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Showing papers by "Polytechnic University of Turin published in 1996"


Journal ArticleDOI
TL;DR: A method to evaluate an upper bound to the bit error probability of a parallel concatenated coding scheme averaged over all interleavers of a given length is proposed and used to shed some light on some crucial questions which have been floating around in the communications community since the proposal of turbo codes.
Abstract: A parallel concatenated coding scheme consists of two simple constituent systematic encoders linked by an interleaver. The input bits to the first encoder are scrambled by the interleaver before entering the second encoder. The codeword of the parallel concatenated code consists of the input bits to the first encoder followed by the parity check bits of both encoders. This construction can be generalized to any number of constituent codes. Parallel concatenated schemes employing two convolutional codes as constituent codes, in connection with an iterative decoding algorithm of complexity comparable to that of the constituent codes, have been previously shown to yield remarkable coding gains close to theoretical limits. They have been named, and are known as, "turbo codes". We propose a method to evaluate an upper bound to the bit error probability of a parallel concatenated coding scheme averaged over all interleavers of a given length. The analytical bounding technique is then used to shed some light on some crucial questions, which have been floating around in the communications community since the proposal of turbo codes.

1,224 citations


Journal ArticleDOI
TL;DR: The separate contributions that the interleaver length and constituent codes give to the overall performance of the parallel concatenated code are characterized, and some guidelines for the optimal design of the constituent convolutional codes are presented.
Abstract: A parallel concatenated convolutional coding scheme consists of two constituent systematic: convolutional encoders linked by an interleaver. The information bits at the input of the first encoder are scrambled by the interleaver before entering the second encoder. The codewords of the parallel concatenated code consist of the information bits followed by the parity check bits of both encoders. Parallel concatenated codes (turbo codes), decoded through an iterative decoding algorithm of relatively low complexity, have been shown to yield remarkable coding gains close to theoretical limits. We characterize the separate contributions that the interleaver length and constituent codes give to the overall performance of the parallel concatenated code, and present some guidelines for the optimal design of the constituent convolutional codes.

495 citations


Journal ArticleDOI
TL;DR: A new family of lattice constellations, based on complex algebraic number fields, which have good performance on Rayleigh fading channels are presented and some of these lattices also present a reasonable packing density and thus may be used at the same time over a Gaussian channel.
Abstract: Recent work on lattices matched to the Rayleigh fading channel has shown how to construct good signal constellations with high spectral efficiency. We present a new family of lattice constellations, based on complex algebraic number fields, which have good performance on Rayleigh fading channels. Some of these lattices also present a reasonable packing density and thus may be used at the same time over a Gaussian channel. Conversely, we show that particular versions of the best lattice packings (D/sub 4/, E/sub 6/, E/sub 8/, K/sub 12/, /spl Lambda//sub 16/, /spl Lambda//sub 24/), constructed from totally complex algebraic cyclotomic fields, present better performance over the Rayleigh fading channel. The practical interest in such signal constellations rises from the need to transmit information at high rates over both terrestrial and satellite links. Some further results in algebraic number theory related to ideals and their factorization are presented and the decoding algorithm used with these lattice constellations are illustrated together with practical results.

366 citations


Journal ArticleDOI
01 Mar 1996
TL;DR: In this paper, the formulation of N = 2, D = 4 supergravity coupled to nv abelian vector multiplets in presence of electric and magnetic charges is presented.
Abstract: We report on the formulation of N = 2, D = 4 supergravity coupled to nv abelian vector multiplets in presence of electric and magnetic charges. General formulae for the (moduli dependent) electric and magnetic charges for the nv + 1 gauge fields are given which reflect the symplectic structure of the underlying special geometry. Model independent sum rules obeyed by these charges are obtained. The specification to Type IIB strings compactified on Calabi-Yau manifolds, with gauge group U(1)h21+1, is given.

314 citations


Journal ArticleDOI
TL;DR: In this article, the eigenfunctions of the Dirac operator on spheres and real hyperbolic spaces of arbitrary dimension are computed by separating variables in geodesic polar coordinates.

