Separation Framework: An Enabler for Cooperative and D2D Communication for Future 5G Networks

Soaring capacity and coverage demands dictate that future cellular networks need to soon migrate towards ultra-dense networks. However, network densification comes with a host of challenges that include compromised energy efficiency, complex interference management, cumbersome mobility management, burdensome signaling overheads and higher backhaul costs. Interestingly, most of the problems, that beleaguer network densification, stem from legacy networks' one common feature i.e., tight coupling between the control and data planes regardless of their degree of heterogeneity and cell density. Consequently, in wake of 5G, control and data planes separation architecture (SARC) has recently been conceived as a promising paradigm that has potential to address most of aforementioned challenges. In this article, we review various proposals that have been presented in literature so far to enable SARC. More specifically, we analyze how and to what degree various SARC proposals address the four main challenges in network densification namely: energy efficiency, system level capacity maximization, interference management and mobility management. We then focus on two salient features of future cellular networks that have not yet been adapted in legacy networks at wide scale and thus remain a hallmark of 5G, i.e., coordinated multipoint (CoMP), and device-to-device (D2D) communications. After providing necessary background on CoMP and D2D, we analyze how SARC can particularly act as a major enabler for CoMP and D2D in context of 5G. This article thus serves as both a tutorial as well as an up to date survey on SARC, CoMP and D2D. Most importantly, the article provides an extensive outlook of challenges and opportunities that lie at the crossroads of these three mutually entangled emerging technologies.Comment: 28 pages, 11 figures, IEEE Communications Surveys & Tutorials 201

Técnicas de equalização híbridas para sistemas heterogéneos na banda das ondas milimétricas

With the constant demand for better service and higher transmission rates current technologies are reaching the limits of the channel capacity. Although, technologies such as MIMO and Heterogeneous systems appear to increase the channel capacity by introducing more antennas at the transceivers making the link between users and base station more reliable. Furthermore, the current spectrum, sub-6GHz, is becoming saturated and due to the properties of such frequencies the deployment of heterogeneous systems can introduce some levels of interference. Towards improving future communication systems a new part of the frequencies spectrum available should be used, researchers have their eyes on the mmWave band. This band allows to increase the carrier frequency and respective signal bandwidth and therefore increase the transmission speeds, moreover the properties of such frequencies unlock some advantages over the frequencies used in the sub-6G band. Additionally, mmWave band can be combined with massive MIMO technology to enhance the system capacity and to deploy more antenna elements in the transceivers. One more key technology that improves the energy efficiency in systems with hundreds of antenna elements is the possibility to combine analog and digital precoding techniques denoted as hybrid architectures. The main advantages of such techniques is that contrary to the full digital precoding processing used in current systems this new architecture allows to reduce the number of RF chains per antenna leading to improved energy efficiency. Furthermore to handle heterogeneous systems that have small-cells within the macro-cell, techniques such as Interference Alignment (IA) can be used to efficiently remove the existing multi-tier interference. In this dissertation a massive MIMO mmWave heterogeneous system is implemented and evaluated. It is designed analog-digital equalizers to efficiently remove both the intra an inter-tier interference. At digital level, an interference alignment technique is used to remove the interference and increase the spectral efficiency. The results showed that the proposed solutions are efficient to remove the macro and small cells interference.Com a constante procura de melhores serviços e taxas de transmissão mais elevadas, as tecnologias atuais estão a atingir os limites de capacidade do canal. Contudo tecnologias como o MIMO e os sistemas heterogéneos permitem aumentar a capacidade do canal através da introdução de mais antenas nos transcetores e através da implementação de pequenos pontos de acesso espalhados pela célula primária, com o intuito de tornar as ligações entre os utilizadores e a estação base mais fiáveis. Tendo também em atenção que o espectro atual, sub-6GHz, está sobrecarregado e que devido às propriedades das frequências utilizadas a implementação de sistemas heterogéneos pode levar a níveis de interferência insustentáveis. Por modo a resolver esta sobrecarga futuros sistemas de comunicação devem aproveitar uma maior parte do espectro de frequências disponível. A banda das ondas milimétricas (mmWave) tem sido apontada como solução, o que permite aumentar a frequência utilizada para transportar o sinal e consequentemente aumentar as velocidades de transmissão. Uma outra vantagem da banda mmWave é que pode ser combinada com a tecnologia MIMO massivo, permitindo implementar mais elementos de antena nos terminais e consequentemente aumentar a capacidade do sistema. Umas das tecnologias desenvolvida para melhorar a eficiência energética em sistemas com centenas de antenas é a possibilidade de combinar técnicas de codificação analógica e digital, designadas como arquiteturas híbridas. A principal vantagem desta técnica é que, contrariamente ao processamento feito nos sistemas atuais, totalmente no domínio digital, esta nova arquitetura permite reduzir o número de cadeias RF por antena. Com o intuito de reduzir a interferência em sistemas heterogéneos, técnicas como o alinhamento de interferência são usadas para separar utilizadores das células secundárias dos utilizadores das células primárias de modo a reduzir a interferência multi-nível existente no sistema geral. Nesta dissertação, é implementado e avaliado um sistema heterogéneo que combina MIMO massivo e ondas milimétricas. Este sistema é projetado com equalizadores analógico-digitais para remover com eficiência a interferência intra e inter-camadas. No domínio digital é utilizada a técnica de alinhamento de interferência para remover a interferência e aumentar a eficiência espectral. Os resultados mostram que as soluções propostas são eficientes para remover a interferência entre as células secundárias e a primária.Mestrado em Engenharia Eletrónica e Telecomunicaçõe

