Showing papers by "Polytechnic University of Turin published in 1998"
TL;DR: This paper describes the statistical models of fading channels which are frequently used in the analysis and design of communication systems, and focuses on the information theory of fading channel, by emphasizing capacity as the most important performance measure.
Abstract: In this paper we review the most peculiar and interesting information-theoretic and communications features of fading channels. We first describe the statistical models of fading channels which are frequently used in the analysis and design of communication systems. Next, we focus on the information theory of fading channels, by emphasizing capacity as the most important performance measure. Both single-user and multiuser transmission are examined. Further, we describe how the structure of fading channels impacts code design, and finally overview equalization of fading multipath channels.
2,017 citations
TL;DR: A conceptual framework for understanding code mobility is presented, centered around a classification that introduces three dimensions: technologies, design paradigms, and applications that support the developer in the identification of the classes of applications that can leverage off of mobile code, in the design of these applications, and in the selection of the most appropriate implementation technologies.
Abstract: The technologies, architectures, and methodologies traditionally used to develop distributed applications exhibit a variety of limitations and drawbacks when applied to large scale distributed settings (e.g., the Internet). In particular, they fail in providing the desired degree of configurability, scalability, and customizability. To address these issues, researchers are investigating a variety of innovative approaches. The most promising and intriguing ones are those based on the ability of moving code across the nodes of a network, exploiting the notion of mobile code. As an emerging research field, code mobility is generating a growing body of scientific literature and industrial developments. Nevertheless, the field is still characterized by the lack of a sound and comprehensive body of concepts and terms. As a consequence, it is rather difficult to understand, assess, and compare the existing approaches. In turn, this limits our ability to fully exploit them in practice, and to further promote the research work on mobile code. Indeed, a significant symptom of this situation is the lack of a commonly accepted and sound definition of the term mobile code itself. This paper presents a conceptual framework for understanding code mobility. The framework is centered around a classification that introduces three dimensions: technologies, design paradigms, and applications. The contribution of the paper is two-fold. First, it provides a set of terms and concepts to understand and compare the approaches based on the notion of mobile code. Second, it introduces criteria and guidelines that support the developer in the identification of the classes of applications that can leverage off of mobile code, in the design of these applications, and, finally, in the selection of the most appropriate implementation technologies. The presentation of the classification is intertwined with a review of state-of-the-art in the field. Finally, the use of the classification is exemplified in a case study.
1,219 citations
TL;DR: The characterization of the proposed double-threshold detector demonstrates that, in most practical situations, the bias of the estimates of the on-off transitions is smaller than 10 ms, the standard deviation may be kept lower than 15 ms, and the percentage of erroneous patterns is below 5%.
Abstract: The aim of this work is to present an original double-threshold detector of muscle activation, specifically developed for gait analysis. This detector operates on the raw myoelectric signal and, hence, it does not require any envelope detection. Its performances are fixed by the values of 3 parameters, namely, false-alarm probability (P/sub fa/), detection probability, and time resolution. Double-threshold detectors are preferable to single-threshold ones because, for a fixed value of the P/sub fa/, they yield higher detection probability; furthermore, they allow the user to select the couple false alarm-detection probability with a higher degree of freedom, thus, adapting the performances of the detector to the characteristics of the myoelectric signal of interest and of the experimental situation. Here, first the authors derive the detection algorithm and describe different strategies for selecting its parameters, then they present the performances of the proposed procedure evaluated by means of computer simulations, and finally they report an example of application to myoelectric signals recorded during gait. The characterization of the proposed double-threshold detector demonstrates that, in most practical situations, the bias of the estimates of the on-off transitions is smaller than 10 ms, the standard deviation may be kept lower than 15 ms, and the percentage of erroneous patterns is below 5%. These results show that this detection approach is satisfactory in research applications as well as in the clinical practice.
337 citations
01 Mar 1998
TL;DR: Soft-input soft-output building blocks (modules) are presented to construct and iteratively decode in a distributed fashion code networks, a new concept that includes, and generalizes, various forms of concatenated coding schemes.
