300 research outputs found
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Scheduling Algorithm for Coordinated Beamforming in Heterogeneous Macro/Pico LTE-Advanced Networks
Pico base stations are an important instrument to increase the capacity of mobile radio networks. Due to the limited spectrum availability it will be necessary to operate macro and pico base stations on the same frequency bands. In this case the transmit power imbalance between different base station types creates new interference situations. Coordinated beamforming is one method of base station cooperation that can be applied to mitigate interference in this scenario. The work presented here describes a scheduler for coordinated beamforming in an LTE-Advanced system which relies on sharing only the feedback information from the mobile stations between the base stations. System level simulation results show that this approach can decrease the interference experienced by the mobile stations attached to the pico base stations
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Scheduling heuristic for reduced complexity of coordinated beamforming in large multi-carrier heterogeneous wireless networks
The research and development of wireless communication systems is often based on relatively simple models of the network topology, the radio channel and the radio propagation. This is considered to be mostly appropriate, as only under these conditions the complex technical problems in this field can be fully solved to their theoretical boundaries. However, it can also be the case that algorithms or concepts created under simplified assumptions perform in a significantly different way, when they are applied in more realistic scenarios.
This Thesis presents research work which can be seen as a step towards extending the existing research on Coordinated Beamforming to a complex network scenario, i.e. to a large-scale heterogeneous multi-carrier network. For this purpose, a complex simulation framework has been developed. This is used to analyse the significant implications the conditions in a complex network can have on the achievable performance gains. In more detail, the out of cluster interference and the number of mobile stations are identified as factors which heavily influence the performance. This knowledge is then used to design a novel scheduling heuristic, designed to be able to adapt to the particular network scenarios and to estimate the extent of the achievable performance gains. Our simulation results show that the new heuristic achieves significant performance gains for a low number of mobile stations (by applying zero forcing precoding) as well as for a high number of mobile stations (by a coordinated resource assignment that intelligently pairs mobile stations when applying maximum ratio transmission). The Thesis also demonstrates that the effect of the out of cluster interference can cause the reduction of the achievable gains. Due to the knowledge of performance limiting factors, the scheduling heuristic is in addition able to realize a trade-off between complexity and performance by excluding transmission parameters from the scheduling process which are not expected to be beneficial
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
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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
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Complexity of coordinated beamforming and scheduling for OFDMA based heterogeneous networks
Coordination is foreseen to be an important component of future mobile radio networks. It is especially relevant in heterogeneous networks, where high power base stations produce strong interference to an underlying layer of low power base stations. This work investigates in detail the achievable performance gains for one coordination technique—coordinated beamforming. It reveals the main factors that influence the throughput of the mobile stations. These findings are combined with an analysis of the computational complexity. As a result, a heuristic algorithm is presented that achieves results close to an exhaustive search with significantly less calculations. Detailed simulation analysis is presented on a realistic network layout
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
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
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