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

Interference control and radio spectrum allocation in shared spectrum access

With demands on the radio spectrum intensifying, it is necessary to use this scarce resource as efficiently as possible. One way forward is to apply flexible authorization schemes such as shared spectrum access. While such schemes are expected to make additional radio resource available and lower the spectrum access barriers, they also bring new challenges toward effectively dealing with the created extra interference which degrades the performance of networks, limiting the potential gains in a shared use of spectrum. In this thesis, to address the interference issue, different spectrum access schemes and deployment scenarios are investigated.  Firstly, we consider licensed shared access where database-assisted TV white space network architecture is employed to facilitate the controlled access of the secondary system to the TV band. The operation of the secondary system is allowed only if the quality of service experienced by the incumbent users is preserved. Furthermore, the secondary system should benefit itself from utilizing the TV band in licensed shared access mode. One challenge for efficient operation of the licensed secondary system is to control the cross-tier interference generated at the TV receiver, taking into account the self-interference in the secondary system.  Secondly, we consider co-primary shared access where multiple operators share a part of their spectrum. This can be done in two different operational levels, users and cells. The user level is done in the context of D2D communications where two users subscribed to different operators can transmit directly to each other. The cell level allows spectrum sharing between two small cells, e.g., indoor and outdoor small cells, in a dense urban environments. The main challenges for such scenarios are to manage the cross-tier interference generated by other users or cells subscribed to different operators, and to identify the amount of radio spectrum each operator contributes.  There are several approaches to reduce the risk of interference, but they often come at a high price in terms of complexity and signaling overhead. In this thesis, we aim to propose low complexity mechanisms that take interference control and radio spectrum allocation into account. The proposed mechanisms are based on tractable models which characterize the effects of the fundamental design parameters on the system behavior in shared spectrum access. The models are leveraged to capture the statistic of the aggregate interference and its effects on the performance metrics

Research in progress and other activities of the Institute for Computer Applications in Science and Engineering

This report summarizes research conducted at the Institute for Computer Applications in Science and Engineering in applied mathematics and computer science during the period April 1, 1993 through September 30, 1993. The major categories of the current ICASE research program are: (1) applied and numerical mathematics, including numerical analysis and algorithm development; (2) theoretical and computational research in fluid mechanics in selected areas of interest to LaRC, including acoustic and combustion; (3) experimental research in transition and turbulence and aerodynamics involving LaRC facilities and scientists; and (4) computer science

Composition and Manufacturing Effects on Electrical Properties of Li/FeS2 Thermal Battery Cathodes

Li/FeS2 thermal batteries provide a stable, robust, and reliable power source capable of long-term electrical energy storage without performance degradation. These systems rely on a eutectic salt that melts at elevated temperature, activating the cell. When the electrolyte melts, the cathode becomes a suspension, with cathode particles suspended in a molten salt. The suspension experiences mechanical deformation, or slumping.\u27 This slump changes the mechanical compression of the cell, as well as the tortuosity and electronic and ionic conductivity of the cell as the cathode mesostructure is reordered in response to the external compressive stress. The combined effect of deformation, component composition, and manufacturing conditions on electrical conductivity has not been studied, yet the cathode electrical properties are critically important to battery performance. This thesis presents simulation results from a computer model in combination with experiments to elucidate the effects of electrical conductivity in FeS2 cathode pellets when composition and manufacturing parameters are varied. Experiments applied impedance spectroscopy measurements of pressed-powder cathode pellets before and after slumping. Pellets were manufactured with variations in pellet density, FeS2 particle size distribution, and FeS2 content. The results showed that prior to slumping, the electrical conductivity increased with pellet density and FeS2 content. After slumping, pellets exhibited greater electrical conductivity, but the effects of processing parameters appear to have been erased, at least within the ranges tested. The conformal decomposition finite element method (CDFEM) was applied to surface-meshed geometric representations of cathode microstructures generated from microcomputed tomography reconstructions. Results from the SIERRA/Aria finite element code indicate that the selected processing and composition parameters do not provide a clear trend on the preslumped electrical conductivity, but density slightly affected the postslumped conductivity. These results indicate that the simulations lacked fidelity compared to experiments. However, the simulations combined with experimental data provide a fundamental look at the effects of processing and composition on thermal battery microstructure and electrical conductivity. The understanding of manufacturing effects on battery performance is not well developed, and this effort represents a step forward in correlated and predicting performance of cells based upon observed manufacturing trends.\u2