Dissertations / Theses on the topic '5G Cellular systems'

Advanced spectrum sharing and resource management techniques are needed in future wireless cellular networks to ensure high data rates to the end users. New system architec- tures will be required, taking into account aspects such as like spectrum resources availabil- ity, deployment and operational costs, as well as power consumption. Thus, it becomes key for the development of the fifth generation of cellular networks (5G) to pursue an efficient exploitation of the wireless medium, in the sense of both using advanced physical (PHY) layer techniques, and also seeking coordination among operators. In this thesis, we analyze the problem of spectrum management within the next generation of cellular networks and we propose new algorithms for spectrum sharing and for interference coordination. In the first part of the thesis, we focus on the spectrum sharing between operators. Firstly, we develop a Long Term Evolution (LTE) standard compliant simulation environ- ment extending the open-source network simulator ns3 to support multi-input multi-output (MIMO) systems and advanced beamforming systems. Then, we present a mathematical analysis for the network performance of non-orthogonal spectrum sharing, connecting it directly with the statistics of the radio channel and we develop some spectrum sharing al- gorithms considering different aspects of the operators coexistence. The analysis is further extended to the performance evaluation of more complex digital beamforming techniques developed in a multi-input-single-output (MISO) system allowing to reach a Pareto equi- librium between the operators. Finally, we consider also an orthogonal spectrum sharing scenario investigating the impact of asymmetries and dynamics of the user demands on the implementation of spectrum sharing techniques. In the second part of the thesis, we extend the concept of spectrum management to two different scenarios. In the first scenario, we consider coordination between multiple cells, e.g. coordinated multipoint (CoMP). In particular, thanks to the exploitation of digital beamforming techniques, we present a novel distributed clustering algorithm that adapts the cluster configuration according to the users distribution and the average cluster size. In the second scenario, we extend the concept of spectrum sharing to the coexistence between different communications system in order to study the feasibility of the deployment of the cellular systems within the mmWave spectrum. In particular, we analyze the impact of the novel cellular networks on the fixed satellite system (FSS). In the last part of the thesis, we focus on the mobility management of the users in a het- erogeneous network. Firstly, we focus on the average performance experienced by a mobile user while crossing a pico/femtocell, as a function of the handover parameters to provide an approximate expression of the average Shannon capacity experienced by a mobile user when crossing the femtocell. Then, we propose a Markov-based framework to model the user state during the handover process and, based on such a model, we derive an optimal context-dependent handover criterion.
I futuri sistemi di comunicazione cellulare dovranno affrontare nei prossimi anni un rapido aumento della domanda di traffico dati mobile rendendo necessario l’utilizzo di avanzate tecniche di condivisione dello spettro e gestione delle risorse. Sara` quindi fonda- mentale lo sviluppo di nuove tecnologie che dovranno considerare aspetti quali la disponi- bilita` di risorse spettrali, i costi di realizzazione ed il consumo di energia. La chiave per lo sviluppo della quinta generazione di sistemi cellulari (5G), sara` quindi la ricerca di un uso piu` efficiente delle risorse wireless, sfruttando nello stesso tempo le piu` avanzate tecniche a livello fisico e la coordinazione tra gli operatori. In questa tesi, vengono analizzati i problemi relativi alla gestione delle risorse spettrali nelle reti cellulari di nuova generazione propo- nendo nuovi algoritmi per la condivisione dello spettro e la gestione delle interferenze. Nella prima parte di questa tesi vengono analizzate tematiche relative alla condivisione dello spettro tra operatori. In primo luogo e` stata implementata un’estensione del simulatore di rete ns3, basata sullo standard Long Term Evolution (LTE) al fine di supportare l’analisi di sistemi multi antenna (MIMO) e di avanzate tecniche di beamforming. E` stata quindi effettuata un’analisi matematica delle performance ottenibili dalla condivisione di spettro non ortogonale connessa direttamente al comportamento statistico del canale radio. Sono stati quindi sviluppati alcuni algoritmi di condivisione dello spettro considerando diversi aspetti della coesistenza tra operatori. L’analisi e` stata quindi estesa alla valutazione di tec- niche di beamforming digitale sviluppate in uno scenario multi-input-single-output (MISO) e atte a realizzare un equilibrio di Pareto tra gli operatori. Al termine di questa sezione sono inoltre stati analizzati alcuni scenari di condivisione ortogonale delle risorse, al fine di studi- are l’impatto delle dinamiche degli utenti sulla implementazione delle tecniche di gestione delle risorse spettrali. Nella seconda parte di questa tesi il concetto di gestione delle risorse e` stato esteso a due ulteriori scenari. Nel primo scenario, si e` considerata la coordinazione tra celle diverse (CoMP). Nello specifico, grazie all’uso di tecniche di beamforming digitale, e` stato ideato un nuovo algoritmo di clustering delle celle capace di adattare la configurazione dei clusters in relazione alla distribuzione degli utenti e alla dimensione dei cluster stessi. Nel secondo scenario, il concetto di condivisione di spettro e` stato esteso alla coesistenza tra diversi sis- temi di comunicazione, al fine di fornire uno studio di fattibilita` sullo sviluppo dei sistemi cellulari all’interno dello spettro delle onde millimetriche. In particolare, e` stato analizzato l’impatto delle nuove reti cellulari su sistemi satellitari fissi (FSS). Nell’ultima parte delle tesi vengono invece trattati aspetti riguardanti la gestione della mobilita` degli utenti all’interno delle reti eterogenee. Inizialmente, sono state analizzate le performance ottenute da un utente mobile nell’attraversare una pico/femto cella in funzione dei parametri di handover, al fine di fornire un espressione della capacita` di Shannon media dell’utente. E’ stato quindi proposto un modello basato su una catena dI Markov atto a studiare lo stato dell’utente durante il processo di handover e, sfruttando tale modello, e` stato derivato un criterio di handover ottimale basato sulle condizioni del contesto.

From the first generation, 1G, to the fourth generation, 4G, the development and technological advancements in telecommunications network systems have been remarkable. Faster and better connections have opened up for new markets, ideas and possibilities, to that extent that there now is a demand that surpasses the supply. Despite all these advancements made in the mobile communications field most of the concept of how the technology works and its infrastructure has remained the same. This however, is about to change with the introduction of the fifth generation (5G) mobile communication. With the introduction of 5G much of the technology introduced will be different from that of previous generations. This change extends to include the entire infrastructure of the mobile communications system. With these major changes, many of the tools available today for telecommunications network evaluation do not really suffice to include the 5G network standard. For this reason, there is a need to develop a new kind of tool that will be able to include the changes brought by this new network standard. In this thesis a simulation framework adapted for the next generation telecommunication standard 5G is set to be developed. This framework should include many of the characteristics that set 5G aside from previous generations.

