When a large number of base stations fail due to the breakdown of some transmission circuit in a mobile cellular network, base stations located in neighboring areas may take over those malfunctioned base stations and continue to provide the access service of mobile communications for users in surrounding areas, thereby reducing the area in which mobile communications are out of service. Therefore, if leased circuits in base stations could complete the route distribution configuration prior to the onset of malfunction, it could decrease the impact of circuit breakdown and traffic loss. Also, the efficiency would be improved if the circuit assignment personnel could complete the job when the leased lines are less, while avoiding reassignment in the future and enhancing the mobile communications operations. In this study, we use a graph structure to represent the present mobile cellular network and establish the route-selection strategies. We define the "Optimal Route Assignment" for a newly constructed base station, which refers to the route assignment that causes least impact on disconnection area when any circuit in the network is broken. We also propose to use A* algorithm for optimal route assignment. However, the computation for the optimal route is time consuming. Measures such as computation time and least hops are considered in designing other strategies for route assignment. These strategies are parametric and we carried out experiments by adjusting and controlling parameters using real routing data. The experimental results demonstrate that there is no single winner among the proposed strategies. We identify a number of best strategies for different operating regions.

Cette thèse porte sur le paradigme « Mobile Edge cloud» qui rapproche le cloud des utilisateurs mobiles et qui déploie une architecture de clouds locaux dans les terminaisons du réseau. Les utilisateurs mobiles peuvent désormais décharger leurs tâches de calcul pour qu’elles soient exécutées par les femto-cellules (FCs) dotées de capacités de calcul et de stockage. Nous proposons ainsi un concept de regroupement de FCs dans des clusters de calculs qui participeront aux calculs des tâches déchargées. A cet effet, nous proposons, dans un premier temps, un algorithme de décision de déportation de tâches vers le cloud, nommé SM-POD. Cet algorithme prend en compte les caractéristiques des tâches de calculs, des ressources de l’équipement mobile, et de la qualité des liens de transmission. SM-POD consiste en une série de classifications successives aboutissant à une décision de calcul local, ou de déportation de l’exécution dans le cloud.Dans un deuxième temps, nous abordons le problème de formation de clusters de calcul à mono-utilisateur et à utilisateurs multiples. Nous formulons le problème d’optimisation relatif qui considère l’allocation conjointe des ressources de calculs et de communication, et la distribution de la charge de calcul sur les FCs participant au cluster. Nous proposons également une stratégie d’éparpillement, dans laquelle l’efficacité énergétique du système est améliorée au prix de la latence de calcul. Dans le cas d’utilisateurs multiples, le problème d’optimisation d’allocation conjointe de ressources n’est pas convexe. Afin de le résoudre, nous proposons une reformulation convexe du problème équivalente à la première puis nous proposons deux algorithmes heuristiques dans le but d’avoir un algorithme de formation de cluster à complexité réduite. L’idée principale du premier est l’ordonnancement des tâches de calculs sur les FCs qui les reçoivent. Les ressources de calculs sont ainsi allouées localement au niveau de la FC. Les tâches ne pouvant pas être exécutées sont, quant à elles, envoyées à une unité de contrôle (SCM) responsable de la formation des clusters de calculs et de leur exécution. Le second algorithme proposé est itératif et consiste en une formation de cluster au niveau des FCs ne tenant pas compte de la présence d’autres demandes de calculs dans le réseau. Les propositions de cluster sont envoyées au SCM qui évalue la distribution des charges sur les différentes FCs. Le SCM signale tout abus de charges pour que les FCs redistribuent leur excès dans des cellules moins chargées.Dans la dernière partie de la thèse, nous proposons un nouveau concept de mise en cache des calculs dans l’Edge cloud. Afin de réduire la latence et la consommation énergétique des clusters de calculs, nous proposons la mise en cache de