Maria-Gabriella Di Benedetto

(UWB) 2 : uncoordinated, wireless, baseborn medium access for UWB communication networks

A MAC protocol for Ultra Wide Band (UWB) radio networks named (UWB)2 is proposed. The algorithm exploits typical features of impulse radio such as large processing gain, and is conceived in conjunction with a synchronization strategy which foresees the presence of a synchronization sequence in each transmitted packet. (UWB)2 adopts a pure Aloha approach; Performance analysis of the synchronization tracking mechanism showed in fact that under the preliminary simplistic hypothesis of an AWGN channel, and for a sufficient number of pulses in the synchronization sequence, a fairly high probability of successful synchronization can be achieved, even in the presence of several users and Multi User Interference (MUI). The multiple access scheme is based on the combination of a common control channel provided by a common Time Hopping (TH) code with dedicated data channels associated to transmitter specific TH codes.Results obtained by simulation indicate that (UWB)2 can be successfully applied when the number of users spans from a few tens to about one hundred, for data rates ranging from a few thousands to a few hundreds of bits per second. Network throughput was above 99.8% in all considered simulation settings. Such achievement confirms that (UWB)2 is a suitable and straightforward solution for large networks of terminals using impulse radio for transmission at low bit rates.

ACOUSTICAL AND PERCEPTUAL STUDY OF GEMINATION IN ITALIAN STOPS

On the basis of theoretical considerations and results from acoustic and perceptual analyses, it is hypothesized that closure duration is the primary cue for gemination in Italian. Results of an acoustic analysis of a large number of single and geminate Italian utterances show two acoustic correlates of gemination: the length of the closure and the length of the vowel preceding the consonant. Other acoustic parameters were not systematically related to gemination. These results were validated perceptually. At the perceptual level, the above cues were used by the listeners in the geminate/nongeminate discrimination; however, closure duration played a major role. Moreover, it was found that the significant lengthening of consonant was only partially compensated by the shortening of the previous vowel and by a small lengthening of the geminate utterance with respect to the nongeminate one. This result suggests that speakers follow a sort of timing (rhythm) which is fixed in duration and depends on the number of syllables in the word: words with equal numbers of syllables do not change in utterance length, an elongated segment being partly compensated by the shortening of another. This process seems to be applied also perceptually suggesting that the timing (rhythm) of a language is also an auditory attitude.

Cognitive Satellite Terrestrial Radios

In this paper we present the concept of cognitive satellite terrestrial radios (CSTR) for hybrid satellite-terrestrial systems (HSTS). The cognitive radio (CR) technology is being motivated by the radio regulatory bodies for efficient utilization of the radio spectrum. The future satellite ground terminals therefore need to integrate and co-exist with the spectrally crowded terrestrial wireless systems and hence we propose the idea of CSTR. The key issues are addressed and the concepts of developing CR based satellite ground terminals in HSTS for dynamic spectrum access on the ground are presented. Furthermore, the concept of 3D-Spatial reuse of the spectrum is also presented using the CSTR considering low elevated satellite ground stations. Two particular HSTS applications to illustrate the CSTR concept, a) the hybrid satellite-UWB (ultra wideband) communication system for personal area networks (PAN) with short range on ground communications, and b) the hybrid satellite-WRAN (wireless regional area networks) for long range on ground communications are presented. In both the applications the satellite uplink and the terrestrial radios adopt the CR functionalities. The key enabling technologies and their integrated architecture for the CSTR are also presented.

Ultra wide band wireless communications: A tutorial

Ultra wide band (UWB) radio has recently attracted increased attention due to its expected unlicensed operation, and potential to provide very high data rates at relatively short ranges. In this article we briefly describe some main candidate multiple access and modulation schemes for UWB communications, followed with their power spectral density calculation and properties. We also present some illustrative capacity results, and provide a discussion of the impact of network topology on multiple access capacity.

Frequency and time variations of the first formant: Properties relevant to the perception of vowel height

Perceptual experiments using consonant–vowel–consonant (CVC) syllables were carried out to examine the perceptual relevance of the first formant frequency (F1) trajectory in the perception of high vowels versus nonhigh vowels. Results show that stimuli characterized by a higher onset frequency and F1 maximum at the beginning of the vocalic portion are perceived as lower vowels than stimuli with a lower F1 onset frequency and F1 maximum toward the end of the vocalic portion. These findings are in agreement with the hypothesis, based on the acoustic analyses of Di Benedetto (1989), that stimuli with higher F1 onset frequencies and F1 maximum at the beginning of the vocalic portion characterize lower vowels. Results are similar for native speakers of different languages, leading to a suggestion that this phenomenon may have either an articulatory or an auditory basis. Possible interpretations based on an overshoot hypothesis or a formant time average theory were investigated through an additional perceptual ...

