G. Setti

Spectral aliasing effects of PWM signals with time-quantized switching instants

This paper investigates the problem of the spectrum effects that appear in the power spectrum density (PSD) of a digitally implemented Pulse Width Modulated (PWM) signal. We recognize that as the digital implementation forces the switching instants to be time-quantized, an aliasing effect modifies the properties of the original PWM spectrum. Furthermore, we analyze, through analytical tools and numerical simulation, such effects for two typical cases: a sinusoidal modulating signal and Pulse Amplitude Modulated (PAM) carrying a maximum information modulating signal.

On the impact of traffic statistics on quality of service for networks on chip

Packet switched networks on chip (NoC) architectures have been proposed as a solution to the global interconnect problem in the nanoscale systems on chip (SoC) design era. An important design consideration for NoC, is silicon cost. Towards the goal of keeping the NoC simple, we pose the following question: under what traffic conditions will quality of service (QoS) be provided without the added complexity of an explicit QoS mechanism? In this paper, we take the first step towards answering this question by empirically analyzing different combinations of traffic patterns and injection processes. Specifically, we analyze the effects of different traffic on latency under two cases: (1) an NoC with no QoS mechanism (i.e. without distinction among different classes of service); and (2) an NoC with the simplest distinction into two classes of service: guaranteed service and best effort.

Sequence synchronization in chaos-based DS-CDMA systems

The aim of this contribution is to consider a further step in the study of the impact of chaos-based techniques on classical DS-CDMA systems. The problem addressed here is the sequence phase acquisition and tracking which is needed to synchronize the spreading and despreading sequences of each link. An acquisition mechanism is proposed and analyzed in depth to identify parameters allowing the study of its performance when classical and chaos-based sequences are employed for spreading. Numerical results show that the adoption of chaos-based techniques may lead to an improvement in link startup delay and expected service availability.

The effects of digital implementation on ZePoC codec

This paper investigates the intrinsic problems of a digital implementation of a ZePoC Codec. We review the basic steps of a ZePoC modulator, showing its intrinsically analog nature. Then we evaluate the loss of performance of a digitally implemented ZePoC modulator, in terms of harmonic distortion within a certain low-pass band. To do this, we developed a fully analytical method to evaluate the effects of nonlinearities over quasiperiodic signals. Finally, an application of the analytical method were shown in an example. The example results suggest that, though ZePoC modulator is theoretically optimal, its digital implementation would unavoidably lead to a high loss in its performance.

Control of Chaos Statistics for Optimization of DS-CDMA Systems

Results of recent theoretical investigations highlighted that the use of chaos in DS-CDMA systems may lead to non-negligible improvements in communication quality for several scenarios. We here briefly review the main steps in this derivation and report the corresponding theoretical prediction. In particular we show that the use of the so-called statistical approach to the study of a chaotic dynamical system allows to characterize and control the statistical features of the processes generated by it. By using such an approach, we highlight the path leading to the generation of chaos-based spreading sequences outperforming classical pseudo-random sequences in two important cases. Over non-selective channels, the ability of chaos-based spreading of minimizing multiple-access interference leads to an average improvement of 60% in Perr with respect to classical spreading. Over selective channels, the possibility of jointly optimizing chaos-based spreading and rake receiver profiles leads to improvements of up to 22% in Perr with respect to systems with either conventional spreading or conventional rake policies.

Statistical modeling of discrete-time chaotic processes-basic finite-dimensional tools and applications

The application of chaotic dynamics to signal processing tasks stems from the realization that its complex behaviors become tractable when observed from a statistical perspective. Here we illustrate the validity of this statement by considering two noteworthy problems—namely, the synthesis of high-electromagnetic compatibility clock signals and the generation of spreading sequences for direct-sequence code-division comunication systems, and by showing how the statistical approach to discrete-time chaotic systems can be applied to find their optimal solution. To this aim, we first review the basic mathematical tools both intuitively and formally; we consider the Perron–Frobenius operator, its spectral decomposition and its tie to the correlation properties of chaotic sequences. Then, by leveraging on the modeling/approximation of chaotic systems through Markov chains, we introduce a matrix/tensor-based framework where statistical indicators such as high-order correlations can be quantified. We underline how, for many particular cases, the proposed analysis tools can be reversed into synthesis methodologies and we use them to tackle the two above mentioned problems. In both cases, experimental evidence shows that the availability of statistical tools enables the design of chaos-based systems which favorably compare with analogous nonchaos-based counterparts.

