Vladimir Lyandres

Minimum BER power loading for OFDM in fading channel

A novel approach to power loading for orthogonal frequency-division multiplexing (OFDM) systems is proposed. The corresponding algorithm minimizes the aggregate bit-error rate, but appears to be rather complicated. Consequently, a much simpler, quasi-optimal loading algorithm is developed. The performance of various power loading strategies known in the literature are compared with the proposed quasi-optimal algorithm in the Rayleigh frequency-selective fading channel.

On the generation of correlated time series with a given probability density function

Abstract The approach presented provides very good results in modelling non-Gaussian time series. It is validated by direct numerical simulation of bimodal and Nakagami distributed sequences with approximately exponential correlation function.

Dynamic systems with random structure: an approach to the generation of nonstationary stochastic processes

Abstract The representation of nonstationary continuous-time, generally non-Gaussian processes with distinguishable states with the help of dynamic systems with random structure are considered. Switching of the partial subsystems is intended to be a Poisson point process and so the model has the Markov property and the generating system itself is described by a set of stochastic nonlinear differential equations. The statistical characteristics of the system output are analyzed.

The generation of diffusion Markovian processes with probability density function defined on part of the real axis

The correlated random process is represented as a solution of a stochastic differential first-order equation (SDE). The case of processes with a probability density function defined on a semi-infinite or finite range is considered. The limitation of the range of the simulated process requires modification of the specific structure of the SDE. The approach presented provides excellent results in modeling significant non-Gaussian processes with approximately an exponential correlation function. It is validated by direct numerical simulation of a uniformly distributed correlated process.

Impulsive noise: a nontraditional approach

Abstract The problem of impulsive interference modeling is considered. The proposed approach is based on the representation of the interference as the discontinuous Markov process observed at the output of the generally nonlinear filter, excited by a Poisson-distributed train of δ-pulses with random or constant energy. The dependence of the probability density and correlation functions of the simulating process on the filter structure and on the excitation characteristics is investigated. Examples of the considered model synthesis are included. The concept suggested should prove useful in simulators of the interference in continuous communication channels and in synthesis of optimal signal processing algorithms in the impulsive environment.

On an approach to moving-average filtering

Abstract A new approach to moving-average filtering is proposed, based on a mathematical description of an input mixture as a finite sum of sinusoidal segments. The proposed filter possesses some advantages: it is efficient when processing very short-duration mixtures and, additionally, the restriction on the closeness of the frequencies of the mixture components is determined only by the resolution of a computer. Among filters other properties a high precision of useful signal recovery and a relative simplicity of construction should be mentioned. Algorithms and the results of computer simulations of the filters performance in different noise environment are presented.

Effective base stations location and frequency assignment in mobile radio networks

Most of mobile radio networks that operate nowadays have been designed based on the classical cellular concept. However, during the last decade, an interest to find alternate design strategies has raised for several reasons. In general, the traffic density cannot be assumed constant throughout, making necessary the relocation of base stations inside the traffic hot spots. If traffic is characterized in a discrete manner, the optimal base stations location problem can be treated as a well-known problem in signal processing called vector quantization. We found that applying such a design strategy, better frequency assignments for a network can be accomplished

The time complexity cost of adjacent channel interference in a heuristic for frequency assignment

In this paper, the analysis of the time complexity that including adjacent channel interference in the computation of the channel-to-interference ratio for fixed frequency assignment in mobile communication systems is presented. A sequential algorithm that solves the frequency assignment problem using nonbinary constraints is described and analyzed considering both, cochannel and adjacent channel interference. Computer simulation results are presented too

An improved heuristic algorithm for frequency assignment in nonhomogeneous cellular mobile networks

We present an improved heuristic sequential algorithm for fixed frequency assignment in mobile radio systems with nonequal cells. This algorithm models the problem using nonbinary constraints and accounts for the interference level and the number of channel requirements to define a degree of difficulty for each cell in order to establish the sequence for the assignment process. Improvements with respect to an existing algorithm are done by accounting for transmitting power and adjacent channel interference, and by introducing a more accurate urban propagation model.

Envelope correlation function of the narrow-band non-Gaussian process

The stationary response of oscillators possessing linear damping and non-linear stiffness to the white Gaussian noise excitation is considered. The original stochastic differential equation (SDE) is used to establish relations between the system parameters and the envelope correlation function. The approximation approach is based on the moment approximation and replacement of the envelope generating SDE by the new one with analytical solution of the corresponding Fokker-Planck equation. The usefulness of the method is illustrated by application to the randomly driven Duffing oscillator.