M. Pratesi

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.

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.

A general analysis of signal strength handover algorithms with cochannel interference

In this paper, the problem of computing cochannel interference statistics in signal strength measurements in mobile radio systems is presented. In a cellular environment with cross-correlated log-normal shadowings, extensions of Wilkinsons method and Schwartz and Yehs (1982) method are proposed for evaluating the statistics of differences between signal strengths that a mobile terminal measures on the links to any pair of base stations in the presence of cochannel interferers. The derived statistics are then used in the performance analysis of relative signal strength handover algorithms. Results provided by the two methods are compared with simulation results, in order to assess their accuracy, and computational issues are addressed. From numerical results, it is also seen that handover algorithm performance has a noticeable dependence on both cross correlation among shadow fadings and the interference level. Finally, it is seen that previous approaches to derive cochannel interference statistics in the presence of log-normal shadowing can be obtained as particular cases.

The W-band data collection experiment of the DAVID mission

The data collection experiment (DCE) of the scientific mission DAVID (DAta and Video Interactive Distribution) of the Italian Space Agency (ASI) will pioneer the use of the W-band for telecommunications experiments. In particular the collection of high volumes of data from remote or virtually remote sites will be achieved through the exploitation of a W-band link in a time window of a few minutes per satellite pass. The experiment will hence demonstrate the capability of the W-band channel to be used reliably for a telecommunication link. At the same time, the experiment will provide useful elements for the characterisation of the W-band channel, in order to be able to design properly future operational systems working at W-band.

Stratospheric relay: potentialities of new satellite-high altitude platforms integrated scenarios

In the frame of the development of future telecommunications systems, an integration of heterogeneous networks (wireline, wireless, terrestrial or space-based) is envisaged. High Altitude Platfonns (HAP) could play a key role, acting as “building blocks” of such systems; therefore, a new research area concerns their integration in satellite scenarios. This paper presents and analyses two conceivable HAPsatellite integrated scenarios, considering both radio and optical communications for the HAP-satellite links.

Modeling of handover initiation in a multicell system scenario

A model is provided for the analysis of handover initiation algorithms in cellular systems. An extension of the Vijayan and Holtzmans (see IEEE Trans. on Vehic. Technol., vol.42, no.8, p.351, 1993) model is achieved, which accounts for: (a) the effects of the angular direction when a mobile moves from a current to a target base station, (b) the presence of more than two base stations, as in actual cellular environments, (c) the effects of cross-correlation of shadow fadings affecting the links between the mobile terminal and the various base stations. From the results it is seen that, for a typical trajectory of the mobile terminal from the current base station, the number of handover might be sensibly increased due to the presence of disturbant stations. Moreover, a further increase is usually observed when cross-correlation is also accounted for.

Performance of signal strength handover algorithms with interference and correlated shadowings

This paper proposes results of an improved analysis of handover initiation algorithms in cellular mobile radio networks. Performance of relative signal strength handover algorithms is derived in a general environment with cross-correlated shadowings and interferers. Numerical results are presented for a bidimensional layout of hexagonal cells as well as for a lineal array of cells. It is seen that both cluster size and cross-correlation parameters may have a noticeable impact on algorithm performance. Hence they should be carefully considered in algorithm design.

Joint characterization of outage probability and handover performance in cellular mobile networks

An approach to performance evaluation of cellular mobile networks is proposed, which includes the behavior of handover algorithms in the computation of outage probability. In a general system scenario, with a central cluster and a first tier of interferers, the average outage probability is computed along a trip of the mobile terminal that involves crossing the boundary between adjacent cells. The effects of correlated co-channel interferers are accounted for in the computation of outage probability, as well as in the dynamics of a relative signal strength handover algorithm. Numerical results are presented in terms of average outage probability versus the average number of handovers at various cluster size and cross-correlation parameters.

Modeling of handover initiation algorithms with correlated co-channel interferers

In this paper an improved analysis of handover initiation algorithms in cellular radio networks is provided. The performance of relative signal strength algorithms is analytically derived in a log-normal shadowing environment, considering a generic number of cells and a generic path of a mobile station. The cross-correlation among shadow fadings is modeled and the presence of co-channel interferers is accounted for by considering a generic cluster size. The latter two features represent the most significant achievements of this work. In fact, numerical results point out that they both have a noticeable impact on the algorithm performance, so that they should be carefully considered in algorithm design. Expressions and results previously reported in literature can be obtained as particular cases.