calculs populaires pour empêcher leur réexécution. Ici, notre contribution est double : d’abord, nous proposons un algorithme de mise en cache basé, non seulement sur la popularité des tâches de calculs, mais aussi sur les tailles et les capacités de calculs demandés, et la connectivité des FCs dans le réseau. L’algorithme proposé identifie les tâches aboutissant à des économies d’énergie et de temps plus importantes lorsqu’elles sont téléchargées d’un cache au lieu d’être recalculées. Nous proposons ensuite d’exploiter la relation entre la popularité des tâches et la probabilité de leur mise en cache, pour localiser les emplacements potentiels de leurs copies. La méthode proposée est basée sur ces emplacements, et permet de former des clusters de recherche de taille réduite tout en garantissant de retrouver une copie en cache. / Mobile Edge Cloud brings the cloud closer to mobile users by moving the cloud computational efforts from the internet to the mobile edge. We adopt a local mobile edge cloud computing architecture, where small cells are empowered with computational and storage capacities. Mobile users’ offloaded computational tasks are executed at the cloud-enabled small cells. We propose the concept of small cells clustering for mobile edge computing, where small cells cooperate in order to execute offloaded computational tasks. A first contribution of this thesis is the design of a multi-parameter computation offloading decision algorithm, SM-POD. The proposed algorithm consists of a series of low complexity successive and nested classifications of computational tasks at the mobile side, leading to local computation, or offloading to the cloud. To reach the offloading decision, SM-POD jointly considers computational tasks, handsets, and communication channel parameters. In the second part of this thesis, we tackle the problem of small cell clusters set up for mobile edge cloud computing for both single-user and multi-user cases. The clustering problem is formulated as an optimization that jointly optimizes the computational and communication resource allocation, and the computational load distribution on the small cells participating in the computation cluster. We propose a cluster sparsification strategy, where we trade cluster latency for higher system energy efficiency. In the multi-user case, the optimization problem is not convex. In order to compute a clustering solution, we propose a convex reformulation of the problem, and we prove that both problems are equivalent. With the goal of finding a lower complexity clustering solution, we propose two heuristic small cells clustering algorithms. The first algorithm is based on resource allocation on the serving small cells where tasks are received, as a first step. Then, in a second step, unserved tasks are sent to a small cell managing unit (SCM) that sets up computational clusters for the execution of these tasks. The main idea of this algorithm is task scheduling at both serving small cells, and SCM sides for higher resource allocation efficiency. The second proposed heuristic is an iterative approach in which serving small cells compute their desired clusters, without considering the presence of other users, and send their cluster parameters to the SCM. SCM then checks for excess of resource allocation at any of the network small cells. SCM reports any load excess to serving small cells that re-distribute this load on less loaded small cells. In the final part of this thesis, we propose the concept of computation caching for edge cloud computing. With the aim of reducing the edge cloud computing latency and energy consumption, we propose caching popular computational tasks for preventing their re-execution. Our contribution here is two-fold: first, we propose a caching algorithm that is based on requests popularity, computation size, required computational capacity, and small cells connectivity. This algorithm identifies requests that, if cached and downloaded instead of being re-computed, will increase the computation caching energy and latency savings. Second, we propose a method for setting up a search small cells cluster for finding a cached copy of the requests computation. The clustering policy exploits the relationship between tasks popularity and their probability of being cached, in order to identify possible locations of the cached copy. The proposed method reduces the search cluster size while guaranteeing a minimum cache hit probability.

