Paging and Registration in Cellular Networks: Jointly Optimal Policies and an Iterative Algorithm

This paper explores optimization of paging and registration policies in cellular networks. Motion is modeled as a discrete-time Markov process, and minimization of the discounted, infinite-horizon average cost is addressed. The structure of jointly optimal paging and registration policies is investigated through the use of dynamic programming for partially observed Markov processes. It is shown that there exist policies with a certain simple form that are jointly optimal, though the dynamic programming approach does not directly provide an efficient method to find the policies. An iterative algorithm for policies with the simple form is proposed and investigated. The algorithm alternates between paging policy optimization and registration policy optimization. It finds a pair of individually optimal policies, but an example is given showing that the policies need not be jointly optimal. Majorization theory and Riesz's rearrangement inequality are used to show that jointly optimal paging and registration policies are given for symmetric or Gaussian random walk models by the nearest-location-first paging policy and distance threshold registration policies.Comment: 13 pages, submitted to IEEE Trans. Information Theor

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Carrier frequency offset recovery for zero-IF OFDM receivers

As trends in broadband wireless communications applications demand faster development cycles, smaller sizes, lower costs, and ever increasing data rates, engineers continually seek new ways to harness evolving technology. The zero intermediate frequency receiver architecture has now become popular as it has both economic and size advantages over the traditional superheterodyne architecture. Orthogonal Frequency Division Multiplexing (OFDM) is a popular multi-carrier modulation technique with the ability to provide high data rates over echo ladened channels. It has excellent robustness to impairments caused by multipath, which includes frequency selective fading. Unfortunately, OFDM is very sensitive to the carrier frequency offset (CFO) that is introduced by the downconversion process. The objective of this thesis is to develop and to analyze an algorithm for blind CFO recovery suitable for use with a practical zero-Intermediate Frequency (zero-IF) OFDM telecommunications system. A blind CFO recovery algorithm based upon characteristics of the received signal's power spectrum is proposed. The algorithm's error performance is mathematically analyzed, and the theoretical results are verified with simulations. Simulation shows that the performance of the proposed algorithm agrees with the mathematical analysis. A number of other CFO recovery techniques are compared to the proposed algorithm. The proposed algorithm performs well in comparison and does not suffer from many of the disadvantages of existing blind CFO recovery techniques. Most notably, its performance is not significantly degraded by noisy, frequency selective channels

Microbial Community Characterization and Pathogen Analysis Within Constructed Wetlands of Varying Scale Designed for Contaminant Removal

Constructed wetlands (CWs) are complex treatment environments, requiring an integrative research approach to improve our understanding of them. The goal of this thesis was to establish an understanding of the functional and structural characteristics of microbial communities within bench-, field- and industrial-scale environmental treatment systems. The impact of pathogenic and/or antibiotic contaminants on these communities based on their functional and structural profiles using community-level physiological profiling (CLPP) and denaturing-gradient gel electrophoresis (DGGE), respectively, was investigated. Under normal operation, bench-, field- and industrial-scale treatment systems were able to produce similarly behaving structural and functional profiles. Increased retention time was consistently associated with communities with low functional capacity and diverse structural properties when compared to areas that initially received pre-treated or untreated wastewater. This indicates that smaller-scale treatment systems may be able to provide similar environments to those in larger-scale treatment systems. However, the normal community profile was not maintained during antibiotic treatment. Based on the metrics used, functional fingerprints displayed metabolic increases after acute addition of antibiotic, which was then followed by a return to preexposure profiles. Conversely, structural fingerprints displayed no acute response, but instead alluded to delayed changes in the proportional abundance of different populations. In addition, the profile was reversed following exposure to untreated industrial wastewater, whereby an increased functional capacity and lowered structural properties were observed. These findings illustrate the dynamic and complex nature of microbial communities in response to selected environmental contaminants

Authenticity and Ephemerality: The Memes of Transcultural Production in Italian Diasporic Culture