Abstract: Soft-input soft-output building blocks (modules) are presented to construct and iteratively decode in a distributed fashion code networks, a new concept that includes, and generalizes, various forms of concatenated coding schemes.
240 citations
TL;DR: This paper surveys representative contributions to power modeling, estimation, synthesis, and optimization techniques that account for power dissipation during the early stages of the design flow that have appeared in the recent literature.
Abstract: Silicon area, performance, and testability have been, so far, the major design constraints to be met during the development of digital very-large-scale-integration (VLSI) systems. In recent years, however, things have changed; increasingly, power has been given weight comparable to the other design parameters. This is primarily due to the remarkable success of personal computing devices and wireless communication systems, which demand high-speed computations with low power consumption. In addition, there exists a strong pressure for manufacturers of high-end products to keep power under control, due to the increased costs of packaging and cooling this type of device. Last, the need of ensuring high circuit reliability has turned out to be more stringent. The availability of tools for the automatic design of low-power VLSI systems has thus become necessary. More specifically, following a natural trend, the interests of the researchers have lately shifted to the investigation of power modeling, estimation, synthesis, and optimization techniques that account for power dissipation during the early stages of the design flow. This paper surveys representative contributions to this area that have appeared in the recent literature.
232 citations
TL;DR: Tables of the "best" recursive systematic convolutional encoders found are presented for various rates, together with the average bit-error probability performances of some turbo codes using them.
Abstract: Recursive systematic convolutional encoders have been shown to play a crucial role in the design of turbo codes. We recall some properties of binary convolutional encoders and apply them to a search for good constituent convolutional codes of turbo codes. Tables of the "best" recursive systematic convolutional encoders found are presented for various rates, together with the average bit-error probability performances of some turbo codes using them.
189 citations
TL;DR: In this paper, a perturbation approach was used to analyze the coherent population trapping in alkali-metal atoms, and closed form transparent solutions were obtained for the coherences existing within the system and the populations of the ground levels and of the excited state.
Abstract: The phenomenon of coherent population trapping in alkali-metal atoms is analyzed by means of a perturbation approach. Closed form transparent solutions are obtained for the coherences existing within the system and the populations of the ground levels and of the excited state. The presence of dark lines and coherent microwave emission from the ground state are made explicit. Experimental results that confirm the theoretical calculations are reported for the case of cesium in a buffer gas. Conclusions are drawn in connection with the application of coherent population trapping to the field of atomic frequency standards.
182 citations
TL;DR: This work proposes a unifying model that enables a uniform description of the problem of discovering association rules, and provides a SQL-like operator, named X⇒Y, which is capable of expressing all the problems presented so far in the literature concerning the mining of association rules.
Abstract: Data mining evolved as a collection of applicative problems and efficient solution algorithms relative to rather peculiar problems, all focused on the discovery of relevant information hidden in databases of huge dimensions In particular, one of the most investigated topics is the discovery of association rules
This work proposes a unifying model that enables a uniform description of the problem of discovering association rules The model provides a SQL-like operator, named MINE RULE, which is capable of expressing all the problems presented so far in the literature concerning the mining of association rules We demonstrate the expressive power of the new operator by means of several examples, some of which are classical, while some others are fully original and correspond to novel and unusual applications We also present the operational semantics of the operator by means of an extended relational algebra
181 citations
01 Apr 1998
TL;DR: This work presents an in-depth evaluation of several mobile code design paradigms against the traditional client-server architecture, within the application domain of network management.
Abstract: The question of whether technologies supporting mobile code are bringing significant benefits to the design and implementation of distributed applications is still an open one. Even more difficult is to identify precisely under which conditions a design exploiting mobile code is preferable over a traditional one. In this work, we present an in-depth evaluation of several mobile code design paradigms against the traditional client-server architecture, within the application domain of network management. The evaluation is centered around a quantitative model, which is used to determine precisely the conditions for the selection of a design paradigm minimizing the network traffic related to management.