Mobile traffic forecasting is a relatively new research area, which is becoming of fundamental importance for next-generation networks. Proactively knowing the user demand allows the system to allocate resources and apply energy-saving decisions properly. Classical models are limited by the stationary assumption of time sequences and fail to take correlations into account. This work presents results on cellular network traffic analysis and prediction, providing a novel, robust, and precise machine learning model to efficiently and dynamically manage network resources in 5G systems.

Future fifth generation (5G) cellular networks have to cope with the expected ten-fold increase in mobile data traffic between 2015 and 2021. To achieve this goal, new technologies are being considered, including massive multiple-input multiple-output (MIMO) systems and millimeter-wave (mmWave) communications. Massive MIMO involves the use of large antenna array sizes at the base station, while mmWave communications employ frequencies between 30 and 300 GHz. In this thesis we study the impact of these technologies on the performance of channel estimators. Our results show that the characteristics of the propagation channel at mmWave frequencies improve the channel estimation performance in comparison with current, low frequency-based, cellular networks. Furthermore, we demonstrate the existence of an optimal angular spread of the multipath clusters, which can be used to maximize the capacity of mmWave networks. We also propose efficient noise variance estimators, which can be employed as an input to existing channel estimators.

En la actualidad, la Internet de las Cosas (Internet of Things, IoT) es una tecnología esencial para la próxima generación de sistemas inalámbricos. La conectividad es la base de IoT, y el tipo de acceso requerido dependerá de la naturaleza de la aplicación. Uno de los principales facilitadores del entorno IoT es la comunicación machine-to-machine (M2M) y, en particular, su enorme potencial para ofrecer conectividad ubicua entre dispositivos inteligentes. Las redes celulares son la elección natural para las aplicaciones emergentes de IoT y M2M. Un desafío importante en las redes celulares es conseguir que la red sea capaz de manejar escenarios de acceso masivo en los que numerosos dispositivos utilizan comunicaciones M2M. Por otro lado, los sistemas celulares han experimentado un tremendo desarrollo en las últimas décadas: incorporan tecnología sofisticada y nuevos algoritmos para ofrecer una amplia gama de servicios. El modelado y análisis del rendimiento de estas redes multiservicio es también una tarea desafiante que podría requerir un gran esfuerzo computacional. Para abordar los desafíos anteriores, nos centramos en primer lugar en el diseño y la evaluación de las prestaciones de nuevos mecanismos de control de acceso para hacer frente a las comunicaciones masivas M2M en redes celulares. Posteriormente nos ocupamos de la evaluación de prestaciones de redes multiservicio y proponemos una nueva técnica analítica que ofrece precisión y eficiencia computacional. Nuestro principal objetivo es proporcionar soluciones para aliviar la congestión en la red de acceso radio cuando un gran número de dispositivos M2M intentan conectarse a la red. Consideramos los siguientes tipos de escenarios: (i) los dispositivos M2M se conectan directamente a las estaciones base celulares, y (ii) forman grupos y los datos se envían a concentradores de tráfico (gateways) que les proporcionan acceso a la infraestructura. En el primer escenario, dado que el número de dispositivos añadidos a la red aumenta continuamente, esta debería ser capaz de manejar el considerable incremento en las solicitudes de acceso. El 3rd Generation Partnership Project (3GPP) ha propuesto el access class barring (ACB) como una solución práctica para el control de congestión en la red de acceso radio y la red troncal. El ajuste correcto de los parámetros de ACB de acuerdo con la intensidad del tráfico es crítico, pero cómo hacerlo de forma dinámica y autónoma es un problema complejo cuya solución no está recogida en las especificaciones del 3GPP. Esta tesis doctoral contribuye al análisis del rendimiento y al diseño de nuevos algoritmos que implementen efectivamente este mecanismo, y así superar los desafíos introducidos por las comunicaciones masivas M2M. En el segundo escenario, dado que la heterogeneidad de los dispositivos IoT y las arquitecturas celulares basadas en hardware imponen desafíos aún mayores para permitir una comunicación flexible y eficiente en los sistemas inalámbricos 5G, esta tesis doctoral también contribuye al diseño de software-defined gateways (SD-GWs) en una nueva arquitectura propuesta para redes inalámbricas definidas por software que se denomina SoftAir. Esto permite manejar tanto un gran número de dispositivos como el volumen de datos que estarán vertiendo en la red. Otra contribución de esta tesis doctoral es la propuesta de una técnica novedosa para el análisis de prestaciones de redes multiservicio de alta capacidad que se basa en un nuevo enfoque del modelizado analítico de sistemas que operan a diferentes escalas temporales. Este enfoque utiliza el análisis del transitorio de una serie de subcadenas absorbentes y lo denominamos absorbing Markov chain approximation (AMCA). Nuestros resultados muestran que para un coste computacional dado, AMCA calcula los parámetros de prestaciones habituales de un sistema con mayor precisión, en comparación con los resultados obtenidos por otr
Nowadays, Internet of Things (IoT) is an essential technology for the upcoming generation of wireless systems. Connectivity is the foundation for IoT, and the type of access required will depend on the nature of the application. One of the leading facilitators of the IoT environment is machine-to-machine (M2M) communication, and particularly, its tremendous potential to offer ubiquitous connectivity among intelligent devices. Cellular networks are the natural choice for emerging IoT and M2M applications. A major challenge in cellular networks is to make the network capable of handling massive access scenarios in which myriad devices deploy M2M communications. On the other hand, cellular systems have seen a tremendous development in recent decades; they incorporate sophisticated technology and algorithms to offer a broad range of services. The modeling and performance analysis of these large multi-service networks is also a challenging task that might require high computational effort. To address the above challenges, we first concentrate on the design and performance evaluation of novel access control schemes to deal with massive M2M communications. Then, we focus on the performance evaluation of large multi-service networks and propose a novel analytical technique that features accuracy and computational efficiency. Our main objective is to provide solutions to ease the congestion in the radio access or core network when massive M2M devices try to connect to the network. We consider the following two types of scenarios: (i) massive M2M devices connect directly to cellular base stations, and (ii) they form clusters and the data is forwarded to gateways that provide them with access to the infrastructure. In the first scenario, as the number of devices added to the network is constantly increasing, the network should handle the considerable increment in access requests. Access class barring (ACB) is proposed by the 3rd Generation Partnership Project (3GPP) as a practical congestion control solution in the radio access and core network. The proper tuning of the ACB parameters according to the traffic intensity is critical, but how to do so dynamically and autonomously is a challenging task that has not been specified. Thus, this dissertation