Valeri Kontorovitch

Exact Closed-Form Expressions for the Distribution, the Level-Crossing Rate, and the Average Duration of Fades of the Capacity of OSTBC-MIMO Channels

This paper deals with some important statistical properties of the channel capacity of multiple-input-multiple-output (MIMO) systems with orthogonal space-time block code (OSTBC) transmission. We assume that all the subchannels are uncorrelated. For OSTBC-MIMO systems, exact closed-form expressions are derived for the probability density function (PDF), the cumulative distribution function (CDF), the level-crossing rate (LCR), and the average duration of fades (ADF) of the channel capacity. Furthermore, it will be shown that these exact closed-form expressions can be used to characterize the channel capacity of single-input-multiple-output (SIMO) and multiple-input-single-output (MISO) systems. In addition, a Gaussian approximation to the exact LCR of the capacity of OSTBC-MIMO systems is derived. The correctness of the derived closed-form expressions and the approximation is confirmed by simulations.

Simulation of Wide Band Channels with non-separable scattering functions

In this paper a new and constructive method useful to simulate Wide Band Channels with non-separable scattering function via the filtering approach is provided. This method is based on the approximation of the Channel by the eigenfunctions taken from the Karhunen-Loève expansion of the Channels. ensemble autocorrelation function at Δt=0. Channel realizations are performed via the filtering of an independent gaussian random process vector by some filter matrix, which is obtained from some manipulations of the correlation statistics of eigenfunctions. An example to clarify this proposal is also presented.

A MIMO Channel Simulator Applying the Universal Basis

In this paper we are presenting the generalized multiple-input multiple-output (MIMO) Kronecker wideband channel simulator by considering the prolate spheroidal wave functions (PSWF) set as a universal basis both for the spatial and temporal correlation properties of the channel.

Enhancing the performance of the CR blind channel estimation algorithm using the Karhunen-Loève expansion

This paper introduces a new formulation for the blind channel estimation problem. In particular, it is found that any possible realization of the discrete time channel impulse response can be expressed as a linear combination of a set of predetermined eigenvectors. These are obtained from a certain “universal” autocorrelation matrix that depends only on the pulse shaping filter and the maximum delay spread of the multi-path channel, and not on the specific characteristics of the power delay profile. This new formulation shows that an interrelation exists between the different sub-channel responses of the single-input multiple-output equivalent model of the over-sampled baseband signal. Thus, the number of free parameters equals the number of signal space eigenvectors and not the number of coefficients in the multi-channel model. Therefore the optimization associated with the CR algorithm [1] can be reformulated as a reduced dimensional minimization problem with a notoriously enhanced estimation performance.

On the second order statistics of SIR in wireless Nakagami channels

The second order statistical properties of the signal to interference ratio (SIR), namely the autocovariance function, are relevant for several studies in wireless communication channels. Formally, the autocovariance function of SIR can be obtained from its two-dimensional probability density function (PDF). However, for the traditional types of fading channels, the analytical two dimensional PDFs of SIR are rather scarce, and it is possible to say that they are either unavailable or have too complex forms. Moreover, this approach does not allow to see how the covariances of the desired signal and the interference participate in the covariance of SIR. In this paper, we show how these inconveniences can be bypassed allowing and exact analysis of the autocovariance function of SIR in Nakagami fast fading channels. The paper focuses on the efficiency of the derived analytical expression and a detailed discussion about the relevant cases.

Computational complexity of narrow band and wide band channel simulators

Some questions such as: is it convenient to simulate channel realizations with the sum of sinusoids or with the filtering approach, are addressed in this work in order to provide a guide on which algorithms and in what situations should be used in the development of channel simulators. The conclusions presented are gathered from the comparison of the methods proposed in the literature to simulate narrowband and wideband separable channels. The comparisons are performed from the point of view of computational complexity and two metrics of approximation error. We also discuss the properties inherent to the algorithms that could determine if the proposals are suitable for channel simulation, such as synthesis complexity and their capability to approximate the conditions encountered in real channels.

Capacity studies of spatially correlated MIMO Rice channels

In this paper, we have studied the statistical properties of the capacity of spatially correlated multiple-input multiple-output (MIMO) Rice channels. We have derived an exact closed-form expression for the probability density function (PDF) and an exact expression for the cumulative distribution function (CDF) of the channel capacity for single-input multiple-output (SIMO) and multiple-input single-output (MISO) systems. Furthermore, an accurate closed-form expression has been derived for the level-crossing rate (LCR) and an accurate expression has been obtained for the average duration of fades (ADF) of the SIMO and MISO channel capacities. For the MIMO case, we have investigated the PDF, CDF, LCR, and ADF based on a lower bound on the channel capacity. The results are studied for a different number of transmit and receive antennas, but the proposed method can also be used to investigate the influence of some key parameters on the channel capacity, such as the antenna spacings of the transmitter and the receiver antenna arrays, and the amplitude of the time-invariant line-of-sight (LOS) component. The analytical expressions are valid for the well-known Kronecker model and an LOS component orthogonal to the direction of motion of the receiver. The correctness of the derived expressions is confirmed by simulations.

High Order Fading Distributions in Nakagami Wireless Channels

The fade duration distribution (FDD) of randomly varying wireless channels has been a research topic for more than forty years. However, for non-Gaussian channels the FDD is up to now an unsolved problem and closed form general solutions are still unknown. In this paper we use an orthogonal series expansion to analyze the FDD for the rather general case of Nakagami fading channels. Our results show that the fade duration distribution, for both asymptotic and no-asymptotic threshold levels, can be approximated by a simple closed form function: the Gamma distribution. This approximation is validated by means of several statistical goodness of fit tests. We show that the parameters of the approximated Gamma distribution can be computed a priori through the fade duration statistics, namely the average and variance. We compare the analytical fade statistics with simulation results.

Noncoherent channel equalization for DDPSK

This paper introduces a novel noncoherent linear channel equalization structure for time dispersive channels subjected to non negligible carrier frequency offsets for double differential phase shift keying (DDPSK) modulation. An optimization criterion for the adjustment of the coefficients of this equalization structure, termed cross-differential minimum mean square error (CDMMSE), is also proposed. In contrast to a previous work in the literature where the equalizer coefficients needed to be iteratively calculated without assurance of global convergence, the proposed CDMMSE criterion accepts a closed form solution. It will be shown that this solution coincides with that of the optimum coherent linear minimum mean square error (MMSE) equalizer when the transmitted symbols possess constant modulus. Simulation results are presented that corroborate the predicted performance of the proposed approach