[pt] O desempenho de sistemas de comunicações modernos que utilizam técnicas de modulação multiportadora como, por exemplo, o OFDM (Orthogonal frequency division multiplexing), é altamente sensível às distorções não lineares geradas principalmente por amplificadores de alta potência (HPAs). De modo a caracterizar completamente estas distorções, os efeitos de memória destes dispositivos têm que ser considerados. Estes efeitos tornam-se mais importantes à medida que a largura de banda do sinal aumenta. Por outro lado, o aumento na duração do símbolo dos sistemas multiportadora torna-o mais sensível às variações de tempo dos canais móveis. Em particular o efeito doppler tende a prejudicar a ortogonalidade entre as sub-portadoras, gerando interferências entre sub-portadoras (Inter-Carrier Interference - ICI). Assim, torna-se importante o estudo dos efeitos de não-linearidades e canais variantes no tempo em sistemas OFDM, principalmente em sistemas de comunicações móveis. Os trabalhos atualmente disponíveis na literatura se limitam a avaliar os efeitos de não linearidades invariantes no tempo ou o efeito de canais lineares variantes no tempo. Assim, no presente trabalho são desenvolvidas expressões matemáticas que permitem avaliar o efeito conjunto de não-linearidades e canais variantes no tempo sobre sinais OFDM. A investigação deste efeito é realizada em dois níveis: efeito sobre o espectro do sinal OFDM e efeito sobre o desempenho do sistema. As expressões analíticas obtidas para ambos os níveis de investigação consideraram a modelagem do canal não-linear variante no tempo por uma Série de Volterra. Resultados numéricos que avaliam o espalhamento espectral e o impacto sobre a taxa de erro de bits em situações específicas são apresentados. / [en] The performance of modern communications systems that use multicarrier modulation techniques such as, for example, OFDM(Orthogonal frequency division multiplexing), is highly sensitive to nonlinear distortions generated mainly by high power amplifiers (HPAs). In order to fully characterize these distortions, the memory effects of these devices must be considered. These effects become more important as the signal bandwidth increases. On the other hand, the increase in symbol duration makes multicarriers systems more sensitive to time variations as those in mobile channels. In particular, the Doppler effect tends to impair the orthogonality between sub-carriers, resulting in inter-carrier interference (ICI). Therefore, the study of the effects of nonlinearities and time-varying channels on OFDM systems performance becomes important, mainly in mobile communications systems. The studies currently available in the literature are limited to evaluating the effects of time invariant non-linearities or the effects of linear time varying channels. In this work, mathematical expressions are developed to evaluate the joint effect of nonlinearities and time-varying channels on OFDM systems. The investigation of these effects is performed at two levels: the effect on the spectrum of OFDM signal and effect on the system s performance. In deriving the analytical expressions related to both levels of investigation the time-varying non-linear channel was modeled by a Volterra Series. Numerical results, obtained for specific situations, illustrate the resulting impact on the OFDM spectrum (spreading) and on the system s bit error rate performance.

Diploma thesis is focused on an analysis of radio conditions of indoor LTE-A mobile networks. Measurements of the Huawei LTE-A radio access network were performed using the R&S TSMW spectral analyser. Results have been processed and discussed. The practical part of diploma thesis also consists of a development of a program for processing the data sets obtained from R&S TSMW spectral analyzer.

