Dissertations / Theses on the topic 'Data handover'

Dizertační práce se zabývá návrhem nového algoritmu řízení handoveru v rámci protokolu Mobile IPv6, který umožní nasazení tohoto protokolu v leteckých datových sítích. Existující algoritmy řízení handoveru sice dosahují dostatečné výkonnosti v konvenčních pozemních bezdrátových sítích disponujích velkou šířkou pásma a nízkou latencí, jako jsou WiFi nebo UMTS, ale jak ukazuje tato práce, nasazení těchto algoritmů prostředí leteckých datových sítí nepřináší očekávané výhody. Analýza ukazuje, že v úzkopásmových leteckých sítích trpí tyto algoritmy řízení handoveru velkou latencí a způsobují značnou režii. Nový algoritmus řízení handoveru v MIPv6 navržený v této práci je založený na jednoduché myšlence: ''Já jsem letadlo, já vím, kam letím!'' To znamená, že pohyb letadla není náhodný, ale vysoce předvídatelný. Díky tomu je možno předvídat handovery mezi přístupovými sítěmi podél očekávané trajektorie letadla a vykonat nezbytné operace pro přípravu handoverů již na zemi, kde je letadlo připojeno k širokopásmové síti letiště. Tato dizertační práce dále uvádí porovnání existujících algoritmů řízení handoveru s nově navrženým pomocí analytické metody ohodnocení handoveru. Díky tomu je možno kvantifikovat výhody, které nový algoritmus přináší a taktéž popsat slabiny algoritmů existujících.

Relevant and quality-assured geographic data is critical information in several steps of the building process. There are many methods for quality-assuring geographic data during data collection, and in the building process, but in order for the data to be useful throughout the life cycle of a facility it is important that the data maintains reliability and quality even after the handover from a building project. The handover of geographic data from building projects has, by municipal management units, been described as inefficient. When designers do not follow the client's requirements the data must be handled manually, which is both time consuming and a possible risk for the quality of the data. In a time that place great demands on efficiency, quality and sustainability, it is not justifiable to manually digitizing data that has previously already been digital, furthermore there is also a risk that the human factor and interpretations affect the data quality. There are factors in the handover process that needs to be prevented in order to achieve an unbroken information supply throughout the life cycle of a facility. In this thesis, a qualitative study has been conducted with the purpose to identify what factors in the handover process prevent quality-assured handover of geographic data from building projects to management organizations. The findings of the study should also result in recommendations of how the City of Stockholm and other municipalities in general can prevent obstacles in the handover process to assure that geographic data maintains its quality throughout the handover. To identify barriers in the handover of geographic data in building projects, the data collection in this study was done through several interviews with project managers, designers and system managers. The results show that important factors for a successful, quality-assured handover of geographic data are related requirements and communication. Final recommendations in order to assure that the geographic data maintains its quality throughout the handover are: early involvement of the management, clear and early communicated requirements, improved communication to achieve a more holistic view, and automated processes that could replace manual work and check data against requirements.

An important application of Machine Learning (ML) in mobile networks is to predict if a user device has coverage on a frequency other than the current serving frequency. This is a use-case called Secondary Carrier Prediction (SCP). In this thesis we deduce if data across different cells and frequencies can be successfully combined when learning this task, thus reducing the number of models that require training. Aggregation of data involves several challenges, such as different prevalences and varying amounts of available data, but more importantly the possibility of achieving synergies in training by exploiting recurring patterns in data. By using an experimental setup in which models are trained and validated on aggregated datasets it is shown that synergies in fact can be achieved through aggregation. The scalability of this task is improved so that the number of models can be reduced with a factor as large as the number of cells times the number of frequencies, while maintaining similar or improved prediction performance.
Prediktion av täckning på sekundära frekvenser är en signifikant tillämpning av maskininlärning inom mobila nätverk. I den här avhandlingen utreds möjligheten att träna modeller på aggregationer av data, med följden att antalet modeller blir färre. Olika klassbalanser och varierande tillgång på data är utmaningar som uppstår vid aggregation, men även möjligheten att uppnå synergier genom att utnyttja återkommande mönster i datat. Med en experimentell uppställning där modeller tränas och valideras på aggregerade dataset visas att synergier kan uppnås genom aggregation. Skalbarheten på denna tillämpning förbättras till den grad att antalet modeller kan reduceras med en faktor lika stor som antalet celler gånger antalet frekvenser, med likvärdig eller förbättrad prediktionsprestanda.