contributes to the performance analysis and optimal design of novel algorithms to implement effectively this barring scheme and overcome the challenges introduced by massive M2M communications. In the second scenario, since the heterogeneity of IoT devices and the hardware-based cellular architectures impose even greater challenges to enable flexible and efficient communication in 5G wireless systems, this dissertation also contributes to the design of software-defined gateways (SD-GWs) in a new architecture proposed for wireless software-defined networks called SoftAir. The deployment of these SD-GWs represents an alternative solution aiming at handling both a vast number of devices and the volume of data they will be pouring into the network. Another contribution of this dissertation is to propose a novel technique for the performance analysis of large multi-service networks. The underlying complexity of the network, particularly concerning its size and the ample range of configuration options, makes the solution of the analytical models computationally costly. However, a typical characteristic of these networks is that they support multiple types of traffic flows operating at different time-scales. This time-scale separation can be exploited to reduce considerably the computational cost associated to determine the key performance indicators. Thus, we propose a novel analytical modeling approach based on the transient regime analysis, that we name absorbing Markov chain approximation (AMCA). For a given computational cost, AMCA finds common performance indicators with greater accuracy, when compared to the results obtained by other approximate methods proposed in the literature.
En l'actualitat, la Internet de les Coses (Internet of Things, IoT) és una tecnologia essencial per a la propera generació de sistemes sense fil. La connectivitat és la base d'IoT, i el tipus d'accés requerit dependrà de la naturalesa de l'aplicació. Un dels principals facilitadors de l'entorn IoT és la comunicació machine-to-machine (M2M) i, en particular, el seu enorme potencial per oferir connectivitat ubiqua entre dispositius intel · ligents. Les xarxes mòbils són l'elecció natural per a les aplicacions emergents de IoT i M2M. Un desafiament important en les xarxes mòbils que actualment está rebent molta atenció és aconseguir que la xarxa siga capaç de gestionar escenaris d'accés massiu en què una gran quantitat de dispositius utilitzen comunicacions M2M. D'altra banda, els sistemes mòbils han experimentat un gran desenvolupament en les últimes dècades: incorporen tecnologia sofisticada i nous algoritmes per oferir una àmplia gamma de serveis. El modelatge i análisi del rendiment d'aquestes xarxes multiservei és també un desafiament important que podria requerir un gran esforç computacional. Per abordar els desafiaments anteriors, en aquesta tesi doctoral ens centrem en primer lloc en el disseny i l'avaluació de les prestacions de nous mecanismes de control d'accés per fer front a les comunicacions massives M2M en xarxes cel · lulars. Posteriorment ens ocupem de l'avaluació de prestacions de xarxes multiservei i proposem una nova tècnica analítica que ofereix precisió i eficiència computacional. El nostre principal objectiu és proporcionar solucions per a alleujar la congestió a la xarxa d'accés ràdio quan un gran nombre de dispositius M2M intenten connectar-se a la xarxa. Considerem els dos tipus d'escenaris següents: (i) els dispositius M2M es connecten directament a les estacions base cel · lulars, i (ii) formen grups i les dades s'envien a concentradors de trànsit (gateways) que els proporcionen accés a la infraestructura. En el primer escenari, atès que el nombre de dispositius afegits a la xarxa augmenta contínuament, aquesta hauria de ser capaç de gestionar el considerable increment en les sol · licituds d'accés. El 3rd Generation Partnership Project (3GPP) ha proposat l'access class barring (ACB) com una solució pràctica per al control de congestió a la xarxa d'accès ràdio i la xarxa troncal. L'ajust correcte dels paràmetres d'ACB d'acord amb la intensitat del trànsit és crític, però com fer-ho de forma dinàmica i autònoma és un problema complex, la solució del qual no està recollida en les especificacions del 3GPP. Aquesta tesi doctoral contribueix a l'anàlisi del rendiment i al disseny de nous algoritmes que implementen efectivament aquest mecanisme, i així superar els desafiaments introduïts per les comunicacions massives M2M en les xarxes mòbils actuals i futures. En el segon escenari, atès que l'heterogeneïtat dels dispositius IoT i les arquitectures cel · lulars basades en hardware imposen desafiaments encara més grans per permetre una comunicació flexible i eficient en els sistemes sense fil 5G, aquesta tesi doctoral també contribueix al disseny de software-defined gateways (SD-GWS) en una nova arquitectura proposada per a xarxes sense fils definides per programari que s'anomena SoftAir. Això permet gestionar tant un gran nombre de dispositius com el volum de dades que estaran abocant a la xarxa. Una altra contribució d'aquesta tesi doctoral és la proposta d'una tècnica innovadora per a l'anàlisi de prestacions de xarxes multiservei d'alta capacitat que es basa en un nou enfocament del modelitzat analític de sistemes que operen a diferents escales temporals. Aquest enfocament utilitza l'anàlisi del transitori d'una sèrie de subcadenes absorbents i l'anomenem absorbing Markov chain Approximation (AMCA). Els nostres resultats mostren que per a un cost computacional donat, AMCA calcula els paràmetres de prestacions habituals d
Tello Oquendo, LP. (2018). Design and Performance Analysis of Access Control Mechanisms for Massive Machine-to-Machine Communications in Wireless Cellular Networks [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/107946
TESIS

Nei prossimi anni è previsto un aumento del traffico dati, e la quinta generazione cellulare 5G dovrà fare affidamento su nuove tecnologie, come le onde millimetriche e il massive-MIMO, per soddisfare tale richiesta. Lo spettro di frequenze sotto i 6 GHz risulta infatti sovra-utilizzato, e le frequenze relative alle onde millimetriche promettono di garantire alte velocità di trasmissione dei dati, grazie alla grande disponibilità di banda, specialmente attorno ai 60 GHz. Nonostante questo aspetto favorevole, si ha però un elevato path loss e la difficoltà nel penetrare gli ostacoli. Per ovviare a tali problemi, l'utilizzo di tecniche di beamforming, ottenibili grazie all'uso congiunto di frequenze a onde millimetriche e massive-MIMO, permette di direzionare il pattern dell'antenna nelle direzioni spaziali desiderate, e di compensare il path loss grazie all'aumento della direttività. Considerando un sistema cellulare 5G, una comunicazione di tipo direttivo impone che i beam dell'utente e della stazione radio base debbano essere allineati per garantire la comunicazione, introducendo possibili ritardi nella fase di accesso iniziale. Di conseguenza, lo studio di algoritmi ad-hoc, progettati per velocizzare questa fase rappresenta un sfida importante per l'ottimizzazione dei futuri sistemi 5G. Nell'ottica quindi di velocizzare l'accesso iniziale nelle reti 5G, in questa tesi prima di tutto mostriamo gli approcci proposti nello stato dell'arte, mettendo in evidenza gli aspetti che possono essere migliorati. Successivamente viene spiegato il simulatore che abbiamo implementato su Matlab, e infine viene introdotto un nuovo algoritmo. In particolare, l'algoritmo proposto si basa sulla memoria degli utenti visti per settore e sull'utilizzo di diverse configurazioni dei beam. Questi due aspetti combinati tra loro risultano innovativi rispetto allo stato dell'arte. I risultati numerici ottenuti dimostrano la bontà della tecnica proposta negli scenari 5G considerati.

