Fabio Graziosi

A unified framework for performance analysis of CSI-assisted cooperative communications over fading channels

In this Letter, we propose a comprehensive framework for performance analysis of cooperative wireless systems using Amplify and Forward (AF) relay methods. The framework relies on the Moment Generating Function (MGF-) based approach for performance analysis of communication systems over fading channels, and on some properties of the Laplace Transform, which allow to develop a single-integral relation between the MGF of a random variable and the MGF of its inverse. Moreover, a simple lower bound for Outage Probability (Pout) and Outage Capacity (OC) computation is also introduced. Numerical and simulation results are provided to substantiate the accuracy of the proposed framework.

A general correlation model for shadow fading in mobile radio systems

We derive an explicit model for the cross-correlation function of the shadowing components affecting the links between a mobile station and two base stations. This model includes both the autocorrelation model proposed in earlier work by Gudmenson in 1991 for the single component, and the cross-correlation early evidenced in the work by Graziano in 1978. The model is useful in analytical computations, e.g., of second order statistics of signal-to-interference ratio. The model can include the behavior of a time-variant cross-correlation at zero-time shift and of a non-homogeneous environment.

Channel Capacity Over Generalized Fading Channels: A Novel MGF-Based Approach for Performance Analysis and Design of Wireless Communication Systems

Since the trail-blazing paper of C. Shannon in 1948, channel capacity has been regarded as the fundamental information-theoretic performance measure to predict the maximum information rate of a communication system. However, in contrast with the analysis of other important performance measures of wireless communication systems, a unified and general approach for computing the channel capacity over fading channels has yet to be proposed. Motivated by this consideration, we propose a novel and unified communication-theoretic framework for the analysis of channel capacity over fading channels. It is shown that the framework can handle various fading channel models, communication types, and adaptation transmission policies. In particular, the specific contributions of this paper are as follows: (1) We introduce a transform operator, called the E i-transform, which is shown to provide a unified tool to compute the channel capacity with either side information at the receiver or side information at the transmitter and the receiver, directly from the moment-generating function (MGF) or the MGF and the truncated MGF of the Signal-to-Noise-Ratio (SNR) at the receiver, respectively; (2) we show that when either a channel inversion or a truncated channel inversion adaptation policy is considered, the channel capacity can readily be computed from the Mellin or the Hankel transform of the MGF of the received SNR, respectively; (3) a simple yet effective numerical method for the analysis of higher order statistics (HOS) of the channel capacity with side information at the receiver is introduced; and (4) some efficient and ad hoc numerical methods are explicitly introduced to allow the efficient computation of the proposed frameworks. Numerical and simulation results are also shown and compared to substantiate the analytical derivation.

A comprehensive framework for performance analysis of dual-hop cooperative wireless systems with fixed-gain relays over generalized fading channels

In the present contribution, we propose a comprehensive framework for the analysis of cooperative dual-hop wireless systems over generalized fading channels, which use an amplify and forward (AF) relaying mechanism with blind and semi-blind relays. In particular, the proposed framework provides either exact results or very accurate bounds for computing the moment generating function (MGF) of the end-to-end signal-to-noise ratio (SNR) for various fading channel models typically encountered in real propagation environments. Furthermore, with the help of the MGF-based approach for performance analysis of wireless systems over fading channels, we will show that important performance indexes can be easily derived from the MGF. With respect to previous published articles on the matter, the main contribution of the paper is twofold: i) by relying on the properties of the Meijer-G function, either exact expressions or accurate bounds for the MGF of the end-to-end SNR are provided, and ii) the analysis encompasses the vast majority of fading channel models. Numerical and simulation results will be compared to substantiate the analytical derivation.

Space Shift Keying (SSK—) MIMO with Practical Channel Estimates

In this paper, we study the performance of space modulation for Multiple-Input-Multiple-Output (MIMO) wireless systems with imperfect channel knowledge at the receiver. We focus our attention on two transmission technologies, which are the building blocks of space modulation: i) Space Shift Keying (SSK) modulation; and ii) Time-Orthogonal-Signal-Design (TOSD-) SSK modulation, which is an improved version of SSK modulation providing transmit-diversity. We develop a single-integral closed-form analytical framework to compute the Average Bit Error Probability (ABEP) of a mismatched detector for both SSK and TOSD-SSK modulations. The framework exploits the theory of quadratic-forms in conditional complex Gaussian Random Variables (RVs) along with the Gil-Pelaez inversion theorem. The analytical model is very general and can be used for arbitrary transmit- and receive-antennas, fading distributions, fading spatial correlations, and training pilots. The analytical derivation is substantiated through Monte Carlo simulations, and it is shown, over independent and identically distributed (i.i.d.) Rayleigh fading channels, that SSK modulation is as robust as single-antenna systems to imperfect channel knowledge, and that TOSD-SSK modulation is more robust to channel estimation errors than the Alamouti scheme. Furthermore, it is pointed out that only few training pilots are needed to get reliable enough channel estimates for data detection, and that transmit- and receive-diversity of SSK and TOSD-SSK modulations are preserved even with imperfect channel knowledge.