LTE-Advanced radio access enhancements: A survey

Long Term Evolution Advanced (LTE-Advanced) is the next step in LTE evolution and allows operators to improve network performance and service capabilities through smooth deployment of new techniques and technologies. LTE-Advanced uses some new features on top of the existing LTE standards to provide better user experience and higher throughputs. Some of the most significant features introduced in LTE-Advanced are carrier aggregation, enhancements in heterogeneous networks, coordinated multipoint transmission and reception, enhanced multiple input multiple output usage and deployment of relay nodes in the radio network. Mentioned features are mainly aimed to enhance the radio access part of the cellular networks. This survey article presents an overview of the key radio access features and functionalities of the LTE-Advanced radio access network, supported by the simulation results. We also provide a detailed review of the literature together with a very rich list of the references for each of the features. An LTE-Advanced roadmap and the latest updates and trends in LTE markets are also presented

Hierarchical Radio Resource Optimization for Heterogeneous Networks with Enhanced Inter-cell Interference Coordination (eICIC)

Interference is a major performance bottleneck in Heterogeneous Network (HetNet) due to its multi-tier topological structure. We propose almost blank resource block (ABRB) for interference control in HetNet. When an ABRB is scheduled in a macro BS, a resource block (RB) with blank payload is transmitted and this eliminates the interference from this macro BS to the pico BSs. We study a two timescale hierarchical radio resource management (RRM) scheme for HetNet with dynamic ABRB control. The long term controls, such as dynamic ABRB, are adaptive to the large scale fading at a RRM server for co-Tier and cross-Tier interference control. The short term control (user scheduling) is adaptive to the local channel state information within each BS to exploit the multi-user diversity. The two timescale optimization problem is challenging due to the exponentially large solution space. We exploit the sparsity in the interference graph of the HetNet topology and derive structural properties for the optimal ABRB control. Based on that, we propose a two timescale alternative optimization solution for the user scheduling and ABRB control. The solution has low complexity and is asymptotically optimal at high SNR. Simulations show that the proposed solution has significant gain over various baselines.Comment: 14 pages, 8 figure

Towards 5th Generation Cellular Mobile Networks

Cellular mobile networks have enabled ubiquitous communications and largely changed the way we live and work. At the same time, the network itself has been undergoing significant changes in the process of meeting our ever increasing demands on data rate and quality of service. In this article, we show the path of the evolution in both standards and techniques, and provide our vision for the future of the cellular networks. We review the evolution of international standards for cellular mobile networks in the last two decades, describe how the network layout has been migrating from rigid cellular architecture to random and dense small cells, and provide an indepth discussion on potential enabling techniques for the next generation (5G) cellular networks, particularly massive MIMO and multiband base-station antennas

Energy Efficient Small Cell Planning For High Capacity Wireless Networks

This thesis presents a new strategy to densify Small Cells (i.e., add more low powered base stations within macro networks) and enhance the coverage and capacity of Heterogeneous Networks. This is accomplished by designing Micro Cell for outdoor applications, Pico and Femtocell for indoor applications. It is shown that, there exists a free space propagation medium in all propagation environments due to Fresnel zones, and the path loss slope within this zone is similar to free space propagation medium. This forms the basis of our development of the present work. The salient feature of the proposed work has two main considerations (a) The cell radius of Small Cells must be within the first Fresnel zone break point, and (b) The minimum inter-cell distance must be greater than twice of Small Cell radius. The proposed network is simulated in real a radio network simulator called ATOLL. The simulation results showed that densify Small Cells not only enhanced the capacity and coverage of Heterogeneous Networks but also improved the carrier to interference ratio significantly. Since the proposed work allows UE (user equipment) to have Line of Sight (LOS) communication with the serving cell, and UE can have higher uplink (UL) signal to interference plus noise ratio (SINR) that will further allow UE to reduce its transmission power, which will consequently lead to a longer battery life for the UE and reduce the interference in the system

Contributions to Analysis and Mitigation of Cochannel Interference in Cellular Wireless Networks

Cellular wireless networks have become a commodity. We use our cellular devices every day to connect to others, to conduct business, for entertainment. Strong demand for wireless access has made corresponding parts of radio spectrum very valuable. Consequently, network operators and their suppliers are constantly being pressured for its efficient use. Unlike the first and second generation cellular networks, current generations do not therefore separate geographical sites in frequency. This universal frequency reuse, combined with continuously increasing spatial density of the transmitters, leads to challenging interference levels in the network. This dissertation collects several contributions to analysis and mitigation of interference in cellular wireless networks. The contributions are categorized and set in the context of prior art based on key characteristics, then they are treated one by one. The first contribution encompasses dynamic signaling that measures instantaneous interference situations and allows only for such transmissions that do not harm each other excessively. A novel forward signaling approach is introduced as an alternative to traditional reverse signaling. Forward signaling allows the interference management decisions to be done at the receiver, where there is more relevant information available. The second contribution analyzes cross-link interference in heterogeneous networks. Cross-link interference is interference between downlink and uplink transmissions that can appear in time-division duplex (TDD) networks. It is shown that uplink reception of small cells can be disturbed considerably by macrocell downlink transmissions. We proposes an intuitive solution to the problem based on power control. Users in small cells have generally enough power headroom as the distance to the small base station is often short. The third contribution provides an extensive analysis of a specific interference managment method that the Long-Term Evolution (LTE) applies in cochannel heterogeneous deployments. We analyze this so-called time muting using a modern stochastic geometry approach and show that performance of the method strongly depends on residual interference in the muted sections of time. The fourth and last contribution analyzes the impact of interference rank, i.e., number of spatial streams at the interferer, on a beamformed or spatially block coded transmission. It is shown that when the interferer chooses to transmit multiple spatial streams, spreading the power in spatial domain has potential to decrease probability of outage at neighbor receiver, especially if the neighbor transmission uses beamforming