1,721,231 research outputs found
Reti di Telecomunicazioni
No full textQuesto volume si pone lo scopo di fornire alcuni degli elementi fondamentali per capire come sono strutturate le moderne Reti di Telecomunicazioni. Nel volume si è cercato di trattare i sistemi sia da un punto di vista quantitativo che qualitativo, con trattazioni il più possibile snelle, tentando di bilanciare la chiarezza e la semplicità con l'esattezza formale. Il capitolo 1 presenta una introduzione relativa alle reti di telecomunicazione, ai servizi ed alle architetture. Nel capitolo 2 vengono presentati alcuni elementi di teoria dei sistemi a coda. Nel capitolo 3 vengono discusse le problematiche relative ai collegamenti punto-punto, con enfasi agli aspetti di rilevamento e correzione degli errori. Il capitolo 4 affronta le problematiche relative alle metodologie di accesso, discutendone alcune fondamentali, didatticamente e storicamente importanti. L'instradamento viene affrontato nel capitolo 5 dove vengono anche riportati ulteriori elementi di teoria dei sistemi a coda necessari per caratterizzare il controllo di flusso. Alcuni protocolli, tra i più diffusi nelle reti locali e metropolitane, vengono analizzati nel capitolo 6. La commutazione di circuito, tipica delle reti per fonia, viene trattata nel capitolo 7. Infine il cap. 8 fornisce alcuni elementi di internetworking, con dettagli relativi ai principali protocolli per reti TCP/IP
Public Administration owned Regional Telecommunication Networks as strategic asset during 2012 earthquake in Emilia-Romagna
No full textTelecom is the domain where innovation and spread of usage registered the quickest and most consistent growth in the latest ten years. Seismic event dated May 2012 in Emilia-Romagna region was a significant example of how spread and diffused presence of two PA (Public Administration) regional telecommunication networks (ERretre Regional Mobile Network for radio emergency and Lepida broadband Network) substantially contributed to address such a catastrophic situation, providing the right premises to its quick overcoming and a strategic criterion for the following reconstruction of the territory. In this situation the importance and the effectiveness of a flexible, modular and configurable regional emergency mobile network such as ERretre has been proved, but at the same time the synergies with Lepida broadband network have emerged, showing a new potential in building an enabling infrastructure not only for new services, but also for new networks
Closed Form Performance Evaluation for Code Period versus Spreading Factor on Asynchronous DS-CDMA Systems
No full textSpreading code period effect on asynchronous DS-CDMA system performance is analyzed through the definition of useful over single interference power ratio, η, by considering random sequences with period P and spreading factor N. The analysis derives a simple η closed form for all possible N and P value combinations
Queue System with Smart ARQ ON Markov Channel for Energy Efficiency
No full textAbstract - This paper is devoted to the analytical investigation
of an ARQ scheme including the possibility to block
the transmissions when the physical layer shows an error
burst. The error model is taken by a two states Markov
model. The ARQ is blocked when the channel is in fault
because it makes not sense to continue to loose energy by
attempting transmission over a non-reliable channel. Two
different thresholds, one to block the transmission and one
to restart it, are considered, and the performance in terms of
average delivery packet number, average energy and average
delay, are computed by means of an analytical approach.
Some results are discussed and compared with simulations
DS-CDMA Systems using q-Level m Sequences: Coding Map Theory
No full textGF(q) m sequences with complex spreading mapping are considered for DS-CDMA systems by referring to three different environments with increasing synchronicity levels. For all environments, performance evaluation is derived both with a deterministic approach requiring spreading sequence specification, and with a statistical derivation, based on the assumption of spreading sequence ergodicity, in order to give closed-form performance theory. The optimal mapping design criterion, through zero-mean complex code mapping, is computed for all environments and validated through several numerical tests. Performance invariance, with respect to sequence levels, has been demonstrated for low synchronous environments, where the proposed sequence gives better performanc
Equal BER with Successive Interference Cancellation DS-CDMA Systems on AWGN and Ricean Channels
No full textAn interference cancellation scheme, based on successive cancellation with decided information bit feedback, is presented, and the performance analyzed in order to obtain the same bit error probability (BER) for each user, when channel estimation and power control are considered to be ideal. The analysis is carried out to obtain the same, optimal, performance on each channel. Furthermore, a possible approximation is introduced to develop an easy power list algorithm and is validated with numerical results. Some considerations both on receiver and transmitted total power gain with respect to the classical integration-and-dump receiver structure are reported
Asymmetric Channel Cooperative Compression
No full textAn asymmetric channel environment is considered
and the slow uplink direction is speeded-up by means of a
new compression scheme, based on a dictionary transmitted
on the downlink channel. The performance of this cooperative
scheme approaches those of perfect knowledge of dictionary and
it improves as much as the download over upload ratio improves.
The letter makes an investigation on this cooperative structure,
on the their performance and on the dictionary compositions
Analytical Formulation for the Synchronization Performance of Q-level M-sequences in DS-CDMA
No full textIn the context of DS-CDMA asynchronous system applications, as in the uplink cellular environment, a spreading process theory based on q-level m-sequences is developed with the aim of improving the acquisition performance with respect to the classic binary case. A very simple sequential acquisition strategy, two-threshold based, is introduced and its performance studied for a generic number of levels of the spreading sequence elements. Moreover, the possibility of avoiding the tracking subsystem is considered. Some synchronization merit factors are defined and characterized to permit fast and easy performance comparison and physical observability. The results presented show that by using q-level m-sequences the tradeoff between acquisition reliability and time can be improved
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