267 citations


Proceedings ArticleDOI
23 Jun 1996
TL;DR: The performance of these codes is within 1 dB from the Shannon limit at a bit error probability of 10/sup -7/ for a given throughput, which outperforms the performance of all codes reported in the past for the same throughput.
Abstract: In this paper, we propose a new solution to parallel concatenation of trellis codes with multilevel amplitude/phase modulations and a suitable bit by bit iterative decoding structure. Examples are given for throughput 2 and 4 bits/sec/Hz with 8 PSK, 16 QAM, and 64 QAM modulations. For parallel concatenated trellis codes in the examples, rate 2/3 and 4/5, 8, and 16-state binary convolutional codes with Ungerboeck mapping by set partitioning (natural mapping), a reordered mapping, and Gray code mapping are used. The performance of these codes is within 1 dB from the Shannon limit at a bit error probability of 10/sup -7/ for a given throughput, which outperforms the performance of all codes reported in the past for the same throughput.

233 citations


Journal ArticleDOI
TL;DR: In this article, a technique for the detection of macroscopic structural damage in elastic structures is described, where the location and quantification of the extent of the damage are performed with genetic algorithms implemented by using the residual force method which is based on conventional modal analysis theory.

226 citations


Journal ArticleDOI
TL;DR: The generalized Tsallis statistics produces a distribution function appropriate to describe the interior solar plasma, thought as a stellar polytrope, showing a tail depleted with respect to the Maxwell-Boltzmann distribution and reduces to zero at energies greater than about 20 k B T.

222 citations


Journal ArticleDOI
TL;DR: By the use of an iterative method the linearized phonon-Boltzmann equation for a dielectric solid subjected to a thermal gradient is solved and it is possible to calculate the thermal conductivity of rare-gas solids starting from the pair potential and accounting for the real Brillouin zone of the lattice.
Abstract: By the use of an iterative method the linearized phonon-Boltzmann equation for a dielectric solid subjected to a thermal gradient is solved in the frame of three-phonon interactions. In this way it is possible to calculate the thermal conductivity of rare-gas solids starting from the pair potential and accounting for the real Brillouin zone of the lattice. The numerical results are in full agreement with experiment and represent a considerable improvement with respect to those previously deduced for an isotropic solid.

213 citations


15 Feb 1996
TL;DR: Two versions of a simplified maximum a posteriori decoding algorithm, which work in a sliding window form, like the Viterbi algorithm, and can thus be used to decode continuously transmitted sequences obtained by parallel concatenated codes, without requiring code trellis termination.
Abstract: In this article, we present two versions of a simplified maximum a posteriori decoding algorithm. The algorithms work in a sliding window form, like the Viterbi algorithm, and can thus be used to decode continuously transmitted sequences obtained by parallel concatenated codes, without requiring code trellis termination. A heuristic explanation is also given of how to embed the maximum a posteriori algorithms into the iterative decoding of parallel concatenated codes (turbo codes). The performances of the two algorithms are compared on the basis of a powerful rate 1/3 parallel concatenated code. Basic circuits to implement the simplified a posteriori decoding algorithm using lookup tables, and two further approximations (linear and threshold), with a very small penalty, to eliminate the need for lookup tables are proposed.

205 citations


Journal ArticleDOI
TL;DR: In this paper, a multilayered composite plate element is proposed that includes both the zig-zag distribution along the thickness co-ordinate of the in-plane displacements and the interlaminar continuity (equilibrium) for the transverse shear stresses.
Abstract: SUMMARY Concerning composites plate theories and FEM (Finite Element Method) applications this paper presents some multilayered plate elements which meet computational requirements and include both the zig-zag distribution along the thickness co-ordinate of the in-plane displacements and the interlaminar continuity (equilibrium) for the transverse shear stresses. This is viewed as the extension to multilayered structures of well-known Co Reissner-Mindlin finite plate elements. Two different fields along the plate thickness co-ordinate are assumed for the transverse shear stresses and for the displacements, respectively. In order to eliminate stress unknowns, reference is made to a Reissner mixed variational theorem. Sample tests have shown that the proposed elements, named RMZC, numerically work as the standard Reissner-Mindlin ones. Furthermore, comparisons with other results related to available higher-order shear deformation theories and to three-dimensional solutions have demonstrated the good performance of the RMZC elements. Major portions of aerospace structures, as well as automotive and ship vehicles consist of flat and curved panels that are used as primary load-carrying components. Due to their obvious advantages, such as critical strength/stiffness-to-weight ratios, an increasing number of these panels are made of laminated composite material. This has led to extensive research activities in the mechanical properties, loading behaviour, structural modelling, and failure assessment of multilayered composite structures. Due to the geometry of laminated structural components, two-dimensional approaches have been extensively used to trace their response. The classical Kirchhoff's plate theory (CLT, Classical Lamination Theory) has revealed its limits when applied to thick panels with high orthotropic ratio.' - The shear deformation theories of Reissner-Mindlin-type (FSDT, First Shear Deformation Theories), even though, they are quite acceptable to study global response of high shear deformable thick composite structures, are not adequate for forecasting local stress-strain characteristics. In fact, some representative problems, exact three-dimensional have shown the failure of FSDT both to fulfill the interlaminar transverse shear stresses continuity at each interface and to describe the so-called zig-zag form' of the

