Gennaro Fedele

MRC performance for binary signals in Nakagami fading with general branch correlation

Exact expressions are derived for the performance of predetection maximal ratio combiner diversity reception with L correlated branches in Nakagami fading. Bit error rates are evaluated for both coherent and noncoherent binary phase-shift-keying and frequency-shift-keying signals, starting from the L-variate moment generating function of the random input power vector. The new formulation presented for the bit error rate, in which the covariance matrix of the fading at the L branches explicitly appears, allows arbitrary branch correlation to be taken into account for any diversity order in the case of identical fading severity on the branches. Results are presented for evaluation of the outage probability, for integer values of fading severity, as well as for the effect of the presence of unbalanced channels with arbitrary correlation.

Optimum and Suboptimum Space-Diversity Detection of Weak Signals in Non-Gaussian Noise

The structure of the locally optimum space-diversity detector for coherent detection of a bandpass signal subject to amplitude fluctuations in the presence of narrow-band non-Gaussian noise is derived and its large-sample performance is evaluated. For easy implementation a suboptimum structure is proposed. It consists of local detectors performing independent local decisions and of a central processor that, working according to simple logical schemes (OR or AND), performs the global decision based on the local ones. Numerical results and a comparison between the performances of both proposed structures are presented and discussed.

Switched Dual Diversity Reception of M-ary DPSK Signals on Nakagami Fading Channels

The paper deals with dual diversity reception of M-ary differential phase-shift keying modulated signals in the presence of additive white Gaussian noise and Nakagami-distributed slow and nonselective fading. The performance of a switched diversity system is analysed and compared to that of the predetection selection diversity combining scheme. The general case of correlated diversity branches is considered, without restrictions on the fading severity parameter. Average symbol error rate formulas are analytically derived in terms of integral expressions that can be easily computed via numerical integration routines. Moreover, the numerical evaluation of the optimum switching threshold is carried out and the influence of the fading severity parameter, the branch correlation, and the cardinality of the symbol alphabet is analysed. Finally, three fixed switching threshold strategies that allow to obtain a satisfactory diversity gain are considered.

Post-detection diversity Nakagami fading channels with correlated branches

We derive a closed-form expression for the performance of the post-detection product detector combiner (PDC) operating on L correlated branches in Nakagami (1960) fading. We consider the 2-DPSK signaling scheme and nonselective slow fading. The average bit error rate (BER) obtained with this scheme is compared to the ideal predetection MRC, showing limited loss. Moreover, the post-detection PDC is shown to outperform the selection diversity combiner (SDC) under the considered case of Nakagami fading.

Performance analysis of SAR change detection technique

The recent advance and diffusion of airborne and satellite SAR systems makes the use of multitemporal SAR images of practical interest for monitoring and control applications, especially when aiming at the identification of moving objects. Change detection is a powerful technique, which allows the detection of slowly moving targets. This is obtained by subtracting on a pixel-by-pixel basis the intensity of two SAR images collected at different times and comparing the absolute value of the difference to a detection threshold. Under ideal conditions, the fixed background is totally correlated and cancels out completely. On the contrary, a slowly moving target changes its position in the two images and is not cancelled. Therefore only its echo crosses the threshold. In practice, a number of factors cause the deviation from the ideal conditions; among the others the temporal decorrelation of the scene due to the internal clutter motion and the presence of misregistration and miscalibration errors. The prediction of change detection performance is essential to the design of SAR based systems for the moving target detection and should take into account all of the possible mismatch causes. In the present paper we aim at a complete mathematical characterization of the performance of change detection under non-ideal conditions. Specifically, Section 2 introduces the change detection technique and discusses some of the possible deviations from the ideal conditions. The analytical derivations are presented in Section 3, together with the discussion of the achieved results. To validate the theory, the obtained performance prediction is compared to the results obtained with real SAR images in Section 4.