The fifth generation (5G) of mobile communication networks is envisioned to enable a variety of novel applications. These applications demand requirements from the network, which are diverse and challenging. Consequently, the mobile network has to be not only capable to meet the demands of one of these applications, but also be flexible enough that it can be tailored to different needs of various services. Among these new applications, there are use cases that require low latency as well as an ultra-high reliability, e.g., to ensure unobstructed production in factory automation or road safety for (autonomous) transportation. In these domains, the requirements are crucial, since violating them may lead to financial or even human damage. Hence, an ultra-low probability of failure is necessary. Based on this, two major questions arise that are the motivation for this thesis. First, how can ultra-low failure probabilities be evaluated, since experiments or simulations would require a tremendous number of runs and, thus, turn out to be infeasible. Second, given a network that can be configured differently for different applications through the concept of network slicing, which performance can be expected by different parameters and what is their optimal choice, particularly in the presence of other applications. In this thesis, both questions shall be answered by appropriate mathematical modeling of the radio interface and the radio access network. Thereby the aim is to find the distribution of the (end-to-end) latency, allowing to extract stochastic measures such as the mean, the variance, but also ultra-high percentiles at the distribution tail. The percentile analysis eventually leads to the desired evaluation of worst-case scenarios at ultra-low probabilities. Therefore, the mathematical tool of queuing theory is utilized to study video streaming performance and one or multiple (low-latency) applications. One of the key contributions is the development of a numeric algorithm to obtain the latency of general queuing systems for homogeneous as well as for prioritized heterogeneous traffic. This provides the foundation for analyzing and improving end-to-end latency for applications with known traffic distributions in arbitrary network topologies and consisting of one or multiple network slices. / Es wird erwartet, dass die fünfte Mobilfunkgeneration (5G) eine Reihe neuartiger Anwendungen ermöglichen wird. Allerdings stellen diese Anwendungen sowohl sehr unterschiedliche als auch überaus herausfordernde Anforderungen an das Netzwerk. Folglich muss das mobile Netz nicht nur die Voraussetzungen einer einzelnen Anwendungen erfüllen, sondern auch flexibel genug sein, um an die Vorgaben unterschiedlicher Dienste angepasst werden zu können. Ein Teil der neuen Anwendungen erfordert hochzuverlässige Kommunikation mit niedriger Latenz, um beispielsweise unterbrechungsfreie Produktion in der Fabrikautomatisierung oder Sicherheit im (autonomen) Straßenverkehr zu gewährleisten. In diesen Bereichen ist die Erfüllung der gestellten Anforderungen besonders kritisch, da eine Verletzung finanzielle oder sogar personelle Schäden nach sich ziehen könnte. Eine extrem niedrige Ausfallwahrscheinlichkeit ist daher von größter Wichtigkeit. Daraus ergeben sich zwei wesentliche Fragestellungen, welche diese Arbeit motivieren. Erstens, wie können extrem niedrige Ausfallwahrscheinlichkeiten evaluiert werden. Ihr Nachweis durch Experimente oder Simulationen würde eine extrem große Anzahl an Durchläufen benötigen und sich daher als nicht realisierbar herausstellen. Zweitens, welche Performanz ist für ein gegebenes Netzwerk durch unterschiedliche Konfigurationen zu erwarten und wie kann die optimale Konfiguration gewählt werden. Diese Frage ist insbesondere dann interessant, wenn mehrere Anwendungen gleichzeitig bedient werden und durch sogenanntes Slicing für jeden Dienst unterschiedliche Konfigurationen möglich sind. In dieser Arbeit werden beide Fragen durch geeignete mathematische Modellierung der Funkschnittstelle sowie des Funkzugangsnetzes (Radio Access Network) adressiert. Mithilfe der Warteschlangentheorie soll die stochastische Verteilung der (Ende-zu-Ende-) Latenz bestimmt werden. Dies liefert unterschiedliche stochastische Metriken, wie den Erwartungswert, die Varianz und insbesondere extrem hohe Perzentile am oberen Rand der Verteilung. Letztere geben schließlich Aufschluss über die gesuchten schlimmsten Fälle, die mit sehr geringer Wahrscheinlichkeit eintreten können. In der Arbeit werden Videostreaming und ein oder mehrere niedriglatente Anwendungen untersucht. Zu den wichtigsten Beiträgen zählt dabei die Entwicklung einer numerischen Methode, um die Latenz in allgemeinen Warteschlangensystemen für homogenen sowie für priorisierten heterogenen Datenverkehr zu bestimmen. Dies legt die Grundlage für die Analyse und Verbesserung von Ende-zu-Ende-Latenz für Anwendungen mit bekannten Verkehrsverteilungen in beliebigen Netzwerktopologien mit ein oder mehreren Slices.

When considering the addition of a mobile presentation channel to an existing web-based application, a key question that has to be answered even before development begins is how the mobile channel's characteristics will impact the user experience and the cost of using the application. If either of these factors is outside acceptable limits, economical considerations may forbid adding the channels, even if it would be feasible from a purely technical perspective. Both of these factors depend considerably on two metrics: The time required to transmit data over the mobile network, and the volume transmitted. The PETTICOAT method presented in this paper uses the dialog flow model and web server log files of an existing application to identify typical interaction sequences and to compile volume statistics, which are then run through a tool that simulates the volume and time that would be incurred by executing the interaction sequences on a mobile channel. From the simulated volume and time data, we can then calculate the cost of accessing the application on a mobile channel, and derive suitable approaches for optimizing cost and response times.

When considering the addition of a mobile presentation channel to an existing web-based application, a key question that has to be answered even before development begins is how the mobile channel’s characteristics will impact the user experience and the cost of using the application. If either of these factors is outside acceptable limits, economical considerations may forbid adding the channels, even if it would be feasible from a purely technical perspective. Both of these factors depend considerably on two metrics: The time required to transmit data over the mobile network, and the volume transmitted. The PETTICOAT method presented in this paper uses the dialog flow model and web server log files of an existing application to identify typical interaction sequences and to compile volume statistics, which are then run through a tool that simulates the volume and time that would be incurred by executing the interaction sequences on a mobile channel. From the simulated volume and time data, we can then calculate the cost of accessing the application on a mobile channel.

In this paper we introduce an analysis framework for mobile workforce automation. The framework is based on the findings from earlier research as well as on an analysis of 27 recent case studies conducted within the field of mobile workforce automation. It consists of a general reference process for mobile work and of a model explaining influencing factors (worker, task, coordination system, information system), optimization goals and their relationships in mobile business processes. The framework can be applied to process modeling, simulation, and optimization as well as to requirements analysis and return on investment calculations. Based on the results of case study evaluation, it is furthermore shown, that recent mobile IT solutions are mainly built for relatively simple processes and cooperation models. Mobilizing more complex processes still seems to be a challenge.

