IRIS Università degli Studi di Bolognahttps://cris.unibo.itIl sistema di repository digitale IRIS acquisisce, archivia, indicizza, conserva e rende accessibili prodotti digitali della ricerca.Tue, 02 Mar 2021 09:35:11 GMT2021-03-02T09:35:11Z101701Optimistic MILP modeling of non-linear optimization problemshttp://hdl.handle.net/11585/281317Titolo: Optimistic MILP modeling of non-linear optimization problems
Abstract: We present a new piecewise linear approximation of non-linear optimization problems. It can be seen as a variant of classical triangulations that leaves more degrees of freedom to define any point as a convex combination of the samples. We show theoretical properties of the approximating functions, and provide computational evidence of the impact of their use within MILP models approximating non-linear problems.
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/11585/2813172014-01-01T00:00:00ZOn the synthesis of periodic signals by discrete pulse-trains and optimisation techniqueshttp://hdl.handle.net/11585/79655Titolo: On the synthesis of periodic signals by discrete pulse-trains and optimisation techniques
Abstract: In this paper, the synthesis of discrete sequences capable of representing analog periodic waveforms and of being transformed into them by mere low-pass filtering is considered. The problem is known to be solvable by modulation techniques such as pulse width modulation or Sigma-Delta. Nonetheless, how close to an optimum such techniques can go is an interesting issue to explore, since the design of such modulators relies on assumptions that can only be approximately respected. To this aim, we develop an exact optimisation framework capable of providing the best and most parsimonious coding possible, which is then used as a benchmark. It is shown that the optimisation problem has very strong features, which could potentially be exploited to speed up convergence or to develop efficient heuristics. At the same time it is verified that the Sigma-Delta performance lag with regards to the optimum is generally very little, so that almost no margin exists for alternative heuristics unless the latter are exploited to optimise on merit factors beyond mere SNR.
Thu, 01 Jan 2009 00:00:00 GMThttp://hdl.handle.net/11585/796552009-01-01T00:00:00ZOn the ultimate limits of chaos-based asynchronous DS-CDMA-II: analytical results and asymptoticshttp://hdl.handle.net/11585/2441Titolo: On the ultimate limits of chaos-based asynchronous DS-CDMA-II: analytical results and asymptotics
Thu, 01 Jan 2004 00:00:00 GMThttp://hdl.handle.net/11585/24412004-01-01T00:00:00ZOn the ultimate limits of chaos-based asynchronous DS-CDMA-I: basic definitions and resultshttp://hdl.handle.net/11585/2442Titolo: On the ultimate limits of chaos-based asynchronous DS-CDMA-I: basic definitions and results
Thu, 01 Jan 2004 00:00:00 GMThttp://hdl.handle.net/11585/24422004-01-01T00:00:00ZCircuito elettronico riconfigurabile come convertitore analogico/digitale e generatore di sequenze binarie autenticamente casualihttp://hdl.handle.net/11585/3225Titolo: Circuito elettronico riconfigurabile come convertitore analogico/digitale e generatore di sequenze binarie autenticamente casuali
Sat, 01 Jan 2005 00:00:00 GMThttp://hdl.handle.net/11585/32252005-01-01T00:00:00ZCoping with saturating projection stages in RMPI-based Compressive Sensinghttp://hdl.handle.net/11585/128686Titolo: Coping with saturating projection stages in RMPI-based Compressive Sensing
Abstract: Though compressive sensing hinges on extracting linear measurements from the signals to acquire, actual implementations introduce nonlinearities whose effect can be far from negligible. We here address the problem of saturation in the circuit blocks needed by a Random Modulation Pre-Integration architecture. To allow a fair a comparison with previous analysis, we rely on a model capturing the essentials of saturations in actual implementations while being able to reproduce more abstract settings considered in the literature. Based on this, we analyze some methods already proposed to cope with simplified saturation mechanisms, briefly discussing their underlying principles. Finally, we introduce a novel approach that takes into account the more realistic model and, at the cost of an almost negligible hardware overhead, is extremely effective in countering saturation effects.