MRC diversity for binary signals in correlated Nakagami fading

Abstract The performance of maximal ratio combiner (MRC) diversity reception with L correlated branches in Nakagami fading is presented. Bit error rate (BER) is evaluated for binary signals starting from the L -variate moment-generating function (MGF) of the random input power vector. In the case of Nakagami fading the L -variate statistics are not uniquely determined by marginal distributions and covariance matrix; in particular, two different joint MGFs are presented for the L -variate Nakagami vector, which give the same marginal density functions and covariance matrix and are easily generated. The two MGFs yield two different closed form expressions for the BER of the MRC diversity with generic branch correlation. The sensible difference in performances suggests that marginal probability density functions (pdfs) and power covariance matrix are not sufficient to completely characterize correlated Nakagami fading.

performances de la Modulation D’amplitude en Quadrature Maire sur des Canaux D’Évanouissement de Nakagami Avec RÉception en DiversitÉ

Ľarticle etudie la probabilite ďerreur du maq m-aire qui est obtenue avec une diversite a l branches. Il analyse les combinaisons de signaux a rapport maximal (mrc) et a selection (sdc) avant detection, pour des valeurs entieres de la severite ďevanouissement et des evanouissements independants. La probabilite ďerreur majeure par symbole est exprimee analytiquement par une somme finie de fonctions hypergeometriques gaussiennes pour des branches equilibrees ayant des valeurs identiques de severite ďevanouissement. Ľanalyse est originale dans le cas sdc. Des resultats numeriques permettent ďidentifier dans quelles conditions operationnelles les techniques de diversite sont efficaces contre les effets ďevanouissements lents non selectifs.This paper presents the error probability performance for M-ary quadrature amplitude modulation (mqam) signalling with L-branch diversity receiver over Nakagami fading channel. Both maximal ratio combining (mrc) and selection diversity combining (sdc) techniques are considered with reference to predetection diversity architecture, in the case of integer values of fading severity and independent fading. Average symbol error probability is analitycally derived in terms of finite sum of Gauss hypergeometric functions for balanced branches with identical values of the fading severity. In particular, performance analysis of sdc for mqam in Nakagami fading is new since it has not been presented in any previous work. Numerical results are presented allowing to identify those operational conditions in which diversity techniques can aid successfully in counteracting the effects of slow and nonselective short-term fading.RésuméĽarticle étudie la probabilité ďerreur du maq m-aire qui est obtenue avec une diversité à l branches. Il analyse les combinaisons de signaux à rapport maximal (mrc) et à sélection (sdc) avant détection, pour des valeurs entières de la sévérité ďévanouissement et des évanouissements indépendants. La probabilité ďerreur majeure par symbole est exprimée analytiquement par une somme finie de fonctions hypergéométriques gaussiennes pour des branches équilibrées ayant des valeurs identiques de sévérité ďévanouissement. Ľanalyse est originale dans le cas sdc. Des résultats numériques permettent ďidentifier dans quelles conditions opérationnelles les techniques de diversité sont efficaces contre les effets ďévanouissements lents non sélectifs.

A phenomenological model for radar signal propagation in evaporation ducts

A phenomenological model is proposed for the propagation of wideband radar pulses through an evaporation duct. The proposed model extends the previous models in two directions: (i) it presents a wideband characterization, thus removing the continuous wave hypothesis of most previous models; (ii) it fully considers the random characteristic of the geometric parameters by providing a statistical model. In particular, a statistical approach is used for the description of the rough sea surface due to the presence of wind and sea swells. The resulting model describes the duct as a random Gaussian fading channel with statistical parameters related to the surface geometrical characteristics. Both the single point statistic of the received signals and the spectral distortion of the transmitted pulses are studied by the proposed model. In particular, the coherence bandwidth is shown to depend essentially on the ratio between the surface standard deviation and the correlation length, i.e., on the local surface slope. As expected, the channel bandwidth decreases as either the sea roughness increases (larger standard deviation) or the surface decorrelates. These results apply both to TE and TM modes and both to exponential and Gaussian models assumed to describe the spatial correlation function of the surface heights.

Determination of the average height of a large region from nadir looking radar sensors

The paper presents a processing technique to be applied to nadir looking radar sensors to gain altimetric data with high precision. Pulse limited altimeters are considered as those in use for the mapping of a surface. High resolution is obtained by means of phase monopulse in the cross-track direction while synthetic aperture processing followed by a proper incoherent technique is proposed for the resolution in the along-track direction.

Rank detectors in correlated K-distributed clutter

The paper deals with the performances of the first and second order rank detectors in presence of correlated K-distributed clutter. First, assuming a perfect knowledge of both clutter shape factor and texture correlation, the detection probability of the rankers is compared to the ideal performance and to that of a cell-averaging detector. Then, an on-line estimator of the shape factor in the correlated environment is introduced, and the corresponding detection losses are analyzed.