Mauro D'Arco

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.

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.

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.

New digital signal-Processing approach for transmitter measurements in third generation Telecommunications systems

The rapid growth of third generation (3G) telecommunications systems has created the need for getting new test equipment as well as getting measurement techniques up and running in a very short time. Trying to satisfy this exigency, a new measurement method for testing 3G transmitters is proposed here. Thanks to the use of time-frequency distributions, the method provides a unified approach for carrying out, automatically and in a very straightforward manner, most measurements needed to fulfill the aforementioned task. After a brief outline of 3G technology basics, some details concerning transmitter tests are given. The fundamental steps of the proposed method are then described with references to a clarifying example, also highlighting advantages with respect to other measurement solutions. At the end, the performance of the method is assessed by means of several experiments on both simulated and emulated signals.

ANOVA-Based Approach for DAC Diagnostics

In order to assess the performance of digital-to-analog converters (DAC) the attention is generally focused on the integral nonlinearity INL. Useful diagnostic tools to detect the causes of poor linearity are the linearity and intermodulation errors, which can be evaluated from INL measurements. Linearity and intermodulation errors highlight and quantify erroneous calibration and unwanted interactions between current sources inside the DAC hardware. Unfortunately, their estimates, particularly those related to high-order intermodulation errors are characterized by high uncertainty. On the base of their very uncertain value, it is difficult to establish if interactions represent relevant factors or not. It is shown that by means of the analysis of variance (ANOVA) the relevance of intermodulation errors can be assessed from a limited set counting a minimum of two INL measurements. ANOVA is in fact capable of distinguishing if the variance in INL measurements has to be addressed to active factors or noise, even if the effect of each factor is widespread upon different elements of the INL array and in different combinations with the other factors.

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.

Clustering-Based Method for Detecting and Evaluating I/Q Impairments in Radio-Frequency Digital Transmitters

An innovative digital-signal-processing method, which is aimed at detecting and evaluating I/Q impairments in radio-frequency digital transmitters, is presented and validated. It takes advantage of a suitable clustering procedure that is capable of matching each symbol in the distorted I/Q diagram to its ideal position, even though concurrent and severe impairments disturb the standard functioning of the transmitter under test. Right identification of impairments, along with accurate evaluation of their amount, is then achieved through the application of original and straightforward measurement algorithms to the recovered symbols. The results of a number of experiments, which are conducted on quadrature-amplitude-modulation signals affected by the known I/Q impairments, show the superior performance of the proposed method over measurement techniques suggested by the European Telecommunications Standards Institute and alternative solutions already presented in literature. Further experiments conducted in the presence of interfering tones or phase jitter give evidence of the methods reliability also in critical measurement conditions.

Evaluating phase noise power spectrum with variable frequency resolution

Measurement of phase noise affecting sinusoidal carriers is dealt with here. A new method is proposed, mainly intended to overcome the limits of two digital signal-processing solutions, already presented by the authors and devoted, respectively, to far-from-the-carrier and close-to-the-carrier phase noise analysis. Thanks to an original measurement procedure, the method optimizes the frequency resolution in the evaluation of phase noise power spectral density; in particular, the closer to the carrier the analysis, the finer the frequency resolution granted. It is possible to obtain accurate and reliable results in a wide range of frequency offsets with no need for heavy computational burden and expensive hardware resources of the adopted data acquisition system. The results of a number of experiments, conducted on actual sinusoidal carriers through a measurement prototype implementing the method, confirm the efficacy and reliability of the proposal.