Předkládaná disertační práce je zaměřena na "heterogenní propojení mobilních zařízení v bezdrátových systémech 5. generace". Navzdory nepochybnému pokroku v rámci navržených komunikačních řešení postrádají mobilní sítě nastupující generace dostatečnou šířku pásma a to hlavně kvůli neefektivnímu využívání rádiového spektra. Tato situace tedy v současné době představuje řadu otázek v oblasti výzkumu. Hlavním cílem této disertační práce je proto návrh nových komunikačních mechanismů pro komunikaci mezi zařízeními v bezprostřední blízkosti s asistencí mobilní sítě a dále pak návrh a implementace algoritmů pro dynamické přidělování frekvenčního spektra v nastupujících mobilních sítích 5G. Navrhnuté komunikační mechanismy a algoritmy jsou následně komplexně vyhodnoceny pomocí nově vyvinutých simulačních nástrojů (kalibrovaných s využitím 3GPP trénovacích dat) a zejména pak v experimentální mobilní síti LTE-A, která se nachází v prostorách Vysokého učení technického v Brně, Česká Republika. Získané praktické výsledky, které jsou podpořeny zcela novou matematickou analýzou ve speciálně navržených charakteristických scénářích, představují řešení pro vlastníka spektra v případě požadavků na jeho dynamické sdílení. Tato metoda tedy představuje možnost pro efektivnější využití spektra v rámci mobilních sítí 5G bez degradace kvality služeb (QoS) a kvality zážitků (QoE) pro koncové uživatele. Vědecký přínos dosažených výsledků dokazuje fakt, že některé z principů představených v této disertační práci byly zahrnuty do celosvětově uznávaného standardu (specifikace) 3GPP Release 12.