Journal ArticleDOI
TL;DR: In this article, the vibrational response of a cracked cantilevered beam to harmonic forcing is analyzed using a finite element model of the beam, in which a so-called closing crack model, fully open or fully closed, is used to represent the damaged element.

Journal ArticleDOI
TL;DR: In this paper, the Evans approach was applied to the Fermi resonance between the narrow 2δ and 2γ levels with the continuum distribution of levels associated with the ν(OH···B) mode coupled with the low-frequency ν (O·· ·B) vibrations and with the external (thermal) librations.
Abstract: The IR spectra of increasing doses of CH3CN interacting with H-ZSM-5, H-MOR, and H-NAFION are investigated and compared. In all cases the formation of neutral hydrogen-bonded adducts is observed and complete vibrational assignment is given. The basic IR spectroscopy of these complexes is discussed in the framework of the Evans approach on the Fermi resonance between the narrow 2δ and 2γ levels with the continuum distribution of levels associated with the ν(OH···B) mode coupled with the low-frequency ν(O···B) vibrations and with the external (thermal) librations. At low dosages the interaction of H2O with H-ZSM-5 and H-MOR gives neutral hydrogen-bonded adducts. At higher dosages these species are transformed into H+(H2O)n (naverage = 3−5) ionic species. This process can be only partially reversed by decreasing the relative pressure of H2O. At low dosage the concentration of ionic species is higher on H-MOR than on H-ZSM-5. The interaction of H2O with the superacidic H-NAFION membrane readily gives directly...

Journal ArticleDOI
TL;DR: A new iterative decoding algorithm for serial concatenation is proposed, and it is shown that the new coding scheme can yield a significant advantage with respect to turbo codes.
Abstract: Serial concatenation of convolutional codes separated by an interleaver has recently been shown, through the use of upper bounds to the maximum likelihood performance, to be competitive with parallel concatenated coding schemes known in the literature as ‘turbo codes’. The most important feature of turbo codes consists in their relatively simple, yet high performance, iterative decoding algorithm. The authors propose a new iterative decoding algorithm for serial concatenation, and show that the new coding scheme can yield a significant advantage with respect to turbo codes.

Journal ArticleDOI
TL;DR: The authors propose an alternative scheme consisting in the serial concatenation of block or convolutional codes and evaluate its average performance in terms of bit error probability.
Abstract: Parallel concatenated coding schemes employing convolutional codes as constituent codes linked by an interleaver have been proposed in the literature as ‘turbo codes’. They yield very good performance in connection with simple suboptimum decoding algorithms. The authors propose an alternative scheme consisting in the serial concatenation of block or convolutional codes and evaluate its average performance in terms of bit error probability.

Journal ArticleDOI
TL;DR: The authors advocate an exceedingly general numerical method for the calculation of P(/spl Delta//spl les/0) based on Gauss-Chebyshev quadratures, which combines simplicity with accuracy.
Abstract: The evaluation of error probabilities in digital communication systems is often amenable to computing a probability of the form P(/spl Delta//spl les/0), where /spl Delta/ is a random variable whose probability distribution is known. As an example, the pairwise error probability of coded modulations can be expressed in this form. The authors advocate an exceedingly general numerical method for the calculation of P(/spl Delta//spl les/0) based on Gauss-Chebyshev quadratures, which combines simplicity with accuracy.

Journal ArticleDOI
TL;DR: In this article, the general form of N = 2 supergravity coupled to an arbitrary number of vector multiplets and hypermultiplets with a generic gauging of the scalar manifold isometries is given.

Journal ArticleDOI
TL;DR: In this article, the authors studied the problem of minimizing total completion time in a two-machine flow shop and proposed a branch and bound method to minimize the total time in the flow shop.

Journal ArticleDOI
TL;DR: In this paper, a systematic investigation of the surface morphology and vibrational properties of CO and NO adsorbed on simple oxides microcrystals with regular crystalline habit and exposing thermodynamically stable and neutral faces is presented.