173 citations
TL;DR: In this article, the authors reported EXAFS data collected at ADONE on a high quality Ti−silicalite (TS-1) sample (Ti = 1.47 wt %) dehydrated in a carefully control...
Abstract: In a previous contribution (J. Phys. Chem. 1994, 98, 4125) we reported EXAFS data collected at ADONE on a high quality Ti−silicalite (TS-1) sample (Ti = 1.47 wt %) dehydrated in a carefully control...
172 citations
TL;DR: In this article, a geometric formulation which describes extended supergravities in any dimension in the presence of electric and magnetic sources is presented, and the underlying duality symmetries of the theories are manifest.
Abstract: A geometric formulation which describes extended supergravities in any dimension in the presence of electric and magnetic sources is presented. In this framework, the underlying duality symmetries of the theories are manifest. Particular emphasis is given to the construction of central and matter charges and to the symplectic structure of all D=4, N-extended theories. The latter may be traced back to the existence, for N>2, of a flat symplectic bundle which is the N>2 generalization of N=2 Special Geometry.
TL;DR: In this paper, a microscopic string analysis of the interaction between two D-branes and the D0-D8 brane system was performed using the boundary state formalism.
TL;DR: OPERA as discussed by the authors is a packet experimental routing architecture (OPERA) based on the optical network interface router design that is optically regenerative and supports optical Internet protocol related functions including label swapping, packet routing and forwarding operations and wavelength reuse.
Abstract: This paper describes experimental and simulation results of the optical packet experimental routing architecture (OPERA) project. The OPERA network is based on a novel optical network interface router design that is optically regenerative and supports optical Internet protocol related functions including label swapping, packet routing and forwarding operations and wavelength reuse. Routing is based on subcarrier multiplexed header addressing, packet-rate wavelength conversion, and arrayed waveguide router technology. The routers are cascadable and use a unique double stage wavelength converter that supports header regeneration/replacement and maintains the payload extinction ratio. This approach overcomes dispersion limitations normally encountered using double sideband subcarrier multiplexing across a network. A discrete time simulation of the physical transport in an 8-hop network is reported. Multihop routing is experimentally demonstrated between two all-optical nodes and three input-output (I-O) ports of a waveguide grating array router. Packet-rate subcarrier header processing and wavelength conversion between six wavelengths is shown with high signal-to-noise ratio (SNR) of recovered payload and headers at each hop.
TL;DR: In this paper, the authors address the problem of the fulfillment of a number of requirements which are essential towards the reliable modeling of multilayered thick plates made of anisotropic composite materials.
TL;DR: This work obtains upper bounds to the average maximum likelihood bit-error probability of double serially concatenated block and convolutional coding schemes and derives design guidelines for the outer, middle, and inner codes that maximize the interleaver gain and the asymptotic slope of the error probability curves.
Abstract: A double serially concatenated code with two interleavers consists of the cascade of an outer encoder, an interleaver permuting the outer codeword bits, a middle encoder, another interleaver permuting the middle codeword bits, and an inner encoder whose input words are the permuted middle codewords. The construction can be generalized to h cascaded encoders separated by h-1 interleavers, where h>3. We obtain upper bounds to the average maximum likelihood bit-error probability of double serially concatenated block and convolutional coding schemes. Then, we derive design guidelines for the outer, middle, and inner codes that maximize the interleaver gain and the asymptotic slope of the error probability curves. Finally, we propose a low-complexity iterative decoding algorithm. Comparisons with parallel concatenated convolutional codes, known as "turbo codes", and with the proposed serially concatenated convolutional codes are also presented, showing that in some cases, the new schemes offer better performance.
23 Feb 1998
TL;DR: This paper presents innovative encoding techniques suitable for minimizing the switching activity of system-level address buses, and targets the reduction of the average number of bus line transitions per clock cycle.