With the upcoming of the fifth generation of cellular networks there are several perfor- mance requirements that need to be satisfied. This thesis focuses on the topic of mobility which allows users to move through the network using the concept of handovers to switch between base stations. However, the thesis also keeps the energy efficiency in mind and investigates a strategy of reducing the energy consumption. Moving across base stations will inevitably lead to some handover failures, a goal of the system developers is to reduce these, but there exists a tradeoff between too early and too late handover failures. This thesis investigates two approaches of lowering the number of failures by letting the net- work self-optimize parameters in the handover procedure based upon the tradeoff. The first approach includes a parameter adaption to an estimated velocity of the users and the second one making a parameter more granular. Simulating different scenarios in a detailed network simulator shows performance gain by adapting handover parameters to the esti- mated velocity, but gathering more data regarding failures is needed before generalizing the conclusions.

Data Handover est une librairie de fonctions adaptée aux systèmes distribués à grande échelle. Dho offre des routines qui permettent d'acquérir des ressources en lecture ou en écriture de façon cohérente et transparente pour l'utilisateur. Nous avons modélisé le cycle de vie de Dho par un automate d'état fini puis, constaté expérimentalement, que notre approche produit un recouvrement entre le calcul de l'application et le contrôle de la donnée. Les expériences ont été menées en mode simulé en utilisant la libraire GRAS de SimGrid puis, en exploitant un environnement réel sur la plate-forme Grid'5000. Par la théorie des files d'attente, la stabilité du modèle a été démontrée dans un contexte centralisé. L'algorithme distribué d'exclusion mutuelle de Naimi et Tréhel a été enrichi pour offrir les fonctionnalités suivantes: (1) Permettre la connexion et la déconnexion des processus (ADEMLE), (2) admettre les locks partagés (AEMLEP) et enfin (3) associer les deux propriétés dans un algorithme récapitulatif (ADEMLEP). Les propriétés de sûreté et de vivacité ont été démontrées théoriquement. Le système peer-to-peer proposé combine nos algorithmes étendus et le modèle originel Dho. Les gestionnaires de verrou et de ressource opèrent et interagissent mutuellement dans une architecture à trois niveaux. Suite à l'étude expérimentale du système sous-jacent menée sur Grid'5000, et des résultats obtenus, nous avons démontré la performance et la stabilité du modèle Dho face à une multitude de paramètres
Data Handover is a library of functions adapted to large-scale distributed systems. It provides routines that allow acquiring resources in reading or writing in the ways that are coherent and transparent for users. We modelled the life cycle of Dho by a finite state automaton and through experiments; we have found that our approach produced an overlap between the calculation of the application and the control of the data. These experiments were conducted both in simulated mode and in real environment (Grid'5000). We exploited the GRAS library of the SimGrid toolkit. Several clients try to access the resource concurrently according the client-server paradigm. By the theory of queues, the stability of the model was demonstrated in a centralized environment. We improved, the distributed algorithm for mutual exclusion (of Naimi and Trehel), by introducing following features: (1) Allowing the mobility of processes (ADEMLE), (2) introducing shared locks (AEMLEP) and finally (3) merging both properties cited above into an algorithm summarising (ADEMLEP). We proved the properties, safety and liveliness, theoretically for all extended algorithms. The proposed peer-to-peer system combines our extended algorithms and original Data Handover model. Lock and resource managers operate and interact each other in an architecture based on three levels. Following the experimental study of the underlying system on Grid'5000, and the results obtained, we have proved the performance and stability of the model Dho over a multitude of parameters

Data Handover est une librairie de fonctions adaptée aux systèmes distribués à grande échelle. Dho offre des routines qui permettent d'acquérir des ressources en lecture ou en écriture de façon cohérente et transparente pour l'utilisateur. Nous avons modélisé le cycle de vie de Dho par un automate d'état fini puis, constaté expérimentalement, que notre approche produit un recouvrement entre le calcul de l'application et le contrôle de la donnée. Les expériences ont été menées en mode simulé en utilisant la libraire GRAS de SimGrid puis, en exploitant un environnement réel sur la plate-forme Grid'5000. Par la théorie des files d'attente, la stabilité du modèle a été démontrée dans un contexte centralisé. L'algorithme distribué d'exclusion mutuelle de Naimi et Tréhel a été enrichi pour offrir les fonctionnalités suivantes: (1) Permettre la connexion et la déconnexion des processus (ADEMLE), (2) admettre les locks partagés (AEMLEP) et enfin (3) associer les deux propriétés dans un algorithme récapitulatif (ADEMLEP). Les propriétés de sûreté et de vivacité ont été démontrées théoriquement. Le système peer-to-peer proposé combine nos algorithmes étendus et le modèle originel Dho. Les gestionnaires de verrou et de ressource opèrent et interagissent mutuellement dans une architecture à trois niveaux. Suite à l'étude expérimentale du système sous-jacent menée sur Grid'5000, et des résultats obtenus, nous avons démontré la performance et la stabilité du modèle Dho face à une multitude de paramètres
Data Handover is a library of functions adapted to large-scale distributed systems. It provides routines that allow acquiring resources in reading or writing in the ways that are coherent and transparent for users. We modelled the life cycle of Dho by a finite state automaton and through experiments; we have found that our approach produced an overlap between the calculation of the application and the control of the data. These experiments were conducted both in simulated mode and in real environment (Grid'5000). We exploited the GRAS library of the SimGrid toolkit. Several clients try to access the resource concurrently according the client-server paradigm. By the theory of queues, the stability of the model was demonstrated in a centralized environment. We improved, the distributed algorithm for mutual exclusion (of Naimi and Trehel), by introducing following features: (1) Allowing the mobility of processes (ADEMLE), (2) introducing shared locks (AEMLEP) and finally (3) merging both properties cited above into an algorithm summarising (ADEMLEP). We proved the properties, safety and liveliness, theoretically for all extended algorithms. The proposed peer-to-peer system combines our extended algorithms and original Data Handover model. Lock and resource managers operate and interact each other in an architecture based on three levels. Following the experimental study of the underlying system on Grid'5000, and the results obtained, we have proved the performance and stability of the model Dho over a multitude of parameters

