Leopoldo Angrisani

Experimental Study of Coexistence Issues Between IEEE 802.11b and IEEE 802.15.4 Wireless Networks

Coexistence issues between IEEE 802.11b wireless communication networks and IEEE 802.15.4 wireless sensor networks, operating over the 2.4-GHz industrial, scientific, and medical band, are assessed. In particular, meaningful experiments that are performed through a suitable testbed are presented. Such experiments involve both the physical layer, through measurements of channel power and the SIR, and the network/transport layer, by means of packet loss ratio estimations. Different configurations of the testbed are considered; major characteristics, such as the packet rate, the packet size, the SIR, and the network topology, are varied. The purpose of this paper is to gain helpful information and hints to efficiently face coexistence problems between such networks and optimize their setup in some real-life conditions. Details concerning the testbed, the measurement procedure, and the performed experiments are provided.

Wavelet network-based detection and classification of transients

A methodology is presented for developing a digital signal-processing architecture capable of simultaneous and automated detection and classification of transient signals. The basic unit of the aforementioned architecture is the wavelet network, which combines the ability of the wavelet transform of analyzing nonstationary signals with the classification capability of artificial neural networks. By exploiting the modularity as well as original strategies concerning wavelet network implementation and training, the method succeeds in enhancing the classification performance with respect to other available solutions.

A measurement method based on an improved version of the chirplet transform for instantaneous frequency estimation

A measurement method for instantaneous frequency estimation is presented in this paper. The method is based on the use of the chirplet transform, a linear time-frequency representation (TFR) allowing additional modifications of each cell on the time-frequency plane with respect to other TFRs. In particular, a modified version of this transform is proposed here; a bending effect can be further imposed on the cells. Thanks both to this feature and a suitable measurement procedure, properly set up by the authors, the method assures a satisfying accuracy in reconstructing the instantaneous frequency trajectory of monocomponent signals as well as a good resolving capability in the analysis of multicomponent signals whose instantaneous frequency trajectories are strongly nonlinear and very close to one another. Theoretical details concerning the chirplet transform and its modified version are first given. Then, the proposed measurement procedure for choosing the optimal values of the parameters of the transform according to the local features of the analyzed signal is described. At the end, the results of several experimental tests conducted both on monocomponent and multicomponent signals are presented; advantages over other solutions are also highlighted.

A New Measurement Method Based on Music Algorithm for Through-the-Wall Detection of Life Signs

A new measurement method for through-the-wall detection of life signs is proposed hereinafter. The method analyzes the phase modulation that a sinusoidal signal, generated by means of a proper continuous-wave microwave transceiver, undergoes when reflected by the chest periodic displacement associated with breathing. It takes advantage of a suitable spatial smoothing decorrelation strategy applied to the traditional algorithm for MUltiple SIgnal Classification (MUSIC), mandated to single out the spectral components of the received phase signal. With respect to other measurement solutions, already available in the literature and exploiting either the traditional discrete-time Fourier transform, or matched filters, or standard singular value decomposition, the proposed method assures competitive performance in detecting the respiratory activity from the received microwave signal and effective noise/clutter rejection. The results of several tests both in simulated and actual scenarios, i.e., people behind walls in a furnished room, prove the efficacy and reliability of the method also in the presence of critical measurement conditions such as low signal-to-noise ratios and chest displacement associated with shallow breathing.

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.

Ultrasonic time-of-flight estimation through unscented Kalman filter

This paper deals with distance or level measurements based on ultrasonic time-of-fight estimation. Moving from a past experience concerning the proposal of a method based on discrete extended Kalman filter (DEKF) to overcome some limitations of already available ultrasonic-based techniques, a new digital signal processing method capable of granting further improvements is presented. The method is based on the unscented Kalman filter (UKF), which is a new extension of the Kalman filter theory mandated to face some DEKF problems, mainly due to its inherent linearization approach. To this aim, UKF is applied to the acquired ultrasonic signal in order to estimate the returned echo envelope as well as to locate its onset more accurately. After describing key features and implementation issues of the new method, the results obtained in a number of tests on simulated and actual ultrasonic signals, which assess its reliability and effectiveness as well as advantages with respect to the previous one, are given.

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 digital signal-processing approach for phase noise measurement

A digital signal-processing method for phase noise measurement is presented. By properly over-sampling the input signal and adopting an optimized coherent demodulation scheme, the method grants acceptable performance in analyzing sinusoidal carriers the frequencies of which range from fractions of Hertz up to hundreds of megahertz. Moreover, the method shows itself a valid alternative both to analog measurement systems, especially for the evaluation of close-to-the-carrier phase noise, and time interval analyzers, particularly for carrier frequencies greater than few units of megahertz. At first, the fundamental stages of the proposed method are described in detail. Its theoretical performance is then derived and compared to that granted by other measurement solutions already available on the market. The results of experiments carried out on actual signal sources are finally presented.

The unscented transform: a powerful tool for measurement uncertainty evaluation

An original approach for uncertainty evaluation in indirect measurements is presented hereinafter. The approach applies the unscented transform to the measurement model (i.e., the functional relationship between output and input quantities) in order to gain a reliable estimate of output expectation and standard deviation (measurement uncertainty). Thanks to some useful properties of the transform, notable limits of the current GUM recommendations can be overcome. In particular, reliable estimates are also granted in the presence of nonlinear and/or nonanalytical measurement models or complex digital signal processing algorithms. A number of numerical tests are conducted on simulated and actual measurement data. Remarkable concurrence between obtained estimates and those granted by Monte Carlo simulations confirms the efficacy of the proposed approach

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.