Research topics

Understanding Impulsive Communications

Generally speaking, we may say that a communication is impulsive whenever the information-bearing signal is burst-like in time. Although this definition may seem loose at first sight, it certainly corresponds to a necessary condition for a communication to be impulsive. Examples of the impulsive concept are: impulse-radio signals, that is, wireless signals occurring within short intervals of time; optical signals conveyed by photons; speech signals represented by sound pressure variations; pulse-position modulated electrical signals; a sequence of arrival/departure events in a queue. Understanding impulsive communications requires to identify what is peculiar to this transmission paradigm, i.e. different from traditional continuous communications.

In order to address the problem of understanding impulsive vs. non-impulsive communications, the framework of investigation must include the following aspects: the different interference statistics directly following from the impulsive structure; the different interaction of the impulsive signal with the physical medium; the actual possibility for impulsive communications of coding information into the time structure, relaxing the implicit assumption made in continuous transmissions that time is a mere support. Peculiar features of interference statistics and of signal-medium interaction may require specific investigations regarding the limitation of traditional transceivers, when naively applied, and lead to novel transceiver design. Information coding in time epochs is yet not well theoretically understood; note that capacity limits depend on those mechanisms that may blur timing information. The mechanisms underlying perturbation noise must be understood and modeled as well.

The current state of the art provides partial answers to a few of the above issues. As a matter of fact, the current understanding of impulsive communications may be pictured as a jigsaw puzzle, with a few pieces in place. The below investigation plan aims at attempting to fill-in the empty spaces, by setting up a comprehensive set of questions and organizing the topics into broad categories. By the end, understanding impulsive communications may also lead to a better understanding of the widely adopted and standardized non-impulsive format.

I. Random Time-Hopping

The topics that are proposed under the “Random Time-Hopping” category originate from the following manuscript:
G. C. Ferrante, M.-G. Di Benedetto, “Spectral Efficiency of Random Time-Hopping CDMA,” submitted to the IEEE Trans. Inf. Theory (online on the arXiv), Nov. 2013

I.1 Capacity region of TH vs. DS

I.2a Spectral efficiency over channels with fading

I.2b Spectral efficiency over channels with multipath

I.3a Spectral efficiency with asynchronism over channels without fading

I.3b Spectral efficiency with asynchronism over channels with fading

I.3c Spectral efficiency with asynchronism over channels with multipath

I.4 Family of codes

I.5 Comparison of TH against FH

II. System design for impulsive communications

The topics that are proposed under the “System design for impulsive communications” category originate from the following manuscript:

G. C. Ferrante, J. Fiorina, M.-G. Di Benedetto, “Robustness of Time Reversal vs. All-Rake Transceivers in Multiple Access Channels,” submitted to the IEEE Trans. Wireless Commun. (online on the arXiv), May 2014

II.1 Transceiver structure analysis: SUMF, ZF, MMSE; TxMF (time reversal), TxZF, TxMMSE

II.2a Digital feedback: channel classification

II.2b Digital feedback: vector quantization for channel representation

II.2c Digital feedback: joint transceiver-channel classification

III. Interference behavior

The topics that are proposed under the “Interference behavior” category originate from the following manuscript:

G. C. Ferrante, M.-G. Di Benedetto, “Closed form asymptotic expression of a random-access interference measure,” IEEE Commun. Lett., Apr. 2014 (online on IEEE Xplore)

III.1 Application of an “integer interference measure” model

III.2 Generalization towards “discrete interference measures” (more slots, more families of labels)

III.3 Analysis of point processes in the context of multiple access (Aloha, CSMA)

III.4 Application to queues

IV. Why impulsive communications: peculiar properties of impulsive signals when interacting with matter and related “perceiver”

The topics that are proposed under the “Why impulsive communications” category originate from the following manuscript:

G. C. Ferrante, “Is a large bandwidth mandatory to maximally exploit the transmit matched-filter structure?," IEEE Commun. Lett., Jun. 2014 (online on IEEE Xplore)

IV.1 Noise models

IV.2a Wireless communications: ISI

IV.2b Wireless communications: Transceivers

IV.3 Speech communication

IV.4 Neural spikes

Do not hesitate to contact us if you wish to set-up a collaboration on one of the listed topics.
gaby at acts dot ing dot uniroma1 dot it (Prof. M.-G. Di Benedetto)
gcf at ieee dot org (G. C. Ferrante)

Speech

I. Gemination in Italian

Gemination can be defined as the clustering of a single consonant into a 'double' or geminate consonant. This phenomenon plays a major role in Italian, a language in which several words change their meaning as a function of the presence or absence of gemination of one consonant in the word. Most often in Italian these words are disyllabic ones forming minimal pairs, with the stress placed on the first syllable of the word. However, gemination can also be observed across words of a same sentence.
Native Italian speakers exhibit a natural attitude in producing disyllabic words of minimal pairs identified by the presence or absence of consonant gemination. Words belonging to minimal pairs are orthographically distinguished by a double grapheme of the geminate consonant (for example: micia (pussy-cat) and miccia (fuse), or casa (house) and cassa (box)). A problem, which is still unsolved, regards the identification of acoustic correlates of singleton vs. geminates, and their perceptual verification.

The Gemination project GEMMA, started at the University of Rome La Sapienza, Italy, in 1992, examines gemination in Italian. The analyzed consonants are stops, liquids, fricatives, nasals, and affricates. Partial results were previously reported for stops in (Esposito and Di Benedetto, 1999) showing how gemination is revealed by time-related parameters, namely, the consonant lengthening and the preconsonant vowel shortening in geminate forms. Relevance of acoustic correlates was confirmed by perceptual experiments.
The GEMMA project was recently revived, and the database used for the analysis was made available at the following link.

A. Esposito and M. G. Di Benedetto, "Acoustic and perceptual study of gemination in Italian stops", J. Acoust. Soc. Am. vol. 106, n. 4, Pt. 1, pp. 2051–2062, October 1999.

2019