With increasing demands on network reliability and speed, network suppliers need to effectivize their communications algorithms. Frequency measurements are a core part of mobile network communications, increasing their effectiveness would increase the effectiveness of many network processes such as handovers, load balancing, and carrier aggregation. This study examines the possibility of using supervised learning to predict the signal of inter-frequency measurements by investigating various learning algorithms and pre-processing techniques. We found that random forests have the highest predictive performance on this data set, at 90.7\% accuracy. In addition, we have shown that undersampling and varying the discriminator are effective techniques for increasing the performance on the positive class on frequencies where the negative class is prevalent. Finally, we present hybrid algorithms in which the learning algorithm for each model depends on attributes of the training data set. These algorithms perform at a much higher efficiency in terms of memory and run-time without heavily sacrificing predictive performance.

With advancements in the mobile network architecture, from the Fourth Generation to the Fifth Generation, a vast number of new use cases becomes available. Many use cases require cloud-based services, where a service is deployed close to the user. For a user to communicate with a service, it connects to the mobile network base station, Fifth Generation Core network and then to the service. When the user changes physical location, the mobile network and the service must apply mobility techniques. This is to prevent tromboned traffic and provide low latency between user and service. When a handover occurs, so that a user’s attachment point to the mobile network is changed from the one base station to another and the User Plane Function changes, the cloud-based service may have to seamlessly move from one cloud to another as well. In this thesis, a Service mobility framework is proposed and implemented, which enables service live migration between edge clouds and it provides simple RESTful APIs. The evaluation of the framework shows that the proposed implementation adds low delays to the total migration time and the service downtime is also shown to be low in the case of video streaming with no service interruption.
Med framsteg i det mobila nätverkets arkitektur, sett från den Fjärde Generationen till den Femte Generationen, så blir nya användningsområden tillgängliga. Bland de nya användningsområdena inkluderas molnbaserade tjänster, där tjänster är placerade nära användare, dessutom har vissa områden behov av dessa molnbaserade tjänster. För att en användare ska kunna kommunicera med en tjänst så måste den först ansluta till det mobila nätverkets basstationer och sedan till Femte Generationens kärnnätverk, för att sedan kunna kommunicera med tjänsten. När användaren förflyttar sig från en plats till en annan, så måste det mobila nätverket och tjänsten tillämpa rörlighetstekniker, som förflyttning av tjänsten. Förflyttningen är för att förhindra trombonerad trafik och att förse låg latens mellan användare och tjänst. När en överlämning sker, d.v.s att en användares kopplingspunkt till det mobila nätverket ändras, från en basstation till en annan, och att User Plane Function ändras, så kan även den molnbaserade tjänsten förflytta sig sömlöst från ett moln till ett annat. I denna avhandling presenteras ett tjänströrlighetsramverk som möjliggör tjänströrlighet mellan moln och erbjuder enkla RESTfulla API:er. Evaluering av ramverket visar att implementationen bidrar med låga fördröjningar till den totala migrations tiden samt att tjänster med videoströmming har lågt driftstopp utan tjänstavbrott.

In this thesis we propose a system for robots to learn through a semisupervised approach from observations, proper handover features for objects that can be applied onto new objects. Using recordings of handovers, features are extracted for the purpose of classifying the objects through unsupervised learning. The results from the classification are used to train a network in a supervised fashion as to properly identify handover class from images. The results of this work show that objects with similar visual features are handed over in similar way and that with a limited amount of data a model can be fitted as to properly predict handover settings for an object that has been previously encountered or not.
I detta examensarbete presenteras ett förslag på ett system för robotar att lära sig på ett autonomt semi-supervised vis egenskaper vid överlämning för olika objekt genom att observera människor, som kan senare även användas till nya objekt. Med hjälp av inspelat material på överlämningar, identifierar vi egenskaper som gör det möjligt att klassificera objekten genom unsupervised learning. Resultaten från denna klassificering kombineras med bilder på objekten som används till att träna ett nätverk på ett supervised vis, som lär sig att förutspå korrekt klass för ett objekt via bilddata. Resultaten från detta arbete visar att objekt som överlämnas på liknande vis även har liknande visuella egenskaper, och med en begränsad mängd med data kan vi träna en modell som med hög träffsäkerhet ger oss inställningarna för överlämningen utav ett objekt vare sig det har påträffats tidigare eller inte.

