Michele Vadursi

On the use of the warblet transform for instantaneous frequency estimation

A new digital signal processing method for instantaneous frequency estimation is proposed here. The attention is mainly paid to signals whose instantaneous frequency trajectories exhibit a periodic evolution versus time. Thanks to an optimized use of the warblet transform, the method assures superior accuracy and resolving capability with respect to other solutions already available in the literature, thus showing itself very attractive in the presence of multicomponent signals characterized by instantaneous frequency trajectories extremely similar and very close to one another. Theoretical notes regarding the warblet transform and its optimized use in the framework of the proposed method are first given. Then, the fundamental steps of the method are described in detail with references to a clarifying example. The results of a number of experiments on emulated and actual signals, aimed at assessing the performance of the method, are finally presented.

Techniques for available bandwidth measurement in IP networks: a performance comparison

As the Internet grows in scale and complexity, the need for accurate traffic measurement increases. Among the different parameters relevant to traffic measurement, the paper pays attention to the available bandwidth of a path. In particular, a performance comparison of three different techniques, devoted to available bandwidth measurement, is attained under different operating conditions. The comparison is based on the outcomes of an extensive experimental activity. Experimental tests are not limited to the mere execution of the software tools that implement the techniques under test; indeed, a proper measurement station comprising a digital counter has been set up by the authors with the aim of gaining a reference value to be compared with results provided by the considered tools. The adoption of a performance evaluation methodology relying on the use of electronic instrumentation for time measurement represents a good example of cross-fertilization between two distinct research areas: networking on one side and electronic measurements on the other. The tools have been tested under different cross-traffic conditions and their performance has been evaluated in terms of the following metrics: concurrence, repeatability, bias, and time. For each cross-traffic scenario and with reference to every performance metric, the paper identifies the tool that provides the best results. Furthermore, an optimal setting for the parameters of each tool has been identified thanks to the extensive experimental activity that has been performed.

A New Approach and a Related Tool for Dependability Measurements on Distributed Systems

In recent years, experts in the field of dependability are recognizing experimental measurements as an attractive option for assessing distributed systems; contrary to simulation, measurement allows monitoring the real execution of a system in its real usage environment. However, the results of a recent survey have highlighted that the way measurements are carried out and measurement results are expressed is far from being in line with the approach commonly adopted by metrology. The scope of this paper is twofold. The first goal is to extend the discussion on the increasing role that measurements play in dependability and on the importance of cross-fertilization between the dependability and the instrumentation and measurement communities. The second objective is to present a different approach to dependability measurements, in line with the common practices in metrology. With regard to this, the paper presents a tool for dependability measurements in distributed systems that allows evaluating the uncertainty of measurement results. The tool is an enhancement of NekoStat, which is a powerful highly portable Java framework that allows analyzing distributed systems and algorithms. Together with the description of the tool and its innovative features, two experimental case studies are presented.

Foundations of Measurement Theory Applied to the Evaluation of Dependability Attributes

Increasing interest is being paid to quantitative evaluation based on measurements of dependability attributes and metrics of computer systems and infrastructures. Despite measurands are generally sensibly identified, different approaches make it difficult to compare different results. Moreover, measurement tools are seldom recognized for what they are: measuring instruments. In this paper, many measurement tools, present in the literature, are critically evaluated at the light of metrology concepts and rules. With no claim of being exhaustive, the paper (i) investigates if and how deeply such tools have been validated in accordance to measurement theory, and (ii) tries to evaluate (if possible) their measurement properties. The intention is to take advantage of knowledge available in a recognized discipline such as metrology and to propose criteria and indicators taken from such discipline to improve the quality of measurements performed in evaluation of dependability attributes.