This dissertation seeks to contribute a new model for the observation, interpretation, and analysis of Italian and American cultures utilising a semiotic-memetic grammar for analysing and interpreting culture as it transforms and disseminates through time and space. Semioticians, linguists, philosophers, historians, and cultural theorists have written on culture and its relation to language, ethnicity, and identity perception. However, the mechanism for the arrival to specific loci is often overlooked. For the purposes of this study, the cultural systems in question are diasporic Italian manifested in the form of the Italian Americans operating in the periphery (USA) and peninsular/insular Italians operating in the centre (Italy). This dissertation addresses the question of how meaning is constructed, maintained, and propagated in the periphery by diasporic peoples with general inferences on both Italian Diasporic culture in the United States, and specifically a cohort of Americans of Italian, mixed Italian descent that reside in Mahoning Valley in the state of Ohio, USA. I argue that using signs that arrived via memes i.e., non-biologically spread cultural data to the United States through migratory flows, American Italians have the ability to semiotically interpret Italian signs thereby maintaining an authentic and ephemeral connection to Italy while in the periphery. In the present study, signs found in the peripheries of Italy as centre that work in unison to create meaning or Memetic Codes Clusters have been identified and defined as interpretable and communicable cultural value systems. They are examples of multimodal structures operating as memes outside of an origination point connecting and maintaining perception to a core culture: cultures that have historically exerted influence due to hegemony, mass communication, and popular appeal. Multiple examples from a selection of targeted audiovisual and literary texts have been correlated with the aforementioned clusters serving as aesthetic markers. Preliminary findings suggest there are discernible semiotic attributes contained in both samples that illustrate the fecundity and hybridisation of Italian culture in the periphery. Keywords: culture, diaspora, Italian America, memes, semiotic

Redefinition of stack efficiency and optimization of stack performance for PEMFCs

In the first part of this work, we present a general redefinition of the PEMFC stack efficiency taking into account all power losses directly connected with the stack performance and the applied stack operating conditions. These are the stack fuel loss, the stack polarization- and reaction entropy- and enthalpy losses, and the theoretical losses for stack feed stream conditioning. In general, the latter includes humidification and pressurization (or pumping) of the reactants as well as pumping of the coolant. Furthermore, examples will be given which power losses are relevant for different applications and which are dominant and have to be considered. By the use of this new figure of merit, the efficiencies of two stacks can be compared to each other in a system-relevant way and can be determined for a given application scenario. In addition, the accompanying redefined balance-of-plant efficiency is a parameter characterizing uniquely the effectiveness of the BoP design and of the BoP components. In the second part of this work, a procedure for the optimization of the PEMFC stack performance will be highlighted. The performance of a stack at a given constant load strongly depends on the operating conditions characterized by 7 parameters. These are the stack temperature, the stoichiometric values of the reactants, the relative humidity of the reactants, and the pressures in both compartments of the stack. The effect of these parameters on the stack performance is non-linear and synergistic. A separate optimization of each single parameter is not meaningful. Therefore, a direct-search algorithm, the Nelder-Mead simplex, was used for the simultaneous optimization of all parameters

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Development and Characterization of a LT-PEMFC Stack with an Extended Operating Temperature Range up to 120 °C

Nowadays, the operation temperature of a polymer electrolyte fuel cell (PEFC) stack for automotive application is about 80 °C. The presented work concerns the characterization of a 30-cell PEFC stack (2.5 kWel) developed at the German Aerospace Center, designed for operating temperatures up to 120 °C for a limited time span. Short-term operation of the stack at higher temperatures would contribute to the improvement of cooling system components with scaled-down dimensions. This concept helps to reduce the vehicle weight and thus to save fuel. In this contribution we present a proof-of-concept of the feasibility of short-term operation for excess temperature events. For this purpose, the stack behaviour was investigated through a series of 20 temperature cycles from 90 to 120 °C at galvanostatic conditions of 70 A (approx. 0.5 A·cm–2 and 1.5 kWel) and without adaption of the gas dew points. The stack power decreased by 21 ± 1 %, with a fully reversible performance recovery at the end of every thermal cycle (see Fig. 1). The higher irreversible degradation rate under these harsh conditions was attributed to the enhanced mechanical stress, which is also correlated to the cycling of the membrane humidity. Furthermore, the results of a long-term steady-state test of 1200 hours under automotive relevant conditions at 80 °C are presented. An end-of-life characterization of the individual cells helped to identify possible causes for performance losses due to catalyst, electrode and membrane degradation. A reduction of electrochemically active surface areas in some cells was ascribed to a platinum catalyst particle growth. Membrane degradation and carbon corrosion occurred additionally, evidenced by increased high frequency resistances and hydrogen crossover rates of the membranes. As result of carbon corrosion, the hydrophobicity of the carbon-based components decreased, causing water accumulation in individual cells