Data Handover, Dho est une librairie de fonctions adaptée aux systèmes distribués à grande échelle. Dho offre des routines qui permettent d'acquérir des ressources en lecture ou en écriture de façon cohérente et transparente pour l'utilisateur. Nous avons modélisé le cycle de vie de Dho par un automate d'état fini puis, constaté expérimentalement, que notre approche produit un recouvrement entre le calcul de l'application et le contrôle de la donnée. Les expériences ont été menées en mode simulé en utilisant la libraire GRAS de SimGrid puis, en exploitant un environnement réel sur la plate-forme Grid'5000. Par la théorie des files d'attente, la stabilité du modèle a été démontrée dans un contexte centralisé. L'algorithme distribué d'exclusion mutuelle de Naimi et Tréhel a été enrichi pour offrir les fonctionnalités suivantes: (1) Permettre la connexion et la déconnexion des processus (ADEMLE), (2) admettre les locks partagés (AEMLEP) et enfin (3) associer les deux propriétés dans un algorithme récapitulatif (ADEMLEP). Les propriétés de sûreté et de vivacité ont été démontrées théoriquement. Le système peer-to-peer proposé combine nos algorithmes étendus et le modèle originel dho. Les gestionnaires de verrou et de ressource opèrent et interagissent mutuellement dans une architecture à trois niveaux. Suite à l'étude expérimentale du système sous-jacent menée sur Grid'5000, et des résultats obtenus, nous avons démontré la performance et la stabilité du modèle Dho face à une multitude de paramètres.

This Master thesis work was carried out at theWireless Center at KTH and it is part of a pilot project. This thesis is conducted for the Institute for Microelectronics and Information Technology (IMIT) at the Royal Institute of Technology (KTH) in Stockholm (Sweden) and for the Department of Telecommunications at Politecnico di Torino in Turin (Italy). This thesis addresses an area with significant potential for offering services to mobile users. In such a scenario users should have minimal interaction with applications which, by taking into account available context information, should be able to make decisions, such as setting up delivery paths between peers without requiring a third party for the negotiation. In wireless reconfigurable networks, the mobile users are on the move and must deal with dynamic changes of network resources. In such a network, mobile users should be able to contact other peers or resources by using the current route. Thus although manual configuration of the network is a possible solution, it is not easily used because of the dynamic properties of the system which would demand too much user interaction. However, existing discovery protocols fall short of accomodating the complexity of reconfigurable and heterogeneous networks. The primary objective of this thesis work was to investigate a new approach at the application level for signaling by taking advantage of SIP’s features. The Session Initiation Protocol (SIP) is used to provide naming and localization of the user, and to provide functionality to invite users to establish sessions and to agree on communication parameters. The Specific Event Notification of the SIP protocol provides a framework for the notification of specific events and I believed that it could be instantiated as solution to the problem for reconfigurable application networks. This thesis proposes a method for providing localization information to SIP User Agents in order to establish sessions for service discovery. Furthermore, this method should consider context meta-data to design strategies effective in heterogeneous networks. A viable solution must support (re)location of users at the application layer when they roam between different wireless networks, such as GPRS and WLAN. An analysis of the implications of the proposed model is presented; in this analysis emphasis has been placed on how this model interacts with existing services.