La quinta generación de redes móviles (5G) se encuentra a la vuelta de la esquina. Se espera provea de beneficios extraordinarios a la población y que resuelva la mayoría de los problemas de las redes 4G actuales. El éxito de 5G, cuya primera fase de estandarización ha sido completada, depende de tres pilares: comunicaciones tipo-máquina masivas, banda ancha móvil mejorada y comunicaciones ultra fiables y de baja latencia (mMTC, eMBB y URLLC, respectivamente). En esta tesis nos enfocamos en el primer pilar de 5G, mMTC, pero también proveemos una solución para lograr eMBB en escenarios de distribución masiva de contenidos. Específicamente, las principales contribuciones son en las áreas de: 1) soporte eficiente de mMTC en redes celulares; 2) acceso aleatorio para el reporte de eventos en redes inalámbricas de sensores (WSNs); y 3) cooperación para la distribución masiva de contenidos en redes celulares. En el apartado de mMTC en redes celulares, esta tesis provee un análisis profundo del desempeño del procedimiento de acceso aleatorio, que es la forma mediante la cual los dispositivos móviles acceden a la red. Estos análisis fueron inicialmente llevados a cabo por simulaciones y, posteriormente, por medio de un modelo analítico. Ambos modelos fueron desarrollados específicamente para este propósito e incluyen uno de los esquemas de control de acceso más prometedores: access class barring (ACB). Nuestro modelo es uno de los más precisos que se pueden encontrar en la literatura y el único que incorpora el esquema de ACB. Los resultados obtenidos por medio de este modelo y por simulación son claros: los accesos altamente sincronizados que ocurren en aplicaciones de mMTC pueden causar congestión severa en el canal de acceso. Por otro lado, también son claros en que esta congestión se puede prevenir con una adecuada configuración del ACB. Sin embargo, los parámetros de configuración del ACB deben ser continuamente adaptados a la intensidad de accesos para poder obtener un desempeño óptimo. En la tesis se propone una solución práctica a este problema en la forma de un esquema de configuración automática para el ACB; lo llamamos ACBC. Los resultados muestran que nuestro esquema puede lograr un desempeño muy cercano al óptimo sin importar la intensidad de los accesos. Asimismo, puede ser directamente implementado en redes celulares para soportar el tráfico mMTC, ya que ha sido diseñado teniendo en cuenta los estándares del 3GPP. Además de los análisis descritos anteriormente para redes celulares, se realiza un análisis general para aplicaciones de contadores inteligentes. Es decir, estudiamos un escenario de mMTC desde la perspectiva de las WSNs. Específicamente, desarrollamos un modelo híbrido para el análisis de desempeño y la optimización de protocolos de WSNs de acceso aleatorio y basados en cluster. Los resultados muestran la utilidad de escuchar el medio inalámbrico para minimizar el número de transmisiones y también de modificar las probabilidades de transmisión después de una colisión. En lo que respecta a eMBB, nos enfocamos en un escenario de distribución masiva de contenidos, en el que un mismo contenido es enviado de forma simultánea a un gran número de usuarios móviles. Este escenario es problemático, ya que las estaciones base de la red celular no cuentan con mecanismos eficientes de multicast o broadcast. Por lo tanto, la solución que se adopta comúnmente es la de replicar e contenido para cada uno de los usuarios que lo soliciten; está claro que esto es altamente ineficiente. Para resolver este problema, proponemos el uso de esquemas de network coding y de arquitecturas cooperativas llamadas nubes móviles. En concreto, desarrollamos un protocolo para la distribución masiva de contenidos, junto con un modelo analítico para su optimización. Los resultados demuestran que el modelo propuesto es simple y preciso, y que el protocolo puede reducir el con
La cinquena generació de xarxes mòbils (5G) es troba molt a la vora. S'espera que proveïsca de beneficis extraordinaris a la població i que resolga la majoria dels problemes de les xarxes 4G actuals. L'èxit de 5G, per a la qual ja ha sigut completada la primera fase del qual d'estandardització, depén de tres pilars: comunicacions tipus-màquina massives, banda ampla mòbil millorada, i comunicacions ultra fiables i de baixa latència (mMTC, eMBB i URLLC, respectivament, per les seues sigles en anglés). En aquesta tesi ens enfoquem en el primer pilar de 5G, mMTC, però també proveïm una solució per a aconseguir eMBB en escenaris de distribució massiva de continguts. Específicament, les principals contribucions són en les àrees de: 1) suport eficient de mMTC en xarxes cel·lulars; 2) accés aleatori per al report d'esdeveniments en xarxes sense fils de sensors (WSNs); i 3) cooperació per a la distribució massiva de continguts en xarxes cel·lulars. En l'apartat de mMTC en xarxes cel·lulars, aquesta tesi realitza una anàlisi profunda de l'acompliment del procediment d'accés aleatori, que és la forma mitjançant la qual els dispositius mòbils accedeixen a la xarxa. Aquestes anàlisis van ser inicialment dutes per mitjà de simulacions i, posteriorment, per mitjà d'un model analític. Els models van ser desenvolupats específicament per a aquest propòsit i inclouen un dels esquemes de control d'accés més prometedors: el access class barring (ACB). El nostre model és un dels més precisos que es poden trobar i l'únic que incorpora l'esquema d'ACB. Els resultats obtinguts per mitjà d'aquest model i per simulació són clars: els accessos altament sincronitzats que ocorren en aplicacions de mMTC poden causar congestió severa en el canal d'accés. D'altra banda, també són clars en què aquesta congestió es pot previndre amb una adequada configuració de l'ACB. No obstant això, els paràmetres de configuració de l'ACB han de ser contínuament adaptats a la intensitat d'accessos per a poder obtindre unes prestacions òptimes. En la tesi es proposa una solució pràctica a aquest problema en la forma d'un esquema de configuració automàtica per a l'ACB; l'anomenem ACBC. Els resultats mostren que el nostre esquema pot aconseguir un acompliment molt proper a l'òptim sense importar la intensitat dels accessos. Així mateix, pot ser directament implementat en xarxes cel·lulars per a suportar el trànsit mMTC, ja que ha sigut dissenyat tenint en compte els estàndards del 3GPP. A més de les anàlisis descrites anteriorment per a xarxes cel·lulars, es realitza una anàlisi general per a aplicacions de comptadors intel·ligents. És a dir, estudiem un escenari de mMTC des de la perspectiva de les WSNs. Específicament, desenvolupem un model híbrid per a l'anàlisi de prestacions i l'optimització de protocols de WSNs d'accés aleatori i basats en clúster. Els resultats mostren la utilitat d'escoltar el mitjà sense fil per a minimitzar el nombre de transmissions i també de modificar les probabilitats de transmissió després d'una col·lisió. Pel que fa a eMBB, ens enfoquem en un escenari de distribució massiva de continguts, en el qual un mateix contingut és enviat de forma simultània a un gran nombre d'usuaris mòbils. Aquest escenari és problemàtic, ja que les estacions base de la xarxa cel·lular no compten amb mecanismes eficients de multicast o broadcast. Per tant, la solució que s'adopta comunament és la de replicar el contingut per a cadascun dels usuaris que ho sol·liciten; és clar que això és altament ineficient. Per a resoldre aquest problema, proposem l'ús d'esquemes de network coding i d'arquitectures cooperatives anomenades núvols mòbils. En concret, desenvolupem un protocol per a realitzar la distribució massiva de continguts de forma eficient, juntament amb un model analític per a la seua optimització. Els resultats demostren que el model proposat és simple i precís
The 5th generation (5G) of mobile networks is just around the corner. It is expected to bring extraordinary benefits to the population and to solve the majority of the problems of current 4th generation (4G) systems. The success of 5G, whose first phase of standardization has concluded, relies in three pillars that correspond to its main use cases: massive machine-type communication (mMTC), enhanced mobile broadband (eMBB), and ultra-reliable low latency communication (URLLC). This thesis mainly focuses on the first pillar of 5G: mMTC, but also provides a solution for the eMBB in massive content delivery scenarios. Specifically, its main contributions are in the areas of: 1) efficient support of mMTC in cellular networks; 2) random access (RA) event-reporting in wireless sensor networks (WSNs); and 3) cooperative massive content delivery in cellular networks. Regarding mMTC in cellular networks, this thesis provides a thorough performance analysis of the RA procedure (RAP), used by the mobile devices to switch from idle to connected mode. These analyses were first conducted by simulation and then by an analytical model; both of these were developed with this specific purpose and include one of the most promising access control schemes: the access class barring (ACB). To the best of our knowledge, this is one of the most accurate analytical models reported in the literature and the only one that incorporates the ACB scheme. Our results clearly show that the highly-synchronized accesses that occur in mMTC applications can lead to severe congestion. On the other hand, it is also clear that congestion can be prevented with an adequate configuration of the ACB scheme. However, the configuration parameters of the ACB scheme must be continuously adapted to the intensity of access attempts if an optimal performance is to be obtained. We developed a practical solution to this problem in the form of a scheme to automatically configure the ACB; we call it access class barring configuration (ACBC) scheme. The results show that our ACBC scheme leads to a near-optimal performance regardless of the intensity of access attempts. Furthermore, it can be directly implemented in 3rd Generation Partnership Project (3GPP) cellular systems to efficiently handle mMTC because it has been designed to comply with the 3GPP standards. In addition to the analyses described above for cellular networks, a general analysis for smart metering applications is performed. That is, we study an mMTC scenario from the perspective of event detection and reporting WSNs. Specifically, we provide a hybrid model for the performance analysis and optimization of cluster-based RA WSN protocols. Results showcase the utility of overhearing to minimize the number of packet transmissions, but also of the adaptation of transmission parameters after a collision occurs. Building on this, we are able to provide some guidelines that can drastically increase the performance of a wide range of RA protocols and systems in event reporting applications. Regarding eMBB, we focus on a massive content delivery scenario in which the exact same content is transmitted to a large number of mobile users simultaneously. Such a scenario may arise, for example, with video streaming services that offer a particularly popular content. This is a problematic scenario because cellular base stations have no efficient multicast or broadcast mechanisms. Hence, the traditional solution is to replicate the content for each requesting user, which is highly inefficient. To solve this problem, we propose the use of network coding (NC) schemes in combination with cooperative architectures named mobile clouds (MCs). Specifically, we develop a protocol for efficient massive content delivery, along with the analytical model for its optimization. Results show the proposed model is simple and accurate, and the protocol can lead to energy savings of up to 37 percent when compared to the traditional approach.
Leyva Mayorga, I. (2018). On reliable and energy efficient massive wireless communications: the road to 5G [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/115484
TESIS

