3,413 research outputs found
Spatial Coordination Strategies in Future Ultra-Dense Wireless Networks
Ultra network densification is considered a major trend in the evolution of
cellular networks, due to its ability to bring the network closer to the user
side and reuse resources to the maximum extent. In this paper we explore
spatial resources coordination as a key empowering technology for next
generation (5G) ultra-dense networks. We propose an optimization framework for
flexibly associating system users with a densely deployed network of access
nodes, opting for the exploitation of densification and the control of overhead
signaling. Combined with spatial precoding processing strategies, we design
network resources management strategies reflecting various features, namely
local vs global channel state information knowledge exploitation, centralized
vs distributed implementation, and non-cooperative vs joint multi-node data
processing. We apply these strategies to future UDN setups, and explore the
impact of critical network parameters, that is, the densification levels of
users and access nodes as well as the power budget constraints, to users
performance. We demonstrate that spatial resources coordination is a key factor
for capitalizing on the gains of ultra dense network deployments.Comment: An extended version of a paper submitted to ISWCS'14, Special Session
on Empowering Technologies of 5G Wireless Communication
Adaptive Multicell 3D Beamforming in Multi-Antenna Cellular Networks
We consider a cellular network with multi-antenna base stations (BSs) and
single-antenna users, multicell cooperation, imperfect channel state
information, and directional antennas each with a vertically adjustable beam.
We investigate the impact of the elevation angle of the BS antenna pattern,
denoted as tilt, on the performance of the considered network when employing
either a conventional single-cell transmission or a fully cooperative multicell
transmission. Using the results of this investigation, we propose a novel
hybrid multicell cooperation technique in which the intercell interference is
controlled via either cooperative beamforming in the horizontal plane or
coordinated beamfroming in the vertical plane of the wireless channel, denoted
as adaptive multicell 3D beamforming. The main idea is to divide the coverage
area into two disjoint vertical regions and adapt the multicell cooperation
strategy at the BSs when serving each region. A fair scheduler is used to share
the time-slots between the vertical regions. It is shown that the proposed
technique can achieve performance comparable to that of a fully cooperative
transmission but with a significantly lower complexity and signaling
requirements. To make the performance analysis computationally efficient,
analytical expressions for the user ergodic rates under different beamforming
strategies are also derived.Comment: Accepted for publication in IEEE Transaction on Vehicular Technolog
Energy Efficient Cooperative Strategies for Relay-Assisted Downlink Cellular Systems Part II: Practical Design
In a companion paper [1], we present a general approach to evaluate the
impact of cognition in a downlink cellular system in which multiple relays
assist the transmission of the base station. This approach is based on a novel
theoretical tool which produces transmission schemes involving rate-splitting,
superposition coding and interference decoding for a network with any number of
relays and receivers. This second part focuses on a practical design example
for a network in which a base station transmits to three receivers with the aid
of two relay nodes. For this simple network, we explicitly evaluate the impact
of relay cognition and precisely characterize the trade offs between the total
energy consumption and the rate improvements provided by relay cooperation.
These closedform expressions provide important insights on the role of
cognition in larger networks and highlights interesting interference management
strategies. We also present a numerical simulation setup in which we fully
automate the derivation of achievable rate region for a general relay-assisted
downlink cellular network. Our simulations clearly show the great advantages
provided by cooperative strategies at the relays as compared to the
uncoordinated scenario under varying channel conditions and target rates. These
results are obtained by considering a large number of transmission strategies
for different levels of relay cognition and numerically determining one that is
the most energy efficient. The limited computational complexity of the
numerical evaluations makes this approach suitable for the optimization of
transmission strategies for larger networks
Opportunistic Jamming for Enhancing Security: Stochastic Geometry Modeling and Analysis
This correspondence studies the secrecy communication of the single-input
single-output multi-eavesdropper (SISOME) channel with multiple single-antenna
jammers, where the jammers and eavesdroppers are distributed according to the
independent two-dimensional homogeneous Poisson point process (PPP). For
enhancing the physical layer security, we propose an opportunistic multiple
jammer selection scheme, where the jammers whose channel gains to the
legitimate receiver less than a threshold, are selected to transmit independent
and identically distributed (\emph{i.i.d.}) Gaussian jamming signals to
confound the eavesdroppers. We characterize the secrecy throughput achieved by
our proposed jammer selection scheme, and show that the secrecy throughput is a
quasi-concave function of the selection threshold.Comment: IEEE Transactions on Vehicular Technology, to appea
Ultra Dense Networks: The New Wireless Frontier for Enabling 5G Access
The extreme traffic load that future wireless networks are expected to
accommodate requires a re-thinking of the system design. Initial estimations
indicate that, different from the evolutionary path of previous cellular
generations that was based on spectral efficiency improvements, the most
substantial amount of future system performance gains will be obtained by means
of network infrastructure densification. By increasing the density of
operator-deployed infrastructure elements, along with incorporation of
user-deployed access nodes and mobile user devices acting as "infrastructure