A evolução da computação móvel melhora a capacidade de comunicação e colaboração das pessoas. Os principais pilares desta transformação são: o desenvolvimento e produção de dispositivos móveis com capacidade multimídia e equipados com duas ou mais interfaces de rede, a disponibilidade de conectividade sem fio ubíqua e a popularização de aplicações sociais online. As redes sociais online merecem destaque pelas funcionalidades que permitem a criação e compartilhamento de conteúdo digital dentro de círculos sociais, também chamado de mídia social. Serviços na web anexam a localização geográfica do dispositivo ao conteúdo digital, criando as chamadas mídias sociais baseadas em localização. Equipadas com seus telefones e tablets, as pessoas estão criando e consumindo mídias sociais em qualquer lugar. Entretanto, é um desafio manter tais dispositivos móveis conectados nos ambientes de rede sem fio atuais e de próxima geração e.g., múltiplos provedores de acesso e múltiplas tecnologias de comunicação. Pesquisas recentes propõem componentes para o gerenciamento de conectividade sem fio que fazem uso simultâneo do contexto de conectividade atual e de um conjunto destes dados coletados no passado. Tais componentes são preditores de mobilidade, mecanismos de handover ou gerenciadores de mobilidade que utilizam dados de contexto de conectividade de forma particular para atingir seus propósitos. Na presente investigação, propomos uma metodologia que orquestra os principais componentes de gerenciamento de conectividade em um laço retro alimentado. Argumentamos que a coleta de dados de contexto de conectividade pode ser projetada como um sistema de sensoreamento, cujo sensores são as interfaces de rede sem fio. Como parte deste sistema de sensoriamento, os círculos sociais podem assistir o gerenciamento de conectividade compartilhando dados de contexto de conectividade. A ideia central é utilizar serviços baseados em localização para compartilhar dados de contexto de conectividade dentro dos círculos sociais. Desta forma, as redes sociais online adicionam escala para o sistema e permite colaboração em volta de dados de contexto recentes, locais, personalizados e sociais. O objetivo é melhorar experiências de conectividade sem fio e.g., métricas de QoS (Quality of Service) como: vazão, latência e qualidade do sinal. Relatamos como os dados de contexto de conectividade são manipulados com um modelo baseado em grafos e métricas como: intensidade do vértice e grau centralidade. Com isso, identificamos áreas com alta densidade de handovers, definimos a reputação dos usuários e revelamos a cobertura das redes. Resultados de experimentos mostram que a colaboração pode melhorar métricas de QoS de ~18 a ~30% se comparado ao uso de um preditor de mobilidade ou um sistema operacional moderno, respectivamente. Esta discussão se desdobra com foco na viabilidade da solução em termos de sobrecarga de armazenamento e consumo de energia. Os promissores resultados experimentais indicam que nossa solução pode melhorar experiências de conectividade sem fio de usuários móveis
The evolution of mobile computing improves communication and collaboration among people. The main pillars of this transformation are: the development and production of mobile devices with multimedia capabilities and equipped with two or more network interfaces, the availability of ubiquitous wireless connectivity and the popularity of online social applications. Online social networks noteworthy features that allow for the creation and sharing of digital content within social circles, also called textit Social Media. Web Services attach the geographic location of the device to the digital content, creating the so-called textit location-based social media. Equipped with their phones and tablets, people are creating and consuming social media anywhere. However, it is a challenge to keep such mobile devices connected in current and next generation wireless network environments textit e.g., multiple ISPs (Internet Service Provider) and multiple communication technologies. Recent researches proposes components for managing wireless connectivity that make simultaneous use of the current and past connectivity context data. Such components are mobility predictors, handovers mechanisms or mobility managers that use connectivity context data in a particular way to achieve its purposes. In this research, we propose feasiable a methodology that orchestrates the main components of the connectivity management in a feedback loop. We argue that the process of gathering connectivity context data can be designed as a sensing system, whose sensors are wireless network interfaces. As part of this sensing system, the social circles may assist the management of connectivity by sharing connectivity context data. The main idea is to use location-based services to share connectivity context data within social circles. Thus, online social networks add scale to the system and enables collaboration around recent, local, and social context data. The goal is to enhance wireless connectivity experiences in terms of QoS ( textit Quality of Service) metrics textit e.g., throughput, latency and signal quality. We report how this data is handled using complex networks metrics e.g., vertexs strength and centrality degree, to identify high density handover areas, define the mobile users reputation and to reveal the networks coverage. Real experiments showed that collaboration can improve QoS metrics from ~18 to ~30% if compared to just use a mobility predictor or a modern operational system, respectively. The discussion unfolds with focus on the collaborations efficiency as function of time, number of users, discovered area size and mobility patterns. The promising experimental results indicate that our solution can enhance mobile users wireless connectivity experiences

The conventional mobile networks consists of macrocells or Evolved NodeB (eNB) which provide good coverage but reduces bandwidth available for a given area. The problem of coverage and lim- itation of bandwidth in a mobile network system is solved by using femtocells or Home Evolved NodeB (HeNB). In this thesis various handover scenarios have been considered for a LTE network having both femtocells (HeNB) and macrocells (eNB). Three handover scenarios: hand-in, hand-out and inter- femtocell and two dierent handover strategies: reactive and proactive handover are considered and analyzed. The mobility of the User Equipment (UE) has also been taken into consideration to achieve an optimal handover procedure. An algorithm has been proposed, which is used to dynamically decide upon the handover policy to be used based on the UE mobility and signal strength from the various available cells. The signaling and latency in handovers is studied using X2 interface between macrocells and femtocells. The proposed algorithm has been studied using the NS-3 simulator.

