With the state-of-the-art IC technology, we can share a variety of digital content stored in our mobile devices via wireless communications. When requests for digital content arrive, base stations have to search for at least one copy of the digital content. We extend the concurrent search approach to efficiently location digital content. In addition, we propose the opportunistic concurrent search scheme in which a base station could use a single channel to page a number of mobile stations simultaneously. We use computer simulations to evaluate the performance and justify the usage of the proposed schemes.

In this thesis, we focus on mobile networks consist of a single base station as the source transceiver, and multiple mobile stations as the receiving party. Applying energy management on multicasting between the base station and mobile stations, network users can conserve the energy consumed while wating for subscribing data contents to come. We referenced the SMBC-D (Scheduling over Multiple Broadcast Channels--the dynamic model) algorithm proposed by R. Cohen et al., grouping users with high request similarity, partitioning channels with a time-division duplexing scheme, and putting mobile stations into sleep mode during channels that include no subscribing data contents. Since SMBC-D statically schedules fixed size channels, groups request fewer data items will idle their channels after finishing their transmision, while groups request more data items take longer time to finish their transmission. For such problem, we propose a heuristic algorithm that makes use of these idle channels by combining adequate consecutive idle channels, to improve channel utility, and lower the overall energy consumed. We also process relevant computer simulations, verifying that our method has better performance.

Ο στόχος αυτής της διπλωματικής ήταν να μελετηθεί και να κατανοηθεί ο τρόπος λειτουργίας των WCDMA ασύρματων δικτύων καθώς και να υπολογιστεί η χωρητικότητα μιας κυψέλης κινητής τηλεφωνίας 3ης γενιάς. Αυτό επιτυγχάνεται μέσω του υπολογισμού των πιθανοτήτων απώλειας κλήσεων (CBP), στην κατερχόμενη ζεύξη (downlink). Δηλαδή στην περίπτωση που το σήμα αποστέλλεται από το σταθμό βάσης στον συνδρομητή. Ο υπολογισμός των πιθανοτήτων απώλειας κλήσεων είναι απαραίτητος στα WCDMA δίκτυα για τον σωστό υπολογισμό της χωρητικότητας (σε erlang) και του network dimensioning. Το αναλυτικό μοντέλο που χρησιμοποιούμαι λαμβάνει υπ’ όψιν του τα εξής: multi-service περιβάλλον, soft blocking, imperfect power control καθώς και την πολυόδευση. Τα αποτελέσματα του αναλυτικού μοντέλου συγκρίνονται μέσω προσομοίωσης και είναι αρκετά ικανοποιητικά. Τέλος εξετάζουμε και την επίδραση του orthogonality factor στην χωρητικότητα του δικτύου. / In WCDMA networks, the Call Blocking Probability (CBP) assessment is necessary for proper cell capacity determination, in respect of traffic load in erlangs, and network dimensioning. This paper focuses on the downlink capacity estimation, through CBP calculation in a WCDMA cell. To this end, we construct an analytical model for the WCDMA cell by taking into consideration the effects of the following: the multi-service environment, soft blocking, imperfect power control and multipath propagation. To analyze the system, we describe the WCDMA cell by a Markov chain, where each system state represents a certain number of resources occupied by the mobile users. We solve the Markov state and provide an efficient recurrent formula for the system occupancy distribution, as well as the so-called local blocking probabilities. Based on them, we calculate the CBP of different service-classes accommodated in the cell versus the total offered traffic load. The WCDMA cell capacity in erlangs is determined by the maximum traffic load which satisfies certain CBP (CBP boundary) per service-class. We evaluate the analytical model through simulation. The results show that the accuracy of the model is very satisfactory. In addition, we show the effect of the intra-cell interference (due to orthogonality factor) on the erlang capacity of the cell.