Abstract: The power dissipated by system-level buses is the largest contribution to the global power of complex VLSI circuits. Therefore, the minimization of the switching activity at the I/O interfaces can provide significant savings on the overall power budget. This paper presents innovative encoding techniques suitable for minimizing the switching activity of system-level address buses. In particular, the schemes illustrated here target the reduction of the average number of bus line transitions per clock cycle. Experimental results, conducted on address streams generated by a real microprocessor, have demonstrated the effectiveness of the proposed methods.
TL;DR: In this article, metakaolin-containing mortars with a water/binder ratio of 0.33 have been compared to silica fume for compressive strength enhancement.
TL;DR: In this paper, a Reissner's mixed variational equation is employed to derive the differential equations, in terms of the introduced stress and displacement variables, that govern the dynamic equilibrium and compatibility of each layer.
Abstract: This paper presents the dynamic analysis of multilayered plates using layer-wise mixed theories. With respect to existing two-dimensional theories at the displacement formulated, the proposed models a priori fulfill the continuity of transverse shear and normal stress components at each interface between two adjacent layers. A Reissner's mixed variational equation is employed to derive the differential equations, in terms of the introduced stress and displacement variables, that govern the dynamic equilibrium and compatibility of each layer. The continuity conditions at the interfaces are used to write corresponding equations at multilayered level. Related standard displacement formulations, based on the principle of virtual displacements, are given for comparison purposes. Numerical results are presented for the free-vibration response (fundamental and higher order frequencies are calculated) of symmetrically and unsymmetrically laminated cross-ply plates. Several comparisons to three-dimensional elasticity analysis and to some available results, related to both layer-wise and equivalent single-layer theories, have shown that the presented mixed models; (1) match the exact three-dimensional results very well and (2) lead to a better description in comparison to results related to other available analysis.
TL;DR: In this article, collisionless magnetic reconnection in a two-dimensional plasma is analyzed, using a twofluid model where electron mass and pressure effects are important, and numerical simulations show the formation of current and vorticity layers along two branches crossing at the stagnation point of the plasma flow.
Abstract: Collisionless magnetic reconnection in a two dimensional plasma is analyzed, using a two-fluid model where electron mass and pressure effects are important. Numerical simulations show the formation of current and vorticity layers along two branches crossing at the stagnation point of the plasma flow. These structures are interpreted on the basis of the Hamiltonian Casimirs (conserved fields) of the fluid plasma model.
TL;DR: In this article, the authors present a general approach to numerically simulate the noise behavior of bipolar solid-state electron devices through a physics-based multidimensional device model, which accounts for noise sources due to carrier velocity and population fluctuations.
Abstract: The paper presents a general approach to numerically simulate the noise behavior of bipolar solid-state electron devices through a physics-based multidimensional device model. The proposed technique accounts for noise sources due to carrier velocity and population fluctuations. The power and correlation spectra of the external current or voltage fluctuations are evaluated through a Green's function, linear perturbation theory equivalent to the classical Impedance Field Method for noise analysis and its generalizations. The numerical implementation of the method is performed through an efficient technique, which allows noise analysis to be carried out with negligible overhead with respect to the small-signal simulation. Some case studies are analyzed in order to compare the present approach with theoretical results from the classical noise theory of p-n junctions and bipolar transistors.
TL;DR: In this article, full scale tests on passive defence against rock falls are presented in a field test site especially designed and built, where the test site has been provided of camera apparatus able to monitor the impact of the block against the fence.
Abstract: Rock restraining net is a device engineered to stop large rockfalls. The system consists of a net vertically supported by steel posts with “energy dissipators” able to dissipate high kinetic energy by large displacements. These fences have been usually placed to protect against rockfalls in mountainous areas but few tests have been developed correctly to define the behaviour of these structures. In this paper full scale tests on passive defence against rock falls are presented. The tests have been carried out in a field test site especially designed and built. The test site has been provided of camera apparatus able to monitor the impact of the block against the fence. The impact energy and the consequent forces and displacements of the fence are studied. The tests have been carried out on many different fence types and have allowed the definition of a well-established design procedure.