碩士
國立中正大學
通訊工程研究所
104
Two-layer cell architecture has been proposed as a candidate for future 5G systems, where the system constitutes of macro cells and small cells. Macro cells use the existing 4G system while small cell use 5G technology to provide higher high data rate and system capacity. A user first camps 4G systems through contention-based random access mechanism, and when very high data rate is needed it is handed over to 5G systems via contention-free random access. Whether the current 4G random access design is able to cope with the very large number of users anticipated in the future 5G systems is theme of this research. In this thesis, the performance of random access in the two-layer cell architecture is studied in realistic channel environment, with MTC (Machine-Type Communications) traffic model proposed by 3GPP. The performance indexes include access success probability, collision probability, the access delay and total power consumption. Numerical results show that the current 4G random access design is not able to achieve the 5G requirements because of high collision probability, and excessive access delay and power consumption. One remedy is to increase the random access opportunity (RAO). Our results show that with 3-times RAO, access success rate is increased to 96%, and collision probability is decreased to 17%, and that significantly improves the random access performance.

碩士
國立交通大學
電信工程研究所
103
In this thesis, we propose two kinds of iterative channel estimation method to suppress the pilot contamination phenomenon in 5G cellular mobile radio communication systems. Due to pilot sequence reuse in different cells, the estimated channel would be contaminated by neighboring cells which use the same pilot. To solve the pilot contamination problems caused by pilot sequence reuse, we first use estimated data sequence as a pilot signal to execute iterative channel estimation. Secondly, as the pilot and data sequences are transmitted in a combined manner, our second proposed method utilizes data sequence as an auxiliary pilot signal in addition to utilizing the orthogonal pilot signal when executing channel estimation. Our simulation results show that these methods can achieve the required BER performance within a acceptable number of iterations.

碩士
國立交通大學
電信工程研究所
108
With the development of the wireless communication technology, the fifth generation(5G) mobile communication standards will be formally released by 2020 and applied to commerce. People from all walks of life dedicate to developing 5G communication system to meet the higher demand of transmission, and space division multiple access (SDMA) is regarded as a key technology. In response to 5G communication system, our lab researches on a possible technique known as the massive antenna multipath division multiple access (MDMA) cellular system. In this thesis, we compare with the performance of two above-mentioned systems under multicellular. For SDMA system, Base station (BS) utilizes directional antennas to effect adaptive beamforming and communicate with mobile station (MS). In uplink (UL), BS uses pilot signals sent by MS to estimate propagation channel and uses minimum mean square error equalizer to recover the user data. In downlink (DL), BS uses channel state information (CSI) estimated in uplink to do pre-equalization. Finally, we simulate UL and DL of MDMA system and SDMA system respectively. Simulation results are given and discussed on the performance of these two systems.

Reduced feedback schemes are a crucial component of orthogonal frequency division multiplexing-based 4G and 5G cellular systems that use downlink scheduling, adaptive modulation and coding, and multiple-input-multiple-output (MIMO). In these systems, the system bandwidth is divided into several subbands. The reduced feedback schemes ensure that the overhead of feeding back the subband-level channel state information from the users to the base station (BS) does not overwhelm the limited-bandwidth uplink feedback channel. Differential feedback is a key component of the reduced feedback schemes specified in both 4G and 5G standards. In it, the user feeds back a 4-bit wideband channel quality indicator (CQI), which indicates the rate that the user can decode if the BS were to transmit to it over the entire system bandwidth, and a 2-bit differential CQI for each subband relative to the wideband CQI. We present a novel modeling and a comprehensive analysis of the throughput of the differential feedback scheme. It incorporates several key and unique aspects of the 4G and 5G standards and encompasses different multi-antenna modes and schedulers. The analysis brings out several insights about how the throughput increases as the correlation between subbands increases and how the feedback scheme reduces the overhead while only marginally reducing the throughput. We then develop a BS-side estimation technique for the widely studied and simpler threshold-based quantized feedback scheme, in which a user feeds back a quantized value of the signal-to-noise ratio for each subband. For it, we derive a novel, throughput-optimal rate adaptation rule in closed-form for different multi-antenna modes. We also develop a computationally simpler near-optimal variant of it and derive an insightful lower bound that characterizes the average throughput gain achieved by the proposed scheme over conventional rate adaptation. Using the insights obtained from the throughput analysis and the BS-side estimation technique for threshold-based quantized feedback, we then develop BS-side estimation for differential feedback. We do so for a more general variant of it in which the differential CQI overhead can be different for different subbands. This provides a new flexibility to the BS to control the feedback overhead and leads to a new throughputoptimal rate adaptation rule for it. It brings out the sub-optimality of the conventional method used in the literature. Our approach incorporates small-scale fading, largescale shadowing, path-loss, and different MIMO modes in single-user and multi-user deployment scenarios. It achieves nearly the same throughput as the scheme currently employed in 4G and 5G, but with much less feedback overhead.