Vowel representation: Some observations on temporal and spectral properties of the first formant frequency

Acoustic analysis of the vocalic portion of consonant–vowel–consonant (CVC) syllables (where V is one of the five vowels [I,q,1,a,v] of American English) spoken by three speakers (two males and one female) in the sentence frame ‘‘The — again’’ is presented. Results of acoustic measurements show that ambiguities between vowels, for each speaker, occur if the vowels are represented by the values of F1 and F2 sampled at the time where F1 reaches its maximum. These ambiguities occur primarily in the F1 dimension. Examination of the F1 trajectories of the vowels for which confusion occurs shows variations in the way F1 reaches its maximum among different vowels. In particular, if two different vowels such as [I] and [q] have the same maximum F1, then F1 for the lower vowel reaches its maximum value earlier. In addition, results show that the F1 onset frequency also might be important in determining vowel height. The implication is that the spectral characteristics at a particular ‘‘target,’’ represented by the...

A novel approach for estimating multi-user interference in impulse radio UWB networks: the pulse collision model

Modeling multi-User Interference (MUI) is crucial in the design of wireless networks. In the case of Impulse Radio (IR)- Ultra Wide Band (UWB) networks, most of the adopted models are inspired by the legacy of the reference literature on spread spectrum communications, and do not address specific features for IR systems, where spectrum spreading is basically obtained by the radiation of very short time-limited pulses. The problem of conceiving a specific model for MUI in IR-UWB networks is addressed in this paper. The reference scenario consists of multiple asynchronous users transmitting IR-UWB signals using Pulse Position Modulation (PPM) in combination with Time Hopping (TH) coding. We provide a novel analytical expression for the average BER based on the observation that interference in IR is provoked by collisions occurring between pulses belonging to different transmissions. The proposed method requires specification of a similar set of system parameters as Gaussian-based approaches, but shows improved accuracy in estimating BER.

UWB body area network coexistence by interference mitigation

This work analyzes the performance of a BAN composed of IEEE 802.15.4a Ultra Wide Band (UWB) sensors in terms of Bit Error Rate (BER), BAN throughput and network lifetime. The BAN performance is evaluated in presence of an external Low Data Rate (LDR) interfering network, that we suppose represented by a second BAN operating in the same hospital room. Coexistence between the two wireless networks is discussed and the reference BAN performance is improved by the adoption of an optimized time hopping code assignment strategy. A possible strategy to extend the lifetime of the network is also introduced.

Tuning UWB signals by pulse shaping: towards context-aware wireless networks

Tuning spectra by pulse shaping is feasible in both impulse radio (IR) and continuous radio transmissions, since, as well known, the impulse response of the pulse shaper affects the spectral properties of radiated signals. What is peculiar to IR-UWB, and makes pulse shaping particularly appealing, is the impulsive nature of the carrier. Given their very short duration, transmitted pulses in different intervals overlap neither on clock beats nor in between two clock beats. Spectrum matching in IR can thus be restricted with reasonable approximation to a single inter-pulse interval, and as such be redirected in a rather straightforward way into a waveform representation problem.This paper analyzes the above problem of tuning radiated IR-UWB signals to reference spectral patterns by pulse shaping, and shows the correspondence between spectrum and waveform matching problems. Examples of application include three case studies: matching the FCC emission masks, mitigating interference in the ISM bands, and reducing inter-system interference for two coexisting UWB networks. The proposed approach goes beyond the signal processing analysis to tentatively propose a procedure and related protocol for integrating spectral adaptation mechanisms into network operating principles.

Combining UWB with Time Reversal for improved communication and positioning

This work investigates the use of Time Reversal (TR) applied to UWB systems for communication and positioning applications. Potential performance boosts, that are achievable over a single UWB communication link by the sole adoption of TR, are investigated. In the case of multiuser UWB communications, it is shown that TR modifies the distribution of Multi User Interference (MUI) and that further performance improvement can be obtained by adapting the receiver to the specific MUI distribution characteristics. As regards UWB positioning, an enhancement in position estimation accuracy can be achieved when TR reinforces DOA estimation thanks to increased robustness to decreased homogeneity in the propagation medium.