碩士
國立臺北科技大學
電腦與通訊研究所
94
Handover refers to the mechanism by which an ongoing call is transferred from one base station (BS) to another. Frequent handovers influence the quality of service, increase the signaling overhead on the network, and degrade throughput in data communications. Because of the impact of shadowing effect the ranking of RSSs from surrounding base stations may vary from time to time and cause a call to be repeatedly handed over back and forth between the BSs, in what is called the “ping-pong effect”. Conventional handover algorithms only consider received signal strength (RSS) and fixed handover threshold, causing many unnecessary handovers in cell borders.This thesis proposes adaptive soft handover and intersystem handover both based on user mobility estimation from GPS to adjust handover hysteresis parameters. The performance was verified by applying the proposed method to a WCDMA system measurement data in urban Taipei city. The result shows that the proposed soft handover algorithm improves the handover number about 20% to 30% over the conventional one. It shows that the proposed intersystem handover algorithm improves the intersystem handover number about 5% to 20% over the conventional one.

碩士
國立成功大學
電腦與通信工程研究所
101
With the increasing of requirements of multimedia services, Long Term Evolution (LTE) technology can improve the quality of high speed data transferring. Due to the movement of UE among base stations, LTE system performs handover. A LTE handover occurs a detach time when user moves form source eNdoeB to target eNodeB. The source eNodeB forwards user data to target eNodeB instead of UE during this interrupt time. This procedure will degrade the system performance according to the delay or lost transmitting data. In order to promote system performance and provide a good service to users during LTE handover, this paper proposes three buffer management algorithms as Blocking, Dropping the Oldest Session and Dropping the Heaviest Session without any modification of handover procedure. When the buffer of target eNodeB is overflowing, the packets in the buffer are discarded through our algorithms. Simulation model is developed to measure the effects on the buffer size. The simulation results show that the DHS has the best performance among our methods.

碩士
國立清華大學
資訊工程學系
99
To transmit bandwidth-intensive applications efficiently, multicast broadcast service (MBS) is one of the important features supported by Mobile WiMAX. As MBS services such as audio and video streaming are usually delay-sensitive, the concept of an MBS zone is also introduced to reduced the handover delay for MBS services. In an MBS zone, the participant BSs transmit the same MBS content synchronously, and MSs do not need to re-register and re-establish the multicast connection during handover between BSs in the same MBS zone. However, when the serving BS and the target BS belong to different MBS zones, the inter-MBS zone handover is performed. The longer inter-MBS zone handover delay and frame offsets between adjacent MBS zones will cause large packet loss and make the QoS of real-time applications infeasible. But the problem of huge packet loss caused by inter-MBS zone handover is little studied. In this paper, we propose an improvement on the inter-MBS zone handover procedure to greatly reduce the handover delay. Moreover, we also propose a data recovery scheme for inter-MBS zone handover by using extra multicast connections as recovery channels for MBS services to minimize the packet loss. Simulation results show that our proposed schemes achieve almost zero packet loss with relatively small number of recovery channels compared to the number of MBS sessions.

M. Tech. Electrical Engineering.
Proposes certain approaches aimed at improving handover from the users point of view, the benefits may include enhanced quality of service, avoidance of handover disruption and reduction of handover rate, irrespective of high traffic loads at the BSs.The proposed scheme improves the network performance by minimising the handover delay time and also enhancing the effective use of radio resources

