Μελέτη βαθμών ελευθερίας σε συστήματα BS-MIMO και υπολογισμός σύνθετης αντίστασης κεραιών ESPAR με χρήση γενετικού αλγορίθμου
Θωμάτος, Ευάγγελος Δ.
The subject of this master thesis is the study of an alternative MIMO system that uses parasitic antennas and is known in the literature as Beamspace MIMO (BS-MIMO). Instead of using multiple active antenna elements, as the traditional MIMO systems, BS-MIMO uses antenna arrays with only one active and multiple parasitic elements (which are often called parasititcs). The most popular implementation of such arrays, are the ESPAR antennas, which offer significant beamforming abilities. This means that these antennas can provide a variety of different radiation patterns, which is feasible by adjusting the effective electromagnetic coupling of the parasitic elements. Furthermore, the spatial spreading and the spatial sampling, of the transmitted and received signals respectively, is not feasible due to the existence of only one active elements. Because of this, the functionality of the BS-MIMO systems is described in the beamspace (BS) domain rather than in the spatial domain. In addition, unlikely with the conventional MIMO that use spatial multiplexing, the BS-MIMO systems multiplex the transmitted signals in the BS domain by using orthogonal radiation patterns that are called basis patterns. In the context of this thesis, it is going to study the degrees of freedom that can be supported by a BS-MIMO system, which are called Aerial Degrees of Freedom (aDoFs). Each aDoF corresponds to a basis pattern of the ESPAR antenna. The state of the art technique of the calculation of the available aDoFs takes only into account the radiated field of the antenna and decomposes it to orthogonal functions which form the basis patterns. In this study, it is going to provide a novel technique for the calculation of the available aDoFs, which takes also into account the channel effect. The proposed technique produces a set of adaptive basis patterns, the use of which maximizes system capacity by effectively exploiting the inherent radio channel properties.