Sun, 01 Jan 2012 00:00:00 GMThttp://hdl.handle.net/11585/1286862012-01-01T00:00:00ZRakeness in the Design of Analog-to-Information Conversion of Sparse and Localized Signalshttp://hdl.handle.net/11585/128685Titolo: Rakeness in the Design of Analog-to-Information Conversion of Sparse and Localized Signals
Abstract: Design of random modulation preintegration systems based on the restricted-isometry property may be suboptimal when the energy of the signals to be acquired is not evenly distributed, i.e., when they are both sparse and localized. To counter this, we introduce an additional design criterion, that we call rakeness, accounting for the amount of energy that the measurements capture from the signal to be acquired. Hence, for localized signals a proper system tuning increases the rakeness as well as the average SNR of the samples used in its reconstruction. Yet, maximizing average SNR may go against the need of capturing all the components that are potentially nonzero in a sparse signal, i.e., against the restricted isometry requirement ensuring reconstructability. What we propose is to administer the trade-off between rakeness and restricted isometry in a statistical way by laying down an optimization problem. The solution of such an optimization problem is the statistic of the process generating the random waveforms onto which the signal is projected to obtain the measurements. The formal definition of such a problems is given as well as its solution for signals that are either localized in frequency or in more generic domain. Sample applications, to ECG signals and small images of printed letters and numbers, show that rakeness-based design leads to nonnegligible improvements in both cases.
Sun, 01 Jan 2012 00:00:00 GMThttp://hdl.handle.net/11585/1286852012-01-01T00:00:00ZRakeness-based approach to compressed sensing of ECGshttp://hdl.handle.net/11585/128690Titolo: Rakeness-based approach to compressed sensing of ECGs
Abstract: Compressed sensing is an analog signal acquisition technique that aims at converting the intrinsic information contained in the signal when some a priori assumptions can be made on its structure. The most common of these assumptions is that the signal is sparse. We here present a methods that works when the signal to acquire is not only sparse but also localized. Benefits of this method will be shown by applying it to ECG signals.
Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/11585/1286902011-01-01T00:00:00ZPractical optimization of EMI reduction in spread spectrum clock generators with application to switching DC/DC convertershttp://hdl.handle.net/11585/529771Titolo: Practical optimization of EMI reduction in spread spectrum clock generators with application to switching DC/DC converters
Abstract: We here consider the most common technique used in spread spectrum clock generators that is the frequency modulation of a timing signal by means of a triangularly shaped waveform. As a first step, we develop a reliable mathematical model of a spectrum analyzer, which allows us to compute the power spectrum as measured by this instrument for any signal put at its input. This is particularly important when considering spread spectrum clocking methods for electromagnetic interference reduction, since international regulations impose constraints on the peak of the spectrum of interfering signals as measured by this instrument. Thanks to the developed mathematical tool, we are able to theoretically prove that the maximum peak reduction of the measured spectrum is achieved for a well-defined frequency of the triangular driving signal. This is in contrast with what one can obtain by optimizing the theoretical power density spectrum, where the minimum interference is ideally obtained when the triangular signal has a vanishing frequency. The results are confirmed by measurements on two commercial dc/dc switching converters.
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/11585/5297712014-01-01T00:00:00ZAn architecture for low-power compressed sensing and estimation in wireless sensor nodeshttp://hdl.handle.net/11585/525171Titolo: An architecture for low-power compressed sensing and estimation in wireless sensor nodes
Abstract: Radio communication is among the most energy consuming tasks in wireless sensor nodes. Reducing the amount of data to be transmitted holds a large power saving potential. The combination of compressed sensing (CS) and local signal parameter estimation can achieve a massive data rate reduction in applications where the primary interest is in the acquisition of a scalar feature of the signal rather than the reconstruction of the entire waveform. In this paper, We propose a compressed estimator, building upon an enhancement of the typical CS signal-modulation scheme via punctured sampling. Specifically, a subset of signal samples and associated weighting coefficients are chosen so as to minimize node power consumption while achieving a given estimation performance. We detail a corresponding puncturing algorithm and present the design of an integrated digital compressed estimation unit in 28nm FDSOI CMOS. In a concrete case study, local estimation combined with subsampling is shown to result in a power reduction of up to an order of magnitude with respect to the standard solution of sampling and transmitting samples for off-board processing.
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/11585/5251712014-01-01T00:00:00Z