Generation of optimal switching pattern for single-phase inverter

In this paper, we propose a preliminary study on a new optimal pulse width modulation (PWM) strategy to encode an oversampled sinusoidal waveform. The optimal encoded signal for single-phase inverter drives is obtained through minimization of spurious harmonics content within a certain band, subject to the constraint of finite time resolution of the encoded signal switching instants. This additional constraint makes impossible to analyze the spectral properties of the switching process with the analytical tools of the traditional programmed PWM techniques. Hence, we developed a new minimization method, which inherits from the traditional ones the harmonic elimination optimality criterion, and we give a detailed description of the novel encoding scheme. In particular, its performance will be compared with respect of traditional modulating schemes for some topic cases, and its advantages and disadvantages will be thoroughly highlighted.

Statistical modeling and design of discrete-time chaotic processes: advanced finite-dimensional tools and applications

With the aim of explaining the formal development behind the chaos-based modeling of network traffic and other similar phenomena, here we generalize the tools presented in the companion paper (Setti et al., 2002) to the case of piecewise-affine Markov maps with a possibly infinite, but countable number of Markov intervals. Since, in doing so, we keep the dimensionality of the space of the observables finite, we still obtain a finite tensor-based framework. Nevertheless, the increased complexity of the model forces the use of tensors of functions whose handling is greatly simplified by extensive z transformation. With this, a systematic procedure is devised to write analytical expressions for the tensors that take into account the joint probability assignments needed to compute any-order expectations. As an example of use, this machinery is finally applied to the study of self-similarity of quantized processes both in the analysis of higher order phenomena as well as in the analysis and design of second-order self-similar sources suitable for artificial network traffic generation.

Chaotic and random point processes: analysis, design and application to hybrid systems

Processes characterised by point events occurring in time are called point processes. Emissions from a radioactive source, action potential in a nerve fibber, traffic flow passing through a designated location on the highway, are all examples of pint processes. In our tutorial we firstly discuss point processes associated with deterministic chaotic dynamics of hybrid systems such a5 power electronic circuits, systems involving switches, impacting mechanical systems, continuous systems controlled by discrete logic (aircraft auto-pilot modes, thermostats, chemical plants with on-off valves and pumps, automobile automatic transmissions). An understanding of bifurcations (qualitative change in a systems dynamical behaviour) is very important for the operation and control of any system. In this tutorial, we seek to develop a theoretical understanding of the bifurcation phenomena that occur in hybrid systems. Well show that such systems yield piecewise smooth maps under sampled-data modelling. Next, well introduce various smooth and non-smooth bifurcations that can happen in such systems. In presenting the border collision bifurcations, well review the various approaches to the problem and present a synthetic theoretical framework that can be readily applied in explaining bifurcation phenomena in hybrid systems. Then we present a systematic approach to the statistical analysis, control and design of hybrid dynamical systems with chaotic behaviour in terms of the statistical properties of

Statistical approach to discrete-time chaotic systems: application of basic and advanced tools to DS-CDMA system optimization

Gives an introduction to DS-CDMA systems. Covers DS-CDMA principle (spreading, synchronization), performance overview, advanced receiver structure and classic versus chaotic spreading sequences. Performance on ideal channels is discussed. Cross-interference analysis, (n,t)-tailed shift performance, performance reformulation as a function of self-interference, performance optimization using the self-interference profile and chaotic optimum map search are all included. Performance on selective channels is also looked at.