Browsing by Author "Loscrì, Valeria"

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Design and performance evaluation of algorithms for wireless self-organizing systems
(2014-11-28) Surace, Rosario; Greco, Sergio; Loscrì, Valeria; Aloi, Gianluca
The work done during the PhD course involves the study of the Self- Organization of wireless sensors, robots and UAV networks. In particular, this thesis investigates how each node composing the system can take advantage from the Self-Organization and from mobility, in a way to optimize some networks parameters as coverage and energy consumption. Self-Organization is a process in which pattern at the global level of a system emerges solely from numerous interactions among the lower-level components of a system. The rules specifying interactions among the systems components are executed using only local information, without reference to the global pattern [1]. Mobility, although still for some types of systems is not considered a primitive of the network: in recent years has been the subject of many studies just as useful feature to achieve certain objectives, not least the energy consumption in transmission. The network issues has been addressed using different approaches from the theoretical studies aimed at finding the maximum achievable performance benchmarks, through the introduction of appropriate optimization models, the proposal of distributed heuristics and more realistic communication protocols, and the use of biology-inspired mechanisms, such as genetic algorithms (GA) and neural networks (NN). The purpose of this type of approach is to move in the direction of networks that are able to self-organize by adapting to different environmental conditions and dynamic as well as hard scenarios (i.e. environment disasters). The rest of the thesis is organized as follows: in Chapter 1 background on Self-Organizing Systems is given. In Chapter 2 we investigate on the impact of the Propagation Environment on Controlled Mobility Algorithms; distributed heuristics to Film Sport Events with Flying Robots in Chapter 3 and Bio- Inspired approaches in Chapter 4. Finally, a new communications protocol for WSN called Decentralized Time-Synchronized Channel Swapping is analyzed in Chapter 5.
Protocol Architectures for wireless networks: issues, perspectives and enhancements
(2012-11-09) Loscrì, Valeria; Talia, Domenico; Marano, Salvatore
In this work we have analyzed different types of wireless networks and we have investigated the behavior of different MAC and routing protocols and different protocol architectures. Specifically, we have analyzed a TDMA MAC protocol for Mobile Ad hoc NETworks called Evolutionary-TDMA (E-TDMA). Based on this protocol we have developed a cross-layer approach that uses multiple linkdisjoint paths for a pair source-destination supporting a soft QoS. For this latter point we have developed a Multipath Forward Algorithm to manage and assign the slots. We have developed two different schemes: QoS scheme 1 and QoS scheme 2 and compared these schemes in terms of throughput, delay and overhead with a well-known multipath protocol routing, the AOMDV over 802.11 MAC protocol and AOMDV over E-TDMA. We have obtained good performance exploiting advantages of a TDMA MAC protocol and a Multipath routing protocol. Simulation results have shown as a cross-layer approach permits good performance in terms of throughput, end-to-end data packets delay and overhead to be obtained. In fact, multipath routing protocols for wireless ad hoc networks have been investigated because the use of alternate paths permits a greater fault-tolerance to be obtained. As far as multipath routing protocol is concerned we have developed and analyzed a multipath routing protocol based on geographic positions of the nodes in the network, Geographic Multipath Protocol (GMP). Results, in terms of throughput and delay, show that the multiple paths with minimum interference are better. We have investigated the cross-layer approach also for Wireless Sensor Networks. Although, this kind of networks could be considered an extension of Ad hoc networks, characteristics of WSNs are so different that protocols explicitly developed for MANETs cannot be directly applied for sensors networks. After analyzed some protocols we have proposed some solutions to increase the lifetime of the sensor networks considering other important parameters as throughput and latency. Finally, our analysis of wireless networks finishes with the analysis of Wireless Mesh Networks. We have investigated multi-hop wireless networks based on the IEEE 802.16 technology. Specifically, we have analyzed the Coordinated Distributed Scheme (CDS) of the IEEE Std. 802.16 and we have developed a MAC module 6 Conlcusions 158 supporting the CDS in ns2. Moreover, we have developed two different totally distributed schemes that do not require any changes of the structure of the hardware used in the 802.16. The two schemes proposed manage the assignment of the control slots (Transmit Opportunity XmtOP), in a different fashion. We have developed the two scheme in ns2 in order to compare them with the CDS of the 802.16. Our approaches permit good performance in terms of throughput and delay to be obtained. Our approaches are independent from parameters of the network as density or topology. On the other hand, the CDS is not robust for different network conditions because the behavior of the scheme depends from the setting of particular parameters.