Ugo Silva Dias

Joint statistics for two correlated Weibull variates

This paper derives closed-form formulas for the joint statistics of two correlated Weibull variates. In particular, the joint probability density function, the general joint moments, and the general correlation coefficient are obtained in terms of well-known fading physical parameters.

On the α-μ Autocorrelation and Power Spectrum Functions: Field Trials and Validation

Indoor and outdoor field trial measurements are used to validate the autocorrelation function derived in an exact manner for the α-µ fading signal. In addition, accurate closed-form approximations for both autocorrelation function and to the power spectrum of the α-µ envelope are obtained and also validated. Comparisons are performed and an excellent fit to the field measurements is found in both isotropic and anisotropic environments.

The Ratio of Independent Arbitrary α-μ Random Variables and its Application in the Capacity Analysis of Spectrum Sharing Systems

General, simple, exact, closed-form expressions for the ratio of independent non-identically distributed α-μ random variables are derived. These important results find applicability in several performance analysis of wireless communication systems, in particular those for which the ratio of signal powers is of relevance. One such application, currently of enormous interest, is the capacity analysis of spectrum sharing networks. Motivated by this, a comprehensive capacity study of spectrum sharing systems undergoing α-μ fading is performed, followed by insightful discussions.

The к-μ Extreme distribution: Characterizing severe fading conditions

This paper presents the к-μ Extreme fading distribution, which is used for characterizing mobile radio propagation under severe fading conditions. The distribution is adjusted to field data extracted from the literature and compared to another model recently proposed elsewhere, namely the Two-Ray model. Adjustment results show that the к-μ Extreme distribution is flexible and suitable to model the severe fading conditions. A closed-form expression for the average BER in non-coherent binary modulation schemes is derived. Finally, performance of the selection combining technique is evaluated in terms of the outage probability.

On the weibull autocorrelation and power spectrum functions: field trials and validation

Indoor and outdoor field trial measurements are used to validate the autocorrelation function derived in an exact manner for the Weibull fading signal. In addition, an accurate closed-form approximation to the power spectrum of the Weibull envelope is obtained and also validated. Comparisons are performed and an excellent fit to the field measurements is found.

On the Distribution of Signal Phase in Body Area Networks

In this letter, we investigate the distribution of the phase component of the complex received signal observed in practical experiments using body area networks. Two phase distributions, the recently proposed κ-μ and η-μ probability densities, which together encompass the most widely used fading models, namely Semi-Gaussian, Rayleigh, Hoyt, Rice, and Nakagami-m, have been compared with measurement data. The κ-μ distribution has been found to provide the best fit over a range of on-body links, while the user was mobile. The experiments were carried out in two dissimilar indoor environments at opposite ends of the multipath spectrum. It has also been found that the uniform phase distribution has not arisen in anyone of the experiments.

On the Nakagaini-m crosscorrelation function

The generic-order crosscorrelation function between two non-identically distributed Nakagami-m fading processes is derived assuming a space-frequency diversity scenario with horizontally spaced omnidirectional antennas at the mobile station. Our result allows for distinct fading parameters, power imbalance, antenna, spacing/angle, and frequency separation. Based on it, the coherence bandwidth and the coherence time/distance of the Nakagami-m channel are also obtained. The latter is found to be practically identical to the coherence time/distance of the Rayleigh channel.

On the capacity of spectrum sharing systems in generalized fading scenarios

Spectrum sharing concepts have been widely employed in the design of practical systems with the aim to improve the utilization efficiency of the radio spectrum. Motivated by this, a comprehensive capacity study of spectrum sharing systems undergoing α-ε fading is performed in this paper. More specifically, assuming identical fading parameters, a closed-form expression for the delay-limited capacity is derived. In addition, based on the power allocation related to the outage capacity, a closed-form expression for the corresponding minimum outage probability is attained. Guidelines on how the ergodic capacity can be evaluated are also presented. Numerical plots are shown in order to investigate the effect of the fading parameters in the system capacity.

Secrecy performance of MIMO Nakagami-m wiretap channels with optimal TAS and different antenna schemes

Transmit antenna selection TAS in wiretap channels has arisen as a simple promising scheme to improve physical layer security. However, up to now, TAS schemes have aimed at maximising the instantaneous signal-to-noise ratio of the legitimate receiver, which by its essence is a sub-optimal strategy from a secrecy point of view. In this paper, unlike previous works, we propose a novel TAS scheme for multiple-input multiple-output wiretap channels by exploiting full channel state information. The proposed scheme achieves higher secrecy performance by selecting an antenna that maximises the secrecy rate. In our analysis, we assume that the receiver Rx and the eavesdropper employ either selection combining SC or maximal-ratio combining MRC to combine the received signals, and this results in four different receiver combining arrangements. By considering Nakagami-m fading, secrecy performance is analysed. Specifically, closed-form expressions for the secrecy outage probability are derived, which can be used as a quality of service metric. Moreover, an asymptotic analysis is carried out and the respective diversity/array gains are obtained. The ergodic secrecy rate is also investigated for the case of multiple-input single-output wiretap channels. Insightful discussions are attained from our analysis. For instance, it is shown that the performance gain of MRC over SC at the Rx does not depend on the number of antennas and combining scheme at the eavesdropper. More interestingly, we observe that such a performance gain is independent of the TAS scheme used at the transmitter Tx. On the other hand, it is shown that the secrecy gap between SC and MRC at the eavesdropper is independent of the number of antennas at the Tx, but it depends on the number of antennas at the Rx. Finally, it is demonstrated that the diversity gain is the same for all antenna configurations. Copyright

The κ-μ phase-envelope joint distribution

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