of parameters to other agents and reduced-dimension parameter estimation.
Distributed low-rank joint iterative estimation algorithms based on alternating
optimization strategies are developed, which can achieve significantly reduced
communication overhead and improved performance when compared with existing
techniques. A computational complexity analysis of the proposed and existing
low-rank algorithms is presented along with an analysis of the convergence of
the proposed techniques. Simulations illustrate the performance of the proposed
strategies in applications of wireless sensor networks and smart grids.Comment: 12 figures, 13 pages. arXiv admin note: text overlap with
arXiv:1411.112
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
Study of Sparsity-Aware Distributed Conjugate Gradient Algorithms for Sensor Networks
This paper proposes distributed adaptive algorithms based on the conjugate
gradient (CG) method and the diffusion strategy for parameter estimation over
sensor networks. We present sparsity-aware conventional and modified
distributed CG algorithms using and log-sum penalty functions. The
proposed sparsity-aware diffusion distributed CG algorithms have an improved
performance in terms of mean square deviation (MSD) and convergence as compared
with the consensus least-mean square (Diffusion-LMS) algorithm, the diffusion
CG algorithms and a close performance to the diffusion distributed recursive
least squares (Consensus-RLS) algorithm. Numerical results show that the
proposed algorithms are reliable and can be applied in several scenarios.Comment: 1 figure, 7 page
Joint Iterative Power Allocation and Linear Interference Suppression Algorithms in Cooperative DS-CDMA Networks
This work presents joint iterative power allocation and interference
suppression algorithms for spread spectrum networks which employ multiple hops
and the amplify-and-forward cooperation strategy for both the uplink and the
downlink. We propose a joint constrained optimization framework that considers
the allocation of power levels across the relays subject to individual and
global power constraints and the design of linear receivers for interference
suppression. We derive constrained linear 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 problems, we develop cost-effective algorithms for adaptive joint
power allocation, and estimation of the parameters of the receiver and the
channels. An analysis of the optimization problem is carried out and shows that
the problem can have its convexity enforced by an appropriate choice of the
power constraint parameter, which allows the algorithms to avoid problems with
local minima. A study of the complexity and the requirements for feedback
channels of the proposed algorithms is also included for completeness.
Simulation results show that the proposed algorithms obtain significant gains
in performance and capacity over existing non-cooperative and cooperative
schemes.Comment: 9 figures; IET Communications, 201
Interference Suppression and Group-Based Power Adjustment via Alternating Optimization for DS-CDMA Networks with Multihop Relaying
This work presents joint interference suppression and power allocation
algorithms for DS-CDMA networks with multiple hops and decode-and-forward (DF)
protocols. A scheme for joint allocation of power levels across the relays
subject to group-based power constraints and the design of linear receivers for
interference suppression is proposed. A constrained minimum mean-squared error
(MMSE) design for the receive filters and the power allocation vectors is
devised along with an MMSE channel estimator. In order to solve the proposed
optimization efficiently, a method to form an effective group of users and an
alternating optimization strategy are devised with recursive alternating least
squares (RALS) algorithms for estimating the parameters of the receiver, the
power allocation and the channels. Simulations show that the proposed
algorithms obtain significant gains in capacity and performance over existing
schemes.Comment: 2 figures. arXiv admin note: substantial text overlap with
arXiv:1301.5912, arXiv:1301.009
Is the assumption of a special system of reference consistent with Special Relativity?
In a previous work we have shown that the null result of the Michelson-Morley
experiment in vacuum is deeply connected with the notion of time. The same is
true for the the postulate of constancy of the two-way speed of light in vacuum
in all frames independently of the state of motion of the emitting body. The
argumentation formerly given is very general and has to be true not only within
Special Relativity and its `equivalence' of all inertial frames, but as well as
in Lorentz-Poincar\'e scenario of a preferred reference frame. This paper is
the second of a trilogy intending to revisit the foundations of Special
Relativity, and addresses the question of the constancy of the one-way speed of
light and of the differences and similarities between both scenarios. Although
they manifestly differ in philosophy, it is debated why and how the assumption
of a "special system of reference experimentally inaccessible" is indeed
compatible with Einstein's Special Relativity, as beautifully outlined and
discussed by John Bell [1]. This rather trivial statement is still astonishing
nowadays to a big majority of scientists. The purpose of this work is to bring
such assertion into perspective, widening the somewhat narrow view of Special
Relativity often presented in textbooks.Comment: 16 pages, 6 figure
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