Spectral and energy efficiency of line-of-sight OAM-MIMO communication systems

Not only high spectral efficiency (SE) but also high energy efficiency (EE) are required for future wireless communication systems. Radio orbital angular momentum (OAM) provides a new perspective of mode multiplexing to improve SE. However, there are few studies on the EE performance of OAM mode multiplexing. In this paper, we investigate the SE and EE of a misaligned uniform concentric circle array (UCCA)-based multi-carrier multimode OAM and multiple-input multiple-output (MCMM-OAM-MIMO) system in the line-of-sight (LoS) channel, in which two transceiver architectures implemented by radio frequency (RF) analog synthesis and baseband digital synthesis are considered. The distance and angle of arrival (AoA) estimation are utilized for channel estimation and signal detection, whose training overhead is much less than that of traditional MIMO systems. Simulation results validate that the UCCA-based MCMM-OAM-MI-MO system is superior to conventional MIMO-OFDM system in the EE and SE performances

Orbital Angular Momentum Waves: Generation, Detection and Emerging Applications

Orbital angular momentum (OAM) has aroused a widespread interest in many fields, especially in telecommunications due to its potential for unleashing new capacity in the severely congested spectrum of commercial communication systems. Beams carrying OAM have a helical phase front and a field strength with a singularity along the axial center, which can be used for information transmission, imaging and particle manipulation. The number of orthogonal OAM modes in a single beam is theoretically infinite and each mode is an element of a complete orthogonal basis that can be employed for multiplexing different signals, thus greatly improving the spectrum efficiency. In this paper, we comprehensively summarize and compare the methods for generation and detection of optical OAM, radio OAM and acoustic OAM. Then, we represent the applications and technical challenges of OAM in communications, including free-space optical communications, optical fiber communications, radio communications and acoustic communications. To complete our survey, we also discuss the state of art of particle manipulation and target imaging with OAM beams

Diffraction Effects in Transmitted Optical Beam

Dizertačná práca pojednáva o vlnových a elektromagnetických javoch, ku ktorým dochádza pri zatienení eliptického Gausovského zväzku kruhovou apretúrou. Najprv boli z Huygensovho-Fresnelovho princípu odvodené dva modely Fresnelovej difrakcie. Tieto modely poskytli nástroj pre zavedenie kontrastu difrakčného obrazca ako veličiny, ktorá kvantifikuje vplyv difrakčných javov na prevádzkové parametre optického spoja. Následne, pomocou nástrojov elektromagnetickej teórie svetla, boli odvodené štyri výrazy (dva presné a dva aproximatívne) popisujúce geometrický útlm optického spoja. Zároveň boli skúmané tri rôzne prípady odsmerovania zväzku - priečne posunutie a uhlové odsmerovanie vysielača, resp. prijímača. Bol odvodený výraz, ktorý tieto prípady kvantifikuje ako útlm elipticky symetrického Gausovského zväzku. Všetky vyššie uvedené modely boli overené v laboratórnych podmienkach, aby sa vylúčil vplyv iných javov. Nakoniec práca pojednáva o návrhu plne fotonického optického terminálu. Najprv bol ukázaný návrh optického vysielača nasledovaný vývojom optomechanickej sústavy prijímača. Pomocou nástrojov geometrickej a maticovej optiky boli vypočítané parametre spoja a odhad tolerancie pri zamierení spoja.The thesis was set out to investigate on the wave and electromagnetic effects occurring during the restriction of an elliptical Gaussian beam by a circular aperture. First, from the Huygens-Fresnel principle, two models of the Fresnel diffraction were derived. These models provided means for defining contrast of the diffraction pattern that can be used to quantitatively assess the influence of the diffraction effects on the optical link performance. Second, by means of the electromagnetic optics theory, four expressions (two exact and two approximate) of the geometrical attenuation were derived. The study shows also the misalignment analysis for three cases -- lateral displacement and angular misalignment of the transmitter and the receiver, respectively. The expression for the misalignment attenuation of the elliptical Gaussian beam in FSO links was also derived. All the aforementioned models were also experimentally proven in laboratory conditions in order to eliminate other influences. Finally, the thesis discussed and demonstrated the design of the all-optical transceiver. First, the design of the optical transmitter was shown followed by the development of the receiver optomechanical assembly. By means of the geometric and the matrix optics, relevant receiver parameters were calculated and alignment tolerances were estimated.