The rapid development of Machine-Type-Communication (MTC) has brought big challenges to cellular networks such as super-dense devices and high-shadowing channels which may substantially decrease the spectrum efficiency and increase devices' power consumption. It is pressing to improve the transmission efficiency for MTC due to the limited wireless spectrum. Lower efficiency may also lead to longer transmission time and more energy consumption which conflict with MTC's requirement of lower power consumption. In order to address the above issues, we propose to apply Network Coding (NC) and Device-to-Device (D2D) communications to MTC devices. Our approach introduces an additional delay for local packet exchange, which is acceptable given that MTC traffic typically has the feature of delay tolerance to certain degree. The benefit of the proposed approach is that the cellular transmissions are no longer user-specific, and thus an additional multi-user diversity gain is achieved. The cellular transmission efficiency will also be increased. How to apply the proposed approach for both downlink and uplink has been studied. For the downlink, in addition to the reduction of cellular resource consumption, the MTC devices' feedback load can also be significantly reduced because the cellular transmissions are not sensitive to user-specific errors. In the uplink, besides the enhanced transmission efficiency for full-buffer traffic, an additional small-data aggregation gain is achieved for MTC small-data traffic. Theoretical performance analyses for both downlink and uplink and the corresponding numerical evaluations are given. Though the proposed NC and D2D approach can improve the transmission efficiency by exploring multi-user diversity gain, poor-quality MTC channels still exist which affect system performance. When the whole group MTC devices in an area experience high shadowing and penetration loss, we have to increase either the resource consumption or the transmitting power to overcome the poor-quality channels. The existing small-cell solution can improve the MTC channel quality, but MTC's unique traffic characteristics and quality of service requirements, as well as other practical issues, make the small-cell deployment unprofi table. Therefore, we propose a solution using Floating Relay (FR) given the mature technologies of Unmanned Aerial Vehicle (UAV). We rst target on the high-shadowing channels of the MTC devices and introduce the FR into the cellular system to improve the transmission efficiency and maximize the system capacity. An optimization problem, given the capacity limit of the FR's back-haul link and the maximum transmission power of each user, is formulated and then theoretically solved. An effective on-line fight path planning algorithm is also proposed. Then, we extend the FR concept to a bigger picture and propose the UAV-assisted heterogeneous cellular solution. Detailed system design and comprehensive analyses on FR-cells deployment including frequency reuse, interference, backhaul resource allocation, and coverage are given. For UAV assisted networking systems, mobility and topology play important roles. How to dispatch a UAV to the optimal location in a mesh network to enhance the coverage and service of the existing network is a critical issue. Given the topology of existing service nodes, a new supplementary UAV can be sent to improve the quality of service especially for the users with poor-quality channels. The location of a newly added UAV is optimized to improve the service quality to the worst point. In summary, we propose two means to improve the transmission efficiency for MTC in this thesis work. The NC and D2D approach can be used when some of the MTC devices have chances to experience better channels because of the fast fading and uneven shadowing. Otherwise, the FR can be applied to proactively improve the channel quality for MTC. The NC and D2D approach sticks to the latest standard in the cellular system and thus provides a down-to-earth and backward-compatible MTC solution for 5G cellular system. The UAV-assisted heterogeneous cellular solution and UAV mesh networks can enable mobile Internet and ultra-reliable low latency communications, respectively. These solutions together effectively and efficiently support MTC, which is key to future proliferation of Internet of Things
Graduate

碩士
國立交通大學
電信工程研究所
104
In the proposed 5G cellular system [1], all users use the same frequency band to transmit data; like CDMA systems, any excessive transmit power will increase the overall interference. Without power control mechanisms, better link quality and system capacity cannot be achieved in the proposed 5G cellular system. We adopt open-loop power control in uplink transmission for combating near-far problem so that equal signal power from the mobiles can be received by the same BS. The performance of uplink power control is evaluated by power control error. Power control in downlink transmission is used to increase system capacity. We make a simplified analysis and simulation to evaluate the capacity of a downlink system with ideal SIR balancing. Besides, the downlink capacity with a practical closed-loop power control method is verified by computer simulation in this thesis.

碩士
國立交通大學
電信工程研究所
106
Through the advance of communication technology, the time of 5G mobile communication is arrived. A possible technique for 5G cellular system is called the TDD massive antenna multipath division multiple access (MDMA) system. In this thesis, we simulate this system under different cellular structures, and evaluate the capacity of uplink(UL) and downlink(DL) systems. In uplink, base station(BS) uses pilot signals sent by mobile stations (MS) to estimate channel and use Parallel-Interference-Cancellation(PIC) and Kalman filter to suppress interference. At last, we use Maximal-Ratio Combining(MRC) to recover the data from each mobile station. In downlink, base station utilizes uplink channel estimation to do Pre-RAKE on data and send it to mobile station. Through simulation, we found that system capacity can be greatly enhanced and lower complexity in uplink and downlink by implementing selected 60 degree sector edge excited zone cellular structure. In practical consideration, we can lower system complexity in uplink and greatly enhance system capacity compare to selected 60 degree sector edge excited zone cellular structure in downlink by implementing selected omni zone cellular structure with 1/4 cell split.

碩士
國立交通大學
電信工程研究所
104
In next ten years, existing mobile communication standards obviously cannot meet with users’ need. In reponse to this, we study on a fifth generation cellular system that uses the method of soft handoff. In this thesis, we research on the improvement of SIR in downlink and uplink system when soft handoff is executed. We consider the cellular system with home cell and four tiers. We start from a cellular system without soft handoff and calculate the SIR distribution. We will then do soft handoff with two base station for these users who cannot achieve the target E_b⁄I_0 and observe the improvement in SIR distribution. We assume in soft handoff, we allow at most three base station. As a result, we will do soft handoff with three base station for these users who cannot achieve the target E_b⁄I_0 and observe the improvement of SIR distribution. At the end, we will investigate for a cellular system with soft handoff for which the target E_b⁄I_0 is achieved, how many traffic channels it can serve at most. And when power control is used, how much additional system capacity it can bring in. From two simulation results, we observe that in the fifth generation downlink system, soft handoff can achieve very good system capacity improvement.

碩士
國立交通大學
電信工程研究所
105
In this thesis, we studied and investigated the synchronization procedure for universal filtered multi-carrier (UFMC) in our proposed 5G massive antenna multipath division multiple access (MDMA) cellular system of downlink transmission. In our system, we consider multicarrier modulation to transmitted traffic data. One of the multicarrier scheme is OFDM, which has the problem of high out-of-band power. UFMC is a novel multicarrier transmission scheme, and it can suppress out-of-band power effectively as compared to OFDM system. In addition, multicarrier schemes are sensitive to time-frequency synchronization. In uplink transmission, pilot sequence can be used for synchronization. However, in downlink transmission, there is no pilot sequence and blind synchronization is need. In CP-OFDM system, CP can be used to execute the coarse synchronization. For UFMC, we proposed the coarse synchronization method which does not require the CP. Also, a fine symbol timing estimation method is proposed to obtain accurate time synchronization to demodulate signal correctly.

碩士
國立交通大學
電信工程研究所
105
With the ever-changing nature of telecommunication technologies, the fifth generation (5G) mobile communication standards will be finalized by 2020. Currently, both the academia and industry are dedicated to the development of possible solutions that meet the challenging demands of the 5G communication systems. In response to this, we research on one of the possible techniques known as the massive antenna multipath division multiple access (MDMA) cellular system. In this thesis, methods for improving channel estimation under this mobile radio communication system are investigated. Two methods for reducing channel estimation error are proposed by exloring channel characteristics from two different aspects. One is the application of the Kalman filter with temporal channel correlations. The other one is the majority-vote-aided path selection with similar multipath channel delay information over receiver antennas. Simulation results are given and discussed on the performance of these two methods.