The Southern African Development Community (SADC) experiences high levels of cross border human traffic due to trade, cultural and language links across the fifteen countries. Technological advances and increased domestic competition have contributed to lower domestic retail tariffs for mobile cellular services. Unfortunately, this has not extended to international mobile roaming (IMR) retail tariffs which remain unacceptably high. These high tariffs have attracted harsh criticism from commentators and prompted calls for regulatory intervention. This study investigates the level of international mobile roaming (IMR) retail tariffs, usage and demand elasticity. It further considers whether competition or regulation play a greater role in reducing these tariffs and whether regulatory intervention is likely to reduce competition. The research took the form of a quantitative study and used an online survey questionnaire as the data collection tool. The results of the study confirmed that international mobile roaming (IMR) retail tariffs are indeed high, resulting in poor uptake by cost conscious travellers who pay for their own cellular usage. The finding that competition plays a greater role than regulation in reducing IMR retail tariffs is not significant. It was concluded that neither competition nor regulation are sufficient on their own to provide increased social welfare. The best result is obtained when competition is allowed to flourish, underpinned by an enabling regulatory framework. Copyright / Dissertation (MBA)--University of Pretoria, 2010. / Gordon Institute of Business Science (GIBS) / unrestricted

No description available.

"This thesis addresses important challenges in the areas of streaming and spatio-temporal databases. It focuses on continuous querying of spatio-temporal environments characterized by (1) a large number of moving and stationary objects and queries; (2) need for near real-time results; (3) limited memory and cpu resources; and (4) different accuracy requirements. The first part of the thesis studies the problem of performance vs. accuracy tradeoff using different location modelling techniques when processing continuous spatio-temporal range queries on moving objects. Two models for modeling the movement, namely: continuous and discrete models are described. This thesis introduces an accuracy comparison model to estimate the quality of the answers returned by each of the models. Experimental evaluations show the effectiveness of each model given certain characteristics of spatio-temporal environment (e.g., varying speed, location update frequency). The second part of the thesis introduces SCUBA, a Scalable Cluster Based Algorithm for evaluating a large set of continuous queries over spatio-temporal data streams. Unlike the commonly used static grid indices, the key idea of SCUBA is to group moving objects and queries based on common dynamic properties (e.g., speed, destination, and road network location) at run-time into moving clusters. This results in improvement in performance which facilitate scalability. SCUBA exploits shared cluster-based execution consisting of two phases. In phase I, the evaluation of a set of spatio-temporal queries is abstracted as a spatial join between moving clusters for cluster-based filtering of true negatives. There after, in phase II, a fine-grained join process is executed for all pairs identified as potentially joinable by a positive cluster-join match in phase I. If the clusters don’t satisfy the join predicate, the objects and queries that belong to those clusters can be savely discarded as being guaranteed to not join individually either. This provides processing cost savings. Another advantage of SCUBA is that moving cluster-driven load shedding is facilitated. A moving cluster (or its subset, called nucleus)approximates the locations of its members. As a consequence relatively accurate answers can be produced using solely the abstracted cluster location information in place of precise object-by-object matches, resulting in savings in memory and improvement in processing time. A theoretical analysis of SCUBA is presented with respect to the memory requirements, number of join comparisons and I/O costs. Experimental evaluations on real datasets demonstrate that SCUBA achieves a substantial improvement when executing continuous queries on highly dense moving objects. The experiments are conducted in a real data streaming system (CAPE) developed at WPI on real datasets generated by the Network-Based Moving Objects Generator."

The world of information technology and communications is in a stage of continuous improvement. These new developments are accompanied by a very rapid data traffic growth, particularly for mobile wireless networks. An important effect is the increase of the consumed energy by the network, particularly the radio access section, i.e. the base station systems. This latter issue causes that operational costs associated to energy consumption become more significant for telecommunication operators. In addition to the question of the availability of energy, this problem has an ecological aspect, due to the CO2 emissions associated with the operation of the network but also an issue related to public health given the effects of electromagnetic radiation from wireless transmission. For these reasons, great research efforts in the so-called field of Green Radio are being done in the recent years. The aim of this thesis consisted of finding ways to reduce the energy consumption in wireless and mobile networks respecting the QoS levels assigned to users. After a study of the state of the art analysing the possible approaches, we proposed a set of energy efficient techniques supported on the cell breathing and hybrid cellular networks (macro/femtocells). Our proposed decision making mechanisms include distributed strategies and other features such as the use of a novel multimetric approach. In our work, we also take into account the energy consumption of mobile devices, an issue that to the best of our knowledge was not quite analysed so far. The use of renewable energy sources is also considered into our proposals. Our thesis work includes the study of the consequences of our radio resource management algorithms on the electromagnetic radiation taking into account the acceptable EM exposure thresholds. In the perspectives of future work, we can mention the improvement of our techniques with learning mechanisms and cognitive radio.