Στόχος της παρούσας διπλωματικής εργασίας είναι η μελέτη της μετάδοσης δεδομένων πάνω από Κινητά Δίκτυα 3ης Γενιάς και συγκεκριμένα του δικτύου UMTS (Universal Mobile Telecommunications Systems). Την τελευταία δεκαετία τόσο η Κυψελωτή Κινητή Τηλεφωνία όσο και το Διαδίκτυο έχουν γνωρίσει τρομακτική εξάπλωση παγκοσμίως. Η ανάγκη του ανθρώπου για κινητικότητα από τη μια, και η ανάγκη για πρόσβαση σε πληροφορία και υπηρεσίες από την άλλη, οδήγησε στη σύγκλιση των δυο παραπάνω «κόσμων» μέσα από τα Κινητά Δίκτυα 3ης Γενιάς. Το δίκτυο UMTS, οδηγείται προς τη φιλοσοφία ενός all-IP δικτύου, που επιτρέπει πρόσβαση υψηλών ταχυτήτων στο Διαδίκτυο. Στην παρούσα διπλωματική εργασία παρουσιάζεται αναλυτικά η αρχιτεκτονική και λειτουργική δομή του UMTS δίκτυο, ξεκινώντας από τα γενικά χαρακτηριστικά του, σε ότι αφορά το χρησιμοποιούμενο φάσμα, την αξιοποίηση του διατιθέμενου εύρους ζώνης και τη δομή των κυψελών του UMTS. Στη συνέχεια παρουσιάζεται η αρχιτεκτονική του δικτύου, με αναφορά στον εξοπλισμό του χρήστη, το Δίκτυο Επίγειας Ασύρματης Πρόσβασης (UTRAN) και το Δίκτυο Κορμού (Core Network), ενώ παρουσιάζονται και τα πρωτόκολλα σηματοδοσίας και επιπέδου χρήστη εντός του UMTS. Στη συνέχεια η εργασία ασχολείται με το θέμα της παροχής Ποιότητας Υπηρεσίας (Quality of Service – QoS) στο δίκτυο UMTS. Παρουσιάζονται οι τάξεις QoS και τα χαρακτηριστικά τους στο UMTS, και οι παράμετροι που αυτές παίρνουν για συγκεκριμένες υπηρεσίες (φωνή, video, εφαρμογές ροής πολυμέσων κτλ.). Παράλληλα με την Ποιότητα Υπηρεσίας, παρουσιάζεται και η υπηρεσία MBMS (Multimedia Broadcast / Multicast Service) που έχει σχεδιαστεί για το UMTS δίκτυο και αναλύεται η δομή και ο τρόπος υλοποίησης των λειτουργιών της, οι διαδικασίες υπηρεσιών MBMS, οι παράμετροι που αυτή παίρνει και γίνεται και ανάλυση των επιμέρους λειτουργιών της. Το δεύτερο μέρος της εργασίας αφορά την πειραματική αξιολόγηση του δικτύου UMTS στον εξομοιωτή ns-2, σε ότι αφορά τη μετάδοση διαφορετικών ειδών κίνησης και την αποτελεσματικότητα των διαφορετικών πρωτοκόλλων. Αρχικά περιγράφεται ο τρόπος παραγωγής κίνησης για τον εξομοιωτή και των μεθόδων που χρησιμοποιήθηκαν προς την κατεύθυνση αυτή. Στη συνέχεια παρουσιάζονται τα αποτελέσματα των πειραμάτων για την απόδοση του πρωτοκόλλου TCP πάνω από το δίκτυο UMTS, και παρουσιάζονται τα προβλήματα που προκύπτουν στη χρήση του πρωτοκόλλου αυτού, κυρίως λόγο του υψηλού bit error rate που παρουσιάζεται στο ασύρματο κανάλι. Μελετώνται σενάρια χρήσης που χρησιμοποιούν τόσο UMTS DCH (Dedicated Channels), όσο και HSDPA (High Speed Downlink Packet Access) μεταδόσεις. Με σκοπό τη μελέτη της μετάδοσης και πολυμεσικού περιεχομένου πάνω από το UMTS, έγιναν αντίστοιχα πειράματα στον εξομοιωτή και διαπιστώθηκε η δυνατότητα του UMTS να εγγυηθεί τις διαφορετικές απαιτήσεις αυτού του είδους κίνησης (κυρίως σε ότι αφορά την καθυστέρηση των πακέτων) και τη «φιλική» προς το TCP πρωτόκολλο συνύπαρξη στο δίκτυο. Τέλος, στη διπλωματική αυτή εργασία προτείνεται ένα σχήμα, για την ανάπτυξη ενός συστήματος μετάδοσης πολυμεσικού περιεχομένου πάνω από UMTS, το οποίο λαμβάνει υπόψη του την τρέχουσα κατάσταση του δικτύου και προσαρμόζει τη ροή των πολυμεσικών δεδομένων σε αυτή. / The purpose of this dissertation is to study data transmission using Third Generation (3G) Mobile Networks and in particular using the Universal Mobile Telecommunications Systems (UMTS) network. Over the last decade, Cellular Mobile Telephony and Internet have spread rapidly worldwide. The need for mobility on the one side and on the other side the need for access to information and services, led to the convergence of the two worlds using Third Generation Mobile Networks. The UMTS network is slowly becoming an all-IP network that allows high speed data Internet connection. This dissertation discusses the UMTS network’s architectural and functional framework starting from the general characteristics of the available bandwidth and the UMTS cells’ structure. The architectural design of the network is presented next with respect to the user’s equipment, the Universal Terrestrial Radio Access Network (UTRAN) and the Core Network, followed by the signaling protocol and the user level within UMTS. After that, the dissertation covers Quality of Service (QoS) issues while using the UMTS network. The two QoS groups are presented along with their UMTS characteristics, and certain parameters for specific services (such as voice, video, multimedia streaming applications, etc.). In addition, the Multimedia Broadcast/Multicast Service (MBMS) is discussed. MBMS is a service designed for the UMTS network and the procedure and services of its functionality are being analysed. The second part of this dissertation deals with the experimental evaluation of the UMTS network in the ns-2 simulator, regarding the transmission of different types of traffic and the efficiency of the different protocols. The method of the traffic generation is being discussed at first, along with the implemented modules. Following that, the results from the experiments on TCP protocol performance over the UMTS air interface are being presented and some issues that raise up due to the high bit error rate that occur in the wireless channel are being discussed. In this case, we study the performance of both UMTS Dedicated Channels (DCH) and the High Speed Downlink Packet Access) transmissions. In order to study the transmission of multimedia content over the UMTS, some experiments took place, and showed that UMTS is able of guaranteeing the different requirements of this type of traffic, especially regarding the packets’ time delays and the friendly behavior against the TCP protocol, when coexisting in the network traffic load. Finally, this dissertation proposes a scheme for developing a multimedia content transmission system over UMTS, which takes into consideration the current state of the network and adapts the multimedia data stream to these conditions.