Tese de doutoramento em Programa Doutoral em Sistemas de Transportes apresentada à Faculdade de Ciências e Tecnologia da Universidade de Coimbra.
All around the World we experience the trends of the last decades on increased urbanization as more and more people shift their living to cities. However, many cities lack the resources to respond to the magnitude of the change in their urban areas, which forces people to compete for the use of land, roads, public transport, and other urban facilities. As a result of the increasing number of people, cities face an increasing number of private vehicles and commuters which in turn cause various problems such as traffic congestion, parking difficulties, traffic accidents, loss of space for productive activities, public transport inadequacy and undesirable environmental impacts. In the past, public authorities followed approaches that nowadays are financially unsustainable, focused mainly on expanding the road network to alleviate the problem. However, many analysts argue that the solution for these problems is better addressed through intelligent planning and management of the existing urban and transportation systems. Planning of the urban and transportation system traditionally relied on the knowledge of present and future problems that are associated to the urban growth such as how much travel will be generated, where these trips will take place, by which mode and on which routes. Creating such plans requires information regarding the movement of people and vehicles, knowledge of constituents of the urban system, and understanding the nature of activities at different places. There are various traditional methods for gathering the raw data necessary for urban and transportation planning. Although these methods have the advantage of providing detailed information, their limited coverage and expensive costs of implementation often make them insufficient. More recently, the spread of massive sensoring, namely through the generalized use of cellphone, is producing massive amounts of data with spatio-temporal detail about our daily activities and traveling patterns, which could be important to the planning of urban and transportation systems given their pervasiveness, low cost, and real time nature. In this thesis we explore the use of cellphone data for profiling the dynamics of urban activities and characterizing flows of people for planning of urban and transportation systems in cities. Three types of passive mobile positioning data were used: (1) Call Volume, which is the number of calls; (2) Erlang, which is used to measure the equivalent cellphone traffic per hour; and (3) Handover, which is the process of transferring an ongoing call from one base station to another without interruption of service. Our observations are based on hourly aggregated cellphone data obtained from a dataset from a telecom company in Lisbon, Portugal. Though passive mobile positioning data is extracted without incurring additional costs and operational risks for the network, it has two main limitations. Firstly, location acquired by this method is at the granularity of a cell sector, which gives uncertainty on the exact location of the collected variables; secondly, it is only acquired when a phone is engaged in a call or short message service. However, we argue that the aggregate cellphone data used in this study remains useful for our analysis, which is at a scale where the lack of a detailed level of precision is not essential. For validation of our results, we collaborated with other data providers in Lisbon to gather different ground truth datasets that could improve our understanding of urban dynamics such as census data, taxi movement, bus movement, traffic count, points of interest, and presence of people. We proposed new approaches to reflect the potential of passive mobile positioning data for urban and transportation planning. Our approach comprises three stages: (1) exploratory data analysis aimed to discover the kind of relationship that emerges between cellular networks data and urban characteristics, activities, and dynamics at a city-scale; (2) use of cellphone data to detect activities associated to the urban areas in what respects to two aspects of activities: spatial patterns of urban activities, and intensities of urban activities along the hours of a day; and (3) extraction of cellular network data for development of models that predict hourly traffic status. Our results confirm that passive mobile positioning data, taking the advantage of its pervasiveness and availability with reasonably less cost, can provide ways to analyse the dynamics of urban activities at a larger scale. In addition, our approach complements traditional urban data collection methods, which are usually made available less frequently to urban and transportation planners, and is especially useful for developing countries where other approaches are too expensive.
Em todo o Mundo continua hoje a verificar-se a tendência das últimas décadas de crescente urbanização à medida que mais e mais pessoas mudam as suas vidas para as cidades. Apesar dessa mudança, muitas cidades não têm os recursos necessários para responder a estas alterações, o que força os seus habitantes a competir pela utilização de recursos escassos como sejam o solo, as estradas, os transportes públicos e outros serviços urbanos. Como resultado deste processo de crescimento da população urbana, observa-se nas cidades o aumento do número de viagens pendulares e correspondente aumento do número de veículos particulares, o que tem como resultado vários problemas como o congestionamento, a escassez de estacionamento, os acidentes, o custo de oportunidade de utilização do espaço ocupado por infraestruturas, a redução do nível de serviço dos transportes coletivos e os impactos ambientais. No passado, as agências governamentais seguiram uma política com custos muito elevados, focada na expansão da rede de estradas para aliviar a pressão sobre o sistema de tráfego. Contudo, muitos analistas discutem esta abordagem argumentando que para mitigar estes problemas será preferível planear e gerir de forma mais inteligente o sistema de mobilidade. Planear as cidades e a sua mobilidade tem tradicionalmente recaído sobre a importância de conhecer os problemas presentes e futuros que estão associados ao crescimento urbano como o número de viagens que são geradas, as suas origens e destinos, modo e caminhos escolhidos. Para um planeamento eficiente é necessária informação acerca dos movimentos das pessoas e dos veículos, conhecer bem as redes existentes, e compreender a natureza das diferentes atividades que são desempenhadas em cada parte da cidade. Há vários métodos tradicionais para recolher os dados necessários ao planeamento urbano e de transportes. Apesar destes métodos terem a vantagem de dar informação muito detalhada, as suas limitações de cobertura e altos custos de implementação e manutenção, por vezes, tornam-nos incomportáveis. Mais recentemente, o aumento da utilização massiva de sensorização, nomeadamente a utilização generalizada de telemóveis está a produzir grandes quantidades de informação com detalhe espácio-temporal acerca das nossas atividades e padrões de deslocação, que poderão ser importantes para o planeamento das cidades e da sua mobilidade dada a sua penetração no território, o seu baixo custo e disponibilidade em tempo real. Nesta tese explorámos a utilização dos telemóveis para traçar o perfil das dinâmicas urbanas e caraterizar os fluxos de pessoas com o objetivo de planear as cidades e os seus sistemas de transportes. Três tipos de informação passiva foram utilizados: (1) volume de chamadas, que é o total de chamadas num intervalo de tempo; (2) Erlang, que é o tempo total de chamadas durante um intervalo de tempo; e (3) a entrega de chamadas num intervalo de tempo, que é o processo de transferir chamadas ativas de uma estação base (torre) para outra estação base. As nossas observações são agregadas ao intervalo de tempo de uma hora, obtidas numa base de dados de comunicações na cidade de Lisboa, Portugal. Apesar da informação passiva móvel ser extraída sem incorrer em custos e riscos de operação da rede, esta tem duas limitações. A primeira está associada a que este método de localização tem lugar à escala do setor de cada célula (estação base), o que conduz à incerteza acerca do local da chamada; a segunda é que a informação diz respeito apenas a chamadas que foram realizadas ou a utilizações do serviço de mensagens. Apesar destas limitações considera-se que os dados dos telemóveis utilizados nesta tese permanecem relevantes para as analises efetuadas que são realizadas a uma escala em que a falta de precisão não deverá ser crítica. Para validar os nossos resultados utilizaram-se várias fontes de informação em Lisboa que permitiram caracterizar a realidade atualmente existente e melhorar a nossa compreensão das respectivas dinâmicas urbanas. As fontes consideradas para validação foram: dados dos sensos, movimento dos táxis, movimento dos autocarros, contagens de tráfego, pontos de interesse e presença de pessoas a cada hora em cada área da cidade. Neste trabalho foram propostas novas abordagens que refletem o potencial dos dados passivos dos telemóveis para o planeamento das cidades e da sua mobilidade. As abordagens seguidas focaram-se em três pontos centrais: (1) exploração dos dados no sentido de descobrir o tipo de relações que se podem encontrar entre os dados dos telemóveis e as características urbanas, atividades e dinâmicas à escala da cidade; (2) análise dos dados dos telemóveis para detetar atividades associadas à área urbana no que respeita a dois aspetos: padrão espacial dessas atividades e intensidade dessas atividades ao longo do dia; (3) utilização dos dados dos telemóveis para desenvolver modelos de previsão do estado do tráfego na rede adjacente às torres. Os resultados confirmam que os dados passivos da utilização dos telemóveis, considerando ainda a sua disponibilidade a baixo custo, podem constituir uma boa forma de analisar as dinâmicas das atividades urbanas a um nível abrangente. Além disso, a abordagem que foi utilizada complementa os métodos tradicionais de recolha de dados, que estão disponíveis com menos frequência para os planeadores da cidade e do sistema de transportes, especialmente em países em vias de desenvolvimento em que outras abordagens são demasiado dispendiosas.
FCT SFRH / BD / 33749 / 2009

