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

Eficiência energética avançada para sistema OFDMA CoMP coordenação multiponto

Doutoramento em Engenharia EletrotécnicaThe ever-growing energy consumption in mobile networks stimulated by the expected growth in data tra ffic has provided the impetus for mobile operators to refocus network design, planning and deployment towards reducing the cost per bit, whilst at the same time providing a signifi cant step towards reducing their operational expenditure. As a step towards incorporating cost-eff ective mobile system, 3GPP LTE-Advanced has adopted the coordinated multi-point (CoMP) transmission technique due to its ability to mitigate and manage inter-cell interference (ICI). Using CoMP the cell average and cell edge throughput are boosted. However, there is room for reducing energy consumption further by exploiting the inherent exibility of dynamic resource allocation protocols. To this end packet scheduler plays the central role in determining the overall performance of the 3GPP longterm evolution (LTE) based on packet-switching operation and provide a potential research playground for optimizing energy consumption in future networks. In this thesis we investigate the baseline performance for down link CoMP using traditional scheduling approaches, and subsequently go beyond and propose novel energy e fficient scheduling (EES) strategies that can achieve power-e fficient transmission to the UEs whilst enabling both system energy effi ciency gain and fairness improvement. However, ICI can still be prominent when multiple nodes use common resources with di fferent power levels inside the cell, as in the so called heterogeneous networks (Het- Net) environment. HetNets are comprised of two or more tiers of cells. The rst, or higher tier, is a traditional deployment of cell sites, often referred to in this context as macrocells. The lower tiers are termed small cells, and can appear as microcell, picocells or femtocells. The HetNet has attracted signiffi cant interest by key manufacturers as one of the enablers for high speed data at low cost. Research until now has revealed several key hurdles that must be overcome before HetNets can achieve their full potential: bottlenecks in the backhaul must be alleviated, as well as their seamless interworking with CoMP. In this thesis we explore exactly the latter hurdle, and present innovative ideas on advancing CoMP to work in synergy with HetNet deployment, complemented by a novel resource allocation policy for HetNet tighter interference management. As system level simulator has been used to analyze the proposed algorithm/protocols, and results have concluded that up to 20% energy gain can be observed.O aumento do consumo de energia nas TICs e em particular nas redes de comunicação móveis, estimulado por um crescimento esperado do tráfego de dados, tem servido de impulso aos operadores m oveis para reorientarem os seus projectos de rede, planeamento e implementa ção no sentido de reduzir o custo por bit, o que ao mesmo tempo possibilita um passo signicativo no sentido de reduzir as despesas operacionais. Como um passo no sentido de uma incorporação eficaz em termos destes custos, o sistema móvel 3GPP LTE-Advanced adoptou a técnica de transmissão Coordenação Multi-Ponto (identificada na literatura com a sigla CoMP) devido à sua capacidade de mitigar e gerir Interferência entre Células (sigla ICI na literatura). No entanto a ICI pode ainda ser mais proeminente quando v arios n os no interior da célula utilizam recursos comuns com diferentes níveis de energia, como acontece nos chamados ambientes de redes heterogéneas (sigla Het- Net na literatura). As HetNets são constituídas por duas ou mais camadas de células. A primeira, ou camada superiora, constitui uma implantação tradicional de sítios de célula, muitas vezes referidas neste contexto como macrocells. Os níveis mais baixos são designados por células pequenas, e podem aparecer como microcells, picocells ou femtocells. A HetNet tem atra do grande interesse por parte dos principais fabricantes como sendo facilitador para transmissões de dados de alta velocidade a baixo custo. A investigação tem revelado at e a data, vários dos principais obstáculos que devem ser superados para que as HetNets possam atingir todo o seu potencial: (i) os estrangulamentos no backhaul devem ser aliviados; (ii) bem como sua perfeita interoperabilidade com CoMP. Nesta tese exploramos este ultimo constrangimento e apresentamos ideias inovadoras em como a t ecnica CoMP poder a ser aperfeiçoada por forma a trabalhar em sinergia com a implementação da HetNet, complementado ainda com uma nova perspectiva na alocação de recursos rádio para um controlo e gestão mais apertado de interferência nas HetNets. Com recurso a simulação a níível de sistema para analisar o desempenho dos algoritmos e protocolos propostos, os resultados obtidos concluíram que ganhos at e a ordem dos 20% poderão ser atingidos em termos de eficiência energética

Enhanced Interference Management Techniques for Heterogeneous Cellular Networks

Interference management is one of the most challenging problems facing wireless communication networks, especially for the cellular wireless communication system that is based on reuse-one deployment. This problem becomes even more noteworthy in the heterogeneous cellular networks (HetNets) where lower power nodes (LPNs) are deployed in the coverage area of the macro base station (MBS). The higher transmit power possessed by the MBS, together with the cell selection procedure employed in HetNet: where a user equipment (UE) may be served by a closer LPN (to enable cell splitting) even though the received power from the MBS could be higher, are some factors that cause interference in HetNet. In the 5th generation mobile networks (5G) when the number of deployed LPNs increases interference will be more serious. This thesis proposes interference management techniques based on beamforming with different level of cooperation amongst base stations in HetNet. In this thesis, we first designed global beamforming vectors that will maximize the weighted sum-rate of HetNet while fulfilling some power and interference constraints. The interference constraint controls the allowable interference from the MBS to other UEs in the HetNet. The global beamforming vectors were achieved using the Branch and Bound technique which is a global optimization method used in solving non-convex optimization problems. The beamformers that maximize the weighted sum-rate of HetNet are designed jointly by all BSs in the HetNet, hence the implementation is done centrally. Since each UE in HetNet has peculiar interference situation, we design a UE-centric clustering scheme, which is capable of determining the BSs in the HetNet that interferes each UE the most at a particular time. Afterward, these BSs coordinate interference with the serving BS of this UE and make resource allocation decisions together to allocate beamforming directions and powers to each UE in the HetNet. This will spatially separate signals sent to each UE, thereby mitigating interference and improving the total data rate achievable in HetNet. HetNet tends to be distributed, also X2-interface which is the backhaul link that connects BSs in the HetNet has a limited capacity which makes it incapable of withstanding huge burdens in its backhaul. We, therefore, design distributed beamforming directions using only local channel state information available at each transmitter. We also develop optimal power allocation scheme for each UE in each cell to maximize the sum-rate of each cell in the HetNet

Adaptive transmission in heterogeneous networks

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/166243/1/cmu2bf00018.pd

Outage-Constrained Beamforming for Two-Tier Massive MIMO Downlink with Pilot Reuse

Massive multiple-input multiple-output (MIMO) systems and small cell networks are both regarded as promising candidates to meet the exponential growth of mobile data traffic for the next generation (5G) wireless communications. Hence, a new kind of multitier networks which combine massive MIMO macro cells with a secondary tier of small cells is proposed to resolve the contradiction of large network coverage and high data rate. In such multitier networks, it is inevitable to allocate nonorthogonal uplink pilot sequences to user equipment (UE) due to the large number of users. We propose a pilot reuse scheme by exploiting the unique architecture of this networks and analyse the special mixed channel state information (CSI) yielded by the pilot reuse scheme. Based on the mixed CSI, we formulate a downlink transmit beamforming problem of minimizing the total power consumption while satisfying the quality of service (QoS) requirements with outage constraints. After decomposing the original problem into simpler subproblems, we provide an efficient algorithm to combine these subproblems and solve them iteratively for generating the beamforming vectors. Monte Carlo simulations show that the average power consumption of the proposed pilot reuse scheme and its associated beamforming algorithm is close to that of the perfect CSI case