Mobile devices are increasingly being relied on for computation intensive and/or communication intensive applications that go beyond simple connectivity and demand more complex processing. This has been made possible by two trends. First, mobile devices, such as smartphones and tablets, are increasingly capable devices with processing and storage capabilities that make significant step improvements with every generation. Second, many improved connectivity options (e.g., 3G, WiFi, Bluetooth) are also available to mobile devices. In the rich computing and communication environment, it is promising but also challenging for mobile devices to take advantage of various available resources to improve the performance of mobile applications. First, with varying connectivity, remote computing resources are not always accessible to mobile devices in a predictable way. Second, given the uncertainty of connectivity and computing resources, their contention will become severe. This thesis seeks to address the connectivity challenges for mobile computing and communication. We propose a set of techniques and systems that help mobile applications to better handle the varying network connectivity in the utilization of various computation and communication resources. This thesis makes the following contributions: We design and implement Serendipity to allow a mobile device to use other encountered, albeit intermittently, mobile devices to speedup the execution of parallel applications through carefully allocating computation tasks among intermittently connected mobile devices. We design and implement IC-Cloud to enable a group of mobile devices to efficiently use the cloud computing resources for computation offloading even when the connectivity is varying or intermittent. We design and implement COSMOS to provide scalable computation offloading service to mobile devices at low cost by efficiently managing and allocating cloud computing resources. We design and implement CoAST to allow collaborative application-aware scheduling of mobile traffic to reduce the contention for bandwidth among communication-intensive applications without affecting their user experience.