A era sem fios em que se vive está intimamente ligada com a massificação de utilização de objetos móveis como são o caso dos tablets, smartphones e computadores portáteis. O conceito de Bring Your Own Device (BYOD) adotado por muitas empresas e instituições e a natureza da exigência dos serviços disponibilizados hoje em dia faz com que as redes Wireless Local Area Network (WLAN) necessitem de evoluir rapidamente para serem capazes de garantir um serviço de qualidade perante estas condições adversas. Desde que foi lançada em 1997, a norma 802.11 tem sofrido sucessivas alterações. As suas versões atuais permitem que serviços com grandes necessidades de taxas de transmissão (e.g., Streaming de vídeo ou Voice Over Internet Protocol VOIP) tenham uma qualidade assegurada. Esta é a norma sem fios mais massificada a nível global sendo inclusivamente a que é disponibilizada no ISCTE – Instituto Universitário de Lisboa (ISCTE-IUL). O presente estudo pretende fazer uma análise da qualidade da WLAN do ISCTE-IUL através dos dados de roaming, que são gerados pelo controlador de rede a todo o momento. O trabalho baseia-se no desenvolvimento de uma arquitetura alternativa de Sistema Integrado de Apoio à Decisão (SIAD), à que existe disponibilizada pelo atual fabricante da rede, a Meru Networks, mas também em metodologias processuais que podem ser executadas para verificação da qualidade de serviço. Esta dissertação tem como objetivo servir de apoio à Direção de Sistemas de Informação (DSI) do ISCTE-IUL, que através da análise dos Dashboards e cubos Multidimensionais OLAP resultantes dos desenvolvimentos, poderá efetuar otimizações na rede, com base nas ocorrências observadas
The wireless age that we live in, is closely stringed to the massification usage of mobile objects like tablets, smartphones and laptops. The Bring Your Own Device (BYOD) concept, which many companies and institutions have adopted, and the demanding nature of today’s available services, raise the need of Wireless Local Area Networks (WLAN) to evolve rapidly in order to guarantee a quality of service before these adverse conditions. Since it was first launched in 1997, the 802.11 standard has been changing successively. The current versions allow services with great transfer rate demanding’s (e.g., Video Streaming or Voice over Internet Protocol, VOIP) to be quality assured. This is the most global used wireless standard and the one that is also available in ISCTE - Instituto Universitário de Lisboa (ISCTE-IUL). The current study intends to do a quality analysis to the ISCTE-IUL WLAN, through the roaming data that is generated by the network controller at all times. The work is based on the development of an alternative architecture for an Integrated Decision Support System, to the existing one that is made available by the network manufacture Meru Networks, and in process methodologies for quality of service verification. This dissertation aims to support the ISCTE-IUL Information System Department (ISD) that with the Dashboards and Multidimensional OLAP Cubes development results will be able to carry network optimizations based on the observed happenings