Third generation mobile communication systems promise a greater data rate and new services to the mobile subscribers. 3G systems support up to 2 Mbps of data rate to a fixed subscriber and 144 Kbps of data rate to a fully mobile subscriber. Code Division Multiple Access (CDMA) is the air interface access scheme widely used in all the 3G communication systems. This access scheme has many inherent advantages m terms of noise immunity, security, coherent combining of multi path signals etc. But all these advantages come at the expense of higher complexity of the receivers. The receivers form the major portion of the processing involved in a base station. The heart of any CDMA receiver is the RAKE. The RAKE receiver separates the different multi-paths received by the antenna by using the properties of the Pseudo Random sequences. The phase and strength of each of these path signals is measured and are used by the coherent combiner, which de-rotates all the signals to a single reference and coherently combines them In general the Base station receivers make use of the top three multi-path signals ranked in terms of their signal energy Hence four RAKE fingers, each catering to single multi-path are needed for receiving a single code channel (3 for coherent combining and one for scanning). One such channel receiver requires a processing power of 860 MIPS (Mega Instructions Per Second). Some of the CDMA standards support up to 90 code channels at the same time. This means that the total processing power required at the base station is about 80 GIPS. This much of processing power will require large number of high end DSPs, which will be a very costly solution. In the current base station architectures these blocks are implemented using ASICs, which are specific to a particular standard and also the algorithms used for the different operations are fixed at the design time itself. This solution is not flexible and is not amenable for SDR (Software defined Radio) architectures for the Base stations. This thesis proposes a Co-Processor solution, which can be attached to a generic DSP or any other processor. The processor can control the Co-Processor by programming its parameter registers using memory mapped register accesses. This co-processor implements only those blocks, which are compute intensive. This co-processor performs all chip-rate processing functions involved m a RAKE receiver. All the symbol-rate functions are implemented through software in the processor. This provides more choices m selecting the algorithms for timing recovery and scanning. The algorithms can be changed through software even after the base station is installed in the field. All the inputs and outputs of the Co-Processor are passed through dual port RAMs with independent read and write clocks. This allows the Co-Processor and the processor to be running on two independent clocks. This memory scheme also increases the throughput as the reads and writes to these memories can happen simultaneously. This thesis introduces a concept of incorporating programmable PN/Gold code generators as part of the Co-Processor, which significantly reduces the amount of memory required to store the Scrambling and Spreading codes. The polynomial lengths as well as the polynomials of the code generator are programmable. The input signal memory has a bus width equal to 4 times the bus width of the IQ signal bus width (4 * 24 = 96 bits) towards the Co-Processor to meet the huge data bandwidth requirement. This memory is arranged as word interleaved memory banks. This can supply one word per memory bank on each clock cycle as long as the accessed words fall in different memory banks. The number of banks is chosen as more than twice that of the number of Correlators/ Rake fingers. This gives more flexibility in choosing the address offsets to different Correlator inputs. This flexibility allows one to use different timing recovery schemes since the number of allowable address offsets for different Correlators is more. The overall complexity of the solution is comparatively less with respect to the generic DSP based solution and much easier to modify for a different standard, when compared to the rigid ASIC based solution. The proposed solution is significantly different from the conventional way of designing the Base station with fixed ASICs and it clearly outweighs the solutions based on conventional approach in terms of flexibility, design complexity, design time and cost.