[pt] Este trabalho apresenta um modelo de tarifação dinâmica cujo objetivo é determinar qual o preço que deve ser cobrado por uma chamada telefônica, originada em uma estação móvel, de forma a maximizar a receita da empresa operadora do serviço móvel celular, garantindo os valores máximos aceitáveis para a probabilidade de bloqueio de uma chamada e para a probabilidade de queda de ligações devido ao handoff. / [en] This work presents a dynamic pricing model whose objective is to determinate the price that should be charged for a telephone call originated in a mobile phone in order to maximize the telephone enterprise revenue as long as it guarantees the maximum acceptable values for the probability of blocking of originating calls and for calls that are requesting a handoff. / [es] Este trabajo presenta un modelo de tarifación dinámica cuyo objetivo es determinar cuál es el precio que deve ser cobrado por una llamada telefónica, originada en una estación móvil, de tal forma que maximize la receta de la empresa operadora del servicio móvil celular, garantizando los valores máximos aceptables para la probabilidad de bloqueo de una llamada y para la probabilidad de caída de conexión debido al handoff.

With the development of mobile networks, customer needs and behaviourshave changed. Mobile communications means so much more than simplevoice communication; there is now mobile Internet with web surfing, videophone,streaming media, and micro blogging. The objective of network optimizationhas gradually shifted from enhancing network performance to improvequality of experience (QoE). Therefore, assessing and optimizing QoEis the trend for optimizing future mobile networks. Today, users want reliable access for their content, wherever they go inthe network. To deliver the best possible experience to mobile broadbandsubscribers, operators need new ways to assess performance that will enablethem to build and manage their networks in the most efficient way. The newparadigmatic eco system (user-interface-network-content) requires novel anddisruptive end-to-end considerations in order to enable and sustain the nextgeneration of services and user experience. Thus, the extraordinary adoptionof mobile connectivity by end users, and the need for optimized bandwidthmanagement network resource, on the one hand, and the growing interest forgood quality content delivery/consumption, is boosting the creation of newnetwork solutions. We consider that by taking advantage of the capacity to support multimedia platforms and applications of mobile devices (e.g. smartphones, tablets,etc.) is possible to incorporate and provide awareness to the wireless infrastructuresin the context of cross-layer systems to manage the resource allocationaccording to expected QoE levels. In this thesis, we address the questionon how to implement QoE-aware mobile networks and evaluate differentschedulers oriented to take advantage of the proposed architecture. We showthat by providing QoE-awareness to the network infrastructure is possible toimprove user’s QoE and generate impacts in the utilization of the networkresources. With this study, we provide insights into the broader question ofwhether future mobile infrastructures can be deployed considering QoE besidesthe classical QoS considerations. / <p>QC 20140521</p>

