942 research outputs found
Optimality of Orthogonal Access for One-dimensional Convex Cellular Networks
It is shown that a greedy orthogonal access scheme achieves the sum degrees
of freedom of all one-dimensional (all nodes placed along a straight line)
convex cellular networks (where cells are convex regions) when no channel
knowledge is available at the transmitters except the knowledge of the network
topology. In general, optimality of orthogonal access holds neither for
two-dimensional convex cellular networks nor for one-dimensional non-convex
cellular networks, thus revealing a fundamental limitation that exists only
when both one-dimensional and convex properties are simultaneously enforced, as
is common in canonical information theoretic models for studying cellular
networks. The result also establishes the capacity of the corresponding class
of index coding problems
Optimal Virtualized Inter-Tenant Resource Sharing for Device-to-Device Communications in 5G Networks
Device-to-Device (D2D) communication is expected to enable a number of new
services and applications in future mobile networks and has attracted
significant research interest over the last few years. Remarkably, little
attention has been placed on the issue of D2D communication for users belonging
to different operators. In this paper, we focus on this aspect for D2D users
that belong to different tenants (virtual network operators), assuming
virtualized and programmable future 5G wireless networks. Under the assumption
of a cross-tenant orchestrator, we show that significant gains can be achieved
in terms of network performance by optimizing resource sharing from the
different tenants, i.e., slices of the substrate physical network topology. To
this end, a sum-rate optimization framework is proposed for optimal sharing of
the virtualized resources. Via a wide site of numerical investigations, we
prove the efficacy of the proposed solution and the achievable gains compared
to legacy approaches.Comment: 10 pages, 7 figure
Cellular Interference Alignment
Interference alignment promises that, in Gaussian interference channels, each
link can support half of a degree of freedom (DoF) per pair of transmit-receive
antennas. However, in general, this result requires to precode the data bearing
signals over a signal space of asymptotically large diversity, e.g., over an
infinite number of dimensions for time-frequency varying fading channels, or
over an infinite number of rationally independent signal levels, in the case of
time-frequency invariant channels. In this work we consider a wireless cellular
system scenario where the promised optimal DoFs are achieved with linear
precoding in one-shot (i.e., over a single time-frequency slot). We focus on
the uplink of a symmetric cellular system, where each cell is split into three
sectors with orthogonal intra-sector multiple access. In our model,
interference is "local", i.e., it is due to transmitters in neighboring cells
only. We consider a message-passing backhaul network architecture, in which
nearby sectors can exchange already decoded messages and propose an alignment
solution that can achieve the optimal DoFs. To avoid signaling schemes relying
on the strength of interference, we further introduce the notion of
\emph{topologically robust} schemes, which are able to guarantee a minimum rate
(or DoFs) irrespectively of the strength of the interfering links. Towards this
end, we design an alignment scheme which is topologically robust and still
achieves the same optimum DoFs
Topological Interference Management through Index Coding
This work studies linear interference networks, both wired and wireless, with
no channel state information at the transmitters (CSIT) except a coarse
knowledge of the end-to-end one-hop topology of the network that only allows a
distinction between weak (zero) and significant (non-zero) channels and no
further knowledge of the channel coefficients' realizations. The network
capacity (wired) and DoF (wireless) are found to be bounded above by the
capacity of an index coding problem for which the antidote graph is the
complement of the given interference graph. The problems are shown to be
equivalent under linear solutions. An interference alignment perspective is
then used to translate the existing index coding solutions into the wired
network capacity and wireless network DoF solutions, as well as to find new and
unified solutions to different classes of all three problems.Comment: Revised for the IEEE Transactions on Information Theor
Spatial networks with wireless applications
Many networks have nodes located in physical space, with links more common
between closely spaced pairs of nodes. For example, the nodes could be wireless
devices and links communication channels in a wireless mesh network. We
describe recent work involving such networks, considering effects due to the
geometry (convex,non-convex, and fractal), node distribution,
distance-dependent link probability, mobility, directivity and interference.Comment: Review article- an amended version with a new title from the origina
Optimal channel allocation with dynamic power control in cellular networks
Techniques for channel allocation in cellular networks have been an area of
intense research interest for many years. An efficient channel allocation
scheme can significantly reduce call-blocking and calldropping probabilities.
Another important issue is to effectively manage the power requirements for
communication. An efficient power control strategy leads to reduced power
consumption and improved signal quality. In this paper, we present a novel
integer linear program (ILP) formulation that jointly optimizes channel
allocation and power control for incoming calls, based on the
carrier-to-interference ratio (CIR). In our approach we use a hybrid channel
assignment scheme, where an incoming call is admitted only if a suitable
channel is found such that the CIR of all ongoing calls on that channel, as
well as that of the new call, will be above a specified value. Our formulation
also guarantees that the overall power requirement for the selected channel
will be minimized as much as possible and that no ongoing calls will be dropped
as a result of admitting the new call. We have run simulations on a benchmark
49 cell environment with 70 channels to investigate the effect of different
parameters such as the desired CIR. The results indicate that our approach
leads to significant improvements over existing techniques.Comment: 11 page
Flexible backhaul design with cooperative transmission in cellular interference networks
Interference is an important factor that limits the rates that can be achieved by mobile users in a cellular network. Interference management through cooperation has emerged as a major consideration for next-generation cellular networks. In this thesis, we focus on the downlink of a sectored hexagonal cellular network, under the assumption of local interference i.e., the interference at each user is only due to transmitters in neighboring sectors. We explore the potential degrees of freedom (DoF) gain in this network under constraints on the cooperation between base-stations. The constraints that we consider are the cooperation order M, and the average backhaul load B, which denote the maximum and the average number of transmitters, respectively, that jointly transmit any message.
We first study the DoF gains in a scenario where mobile receivers can be associated to any neighboring cell but no cooperative transmission is allowed, and derive bounds on the maximum achievable per user DoF for orthogonal schemes. We then show that by combining cooperative transmission with flexible message assignment to the transmitters, it is possible to achieve a per user DoF strictly greater than that without cooperation. The proposed cooperative transmission scheme does not require extra backhaul capacity, as it uses a smart assignment of messages to transmitters to meet an average backhaul load constraint of one message per transmitter. The schemes presented are simple zero-forcing beamforming schemes that require linear precoding over a single time/frequency slot (one-shot). Similar schemes are proposed which achieve a per user DoF greater than half with a minimal increase in the backhaul load. These results are derived for networks with intra-cell interference and networks without intra-cell interference
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