To θέμα του εντοπισμού των κινητών τηλεφώνων έχει τραβήξει την προσοχή τα τελευταία χρόνια εξαιτίας των απαιτήσεων της Ομοσπονδιακής Επιτροπής Επικοινωνιών για το Enhanced 911 η οποία είναι μια υπηρεσία συναγερμού. Τα ασύρματα συστήματα επικοινωνίας 3ης γενιάς ηταν τα πρώτα που υιοθέτησαν στρατηγικές εύρεσης θέσης στα στάνταρντ τους. Στην διαδικασία της εύρεσης της θέσης υπάρχουν 3 βασικές κατηγορίες μετρήσεων που μπορούμε να χρησιμοποιήσουμε. Η πρώτη εκτιμά το κινητό βασίζοντας τις μετρήσεις στην λαμβανόμενη ισχύ σήματος. Η δεύτερη κάνει χρήση των χρόνων άφιξης ή της διαφοράς των χρόνων άφιξης στους σταθμούς βάσης. Η τρίτη κατηγορία έχει να κάνει με τις γωνίες άφιξης στους σταθμούς βάσης. Όλες οι παραπάνω κατηγορίες μετρήσεων υποβαθμίζονται έντονα από την NLOS διάδοση. Η απουσία ενός LOS μονοπατιού μπορεί να βλάψει σημαντικά την εκτίμηση της πραγματικής θέσης του κινητού. Αντικείμενο της παρούσας διπλωματικής είναι η συγκριτική αξιολόγηση και μελέτη κάποιων δημοφιλών τεχνικών εντοπισμού θέσης απλών και υβριδικών κάτω από διαφορετικά ΝLOS περιβάλλοντα και σε συνδυασμό με άλλες εξίσου σημαντικές παραμετρους όπως ειναι το διαθέσιμο πλήθος σταθμών βάσης σε μια περιοχή, η γεωμετρία ή με άλλα λόγια η θέση του κινητού σε σχέση με τους σταθμους βάσης. Προτείνεται επίσης και μια υβριδική τεχνική για την αντιμετώπιση των παραπάνω καταστρεπτικών επιπτώσεων του NLOS φαινομένου. / The problem of mobile location estimation has recently drawn attention due to Federal Communications Commission (FCC) demands of Enhanced-911 (E911) emergency service. Third Generation (3G) wireless systems were the first to adopt location estimation techniques into their standards. There are three basic types of measurements that can be used for location estimation. The first type includes Received Signal Strength measurements. The second type uses Time of Arrival or Time Difference of Arrival measurements of the signal to the base stations. The third type deals with Angle of Arrival measurements of the received signal. The subject of this work is the comparative evaluation and study of certain popular, simple and hybrid location estimation techniques, under different NLOS environments and in conjunction with other equally important parameters such as the number of available base stations, the geometry of the problem and the position of the mobile relative to the base stations. A hybrid method is also suggested for mitigating the destructive consequences of the NLOS effect.

Uninterrupted network connectivity is vital for real-time and mission-critical communication networks. The failure of Base Stations due to unforeseen circumstances such as natural disasters or emergencies can affect the coverage and capacity provided by terrestrial communication networks. The use of Unmanned Aerial Vehicles (UAVs) or drones in cellular networks is an upcoming area of research interest in 5G where the public sector and the communication service providers are fervently discussing it. The drones can be rapidly deployed to bridge the gaps in coverage or capacity of the network due to unforeseen circumstances. This thesis explores drone base stations' use for a simple hexagonal cell deployment scenario where the deployable base stations replace two failed macro base stations to improve the mean network capacity. Simulations show that the introduction of the deployable base stations indeed helps improve mean network capacity in case of one or multiple macro base station fail. The Genetic Algorithm is used to achieve Pareto optimality between downlink and uplink capacity of the simulated network. The simulation results show that introducing deployable nodes in a network can improve the network's capacity while also giving near-optimal transmit power values. / Oavbruten nätverksanslutning är avgörande för realtids- och missionskritiska kommunikationsnätverk. Fel på basstationer på grund av oförutsedda omständigheter som naturkatastrofer eller nödsituationer kan påverka täckningen och kapaciteten som tillhandahålls av markbundna kommunikationsnätverk. Användningen av Unmanned Aerial Vehicles (UAV) eller drönare i cellulära nätverk är ett kommande område av forskningsintresse inom 5G där den offentliga sektorn och leverantörerna av kommunikationstjänster ivrigt diskuterar det. Drönarna kan snabbt sättas in för att överbrygga klyftorna i nätverkets täckning eller kapacitet på grund av oförutsedda omständigheter. Denna avhandling utforskar drönarbasstationers användning för ett enkelt scenarie för hexagonal celldistribution där de utplacerbara basstationerna ersätter två misslyckade makrobasstationer för att förbättra den genomsnittliga nätverkskapaciteten. Simuleringar visar att introduktionen av de utplacerbara basstationerna verkligen hjälper till att förbättra den genomsnittliga nätverkskapaciteten i händelse av att en eller flera makrobasstationer misslyckas. Den genetiska algoritmen används för att uppnå Pareto-optimalitet mellan nedlänks- och upplänkkapaciteten i det simulerade nätverket. Simuleringsresultaten visar att införandet av utplacerbara noder i ett nätverk kan förbättra nätverkets kapacitet samtidigt som det ger nästan optimala värden för sändningseffekt.