A comprehensive framework for performance analysis of cooperative multi-hop wireless systems over log-normal fading channels

In this paper, we propose a comprehensive framework for performance analysis of multi-hop multi-branch wireless communication systems over log-normal fading channels. The framework allows to estimate the performance of amplify and forward (AF) relay methods for both channel state information (CSI-) assisted relays, and fixed-gain relays. In particular, the contribution of this paper is twofold: i) first of all, by relying on the Gauss quadrature rule (GQR) representation of the moment generation function (MGF) for a log-normal distribution, we develop accurate formulas for important performance indexes whose accuracy can be estimated a priori and just depends on GQR numerical integration errors; ii) then, in order to simplify the computational burden of the former framework for some system setups, we propose various approximations, which are based on the Improved Schwartz-Yeh (I-SY) method. We show with numerical and simulation results that the proposed approximations provide a good trade-off between accuracy and complexity for both Selection Combining (SC) and Maximal Ratio Combining (MRC) cooperative diversity methods.

Generalized moment matching for the linear combination of lognormal RVs: application to outage analysis in wireless systems

Moving from the need for a simple and versatile method for outage computation in various contexts of interest in wireless communications, in this paper we propose a lognormal approximation for the linear combination of a set of lognormal random variables (RV) with one-sided random weights. The approximation is based on a generalization of the well known moment matching approximation (MMA) for the sum of lognormal RVs, and it allows quite simple handling of the power sum of interfering signals even in rather complicated scenarios. Specifically, composite multiplicative channel models with unequal parameters can be handled, and generic (unequal) correlation patterns for some channel components can be handled with reference to any pair of signals. At this stage of the computation, only moments of the random weights are required. The probability density function of the random weight for the useful signal component may be required in computing outage probability, and numerical methods may be only required to solve a single integral at this second stage. The suitability of the approximation is examined by evaluating outage performance for various values of system parameters in some contexts of interest, namely spread spectrum systems and typical reuse-based systems with composite Rayleigh-lognormal and Nakagami-lognormal channels.

A multicell model of handover initiation in mobile cellular networks

A model is provided for the analysis of handover initiation algorithms in cellular systems, which are based on the averages of signal strength measurements and hysteresis. An extension of Vijayans and Holtzmans (1993) model is achieved, which accounts for: (1) the effects of the angular direction when a mobile terminal moves from a current to a target base station; (2) the presence of more than two base stations; and (3) the effects of cross correlation of shadow fadings affecting the links between the mobile terminal and the various base stations. The level crossing theory of Gaussian processes is used to derive the algorithm performance. The results obtained from the model are in good agreement with those obtained from simulations. It is seen that the model tends to underestimate the algorithm performance, thus yielding a lower performance bound and guaranteeing an intrinsic design margin. It is also seen that, for a typical trajectory of the mobile terminal from the current base station, the number of handovers might be noticeably increased due to the presence of disturbant stations. Moreover, when cross correlation among shadow fadings is also accounted for, significant variations are observed in both the number of handovers and handover delay. As a final result, tradeoff curves are derived and presented for the most general case.

Distributed data fusion over correlated log-normal sensing and reporting channels: Application to cognitive radio networks

In this Letter, we propose an advanced framework for performance analysis and design of decentralized data fusion problems. In particular, the performance of a multilayer system setup for data detection, which includes realistic sensing/reporting channels and correlated log-normal shadow-fading in all wireless links of the cooperative network, will be studied. The system setup will be used to analyze the performance of cooperative spectrum sensing problems adopting an amplify-and-forward (AF) relay protocol.We will show that, even though often overlooked in typical cooperative spectrum sensing analysis, shadowing correlation on the reporting channel can yield similar performance degradations as shadowing correlation on the sensing channel. All findings will be substantiated via theoretical arguments and Monte Carlo simulations, and, in particular, novel approximation methods to account for correlated log-normal shadowing in cooperative spectrum sensing problems will be introduced in this paper.

Outage analysis in mobile radio systems with generically correlated log-normal interferers

A novel methodology is proposed for computing the outage probability in mobile radio systems in the presence of log-normal shadowing. A relevant feature is that the proposed analysis assumes a general correlation for any pair of links. Various approaches are considered to compute the statistics of user signal-to-interference ratio (SIR), namely Schwartz and Yehs method, Wilkinsons method, and Fentons method. By a simple reformulation of the problem, these methods can be used to calculate in a straightforward way the parameters of the SIR. The accuracy of the methods is checked in a number of situations of interest. Moreover, when the same correlation is assigned to any pair of links, the novel analysis is more accurate than previously proposed approaches.