3,717 research outputs found
MoMo: a group mobility model for future generation mobile wireless networks
Existing group mobility models were not designed to meet the requirements for
accurate simulation of current and future short distance wireless networks
scenarios, that need, in particular, accurate, up-to-date informa- tion on the
position of each node in the network, combined with a simple and flexible
approach to group mobility modeling. A new model for group mobility in wireless
networks, named MoMo, is proposed in this paper, based on the combination of a
memory-based individual mobility model with a flexible group behavior model.
MoMo is capable of accurately describing all mobility scenarios, from
individual mobility, in which nodes move inde- pendently one from the other, to
tight group mobility, where mobility patterns of different nodes are strictly
correlated. A new set of intrinsic properties for a mobility model is proposed
and adopted in the analysis and comparison of MoMo with existing models. Next,
MoMo is compared with existing group mobility models in a typical 5G network
scenario, in which a set of mobile nodes cooperate in the realization of a
distributed MIMO link. Results show that MoMo leads to accurate, robust and
flexible modeling of mobility of groups of nodes in discrete event simulators,
making it suitable for the performance evaluation of networking protocols and
resource allocation algorithms in the wide range of network scenarios expected
to characterize 5G networks.Comment: 25 pages, 17 figure
Spectral Efficiency of Random Time-Hopping CDMA
Traditionally paired with impulsive communications, Time-Hopping CDMA
(TH-CDMA) is a multiple access technique that separates users in time by coding
their transmissions into pulses occupying a subset of chips out
of the total included in a symbol period, in contrast with traditional
Direct-Sequence CDMA (DS-CDMA) where . This work analyzes
TH-CDMA with random spreading, by determining whether peculiar theoretical
limits are identifiable, with both optimal and sub-optimal receiver structures,
in particular in the archetypal case of sparse spreading, that is,
. Results indicate that TH-CDMA has a fundamentally different
behavior than DS-CDMA, where the crucial role played by energy concentration,
typical of time-hopping, directly relates with its intrinsic "uneven" use of
degrees of freedom.Comment: 26 pages, 13 figure
Consonant gemination in Italian: the affricate and fricative case
Consonant gemination in Italian affricates and fricatives was investigated,
completing the overall study of gemination of Italian consonants. Results of
the analysis of other consonant categories, i.e. stops, nasals, and liquids,
showed that closure duration for stops and consonant duration for nasals and
liquids, form the most salient acoustic cues to gemination. Frequency and
energy domain parameters were not significantly affected by gemination in a
systematic way for all consonant classes. Results on fricatives and affricates
confirmed the above findings, i.e., that the primary acoustic correlate of
gemination is durational in nature and corresponds to a lengthened consonant
duration for fricative geminates and a lengthened closure duration for
affricate geminates. An inverse correlation between consonant and pre-consonant
vowel durations was present for both consonant categories, and also for both
singleton and geminate word sets when considered separately. This effect was
reinforced for combined sets, confirming the hypothesis that a durational
compensation between different phonemes may serve to preserve rhythmical
structures. Classification tests of single vs. geminate consonants using the
durational acoustic cues as classification parameters confirmed their validity,
and highlighted peculiarities of the two consonant classes. In particular, a
relatively poor classification performance was observed for affricates, which
led to refining the analysis by considering dental vs. non-dental affricates in
two different sets. Results support the hypothesis that dental affricates, in
Italian, may not appear in intervocalic position as singletons but only in
their geminate form.Comment: Submitted to Speech Communication. arXiv admin note: substantial text
overlap with arXiv:2005.0696
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