Journal ArticleDOI
TL;DR: In this article, the authors present the theoretical considerations that justify the choice of specific time-frequency transforms for processing nonstationary myoelectric signals as a method of studying fatigue prior to the failure point.
Abstract: This article presents the theoretical considerations that justify the choice of specific time-frequency transforms for processing nonstationary myoelectric signals as a method of studying fatigue prior to the failure point. It shows some preliminary results obtained by applying these techniques to computer-synthesized realizations of stochastic processes, as well as to real signals detected during different types of dynamic contractions of healthy human volunteers. Five different time-frequency transforms were applied in this study (the Wigner-Ville, the smoothed Wigner-Ville, the Cone kernel, the reduced interference, and the Choi-Williams), but for the sake of brevity, this article reports only the results obtained by applying the Choi-Williams transform, because the authors found it to be the most suitable for processing these specific signals.

Journal ArticleDOI
TL;DR: Simulation results show that the throughput limitations and the fairness problems inherent in the network topology can be overcome with relatively simple protocols.
Abstract: The paper illustrates novel proposals for medium access control protocols in all-optical packet networks based on WDM multichannel ring topologies where nodes are equipped with one fixed-wavelength receiver and one wavelength-tunable transmitter. Such networks provide separate slotted channels for disjoint subsets of destination nodes. Three access protocols based on local status information are described. A channel inspection capability is assumed to be available for the implementation of the access protocols. Global fairness control algorithms derived from those adopted in the Metaring high-speed metropolitan area network are also proposed. Access delays and throughputs are taken as performance Indices for a simulation-based comparison of the proposed protocols, in the case of a 16-node multiring with either balanced or unbalanced traffic. Simulation results show that the throughput limitations and the fairness problems inherent in the network topology can be overcome with relatively simple protocols.

Proceedings ArticleDOI
11 Dec 1996
TL;DR: In this article, a probabilistic approach for robustness analysis of control systems affected by bounded uncertainty is presented. But the authors focus on the problem of estimating the number of samples required to estimate the probability that a given performance level is attained given a certain accuracy and confidence.
Abstract: In this paper, we study robustness analysis of control systems affected by bounded uncertainty. Motivated by the difficulty to perform this analysis when the uncertainty enters into the plant coefficients in a nonlinear fashion, we study a probabilistic approach. In this setting, the uncertain parameters q are random variables bounded in a set Q and described by a multivariate density function f(q). We then ask the following question: Given a performance level, what is the probability that this level is attained? The main content of this paper is to derive explicit bounds for the number of samples required to estimate this probability with a certain accuracy and confidence apriori specified. It is shown that the number obtained is inversely proportional to these thresholds and it is much smaller than that of classical results. Finally, we remark that the same approach can be used to study several problems in a control system context. For example, we can evaluate the worst-case H/sup /spl infin// norm of the sensitivity function or compute /spl mu/ when the robustness margin is of concern.

Journal ArticleDOI
TL;DR: A prototype system named GATTO is used to assess the effectiveness of the approach in terms of result quality and CPU time requirements and the results are the best ones reported in the literature for most of the largest standard benchmark circuits.
Abstract: This paper deals with automated test pattern generation for large synchronous sequential circuits and describes an approach based on genetic algorithms. A prototype system named GATTO is used to assess the effectiveness of the approach in terms of result quality and CPU time requirements. An account is also given of a distributed version of the same algorithm, named GATTO*. Being based on the PVM library, it runs on any network of workstations and is able to either reduce the required time, or improve the result quality with respect to the monoprocessor version. In the latter case, in terms of Fault Coverage, the results are the best ones reported in the literature for most of the largest standard benchmark circuits. The flexibility of GATTO enables users to easily tradeoff fault coverage and CPU time to suit their needs.

Journal ArticleDOI
TL;DR: The authors compute the capacity of bit-interleaved coded modulation (BICM) in the case of ideal interleaving, and show that for most signal sets with Gray labelling, this turns out to be almost equal to thecapacity of the signal sets themselves.
Abstract: The authors compute the capacity of bit-interleaved coded modulation (BICM) in the case of ideal interleaving. They show that for most signal sets with Gray labelling, this turns out to be almost equal to the capacity of the signal sets themselves. This implies that BICM can achieve the same coding gain as TCM.