10 Aug 1998
TL;DR: It is shown that, by using buffers, energy consumption of the memory subsystem may be reduced by as much as 13% for certain data cache configurations and by asmuch as 23% forcertain instruction cache configurations without adversely effecting processor performance or on-chip energy consumption.
Abstract: In this paper, we propose several different data and instruction cache configurations and analyze their power as well as performance implications on the processor. Unlike most existing work in low power microprocessor design, we explore a high performance processor with the latest innovations for performance. Using a detailed, architectural-level simulator, we evaluate full system performance using several different power/performance sensitive cache configurations such as increasing cache size or associatively and including buffers along side L1 caches. We then use the information obtained from the simulator to calculate the energy consumption of the memory hierarchy of the system. As an alternative to simply increasing cache associatively or size to reduce lower-level memory energy consumption (which may have a detrimental effect on on-chip energy consumption), we show that, by using buffers, energy consumption of the memory subsystem may be reduced by as much as 13% for certain data cache configurations and by as much as 23% for certain instruction cache configurations without adversely effecting processor performance or on-chip energy consumption.
TL;DR: A review of hydrogen isotopes-materials interactions in various materials of interest for fusion reactors is presented in this article, where the relevant parameters cover mainly diffusivity, solubility, trap concentration and energy difference between trap and solution sites.
TL;DR: In this paper, two different categories of knock detection methods, based both on frequency domain manipulations of the cylinder pressure signal and on cylinder head vibration analysis, were extensively compared through an experimental investigation carried out on a Wartsila W50DF engine.
Abstract: In dual fuel engines operating on gas mode knock represents one of the major constraints on performance and efficiency, because it limits the maximum value of the engine compression ratio and of the boost pressure. The detection of abnormal combustion onset and the evaluation of knock intensity is therefore a crucial issue in engine development. In this work two different categories of knock detection methods, based both on frequency domain manipulations of the cylinder pressure signal and on cylinder head vibration analysis, were extensively compared through an experimental investigation carried out on a Wartsila W50DF engine. After a detailed literary review, the following three knock indicators were chosen to be examined through the experimental analysis: • maximum peak to peak value of the band-pass filtered pressure or vibration signal; • mean square value of the band-pass filtered pressure or vibration signal; • integral of the absolute value of the first derivative of band-pass filtered pressure or vibration signal. Different criteria for the identification of knocking cycles were evaluated, based on the comparison of the individual cycle knock indicator level with a constant threshold or on a statistical approach. While constant threshold approach was shown to be suitable for in cylinder pressure methods at constant engine load and speed (as for genset applications), the use of a statistical approach appeared to be mandatory for a fixed propeller pitch engine applications. Moreover the statistical approach turned out to be more reliable and robust in case of use of vibration based methods and therefore more suitable for the implementation on mass-produced engines. Finally, by means of a proper choice of filtering frequencies and of the accelerometer position, the influence of the engine transfer function on the vibration signal was remarkably reduced, thus allowing an easier and more reliable detection of knocking cycles, as well as a ranking of knocking cycles on the base of their intensity, thus paving the way to future finer engine control strategies development
TL;DR: Data concerning the quality and the performance of the automatically synthesized encoding/decoding circuits, as well as the results obtained for a realistic core-based design, indicate the practical usefulness of the proposed power optimization strategy.
Abstract: This paper presents a solution to the problem of reducing the power dissipated by a digital system containing an intellectual proprietary core processor which repeatedly executes a special-purpose program. The proposed method relies on a novel, application-dependent low-power address bus encoding scheme. The analysis of the execution traces of a given program allows an accurate computation of the correlations that may exist between blocks of bits in consecutive patterns; this information can be successfully exploited to determine an encoding which sensibly reduces the bus transition activity. Experimental results, obtained on a set of special-purpose applications, are very satisfactory; reductions of the bus activity up to 64.8% (41.8% on average) have been achieved over the original address streams. In addition, data concerning the quality and the performance of the automatically synthesized encoding/decoding circuits, as well as the results obtained for a realistic core-based design, indicate the practical usefulness of the proposed power optimization strategy.
