1,721,172 research outputs found
Le tecnologie per la banda larga : stato dell'arte e prospettive
No full textRassegna sulle tecnologie abilitanti per la larga band
Le reti wireless: stato dell'arte e prospettive
No full textIl seminario presenta una rassegna sulle tecnologie wireless disponibili e quelle che lo saranno a breve e lungo termine
Le reti Mesh: caratteristiche, architettura e il loro impatto sulle reti attuali
No full textRassegna sulle tecnologie di telecomunicazioni abilitanti per la rete pubblica di nuova generazion
Prospettive al 2010: i nuovi scenari tecnologici nelle telecomunicazioni
No full textIl seminario affronta i fondamenti e le problematiche delle Next Generation Networks, della tecnologia cognitive radio e delle Reti Mes
Mobile ad Hoc Networks: the DHT paradigm
No full textIn this thesis, the adoption of the hierarchical routing paradigm to achieve a scalable network layer for ad hoc networks has been proposed. The main concept of hierarchical routing is to keep, at any node, complete routing information about nodes which are close to it and lesser information about nodes located further away. The Augmented Tree-based Routing protocol, a routing protocol for ad hoc networks exploiting both a location-aware addressing schema and a distribute hash table (DHT) system, has been proposed. The adopted addressing schema allows nodes to adopt hierarchical routing, limiting so the overhead introduced in the network, while the DHT system provides the mapping between transient identifiers and node identities. Since the Augmented Tree-based Routing protocol adopts a multi-path strategy and since most studies in the area of multi-path routing focus on heuristic methods and the performances of these strategies are commonly evaluated by numerical simulations, an analytical framework to evaluate the performance gain achieved by multi-path routing has been proposed. The framework is based on on graph theory and on terminal-pair routing reliability (TPRR) as performance measure. Moreover, some features of the proposed protocol has been exploited design a peer-to-peer (P2P) system over a mobile ad hoc network (MANET) resorting to a cross-layer approach. It has been proved that simply deploying P2P systems over MANETs may cause poor performances. By coupling both the direct and the indirect key-based routing at the network layer and by resorting to the same hierarchical address space structure of ATR, we are able to build a P2P overlay network in which the logical proximity agrees with the physical one, limiting so the message overhead and avoiding the redundancy. Finally, by extending the proposed location-aware addressing to match with the opportunistic forwarding protocol, a novel routing protocol for disruption tolerant network (DTN) and delay tolerant network (DTN) has been proposed. By exploiting both the temporal diversity and the broadcast nature of the wireless propagation, such a protocol can enable connectivity in ad hoc environments characterized by non stationary wireless propagation as well as sparse topologies
TECNICHE DI EQUALIZZAZIONE E SOPPRESSIONE DELLINTERFERENZA A BANDA STRETTA PER SISTEMI MULTIPORTANTE
No full textThe Role of the Widely Linear Processing in the Narrowband and Wideband Systems
No full textIn this thesis, the role of the Widely-Linear processing in the narrowband and wideband systems has been proposed. With reference to narrowband systems, we analyzed the linear (L) constant modulus (CM) cost function under the general assumptions that improper modulation schemes of practical interest are employed. This study allows one to determine a broad family of undesired minima of the CM cost function, which do not lead to perfect symbol recovery in the absence of noise. Successively, we applied widely linear (WL) approach to the same context, providing the mathematical conditions assuring perfect symbol recovery in the absence of noise. Furthermore, we enlightened that, similarly to the L-CM equalizer, the performances of WL-CM equalizers suffer from the presence of undesired global minima. To overcome this drawback we proposed to resort to a constraint WL-CM equalizer. In the context of wideband systems, with reference to direct-sequence CDMA (DS-CDMA) technique, we developed a performance comparisons among ideal and data-estimated WL- and L-MOE (minimum output energy) receivers. As regard to the ideal implementation, we investigated the relative performances of the WL-MOE and L-MOE receivers in the high-SNR regime. In such a case, we provided a necessary and sufficient condition on the spreading codes, which allows the WL-MOE receiver to achieve perfect multiple access interference (MAI) suppression. As regard the data-estimated versions of the WL-MOE and L-MOE receivers, we derived easily interpretable formulas, which allow one to obtain clear insights about the effects of different parameters on performances. In addition, we have extended the previous analysis accounting for the effects of channel-estimation errors. Specifically, we presented a comprehensive performance comparison between different versions of the data-estimate L- and WL-MOE receivers with blind channel estimation. We derived easily interpretable formula that suggest that when considering finite sample-size implementation, the WL-MOE receiver with channel estimation is able to assure a significant performance gain (for low-to-moderate values of the SNR) with respect to its linear counterpart only when it is built by resorting to a more sophisticated implementation. In such a case, for a given channel length, it allows one to work with an increased number of users which makes it a viable choice in heavily-congested DS-CDMA networks. Finally, in the last part of this thesis, we addressed the problem of deriving mathematical conditions guaranteeing perfect symbol recovery in the absence of noise for either cyclic-prefix (CP) based or zero-padding (ZP) based multicarrier-CDMA (MC-CDMA) downlink transmissions, which employ frequency-domain symbol-spreading. The conditions derived are channel-independent and are expressed in terms of relatively simple system design constraints, regarding the maximum number of allowable users and their spreading sequences. Specifically, it was first shown that, similarly to a ZP-based MC-CDMA downlink, L-zero-forcing (ZF) can be guaranteed for a CP-based MC-CDMA downlink, even when the channel transfer function exhibits nulls on some used subcarriers. On the other hand, when the information-bearing symbols are improper, it was shown that, for both CP- and ZP-based systems, WL-ZF allows one to successfully operate even in overloaded scenarios, by doubling the system capacity, regardless of the channel zero locations. However, such an increased throughput can be achieved as long as appropriate complex-valued spreading codes are use
Character error probabilities for fading M-ary CPSK signals subject to Gaussian and impulsive noise
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