Proceedings ArticleDOI
23 Jun 1996
TL;DR: New decoding algorithms to be embedded in the iterative decoding strategy of parallel concatenated convolutional codes are derived from the optimum maximum-a-posteriori algorithm and permit a continuous decoding of the coded sequence without requiring trellis termination of the constituent codes.
Abstract: We propose new decoding algorithms to be embedded in the iterative decoding strategy of parallel concatenated convolutional codes. They are derived from the optimum maximum-a-posteriori algorithm and permit a continuous decoding of the coded sequence without requiring trellis termination of the constituent codes. Two basic versions of the continuous algorithm and their suboptimum simplifications are described. Simulation results refer to the applications of the new algorithms to a highly efficient rate 1/3 concatenated code; they show performance only 0.6 dB worse than the Shannon limit.

Proceedings ArticleDOI
06 Oct 1996
TL;DR: A flux-observer based control scheme is proposed, capable of overcoming most of the above problems of synchronous reluctance motors, and has been implemented on a prototype drive, adopting a 17 Nm, 8,000 RPM motor.
Abstract: Based on a (d,q) synchronous frame, the control problems of synchronous reluctance motors are outlined. In particular, the effect of magnetic saturation, core loss, and angular measurement errors of various types are evidenced. A flux-observer-based control scheme, capable of overcoming most of the above problems, is proposed. The proposed control has been implemented on a prototype drive, adopting a 17-N/spl middot/m 8000-r/min motor. The experimental results show quite a good performance, with particular emphasis on those applications which require a large constant-power speed range.

Journal ArticleDOI
TL;DR: An approximate Karhunen-Loeve expansion for a random fading process characterised by an autocorrelation function was given in this article, where the autocorerelation function is defined as a Bessel function and fd is the process fading rate.
Abstract: An approximate Karhunen-Loeve expansion is given for a random fading process characterised by an autocorrelation function Rḡ(τ) = J0(2πfdτ), J0(x) is the zeroth order Bessel function and fd is the process fading rate.

Journal ArticleDOI
TL;DR: A new numerical approach for solving Volterra integral equations of the second kind when the kernel contains a mild singularity is introduced.
Abstract: We introduce a new numerical approach for solving Volterra integral equations of the second kind when the kernel contains a mild singularity. We give a convergence result. We also present numerical examples which show the performance and efficiency of our method.

Proceedings ArticleDOI
10 Nov 1996
TL;DR: An optimized traversal technique particularly oriented to the exact exploration of the state space of large machines, and an effective use of secondary memory allows us to store relevant portions of BDDs and to regularize access to memory, resulting in less page faults.
Abstract: BDD-based symbolic traversals are the state-of-the-art technique for reachability analysis of Finite State Machines. They are currently limited to medium-small circuits for two reasons: peak BDD size during image computation and BDD explosion for representing state sets. Starting from these limits, this paper presents an optimized traversal technique particularly oriented to the exact exploration of the state space of large machines. This is possible thanks to: 1) temporary simplification of a Finite State Machine by removing some of its state elements, 2) a "divide-and-conquer" approach based on state set decomposition. An effective use of secondary memory allows us to store relevant portions of BDDs and to regularize access to memory, resulting in less page faults. Experimental results show that this approach is particularly effective on the larger ISCAS'89 and ISCAS'89-addendum'93 circuits.

Proceedings ArticleDOI
05 Aug 1996
TL;DR: In this article, axial flux induction and synchronous machines as wheel motor application are presented, and some considerations for each motor type are drawn by the authors, and they focus the attention on the small electric city cars to be used in European towns where the environment pollution problems are quite heavy.
Abstract: For electric car propulsion systems, the wheel motor is an application that requires electrical machine shape flexibility, compactness, robustness, high efficiency and high torque. The axial flux machine is an interesting solution, where the motor is directly coupled or inside the driven wheel. In this paper, axial flux induction and synchronous machines as wheel motor application are presented, and some considerations for each motor type are drawn by the authors. The structure with two rotors seems to be a very promising solution for both induction and synchronous machines. The twin rotor structures allow saving of the motor active material: stator winding copper or stator core iron. Thus the machines can have higher power density and efficiency in comparison with two individual motors. In addition, for the induction case, the two rotors can rotate at different speeds, and thus the motor can act as a mechanical differential, even if supplied by a single invertor. The axial flux PM motor with two rotors is very compact and can be integrated inside the wheel. Since the identification of a unique drive solution for any type of electric vehicle, the authors focus the attention on the small electric city cars to be used in European towns where the environment pollution problems are quite heavy.