Study of decoupled uplink and downlink access in 5G heterogeneus systems

El projecte analitzarà les funcionalitats i problemàtiques de l'Internet tàctil.Uplink and downlink decoupling (DUDe) is a disruptive technique that has been proposed recently to reduce the uplink and downlink imbalance problem, which occurs in HetNets due to the strong transmit power disparities between macro and small cells. In this thesis, previous research done on DUDe, in particular the association probability derivation, is used to calculate how the capacity is affected when the association is made to any SCell in the scenario. This specific situation is highly realistic since one or several small cells might be unavailable due to overload reasons. Therefore, one of the main objectives of this thesis is to evaluate and compare the potential capacity gains of decoupling to any other small cell in the scenario with respect to the macro cell, association that follows classical downlink received power policies. Decoupling uplink from the macro cell can improve as well the uplink outage, metric also evaluated and compared in this study. Moreover, there is a strong trend in research to empower multi-connectivity solutions, where one user has more than one uplink connection. We refer to this case as a dual connectivity scenario, and the uplink is further studied by allowing decoupled associations in dual connectivity scenarios. Dual connectivity in the uplink is highly controversial, since the user has limited power to share between two different access points. Therefore, a part from comparing the decoupled association performance with the downlink received power policies, this study compares the performance of multi-connectivity against having one single serving cell. In this case, a comparison is done with respect to the best uplink serving cell. Results show that decoupling the access increases the capacity even if there are some SCells unreachable and presents great performance on DC scenario.El uplink and downlink decoupling (DUDe) es una novedosa técnica propuesta recientemente para reduir el problema del uplink and downlink imbalance. El uplink and downlink imbalance ocurre cuando las potencias de las antenas de una heterogeneus network (HetNet) son muy dispares. En este proyecto, teniendo en cuenta la investigación realitzada hasta la fecha sobre el DUDe (especialmente sobre la probabilidad de asociación), se calcula la capacidad asociándose a cualquier SCell. Esta situación es muy importante ya que puede ser que algunes celdas sean inalcanzables por el usuario debido a que puedn estar sobrecargadas. Por este motivo, uno de los principales objetivos del proyecto es aavaluar la mejora de capacidad al relaizar el DUDe con cualquier SCell y mantenir la asociaciín con la MCell tal y como se ha hecho hasta ahora. Esta técnica se llama downlink receive power (DRP). El DUDe también mejora la outage probability, indicador que también se evalua en el estudio. En los estudios mas recientes también se trabaja con dual connectivity para mejorar las prestacions de la conexión. Aunque dividir la transmisión en el enlace de subida puede disminuir la capacidad debido a la baja potencia del usuario, se compara la capacidad de desacoplar el acceso en dual connectivity con el escenario de single best association. Los resultados muestran que el DUDe aumenta la capacidad aun teniendo algunes SCells inalcanzables. También se ha demostrado que el DUDe funciona perfectamente con la dual connectivity.L’Uplink and downlink decoupling és una innovadora tècnica que ha sigut proposada recentment per reduir el problema de l’uplink and downlink imbalance. L’uplink and downlink imbalance es dona a les heterogeneus networks (HetNets) degut a la disparitat de potències entre les diferents antenes. Durant aquest projecte, tenint en compte la recent recerca sobre DUDe (sobretot sobre la probabilitat d’associació), s’utilitza per calcular la capacitat a qualsevol SCell. Aquesta situació és molt important d’analitzar ja que pot ser possible que algunes no estiguin accessibles per sobrecàrrega. Per aquest motiu, un dels principals objectius del projecte és avaluar la millora de capacitat entre realitzar el DUDe a qualsevol SCell i mantenir l’associació amb la MCell com s’havia fet fins ara, el que es coneix com downlink receive power (DRP). El DUDe també comporta moltes millores a la outage probability, indicador que també s’avalua a l’estudi. En els estudis més recents també treballen amb dual connectivity per millorar les prestacions. Tot i que dividir la transmissió a l’enllaç de pujada pot comportar perdre capacitat degut a la baixa potència de l’usuari, es compara la capacitat amb el DUDe en un escenari de dual connectivity amb el cas de single best association. Els resultats mostren que el fet de desacoblar l’accés augmenta la capacitat de la connexió tot i tenir algunes SCells inabastables. També s’ha demostrat que el DUDe funciona perfectament amb la dual connectivity

Decoupled Downlink and Uplink Access for Aerial Terrestrial Heterogeneous Cellular Networks