Federated learning faces a challenge when dealing with highly heterogeneous data and it can sometimes be inadequate to adopt an approach where a single model is trained for usage at all nodes in the network. Different approaches have been investigated to succumb this issue such as adapting the trained model to each node and clustering the nodes in the network and train a different model for each cluster where the data is less heterogeneous. In this work we study the possibilities to improve the local model performance utilizing the hierarchical setup that comes with clustering the participating clients in the network. Experiments are carried out featuring a Long Short-Term Memory network to perform time series forecasting to evaluate different approaches utilizing the hierarchical setup and comparing them to standard federated learning approaches. The experiments are done using a dataset collected by Ericsson AB consisting of handovers recorded at base stations in an European city. The hierarchical approaches didn’t show any benefit over common two-level approaches. / Federated Learning står inför en utmaning när det gäller att hantera data med en hög grad av heterogenitet och det kan i vissa fall vara olämpligt att använda sig av en approach där en och samma modell är tränad för att användas av alla noder i nätverket. Olika approacher för att hantera detta problem har undersökts som att anpassa den tränade modellen till varje nod och att klustra noderna i nätverket och träna en egen modell för varje kluster inom vilket datan är mindre heterogen. I detta arbete studeras möjligheterna att förbättra prestandan hos de lokala modellerna genom att dra nytta av den hierarkiska anordning som uppstår när de deltagande noderna i nätverket grupperas i kluster. Experiment är utförda med ett Long Short-Term Memory-nätverk för att utföra tidsserieprognoser för att utvärdera olika approacher som drar nytta av den hierarkiska anordningen och jämför dem med vanliga federated learning-approacher. Experimenten är utförda med ett dataset insamlat av Ericsson AB. Det består av "handoversfrån basstationer i en europeisk stad. De hierarkiska approacherna visade inga fördelar jämfört med de vanliga två-nivåapproacherna.

Submitted by Sandro Camargo (sandro.camargo@unipampa.edu.br) on 2015-05-09T22:22:57Z No. of bitstreams: 1 126110018.pdf: 3775876 bytes, checksum: 4a58f20709bf7c39682924a84079246d (MD5) / Made available in DSpace on 2015-05-09T22:22:58Z (GMT). No. of bitstreams: 1 126110018.pdf: 3775876 bytes, checksum: 4a58f20709bf7c39682924a84079246d (MD5) Previous issue date: 2014-09-08 / Neste trabalho, são apresentadas diferentes técnicas que possibilitam a obtenção de característica dupla-faixa para antenas de microfita especificamente voltadas para aplicações em estações rádio-base de telefonia móvel celular no Brasil. As faixas de frequência de interesse encontram-se no intervalo de 0,824 GHz a 0,960 GHz para a banda inferior e 1,710 GHz a 2,165 GHz para a banda superior. Além de atender as especificações técnicas de faixa de passagem, devem ser atendidos os requisitos de coeficiente de reflexão, polarização, ganho, largura de feixe de irradiação e impedância de entrada na faixa de interesse. Primeiramente, para obtenção de antenas de microfita com característica multibanda, descreve-se a técnica em que são dispostas fendas nos elementos irradiadores, onde são estudadas três topologias de antenas, explicando-se os princípios de funcionamento e destacando-se as particularidades de cada geometria. As três antenas são analisadas e projetadas com o auxílio do software comercial de simulação eletromagnética Ansoft Designer ® , visando levantar os parâmetros elétricos através de diversos estudos paramétricos em função da variação das dimensões das antenas para compreender melhor o comportamento de cada estrutura simulada. A antena com elemento irradiador em forma de H foi a única que cumpriu os requisitos em termos de faixa de passagem e diagramas de irradiação para operação em sistemas de telefonia móvel celular. No entanto, esta geometria resultou em dimensões físicas consideráveis, pois necessita da utilização de múltiplas camadas dielétricas, acarretando em um protótipo de volume considerável e de elevado custo de produção. Outra técnica estudada foi a sobreposição de elementos irradiadores, porém a mesma não é investigada detalhadamente em função de o custo de produção da antena ser mais elevado em comparação a topologias coplanares. Em seguida, uma técnica com irradiadores em fenda anelar e dupla alimentação é proposta. A antena é projetada considerando-se duas