The flexibility of future mobile networks exploiting modern technologies such as cloud-optimized radio access and software-defined networks opens a gateway to deploying dynamic strategies for live and on-demand content delivery. Traditional live broadcasting systems are spectral inefficient. It takes up a lot more radio spectrum than that of mobile networks, to cover the same size of an area. Furthermore, content caching at base stations reduces network traffic in core networks. However, numerous duplicated copies of contents are still transmitted in the unicast fashion in radio access networks. It consumes valuable radio spectrum and unnecessary energy. Finally, due to the present of numerous mobile receivers with a wide diversity of wireless channels in a base station coverage area, it is a challenge to select a proper modulation scheme for video broadcasting to optimize the quality of services for users. In this thesis, the challenges and the problems in the current strategies for content delivery are addressed. A holistic novel solution is proposed that considers user preferences, user mobility, device-to-device communication, physical-layer resource allocation, and video quality prediction. First, a system-level scheduling framework is introduced to increase the spectral efficiency on broadcasting live contents onto mobile networks. It considers the audience preferences for allocating radio resources spatially and temporally. Second, to reduce the redundant transmissions in radio access networks, a content distribution system that exploits user mobility is proposed that utilizes the urban-scale user mobility and broadcasting nature of wireless communication for delay-tolerant large size content. Third, to further reduce the energy consumption in network infrastructure, a content distribution system that relies on both user mobility, and device-to-device communication is proposed. It leverages the mobile users as content carriers to offload the heavy mobile traffic from network-level onto device-level. Fourth, to mitigate the multi-user channel diversity problem, a cross-layer approach is deployed to increase the video quality for users especially for those who have a low signal-to-noise ratio signal. Finally, data mining techniques are employed to predict video qualities of wireless transmissions over mobile networks. The holistic solution has been empirically developed and evaluated. It achieves high spectral and energy efficiency and mitigates the video quality degradation in mobile networks.

Magister Legum - LLM / This paper analyses how the Zimbabwean economic history has led to the perception and attitude of the population towards the financial industry. It has been blighted by extremes to the extent that in 2008 the Zimbabwe economy had one of the highest hyperinflation rate in the world. Pettinger sums up the hyperinflation journey of Zimbabwe as having begun in the 1990s shortly after the disastrous land reform. This is where private farms were grabbed from landowners and re-allocated to mostly peasant farmers who had no technical know-how in farming. It was also a time when the country was involved in an unbudgeted and unsolicited second Congo civil war necessitating that the Government increase salaries to cater for soldiers and other officials assigned to the Congo. Earlier on the government had buckled under pressure from former war liberators (war veterans) and paid out unbudgeted bonuses.

As the mobile communication world expands in size and complexity, the need for testing the solutions in a controlled environment before deployment is as pronounced as ever. Simultaneously, new tools and products are developed to optimize the process and reduce costs. One tool that allows for testing the system under varying network conditions during development is a network emulator, which lies in between a classic network simulator and real-world network testing, providing high flexibility and repeatability in experiments and is expected to behave closer to a real-world network than a network simulator would. One established network emulator is the Itrinegy Network Emulator (INE). This paid product comes with a physical device and a software GUI and has been on the market for almost two decades. On the other end of the network emulation spectrum, the Znail Network Emulator is found: an open-source software-based network emulator designed to run on a single-board computer (e.g., a Raspberry Pi), which has been developed in the last five years in a nonenterprise-manner. In this thesis, these two network emulators are evaluated and compared against each other, aiming to investigate what functionality they offer and evaluate their emulation accuracy level. To do this, a testbed is set up to perform experiments by sending network traffic from a client to a server. The network emulator is placed between the hosts, acting as a bridge and applying different network conditions to the passing network traffic. The functionality comparison demonstrates that Znail offers minimal configuration options compared to the INE: only the most basic network conditions can be achieved with Znail. The results from the testbed experiments show that both emulators perform well when only one network parameter is applied at a time. However, when using more complex configurations with combinations of multiple network parameters, INE is overall superior in accuracy and stability, and Znail is deficient in several sectors. Although, the results also show that INE has some frailties in achieving correct emulation accuracy when combined with low bandwidth levels. Through the emulator functionality comparison and accuracy evaluation, this thesis argues that Znail can be a good choice of emulator in smaller establishments and for the at-home developer, while the INE is a better choice for larger organizations where stability and reliability are crucial.