Jose Candido Silveira Santos Filho

On the second-order statistics of Nakagami fading simulators

We derive important second-order statistics-joint distribution of the envelope and its time derivative, second-order distribution, autocorrelation, level crossing rate, and average fade duration-of an existing Nakagami fading simulator, and show that these statistics but the autocorrelation differ considerably from the well-established statistics of the classical simulator.

On the simulation and correlation properties of phase-envelope nakagami fading processes

The aim of this Letter is twofold: to propose a simulator for both the phase and the envelope of Nakagami fading channels with arbitrary parameters and to derive precise closed-form approximations to the correlation functions of the Nakagami envelope, phase, and quadrature components.

Outage analysis of a spectrally efficient scheme for multiuser cognitive relaying networks with spectrum sharing constraints

This paper investigates the outage performance of a spectrally efficient scheme for multiuser cognitive relaying networks under spectrum sharing constraints. In the proposed setup, we consider a secondary network composed by one source node communicating with the best one out of L available destinations, selected according to the channel quality of the direct links. If the selected direct link drops below a given threshold, a half-duplex decode-and-forward relaying transmission strategy is invoked, and then the selected secondary destination employs a maximal-ratio combining technique to combine the received signals from the secondary source and relay. In our analysis, the overall transmit power at the secondary network is considered to be limited by the maximum tolerable interference power at the primary user receiver, as well as by the maximum transmit power available at the secondary nodes. A closed-form expression for the outage probability is obtained and validated by Monte Carlo simulations. Moreover, an asymptotic analysis is carried out and reveals that the achievable diversity order equals L+1.

Correlation Between Signals From Spaced Antennas of Stationary Meteorological Radars

This paper derives a general analytical expression for the correlation coefficient of signals received by two identical spaced antennas in a radar system used to detect meteorological phenomena such as rain and clouds. Such a correlation coefficient is found as a function of the relevant physical parameters, namely, distance between antennas (baseline distance), signal bandwidth, and antenna directivity. One of the antennas transmits the signal and receives its echoes from the scatterers, characterizing a monostatic radar, whereas the other antenna only receives these echoes, characterizing a bistatic radar. Our approach can be easily extended to nonidentical antennas.

Simple accurate closed-form approximations for the crossing rates of Weibull fading channels in multibranch diversity systems

In this paper, we propose accurate closed-form approximate expressions for the level crossing rate (LCR) of the envelope of equal-gain and maximal-ratio combining receivers operating on independent Weibull fading channels. Due to the inherent intricacy of the exact formulation, in which the LCR is given in terms of multiple integrals, our closed-form approximations play a crucial role in this issue as far as the computational evaluation is concerned. In addition, sample numerical curves are plotted to illustrate the excellent agreement between exact and closed-form approximate formulations for such diversity scenarios.

An Efficient Power Allocation Scheme for Multirelay Systems With Lossy Intra-Links

The so-called chief executive officer problem suggests that the source message can be recovered at the destination by merging a set of corrupted replicas forwarded by multiple relays, as long as these replicas are sufficiently correlated with the original message. In this paper, we build on Slepian-Wolf’s correlated source coding theorem to design a simple, yet efficient power allocation scheme for a multirelay system, in which the direct link is unavailable to convey information. In such a system, the replicas forwarded by the relays are allowed to contain intra-link errors due to previous unreliable hops, and the destination is supposed to retrieve the source message by jointly decoding all received replicas. Importantly, the proposed power allocation is asymptotically optimal at high signal-to-noise ratio.

A distributed and spectrally efficient link selection scheme for multiuser multirelay networks with transmit beamforming

A distributed and spectrally efficient link selection scheme for multiuser multirelay cooperative networks with transmit beamforming is proposed and analyzed in terms of outage probability and mean spectral efficiency. More specifically, we consider a network composed by a base station equipped with M antennas which is communicating with one out of L single-antenna mobile stations under the aid of one out of N single-antenna, variable-gain amplify-and-forward relay stations. Either the direct link or the dual-hop relaying link is selected for each communication process by following a distributed link selection scheme. Single-integral expressions for upper and lower bounds of the outage probability and mean spectral efficiency are obtained and validated by Monte Carlo simulations. Furthermore, closed-form expressions derived from the asymptotic analysis of the outage probability reveal that the proposed system achieves full diversity order, which is equal to ML+N. Importantly, it is shown that the mean spectral efficiency is always higher than half of that one attained by direct transmission.

Level Crossing Rates and Average Fade Durations for Diversity-Combining of Non-identical Correlated Hoyt Signals

In this paper, exact expressions for the level crossing rate (LCR) and average fade duration (AFD) for two-branch selection, equal-gain and maximal-ratio combining systems in a Hoyt fading environment are presented. The expressions apply to unbalanced, non-identical, correlated diversity channels and have been validated by specializing the general results to some particular cases whose solutions are known. In passing, the joint bidimensional envelope-phase Hoyt distribution with arbitrary fading parameters is obtained

General Exact Level Crossing Rates and Average Fade Durations of Dual Diversity Combiners over Non-Identical Correlated Ricean Channels

General exact expressions for the level crossing rate and average fade duration of dual-branch selection, equal-gain, and maximal-ratio combiners operating over non-identical correlated Ricean channels are derived. Sample numerical results are discussed by specializing the general expressions to a space-diversity system with horizontally spaced omnidirectional antennas at the mobile station. When the antennas are perpendicular to the direction of the vehicle motion, the average fade duration is loosely dependent on the antenna spacing and on the Ricean factor, being almost identical to that of the independent fading condition. When the antennas are parallel to the direction of the vehicle motion, the level crossing rate can be reduced below the value obtainable for independent fading signals. In this case, if a line-of-sight component exists, a further improvement in the average fade duration over the independent condition may be also achieved.