碩士
國立交通大學
電信工程研究所
105
Our proposed 5G massive antenna multipath division multiple access (MDMA) cellular system is an interference-limited system. All users use the same time slot and frequency band to transmit data; like CDMA system, the signal-to-interference ratio is a major impact on the system capacity. Hence, in data transmission, the use of trellis-coded modulation (TCM), which can tolerate more interference, can achieve better system capacity. In this thesis, the concept of TCM is introduced, and the performances of several kinds of TCM are investigated. Also, the uplink and downlink power control process used in our system are introduced. With actually implementation of power control process in our simulation, we show the system capacity gain of MDMA cellular system through using trellis-coded modulation in data transmission.

碩士
國立交通大學
電信工程研究所
106
In 5G cellular system, there exists the problem of initial cell search when the mobile boots up in the cellular system. In this thesis, we studied the cell search procedure in 5G massive antenna multipath division multiple access (MDMA) cellular system. In our proposed system, traffic data is transmitted by orthogonal frequency division multiplexing (OFDM) in frequency domain, and control data is transmitted by polyphase sequence in time domain. A frame structure design is proposed in order to support mobile station with velocity lower than 90 m/s, then, the initial cell search procedure is divided into three different stages. In the first stage, we use conventional synchronization algorithm that uses cyclic prefix (CP) to estimate symbol timing offset (STO) and fractional frequency offset (FCFO), the STO estimation is combined with median filter to eliminate the effect of outlier in symbol timing estimation. In the second stage, we use primary control tone (PCT) as an indicator on whole transmission spectrum to estimate the integer frequency offset (ICFO), PCT transmission is also combined with the antenna hopping technique and is averaged over several symbols to obtain diversity. In the final stage, preamble and cell ID sequence is set to be a modified ZC sequence and transmitted in time domain after we explored the property of modified ZC sequence. We use the matched filter (MF) that matches modified ZC sequence to detect frame header and cell ID after being averaged over several frames for reliability. The simulation results are shown under the corresponding cellular environment.

碩士
國立交通大學
電信工程研究所
105
In next ten years, existing communication standards obviously cannot meet with the needs of future 5G mobile communications. In response to this, we research on one of the possible techniques in 5G cellular system, which is a TDD massive antenna multipath division multiple access (MDMA) system. In this thesis, channel estimation for massive antenna MDMA mobile radio communication system based on different pilot sequences are investigated. We explored Orthogonal Frequency-Division Multiplexing (OFDM) and adopt maximum ratio combining in uplink (UL). We use different pilot sequences combined with data sequence as our transmitted signal in UL and estimate channels at base station (BS). With parallel interference cancellation (PIC) method, bit error rate (BER) can be improved further. We also utilize the method of combining user data and pilot sequence together to estimate channels. Besides, we do circular shift on Zadoff-Chu sequences and find that it has better performance than traditional Zadoff-Chu sequence. Finally, for the OFDM system, we use different pilot sequences to analyze the number of users which can be served by the MDMA system.

碩士
國立交通大學
電信工程研究所
105
In the 5G cellular system, we propose a massive antenna multipath division multiple access (MDMA) system which is interference-limited. The system capacity and BER performance are both affected by interference from other users. In this thesis, we focus on the discussion of uplink multiuser detection method for parallel interference cancellation (PIC). For the purpose of reducing interference from other users and improving the BER performance, we propose two methods to improve the performance of PIC, which are partial PIC and soft decision. Finally, we evaluate the PIC performance through computer simulation and discuss the difference from using these two methods in our system.

碩士
國立交通大學
電信工程研究所
106
For the 5G cellular system, we proposed a massive antenna multipath division multiple access (MDMA) system which is interference-limited. The system capacity and BER performance are both affected by interference from other users. In this thesis, we focus on the discussion of downlink control signal detection with interference from other users. We use DPSK spread spectrum modulation to transmit control data. For the purpose of reducing interference we use spread spectrum technology to improve the performance of control signal BER. We propose different methods to detect path and compare different path selection methods. Finally, we evaluate the control data detection performance through computer simulation.

碩士
國立交通大學
電信工程研究所
106
The proposed 5G Massive Antenna MDMA cellular system is an interference limited system [1], any excessive transmission power of data will aggravate the interference. In this thesis, we research on several power control algorithms and soft handoff methods in order to suppress the interference and improve the system capacity. The enhanced SIR power control algorithm is proposed to increase the system capacity and decrease the convergence rate of power control algorithm. Besides, the power ratio for soft handoff is adjusted to suppress both inter-cell and intra-cell interference. In addition, after soft handoff the modified SIR power control algorithm is used to further suppress the interference, so that we can achieve much better system capacity improvement.

碩士
國立交通大學
電信工程研究所
106
The requirement for all aspects of mobile phones increases along with the popularization of mobile phones. Among all of them, the most obvious part is very high data rate. Therefore, the fifth generation (5G) mobile communication systems are scheduled to start formally in 2020. Both the academia and industry devote themselves to the development of the 5G communication systems at present and look forward to satisfy the requirement of very high data rate. In response to the research of 5G communication systems, we propose a possible solution which is named massive antenna multipath division multiple access (MDMA) cellular system. In this thesis, we first integrate all the transmission techniques which have been researched previously for this system. And these techniques include Kalman filter (KF)、majority vote aided path selection、parallel interference cancellation (PIC)、trellis-coded modulation (TCM) and cyclic-shifted ZC sequences. After integrating them with massive antenna, the BER and channel estimation error are reduced. Furthermore, we find there are some weak points in the original transmission model. So we also propose a refined system with a new transmission model which also works well with all the transmission techniques above. Simulation results of both the integrated and the refined MDMA systems are given and discussed in details.

碩士
國立交通大學
電信工程研究所
104
In the 5G cellular system, there exists the problem of synchronization and cell search when the mobile boots up. In this thesis, we propose a new method to execute synchronization and cell search. The cell search procedure is discussed and is divided into four different stages in the 5G cellular system. The users' data signals are transmitted in the time domain and we execute cell search according to control signals transmitted in the frequency domain at the same time. In the first stage, we use the received signal with the proposed algorithm to estimate symbol timing and fractional carrier frequency offset (FCFO) in the time domain, this method does not require any additional preamble to do cross correlation. In the second stage, we use a primary control tone to detect integer carrier frequency offset (ICFO) in the frequency domain. In the third phase, we use the secondary control tones to obtain cell ID after adjustment of ICFO. In the fourth stage, we use the control data, which is carried by the secondary control tones, to detect frame header by differential detection. The cell search procedure ends when the above four stages are completed. In our simulation results, we show that the proposed joint symbol timing, FCFO estimation, cell ID detection, and frame header detection algorithms have superior performances even with the interference of users' data.