Poer Measurement in Digital Wireless Communications Systems through Parametric Spectral Estimation

Power measurement in digital wireless communication systems often suffers from poor repeatability, usually accompanied by a low accuracy. To face the problem, the use of parametric spectral estimators is investigated in this paper. In particular, a new method is proposed, which first estimates the power spectral density (PSD) of the analyzed signal through Burgs solution, and then evaluates the power by applying straightforward measurement algorithms to the estimated PSD. The results of a number of experiments, carried out on both laboratory and actual signals peculiar to digital wireless communication systems, assess the efficacy and reliability of the method. Moreover, a comparison of the achieved performance to that offered by an alternative measurement solution, already proposed by the authors and based on nonparametric PSD estimation, shows that the method allows for a significant reduction of measurement time, while exhibiting the same repeatability.

Performance measurement of IEEE 802.11b-based networks affected by narrowband interference through cross-layer measurements

Researches and development efforts in wireless networking and systems are progressing at an incredible rate. Among them, measurement and analysis of performance achieved at network layer and perceived by end users is an important task. In particular, recent advances concerning IEEE 802.11b-based networks seem to be focused on the measurement of key parameters at different protocol levels in a cross-layered fashion, because of their inherent vulnerability to in-channel interference. By adopting a cross-layer approach on a real network set-up operating in a suitable experimental testbed, packet loss against signal-to-interference ratio in IEEE 802.11b-based networks is hereinafter assessed. Results of several measurements aimed at establishing the sensitivity of IEEE 802.11b carrier sensing mechanisms to continuous interfering signals and evaluating the effects of triggered interference on packet transmission.

Measuring wireless links capacity

Capacity of a link is a key metric for network design and management. Several tools for capacity measurement are present in the literature and they provide satisfying results when used over wired networks. Their performance over wireless links, however, is not as good, although the techniques they are based on should not suffer from changes at physical layer. This paper accounts for a performance assessment of four tools for capacity measurement, carried out over a wireless link located in a semi-anechoic chamber. The measurement station is designed to guarantee channel stationarity and interference-free measurement conditions, and the performance assessment takes advantage of a proper reference value for the measurand, which is obtained from physical layer measurements. The experimental analysis highlights that the performance of the tools is strongly dependent on the characteristics of the network interface cards that are used, whereas the reference value of capacity, measured at physical layer, does not actually change.

Modeling DAC Output Waveforms

Digital-to-analog converters (DACs) are widely employed in control and automation, test and measurement, and communication systems. However, guidelines for the definition of static and dynamic features of DACs, as well as models capable of describing the different effects of the major nonidealities or drawbacks the DAC can suffer from, are still incomplete. This paper presents a new model capable of describing the functioning of a real DAC affected by horizontal quantization, clock modulation, vertical quantization and integral nonlinearity. The model permits evaluating the effects of the aforementioned nonidealities through straightforward formulas, which are characterized by a low computational burden. Results of experiments conducted on a real DAC to verify the reliability of the model are also shown.

Error vector-based measurement method for radiofrequency digital transmitter troubleshooting

The rapid growth of modern telecommunications systems has created the need to get new test equipment and measurement techniques operational in a very short time. Performance assessment of radiofrequency digital transmitters, with special regard to the troubleshooting of their I/Q modulation section, calls for new, reliable, and time-effective measurement methods because those based on the analysis of constellation diagrams, currently supported by major manufacturers, show some intrinsic limitations. To overcome these limitations, a new measurement method based on the use of the error vector is proposed in the paper. It works properly when only one or two I/Q impairments are significant, and assures comparable accuracy and reduced measurement time with respect to other solutions already presented in the literature. Besides describing the fundamental steps and basic relations characterizing the proposed method, the paper gives details of the extended experimental activity carried out on actual telecommunication signals in order to assess the performance.

An Efficient Pre-Processing Scheme to Enhance Resolution in Band-Pass Signals Acquisition

The paper presents a pre-processing scheme to enhance the resolution of data acquisition systems (DASs) in the presence of band-pass input signals. The proposed solution permits to acquire a seamless data stream with improved resolution and is designed to be efficient in terms of hardware requirements and processing time. In the paper, details on the designed architecture are given, along with an analytical comparison of the resolution improvement achievable with respect to existing techniques. The performance of the solution is assessed through a number of simulative and experimental tests on band-pass signals.