prosumers", it is expected that having one or more access nodes exclusively
dedicated to each user will become feasible, introducing the ultra dense
network (UDN) paradigm. Although it is clear that UDNs are able to take
advantage of the significant benefits provided by proximal transmissions and
increased spatial reuse of system resources, at the same time, large node
density and irregular deployment introduce new challenges, mainly due to the
interference environment characteristics that are vastly different from
previous cellular deployments. This article attempts to provide insights on
fundamental issues related to UDN deployment, such as determining the
infrastructure density required to support given traffic load requirements and
the benefits of network-wise coordination, demonstrating the potential of UDNs
for 5G wireless networks.Comment: to appear in IEEE Vehicular Technology Magazin
Small Cell Deployments: Recent Advances and Research Challenges
This paper summarizes the outcomes of the 5th International Workshop on
Femtocells held at King's College London, UK, on the 13th and 14th of February,
2012.The workshop hosted cutting-edge presentations about the latest advances
and research challenges in small cell roll-outs and heterogeneous cellular
networks. This paper provides some cutting edge information on the developments
of Self-Organizing Networks (SON) for small cell deployments, as well as
related standardization supports on issues such as carrier aggregation (CA),
Multiple-Input-Multiple-Output (MIMO) techniques, and enhanced Inter-Cell
Interference Coordination (eICIC), etc. Furthermore, some recent efforts on
issues such as energy-saving as well as Machine Learning (ML) techniques on
resource allocation and multi-cell cooperation are described. Finally, current
developments on simulation tools and small cell deployment scenarios are
presented. These topics collectively represent the current trends in small cell
deployments.Comment: 19 pages, 22 figure
Downlink Performance Analysis for a Generalized Shotgun Cellular System
In this paper, we analyze the signal-to-interference-plus-noise ratio (SINR)
performance at a mobile station (MS) in a random cellular network. The cellular
network is formed by base-stations (BSs) placed in a one, two or three
dimensional space according to a possibly non-homogeneous Poisson point
process, which is a generalization of the so-called shotgun cellular system. We
develop a sequence of equivalence relations for the SCSs and use them to derive
semi-analytical expressions for the coverage probability at the MS when the
transmissions from each BS may be affected by random fading with arbitrary
distributions as well as attenuation following arbitrary path-loss models. For
homogeneous Poisson point processes in the interference-limited case with
power-law path-loss model, we show that the SINR distribution is the same for
all fading distributions and is not a function of the base station density. In
addition, the influence of random transmission powers, power control, multiple
channel reuse groups on the downlink performance are also discussed. The
techniques developed for the analysis of SINR have applications beyond cellular
networks and can be used in similar studies for cognitive radio networks,
femtocell networks and other heterogeneous and multi-tier networks.Comment: 30 pages, 8 figures, re-submitted to Transactions on Communications
on Sep-12 2012, initial submission to Transactions on Communications on
26-Apr 201
An Upper Bound on Multi-hop Transmission Capacity with Dynamic Routing Selection
This paper develops upper bounds on the end-to-end transmission capacity of
multi-hop wireless networks. Potential source-destination paths are dynamically
selected from a pool of randomly located relays, from which a closed-form lower
bound on the outage probability is derived in terms of the expected number of
potential paths. This is in turn used to provide an upper bound on the number
of successful transmissions that can occur per unit area, which is known as the
transmission capacity. The upper bound results from assuming independence among
the potential paths, and can be viewed as the maximum diversity case. A useful
aspect of the upper bound is its simple form for an arbitrary-sized network,
which allows insights into how the number of hops and other network parameters
affect spatial throughput in the non-asymptotic regime. The outage probability
analysis is then extended to account for retransmissions with a maximum number
of allowed attempts. In contrast to prevailing wisdom, we show that
predetermined routing (such as nearest-neighbor) is suboptimal, since more hops
are not useful once the network is interference-limited. Our results also make
clear that randomness in the location of relay sets and dynamically varying
channel states is helpful in obtaining higher aggregate throughput, and that
dynamic route selection should be used to exploit path diversity.Comment: 14 pages, 5 figures, accepted to IEEE Transactions on Information
Theory, 201
Energy-Efficient Scheduling and Power Allocation in Downlink OFDMA Networks with Base Station Coordination
This paper addresses the problem of energy-efficient resource allocation in
the downlink of a cellular OFDMA system. Three definitions of the energy
efficiency are considered for system design, accounting for both the radiated
and the circuit power. User scheduling and power allocation are optimized
across a cluster of coordinated base stations with a constraint on the maximum
transmit power (either per subcarrier or per base station). The asymptotic
noise-limited regime is discussed as a special case. %The performance of both
an isolated and a non-isolated cluster of coordinated base stations is examined
in the numerical experiments. Results show that the maximization of the energy
efficiency is approximately equivalent to the maximization of the spectral
efficiency for small values of the maximum transmit power, while there is a
wide range of values of the maximum transmit power for which a moderate
reduction of the data rate provides a large saving in terms of dissipated
energy. Also, the performance gap among the considered resource allocation
strategies reduces as the out-of-cluster interference increases.Comment: to appear on IEEE Transactions on Wireless Communication
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