portas independentes, uma para cada banda de operação, formando uma antena de dois acessos altamente isolados. Simulações com o software HFSS TM mostraram que é possível satisfazer as especificações para operação em estações rádio-base de telefonia móvel celular. A grande vantagem desta estrutura é a possibilidade de utilização de apenas um laminado de micro-ondas, o que reduz o custo de produção em comparação a outras topologias. Protótipos foram construídos e caracterizados experimentalmente para validar o projeto realizado no simulador eletromagnético. Constatou-se a presença de discrepâncias entre os resultados simulados e medidos. Após simulações paramétricas, verificou-se que o processo de construção alterou a geometria do protótipo em relação ao modelo de simulação. Após a inclusão das imperfeições do processo construtivo no modelo, foi possível estimar as mudanças necessárias no protótipo. Após os devidos ajustes realizados em bancada, os resultados medidos exibiram boa concordância com a previsão teórica. Por fim, realizou-se um estudo de viabilidade da utilização da antena em fenda anelar dupla-faixa para composição de uma rede de antenas para estações rádio-base. A análise teve como principal objetivo verificar a possibilidade de síntese de diagramas de irradiação em forma de cossecante ao quadrado em ambas as bandas de operação. Excelente resultado foi obtido para a banda inferior, enquanto que algumas limitações foram encontradas na banda superior. / In this work we present different techniques for achieving the dual-band feature for microstrip antennas aimed to be used in the mobile communication base stations of Brazil. The focused frequency range for lower and higher bands is in the 0.824-0.960 GHz and 1.710-2.165 GHz intervals, respectively. In addition to comply with the technical specifications, the solution is also supposed to meet the requirements of return loss, polarization, gain, beamwidth radiation and input impedance in the focused frequency range. Initially, in order to obtain microstrip antennas with dual-band characteristic, we describe the technique in which slots are placed in the irradiating elements. Three antenna topologies are analyzed in its operation principles, emphasizing the particularities of each geometry. The antennas are designed with support of Ansoft Designer ® , a commercial software that simulates electromagnetic features, in order to find out the electrical parameters through parametric studies and to better understand the behavior of each simulated structure. These studies considered the variation in the dimensions of antennas. The H-shaped microstrip antenna was the only one able to fulfill the requirements of bandwidth and irradiation diagrams for operation in mobile communication. However, this geometry originated an antenna of considerable physical dimensions, because it requires the use of multiple dielectric layers, resulting in a prototype of considerable volume and high production cost. Another technique studied was the stacking of irradiating elements. However it isn’t investigated in detail because of the production cost of the antenna, which is higher than the ones of coplanar topologies. After all that, we propose a technique based in annular-slot antennas and double feed. The antenna is designed considering two independent ports, one for each band of operation, making an antenna of two highly insulated accesses. Simulations by the HFSS TM software have shown that it’s possible to comply with the specifications for operation in base stations of the mobile communication. The biggest advantage of this structure over other topologies is that it may be made of only one microwave laminate, reducing the production cost. Prototypes were built and measured to validate the design in the electromagnetic simulator. It was noted the discrepancies between the simulated and measured results. After running parametric simulations, we found out that the building process of the prototype changed the geometry of the simulation model. We included these imperfections in the model and it was possible to estimate the necessary changes in the prototype. After inclusion of the adjustments, the measured results behaved just alike the theoretical prediction. Finally, we’ve done a feasibility study on the use of the dual-band annular slot antenna for making an array of antennas for base stations. The study aimed to verify the suitability of synthetizing squared-cosecant shaped pattern in both operation bands. We got excellent results for the lower band, although some limitations were found for the higher band.