Performance Limits of Compressive Sensing Channel Estimation in Dense Cloud RAN

Towards reducing the training signaling overhead in large scale and dense cloud radio access networks (CRAN), various approaches have been proposed based on the channel sparsification assumption, namely, only a small subset of the deployed remote radio heads (RRHs) are of significance to any user in the system. Motivated by the potential of compressive sensing (CS) techniques in this setting, this paper provides a rigorous description of the performance limits of many practical CS algorithms by considering the performance of the, so called, oracle estimator, which knows a priori which RRHs are of significance but not their corresponding channel values. By using tools from stochastic geometry, a closed form analytical expression of the oracle estimator performance is obtained, averaged over distribution of RRH positions and channel statistics. Apart from a bound on practical CS algorithms, the analysis provides important design insights, e.g., on how the training sequence length affects performance, and identifies the operational conditions where the channel sparsification assumption is valid. It is shown that the latter is true only in operational conditions with sufficiently large path loss exponents.Comment: 6 pages, two-column format; ICC 201

The Design and Optimization of Jet-in-Cross-Flow (JICF) for Engineering Applications: Thermal Uniformity in Gas-turbines and Cavitation Treatment in Hydro-turbines

Jet-in-cross-flow (JICF) is a well-known term in thermal flows field. Ranging from the normal phenomenon like the volcano ash and dust plumes to the designed film cooling and air fuel mixing for combustion, JICF is always studied to understand its nature at different conditions. Realizing the behavior of interacting flows and importance of many variables lead to the process of reiterating the shapes and running conditions for better outcomes or minimizing the losses. Summarizing the process under the name of optimization, two JICF applications are analyzed based on the principles of thermodynamics and fluid mechanics, then some redesigns are proposed to reach the optimal statuses for the goals sought. Correlations and recommendations are given between the input variables and the outputs. In the first application, annular thermal mixing chamber, the cold stream penetrates the axial hot flow as circumferential inward jets. Thermal uniformity of the exit mixture is the target to maximize, and accordingly, a streamlined body is firstly suggested to be placed at the center of the chamber to divert the hot stream towards the cold one. Following the idea, the shape and dimensions (length and maximum diameter) are tested experimentally with four 3-D printed bodies expressing different aspect, blockage, and profile ratios. Later, an Analysis LED Design stage (numerical then experimental) checked the effect of adding swirlers on the best streamlined shape. Swirlers shape, number, and height are examined for the relation with the uniformity and pressure drop. By defining a decision-making variable (useful efficiency), the two contradicting variables were consolidated into one, and the swirlers performance was easier to be quantified and the most efficient one was nominated. At the final stage, a numerical study searched the optimal design(s) using design of experiment and optimization (Global and Hybrid) algorithms. The study sought the optimality of the dimensional aspects (diameter, length, and position) of the swirling streamlined body based on minimizing the contradicting objectives. The results were represented by Pareto curve, correlation matrix, parallel axes, and response surface model. It was understood that the optimization can offer improvement of 68% and 15% to the uniformity number and the pressure drop respectively. On the other hand, aeration treatment for cavitating flow in axial Kaplan turbine was considered for the second engineering application. Using CFD models of a 7.5-cm hydro-turbine, cavitation situation was simulated, then air is injected from the housing to redistribute around the blades of the rotor. The value of the vapor fraction is tracked over the blades and the hub areas throughout the time of turbine cycles. Comparison is achieved by evaluating an average value for the vapor fraction at each case. Air mass flowrate and ports distribution are found to be effective in reducing the cavitation phenomena. Proposed linear aeration distributor on the housing presented a promising technology for spreading the air over the blade chord in a better way than the circumferential distribution. The study allowed the understanding of the flow behavior (in terms of air flow, liquid pressure, and cavitation formations) and turbine performance (i.e. mechanical power) at different air injection locations and turbine rotational speeds. A broader view of research investigated the functionality of linear aeration distributor on the hub with an air supply going through a hollow shaft. The invention of the hub air injection targets the marine industry (i.e. propellers) where the housing/shrouds do not exist, but it also can be a competitor to the housing air injection technology as well. For the two aeration approaches (housing and hub), the conducted numerical investigations were based on the vapor mitigation and power regain in the Kaplan turbine, meanwhile the experimentation looked for the vapor and motor power reduction for the propeller operation. A good agreement (qualitatively and quantitatively) was found between matching cases created for such purpose using tools for high-speed imaging, statistical analysis for turbulent flow, image processing and power measurements. Finally, the dissertation sets some recommendations for the continuation of the researches on the two applications (thermal uniformity and aeration treatments) for better jets interaction with the cross flow by the consideration of the addition/orientation of guide vanes and the relocation of the jets on the turbine blades respectively

A Comprehensive Survey of the Tactile Internet: State of the art and Research Directions

The Internet has made several giant leaps over the years, from a fixed to a mobile Internet, then to the Internet of Things, and now to a Tactile Internet. The Tactile Internet goes far beyond data, audio and video delivery over fixed and mobile networks, and even beyond allowing communication and collaboration among things. It is expected to enable haptic communication and allow skill set delivery over networks. Some examples of potential applications are tele-surgery, vehicle fleets, augmented reality and industrial process automation. Several papers already cover many of the Tactile Internet-related concepts and technologies, such as haptic codecs, applications, and supporting technologies. However, none of them offers a comprehensive survey of the Tactile Internet, including its architectures and algorithms. Furthermore, none of them provides a systematic and critical review of the existing solutions. To address these lacunae, we provide a comprehensive survey of the architectures and algorithms proposed to date for the Tactile Internet. In addition, we critically review them using a well-defined set of requirements and discuss some of the lessons learned as well as the most promising research directions

Computational Methods in Science and Engineering : Proceedings of the Workshop SimLabs@KIT, November 29 - 30, 2010, Karlsruhe, Germany

In this proceedings volume we provide a compilation of article contributions equally covering applications from different research fields and ranging from capacity up to capability computing. Besides classical computing aspects such as parallelization, the focus of these proceedings is on multi-scale approaches and methods for tackling algorithm and data complexity. Also practical aspects regarding the usage of the HPC infrastructure and available tools and software at the SCC are presented