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Distributed Beamforming Phase Synchronization Algorithms with multiple spatial constraints

In this thesis, we tested performance of two classes of distributed phase synchronization algorithms for distributed beamforming in the presence of multiple spatial constraints. The originality of the work consists in testing performance of the deterministic synchronization with multiple spatial constraints, and comparing it with the random in many different scenario conditions. Thanks to DBF, independent and randomly located sensor in a WSN are able to coordinate their antenna resources to form a virtual array that directs a beam in the desired direction of transmission, thus delivering a common message to a distant receiver. Directional beams facilitate separation of signals in the spatial domain enabling SDMA techniques and increasing throughput. Moreover, DBF allows for reduction of transmitted power of each sensor. At the beginning, we gave an introduction on the basic definitions and relationships that are used to analyze and synthesize arrays. Then, we have introduced the concept of DBF, and in particular we focused our attention on principal phase synchronization schemes proposed in literature. Among all the solutions, we recognized in the One-Bit Feedback algorithm the best solution in terms of semplicity and scalability. This is an iterative protocol: in each time slot, each node applies a phase adjustment to its signal and decides whether to keep or discard the phase shift on the basis of a one bit feedback from the receiver. We have distinguished two different approaches: the random and the deterministic one. The deterministic approach shows to have better performance with respect to the random in terms of convergence speed, both in a single spatial contraint case, and in a multiple spatial constraint case.

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Chapter 1 Centralized Beamforming This chapter refers to the theory in [1] and provides a brief overview on array pro- cessing theory. An array is used to filter a desired signal in the space-time domain by exploiting its spatial characteristics. This filtering may be expressed in terms of a dependence upon an angle or a wavenumber. The design of arrays to achieve cer- tain performance criteria involves trade-offs among the array geometry, the number of sensors, signal to noise and signal to interference ratios. There are two aspects of array design that determine its performance as a filter: the geometry and the complex weightings of the data at each sensor output. 1.1 Array Processing In this section, we discuss the principal aspects concerning array processing. An array consists of a certain number of radiating elements and it is characterized by four features: a) array configuration b) temporal characteristics of the signal and the interference c) spatial characteristics of the signal and the interference d) objective of the array processing The array configuration consists of two parts: a1) antenna pattern of the individual elements (isotropic or anisotropic pattern) 3

Tesi di Laurea Magistrale

Facoltà: Ingegneria

Autore: Valerio Nuccio Contatta »

Composta da 89 pagine.


Questa tesi ha raggiunto 49 click dal 11/12/2012.


Consultata integralmente una volta.

Disponibile in PDF, la consultazione è esclusivamente in formato digitale.