TL;DR: In this paper, a mixed acetic-fatty anhydride, formed in situ, accounts for the grafting of the fatty moiety, was obtained after 5 h at 130°C with an average of 2.2 acetyl groups and 0.8 fatty substituents per anhydroglucose unit.
Abstract: Homogeneous esterification of cellulose with saturated fatty acids (n-octanoic to n-octadecanoic) was accomplished with acetic anhydride co-reactant in lithium chloride/N,N-dimethylacetamide (LiCl/DMAc) medium. Cellulose mixed triesters (CMT) were obtained after 5 h at 130°C with an average of 2.2 acetyl groups and 0.8 fatty substituents per anhydroglucose unit. A mixed acetic-fatty anhydride, formed in situ, accounts for the grafting of the fatty moiety. The purified products were characterized and compared to the analogous cellulose simple fatty triesters (CST) that were synthesized from fatty acid chlorides in pyridine medium. Dynamic contact angle with water, glass transition, and storage moduli were correlated with the length of the fatty substituents. The CMT proved to be highly hydrophobic and more mechanically resistant than the CST.
18 May 1998
TL;DR: This paper describes a client-server architecture for the remote control of instrumentation over the Internet network that allows multi-user, multi-instruments sessions to be obtained by means of a queueing process and provides instrument locking capability.
Abstract: This paper describes a client-server architecture for the remote control of instrumentation over the Internet network. The proposed solution allows multi-user, multi-instruments sessions to be obtained by means of a queueing process and provides instrument locking capability. Client applications can be easily developed by using conventional high-level programming languages or well-assessed virtual instrumentation frameworks. Performance tests are reported, which show the low overhead due to network operations with respect to the direct control of the instruments.
TL;DR: In this paper, it was shown that the manifold structure on ℳμ is the natural domain for the mixture connection and for its dual, the exponential connection, and that the bundle connection pair (ℱα, ∇α) is simply (isomorphic to) the pull-back of the Amari embedding.
Abstract: The non-parametric version of Information Geometry has been developed in recent years. The first basic result was the construction of the manifold structure on ℳμ, the maximal statistical models associated to an arbitrary measure μ (see Ref. 48). Using this construction we first show in this paper that the pretangent and the tangent bundles on ℳμ are the natural domains for the mixture connection and for its dual, the exponential connection. Second we show how to define a generalized Amari embedding AΦ:ℳμ→SΦ from the Exponential Statistical Manifold (ESM) ℳμ to the unit sphere SΦ of an arbitrary Orlicz space LΦ. Finally we show that, in the non-parametric case, the α-connections ∇α(α∈(-1,1)) must be defined on a suitable α-bundle ℱα over ℳμ and that the bundle-connection pair (ℱα, ∇α) is simply (isomorphic to) the pull-back of the Amari embedding Aα: ℳμ→S2/1-α were the unit sphere S2/1-αcL2/1-α is equipped with the natural connection.
TL;DR: The purpose was to identify whether changes in the instantaneous median frequency among concurrently active paraspinal muscles during repetitive trunk extension produces a 'fatigue pattern' that is indicative of normal functioning, and whether this pattern is different when the subject produces a sustained isometric trunk extension.
TL;DR: In this article, a unified approach to rank one symmetric spaces of the non-compact type is given, including proofs of their basic properties and their classification, with the development of a formalism to facilitate future computations.
Abstract: We give an elementary unified approach to rank one symmetric spaces of the noncompact type, including proofs of their basic properties and of their classification, with the development of a formalism to facilitate future computations. Our approach is based on the theory of Lie groups of H-type. An algebraic condition of H-type algebras, called J2,is crucial in the description of the symmetric spaces. The classification of H-type algebras satisfying J2 leads to a very simple description of the rank one symmetric spaces of the noncompact type. We also prove Kostant’s double transitive theorem; we describe explicitly the Riemannian metric of the space and the standard decompositions of its isometry group. Examples of the use of our theory include the description of the Poisson kernel and the admissible domains for convergence of Poisson integrals to the boundary.