Optimization of Mobility Parameters using Fuzzy Logic and Reinforcement Learning in Self-Organizing Networks

In this thesis, several optimization techniques for next-generation wireless networks are proposed to solve different problems in the field of Self-Organizing Networks and heterogeneous networks. The common basis of these problems is that network parameters are automatically tuned to deal with the specific problem. As the set of network parameters is extremely large, this work mainly focuses on parameters involved in mobility management. In addition, the proposed self-tuning schemes are based on Fuzzy Logic Controllers (FLC), whose potential lies in the capability to express the knowledge in a similar way to the human perception and reasoning. In addition, in those cases in which a mathematical approach has been required to optimize the behavior of the FLC, the selected solution has been Reinforcement Learning, since this methodology is especially appropriate for learning from interaction, which becomes essential in complex systems such as wireless networks. Taking this into account, firstly, a new Mobility Load Balancing (MLB) scheme is proposed to solve persistent congestion problems in next-generation wireless networks, in particular, due to an uneven spatial traffic distribution, which typically leads to an inefficient usage of resources. A key feature of the proposed algorithm is that not only the parameters are optimized, but also the parameter tuning strategy. Secondly, a novel MLB algorithm for enterprise femtocells scenarios is proposed. Such scenarios are characterized by the lack of a thorough deployment of these low-cost nodes, meaning that a more efficient use of radio resources can be achieved by applying effective MLB schemes. As in the previous problem, the optimization of the self-tuning process is also studied in this case. Thirdly, a new self-tuning algorithm for Mobility Robustness Optimization (MRO) is proposed. This study includes the impact of context factors such as the system load and user speed, as well as a proposal for coordination between the designed MLB and MRO functions. Fourthly, a novel self-tuning algorithm for Traffic Steering (TS) in heterogeneous networks is proposed. The main features of the proposed algorithm are the flexibility to support different operator policies and the adaptation capability to network variations. Finally, with the aim of validating the proposed techniques, a dynamic system-level simulator for Long-Term Evolution (LTE) networks has been designed

Backhaul Link Enhancement and Radio Resource Management for Relay Deployments

Mobile networks are experiencing a dramatic increase in the data traffic. Besides, a continuously growing number of users expect mobile broadband access with the utmost in quality and ubiquitous connectivity. In this regard, multi-hop decode-and-forward relaying is a promising enhancement to existing radio access networks to fulfill the challenging requirements in a cost-efficient way and, thus, is an integral part of the Fourth Generation (4G) standards. Nevertheless, in order to fully exploit the potential benefits of relay deployments, proper radio resource management (RRM) is necessary. The research in this thesis has contributed to cellular relay deployments for future mobile networks. Concretely, we have developed key RRM concepts with a particular focus on the uplink (UL) system performance to complement the existing literature. We have demonstrated the performance of these concepts by taking Third Generation Partnership Project (3GPP) Long-Term Evolution (LTE) Release 10 and beyond (LTE-Advanced) Type 1 inband relaying as a practical framework, and by considering urban and suburban scenarios. First, by performing relay site planning (RSP) we aim at improving the quality of the wireless backhaul which is crucial for the end-to-end user performance. Then, we analyze UL power control (PC) and verify its importance and applicability in relay deployments. In this context, we propose manual and automated optimizations to tune PC parameters on all links to further enhance the system performance. Moreover, we study the energy efficiency by taking into account throughput (TP) per power consumption. Further, we investigate various resource sharing strategies among and within the links. Via proposed approaches, performance enhancement is targeted along with higher system fairness and more flexible resource allocation. In addition, we address a key issue regarding the small coverage area of an RN cell in the overlaying macrocell, which results in load imbalances, inefficient resource utilization, and increased UL inter-cell interference. Specifically, we apply practical cell range extension (CRE) techniques to cope with these drawbacks. Performance evaluations reveal that relay deployments clearly outperform macrocell-only deployments in terms of TP as well as TP per power consumption provided that proper RRM is performed. Our results also verify that the use of RSP yields substantial improvements. Furthermore, our results show that the proposed RRM concepts and the associated joint optimization strategies can fulfill the aforementioned goals while achieving significant system performance enhancements