Polarization and index modulations : a theoretical and practical perspective

Radiocommunication systems have evolved significantly in recent years in order to meet present and future demands. Historically, time, frequency and more recently, spatial dimensions have been used to improve capacity and robustness. Paradoxically, radiocommunications that leverage the polarization dimension have not evolved at the same pace. In particular, these communications are widely used by satellites, where several streams are multiplexed in each orthogonal polarization. Current communication trends advocate for simplifying and unifying different frameworks in order to increase flexibility and address future needs. Due to this, systems that do not require channel information are progressively gaining traction, as they help to improve the overall quality of the network instead of that of specific users only. The search for new paradigms aimed at improving the quality of wireless communications is unstoppable. In order to increase the capacity of current communications systems, new horizons and physical dimensions must be explored. This dissertation aims at challenging this perspective and promoting the use of polarization in new radiocommunication systems. Consequently, the goal of this thesis is twofold: first, we aim at increasing the current capacity of point-to-point and point-to-multipoint links. Secondly, we introduce new mechanisms to increase the robustness of communications in particularly hostile environments. In this context, this thesis advocates for the use of polarization as a dimension to be exploited in radiocommunications. In addition to the use of polarization, index modulations help increase transmission rates whilst improving robustness against errors and imperfections with a low computational complexity. Thus, the study of polarization in these systems is essential. This dissertation explores primordial aspects in this area, such as channel capacity, transmitter and receiver design and performance benchmarking with current systems. Finally, we identify and discuss various characteristic aspects of polarization. In this thesis, the reader will navigate the mathematical foundations of the proposed concepts as well as their implementation in real-life scenarios.La cerca de nous paradigmes que milloren la qualitat de les comunicacions inalàmbriques és constant i imparable. Per aquesta raó es fa necessari buscar nous horitzons i noves dimensions físiques que permetin incrementar la capacitat actual de les comunicacions. La present dissertació vol canviar aquesta perspectiva i potenciar l'ús de la polarització en els nous sistemes de radiocomunicacions. L'objectiu d'aquesta tesi doctoral és doble: primer, incrementar la capacitat actual dels enllaços punt a punt i punt a multipunt i, segon, dotar-los de millor robustesa davant d'entorns hostils. Per això, aquesta tesi presenta la polarització com a una dimensió a explotar en les radiocomunicacions. Paral·lelament, les modulacions per índex incrementen la velocitat de transmissió, alhora que proporcionen una major robustesa davant errors i imperfeccions, tot mantenint una baixa complexitat computacional. Així doncs, l'estudi de la polarització en aquests sistemes es fa necessari i primordial. El present manuscrit estudia aspectes com la capacitat de canal en aquests àmbits, el seu disseny tant del transmissor com del receptor, així com comparacions amb sistemes existents. Finalment, també s'analitzen diferents aspectes característics i únics de la polarització i es proposa una nova modulació en 3 dimensions, únicament possible utilitzant la polarització. En aquesta dissertació el lector podrà trobar els fonaments matemàtics que sustenten el que es presenta així com implementacions realistes de les diferents propostes en entorns real