411 research outputs found
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
Approaching universal frequency reuse through base station cooperation
Base Station (BS) architectures are a promising cellular wireless solution to mitigate
the interference issues and to avoid the high frequency reuse factors implemented
in conventional systems. Combined with block transmission techniques, such as Orthogonal
Frequency-Division Multiplexing (OFDM) for the downlink and Single-Carrier with
Frequency-Domain Equalization (SC-FDE) for the uplink, these systems provide a significant
performance improvement to the overall system. Block transmission techniques are
suitable for broadband wireless communication systems, which have to deal with strongly
frequency-selective fading channels and are able to provide high bit rates despite the channel
adversities. In BS cooperation schemes users in adjacent cells share the same physical
channel and the signals received by each BS are sent to a Central Processing Unit (CPU)
that combines the different signals and performs the user detections and/or separation,
which can be regarded as a Multi-User Detection (MUD) technique. The work presented
in this thesis is focused on the study of uplink transmissions in BS cooperations systems,
considering single carrier block transmission schemes and iterative receivers based on the
Iterative-Block Decision Feedback Equalization (IB-DFE) concept, which combined with
the employment of Cyclic Prefix (CP)-assisted block transmission techniques are appropriate
to scenarios with strongly time-dispersive channels. Furthermore, the impact of the
sampling and quantization applied to the received signals from each Mobile Terminal (MT)
to the corresponding BS is studied, with the achievement of the spectral characterization
of the quantization noise. This thesis also provides a conventional analytical model for the
BER (Bit Error Rate) performance complemented with an approach to improve its results.
Finally, this thesis addresses the contextualization of BS cooperation schemes in clustered
C-RAN (Centralized-Radio Access Network)-type solutions.As arquitecturas BS cooperation são uma solução promissora de redes celulares sem
fios para atenuar o problema da interferência e evitar os factores de reuso elevados, que
se encontram implementados nos sistemas convencionais. Combinadas com técnicas de
transmissão por blocos, como o OFDM para o downlink e o SC-FDE no uplink, estes
sistemas fornecem uma melhoria significativa no desempenho geral do sistema. Técnicas
de transmissão por blocos são adequadas para sistemas de comunicações de banda larga
sem fios, que têm que lidar com canais que possuem um forte desvanescimento selectivo
na frequência e são capazes de fornecer ligações com taxas de transmissão altas apesar
das adversidades do canal. Em esquemas BS cooperation os terminais móveis situados em
células adjacentes partilham o mesmo canal físico e os sinais recebidos em cada estação
de base são enviados para uma Unidade Central de Processamento (CPU) que combina
os diferentes sinais recebidos associados a um dado utilizador e realiza a detecção e/ou
separação do mesmo, sendo esta considerada uma técnica de Detecção Multi-Utilizador
(MUD). O trabalho apresentado nesta tese concentra o seu estudo no uplink de transmissões
em sistemas BS cooperation, considerando transmissões em bloco de esquemas monoportadoras
e receptores iterativos baseados no conceito B-DFE, em que quando combinados
com a implementação de técnicas de transmissao por blocos assistidas por prefixos cíclicos
(CP) são apropriados a cenários com canais fortemente dispersivos no tempo. Além disso, é
estudado o impacto do processo de amostragem e quantização aplicados aos sinais recebidos
de cada terminal móvel para a estação de base, com a obtenção da caracterização espectral
do ruído de quantização. Esta tese também fornece um modelo analítico convencional para
a computação do desempenho da taxa de erros de bit (BER), com um método melhorado
para o mesmo. Por último, esta tese visa a contextualização dos sistemas BS cooperation
em soluções do tipo C-RAN
Spectral Efficient and Energy Aware Clustering in Cellular Networks
The current and envisaged increase of cellular traffic poses new challenges
to Mobile Network Operators (MNO), who must densify their Radio Access Networks
(RAN) while maintaining low Capital Expenditure and Operational Expenditure to
ensure long-term sustainability. In this context, this paper analyses optimal
clustering solutions based on Device-to-Device (D2D) communications to mitigate
partially or completely the need for MNOs to carry out extremely dense RAN
deployments. Specifically, a low complexity algorithm that enables the creation
of spectral efficient clusters among users from different cells, denoted as
enhanced Clustering Optimization for Resources' Efficiency (eCORE) is
presented. Due to the imbalance between uplink and downlink traffic, a
complementary algorithm, known as Clustering algorithm for Load Balancing
(CaLB), is also proposed to create non-spectral efficient clusters when they
result in a capacity increase. Finally, in order to alleviate the energy
overconsumption suffered by cluster heads, the Clustering Energy Efficient
algorithm (CEEa) is also designed to manage the trade-off between the capacity
enhancement and the early battery drain of some users. Results show that the
proposed algorithms increase the network capacity and outperform existing
solutions, while, at the same time, CEEa is able to handle the cluster heads
energy overconsumption
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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
On the Performance Gain of NOMA over OMA in Uplink Communication Systems
In this paper, we investigate and reveal the ergodic sum-rate gain (ESG) of
non-orthogonal multiple access (NOMA) over orthogonal multiple access (OMA) in
uplink cellular communication systems. A base station equipped with a
single-antenna, with multiple antennas, and with massive antenna arrays is
considered both in single-cell and multi-cell deployments. In particular, in
single-antenna systems, we identify two types of gains brought about by NOMA:
1) a large-scale near-far gain arising from the distance discrepancy between
the base station and users; 2) a small-scale fading gain originating from the
multipath channel fading. Furthermore, we reveal that the large-scale near-far
gain increases with the normalized cell size, while the small-scale fading gain
is a constant, given by = 0.57721 nat/s/Hz, in Rayleigh fading
channels. When extending single-antenna NOMA to -antenna NOMA, we prove that
both the large-scale near-far gain and small-scale fading gain achieved by
single-antenna NOMA can be increased by a factor of for a large number of
users. Moreover, given a massive antenna array at the base station and
considering a fixed ratio between the number of antennas, , and the number
of users, , the ESG of NOMA over OMA increases linearly with both and
. We then further extend the analysis to a multi-cell scenario. Compared to
the single-cell case, the ESG in multi-cell systems degrades as NOMA faces more
severe inter-cell interference due to the non-orthogonal transmissions.
Besides, we unveil that a large cell size is always beneficial to the ergodic
sum-rate performance of NOMA in both single-cell and multi-cell systems.
Numerical results verify the accuracy of the analytical results derived and
confirm the insights revealed about the ESG of NOMA over OMA in different
scenarios.Comment: 51 pages, 7 figures, invited paper, submitted to IEEE Transactions on
Communication
Control-data separation architecture for cellular radio access networks: a survey and outlook
Conventional cellular systems are designed to ensure ubiquitous coverage with an always present wireless channel irrespective of the spatial and temporal demand of service. This approach raises several problems due to the tight coupling between network and data access points, as well as the paradigm shift towards data-oriented services, heterogeneous deployments and network densification. A logical separation between control and data planes is seen as a promising solution that could overcome these issues, by providing data services under the umbrella of a coverage layer. This article presents a holistic survey of existing literature on the control-data separation architecture (CDSA) for cellular radio access networks. As a starting point, we discuss the fundamentals, concepts, and general structure of the CDSA. Then, we point out limitations of the conventional architecture in futuristic deployment scenarios. In addition, we present and critically discuss the work that has been done to investigate potential benefits of the CDSA, as well as its technical challenges and enabling technologies. Finally, an overview of standardisation proposals related to this research vision is provided
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