To enable reliable connectivity in highly dynamic and dense communication environments, aerial-terrestrial heterogeneous cellular networks (AT-HCNs) have been proposed as a plausible enhancement to the conventional terrestrial HCNs (T-HCNs). In dense urban scenarios, users are often located in clusters and demand high bandwidth in both downlink (DL) and uplink (UL). We investigate this scenario and model the spatial distribution of clustered users using a Matern cluster process (MCP). Based on our analysis we then argue that decoupling of DL and UL in such a setting can significantly improve coverage performance and spectral efficiency. We further obtain closed-form expressions for the system coverage probability, spectral efficiency, and energy efficiency by using the Fox H-function. The obtained results confirm the validity of the proposed analytical model. Our simulations further indicate a significant performance improvement using decoupled access and provide quantitative insights on AT-HCN system design

Clustered Jamming in Aerial HetNets with Decoupled Access

The tremendous increase in wireless connectivity demand will result in the degradation of the service quality and the scarcity of network capacity and coverage in the beyond 5 th generation era. To ensure reliable connectivity and enhance the network’s performance, the evolution of heterogeneous networks (HetNets) must incorporate aerial platforms in addition to traditional terrestrial base stations. The performance of Aerial-HetNets (A-HetNets) is largely dependent on the users’ association. The conventional user-association scheme based on downlink received power provides sub-optimal performance for the edge users. For this reason, decoupled user-association along with the reverse frequency allocation (RFA) strategy has been employed in A-HetNets. The performance of A-HetNets is also affected if wide-band jammers (WBJs) are present in the vicinity and impose jamming interference. In this paper, a two-tier A-HetNet with RFA and decoupled access is analyzed in the presence of jamming interference. The obtained results show that for a signal-to-interference ratio threshold of −20 dBm, the percentage decrease in the coverage probability of the decoupled access due to WBJ activity is up to 7.4%, 13.5%, and 19.7%, for the average number of WBJs equal to 2, 4, and 6, respectively. The performance of the decoupled access in A-HetNets is further decreased by increasing the transmit power of the WBJs while it is increased by increasing the radius of the WBJ’s cluster

Design and Performance Analysis of Next Generation Heterogeneous Cellular Networks for the Internet of Things

The Internet of Things (IoT) is a system of inter-connected computing devices, objects and mechanical and digital machines, and the communications between these devices/objects and other Internet-enabled systems. Scalable, reliable, and energy-efficient IoT connectivity will bring huge benefits to the society, especially in transportation, connected self-driving vehicles, healthcare, education, smart cities, and smart industries. The objective of this dissertation is to model and analyze the performance of large-scale heterogeneous two-tier IoT cellular networks, and offer design insights to maximize their performance. Using stochastic geometry, we develop realistic yet tractable models to study the performance of such networks. In particular, we propose solutions to the following research problems: -We propose a novel analytical model to estimate the mean uplink device data rate utility function under both spectrum allocation schemes, full spectrum reuse (FSR) and orthogonal spectrum partition (OSP), for uplink two-hop IoT networks. We develop constraint gradient ascent optimization algorithms to obtain the optimal aggregator association bias (for the FSR scheme) and the optimal joint spectrum partition ratio and optimal aggregator association bias (for the OSP scheme). -We study the performance of two-tier IoT cellular networks in which one tier operates in the traditional sub-6GHz spectrum and the other, in the millimeter wave (mm-wave) spectrum. In particular, we characterize the meta distributions of the downlink signal-to-interference ratio (sub-6GHz spectrum), the signal-to-noise ratio (mm-wave spectrum) and the data rate of a typical device in such a hybrid spectrum network. Finally, we characterize the meta distributions of the SIR/SNR and data rate of a typical device by substituting the cumulative moment of the CSP of a user device into the Gil-Pelaez inversion theorem. -We propose to split the control plane (C-plane) and user plane (U-plane) as a potential solution to harvest densification gain in heterogeneous two-tier networks while minimizing the handover rate and network control overhead. We develop a tractable mobility-aware model for a two-tier downlink cellular network with high density small cells and a C-plane/U-plane split architecture. The developed model is then used to quantify effect of mobility on the foreseen densification gain with and without C-plane/U-plane splitting

A new look at physical layer security, caching, and wireless energy harvesting for heterogeneous ultra-dense networks

Heterogeneous ultra-dense networks enable ultra-high data rates and ultra-low latency through the use of dense sub-6 GHz and millimeter-wave small cells with different antenna configurations. Existing work has widely studied spectral and energy efficiency in such networks and shown that high spectral and energy efficiency can be achieved. This article investigates the benefits of heterogeneous ultra-dense network architecture from the perspectives of three promising technologies, physical layer security, caching, and wireless energy harvesting, and provides an enthusiastic outlook toward application of these technologies in heterogeneous ultra-dense networks. Based on the rationale of each technology, opportunities and challenges are identified to advance the research in this emerging network

Closed form analysis of Poisson cellular networks: a stochastic geometry approach

Ultra dense networks (UDNs) allow for efficient spatial reuse of the spectrum, giving rise to substantial capacity and power gains. In order to exploit those gains, tractable mathematical models need to be derived, allowing for the analysis and optimization of the network operation. In this course, stochastic geometry has emerged as a powerful tool for large-scale analysis and modeling of wireless cellular networks. In particular, the employment of stochastic geometry has been proven instrumental for the characterization of the network performance and for providing significant insights into network densification. Fundamental issues, however, remain open in order to use stochastic geometry tools for the optimization of wireless networks, with the biggest challenge being the lack of tractable closed form expressions for the derived figures of merit. To this end, the present thesis revisits stochastic geometry and provides a novel stochastic geometry framework with a twofold contribution. The first part of the thesis focuses on the derivation of simple, albeit accurate closed form approximations for the ergodic rate of Poisson cellular networks under a noise limited, an interference limited and a general case scenario. The ergodic rate constitutes the most sensible figure of merit for characterizing the system performance, but due to the inherent intractability of the available stochastic geometry frameworks, had not been formulated in closed form hitherto. To demonstrate the potential of the aforementioned tractable expressions with respect to network optimization, the present thesis proposes a flexible connectivity paradigm and employs part of the developed expressions to optimize the network connectivity. The proposed flexible connectivity paradigm exploits the downlink uplink decoupling (DUDe) configuration, which is a promising framework providing substantial capacity and outage gains in UDNs and introduces the DUDe connectivity gains into the 5G era and beyond. Subsequently, the last part of the thesis provides an analytical formulation of the probability density function (PDF) of the aggregate inter-cell interference in Poisson cellular networks. The introduced PDF is an accurate approximation of the exact PDF that could not be analytically formulated hitherto, even though it constituted a crucial tool for the analysis and optimization of cellular networks. The lack of an analytical expression for the PDF of the interference in Poisson cellular networks had imposed the use of intricate formulas, in order to derive sensible figures of merit by employing only the moment generating function (MGF). Hence, the present thesis introduces an innovative framework able to simplify the analysis of Poisson cellular networks to a great extent, while addressing fundamental issues related to network optimization and design.Las redes ultra densas (UDNs) permiten una reutilización espacial del espectro, proporcionando ventajas en términos de mejora de capacidad y ahorro de potencia. Para explotar estas ventajas se necesitan modelos matemáticos simples que permitan el análisis y la optimización de la operación de la red. Por esta razón, la geometría estocástica se ha convertido en una potente herramienta para el análisis de redes celulares. En particular, el empleo de la geometría estocástica ha sido fundamental para la caracterización del rendimiento de la red y para proporcionar información importante sobre la densificación de la misma. Sin embargo, hay problemas fundamentales que deben resolverse para utilizar estas herramientas de geometría estocástica, siendo el mayor desafío la falta de expresiones simples de forma cerrada para las funciones objetivo de interés. Por este motivo, la presente tesis examina la geometría estocástica y proporciona un marco novedoso con una doble contribución. La primera parte de la tesis se centra en la derivación de aproximaciones cerradas simples pero ajustadas para la capacidad ergódica de las redes de Poisson en escenarios limitados por ruido, por interferencia y por ambos. La capacidad ergódica constituye la figura de mérito más apropiada para caracterizar el rendimiento del sistema, pero no se ha formulado en forma cerrada debido a la complejidad inherente de las expresiones de geometría estocástica disponibles. Para demostrar el potencial de las expresiones simples propuestas, la presente tesis propone un paradigma de conectividad flexible y utiliza parte de las expresiones desarrolladas para optimizar la conectividad de la red. El paradigma de conectividad flexible propuesto explota la configuración de "Downlink Uplink Decoupling" (DUDe), que es un marco que proporciona ventajas sustanciales en términos de incremento de capacidad y reducción de la probabilidad de bloqueo en UDNs e introduce mejoras de conectividad DUDe en la era de 5G. Más adelante, la última parte de la tesis proporciona una formulación analítica de la función de densidad de probabilidad (PDF) de la interferencia agregada en las redes celulares de Poisson. La PDF desarrollada es una aproximación precisa de la PDF exacta que hasta ahora no se ha podido formular analíticamente, a pesar de que se trata de una herramienta crucial para el análisis y la optimización de las redes celulares. La falta de una expresión analítica para la PDF de la interferencia en las redes celulares de Poisson había impuesto el uso de fórmulas complejas, a fin de derivar funciones objetivas apropiadas empleando solo la función generadora de momentos (MGF). Por lo tanto, la presente tesis presenta un marco innovador capaz de simplificar el análisis de las redes celulares de Poisson y así resolver problemas fundamentales relacionados con la optimización y el diseño de la red