259 research outputs found
On the Optimality of Treating Inter-Cell Interference as Noise in Uplink Cellular Networks
In this paper, we explore the information-theoretic optimality of treating
interference as noise (TIN) in cellular networks. We focus on uplink scenarios
modeled by the Gaussian interfering multiple access channel (IMAC), comprising
mutually interfering multiple access channels (MACs), each formed by an
arbitrary number of transmitters communicating independent messages to one
receiver. We define TIN for this setting as a scheme in which each MAC (or
cell) performs a power-controlled version of its capacity-achieving strategy,
with Gaussian codebooks and successive decoding, while treating interference
from all other MACs (i.e. inter-cell interference) as noise. We characterize
the generalized degrees-of-freedom (GDoF) region achieved through the proposed
TIN scheme, and then identify conditions under which this achievable region is
convex without the need for time-sharing. We then tighten these convexity
conditions and identify a regime in which the proposed TIN scheme achieves the
entire GDoF region of the IMAC and is within a constant gap of the entire
capacity region.Comment: Accepted for publication in IEEE Transactions on Information Theor
Sub-optimality of Treating Interference as Noise in the Cellular Uplink
Despite the simplicity of the scheme of treating interference as noise (TIN),
it was shown to be sum-capacity optimal in the Gaussian 2-user interference
channel in \cite{ShangKramerChen,MotahariKhandani,AnnapureddyVeeravalli}. In
this paper, an interference network consisting of a point-to-point channel
interfering with a multiple access channel (MAC) is considered, with focus on
the weak interference scenario. Naive TIN in this network is performed by using
Gaussian codes at the transmitters, joint decoding at the MAC receiver while
treating interference as noise, and single user decoding at the point-to-point
receiver while treating both interferers as noise. It is shown that this naive
TIN scheme is never optimal in this scenario. In fact, a scheme that combines
both time division multiple access and TIN outperforms the naive TIN scheme. An
upper bound on the sum-capacity of the given network is also derived.Comment: 5 pages, 3 figures, typos correcte
Extended Generalized DoF Optimality Regime of Treating Interference as Noise in the X Channel
The simple scheme of treating interference as noise (TIN) is studied in this
paper for the 3 x 2 X channel. A new sum-capacity upper bound is derived. This
upper bound is transformed into a generalized degrees-of-freedom (GDoF) upper
bound, and is shown to coincide with the achievable GDoF of scheme that
combines TDMA and TIN for some conditions on the channel parameters. These
conditions specify a noisy interference regime which extends noisy interference
regimes available in literature. As a by-product, the sum-capacity of the 3 x 2
X channel is characterized within a constant gap in the given noisy
interference regime.Comment: 5 pages, 2 figure
Uplink CoMP under a Constrained Backhaul and Imperfect Channel Knowledge
Coordinated Multi-Point (CoMP) is known to be a key technology for next
generation mobile communications systems, as it allows to overcome the burden
of inter-cell interference. Especially in the uplink, it is likely that
interference exploitation schemes will be used in the near future, as they can
be used with legacy terminals and require no or little changes in
standardization. Major drawbacks, however, are the extent of additional
backhaul infrastructure needed, and the sensitivity to imperfect channel
knowledge. This paper jointly addresses both issues in a new framework
incorporating a multitude of proposed theoretical uplink CoMP concepts, which
are then put into perspective with practical CoMP algorithms. This
comprehensive analysis provides new insight into the potential usage of uplink
CoMP in next generation wireless communications systems.Comment: Submitted to IEEE Transactions on Wireless Communications in February
201
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
Cellular Networks With Finite Precision CSIT: GDoF Optimality of Multi-Cell TIN and Extremal Gains of Multi-Cell Cooperation
We study the generalized degrees-of-freedom (GDoF) of cellular networks under
finite precision channel state information at the transmitters (CSIT). We
consider downlink settings modeled by the interfering broadcast channel (IBC)
under no multi-cell cooperation, and the overloaded
multiple-input-single-output broadcast channel (MISO-BC) under full multi-cell
cooperation. We focus on three regimes of interest: the mc-TIN regime, where a
scheme based on treating inter-cell interference as noise (mc-TIN) was shown to
be GDoF optimal for the IBC; the mc-CTIN regime, where the GDoF region
achievable by mc-TIN is convex without the need for time-sharing; and the
mc-SLS regime which extends a previously identified regime, where a simple
layered superposition (SLS) scheme is optimal for the 3-transmitter-3-user
MISO-BC, to overloaded cellular-type networks with more users than
transmitters. We first show that the optimality of mc-TIN for the IBC extends
to the entire mc-CTIN regime when CSIT is limited to finite precision. The
converse proof of this result relies on a new application of aligned images
bounds. We then extend the IBC converse proof to the counterpart overloaded
MISO-BC, obtained by enabling full transmitter cooperation. This, in turn, is
utilized to show that a multi-cell variant of the SLS scheme is optimal in the
mc-SLS regime under full multi-cell cooperation, albeit only for 2-cell
networks. The overwhelming combinatorial complexity of the GDoF region stands
in the way of extending this result to larger networks. Alternatively, we
appeal to extremal network analysis, recently introduced by Chan et al., and
study the GDoF gain of multi-cell cooperation over mc-TIN in the three regimes
of interest. We show that this extremal GDoF gain is bounded by small constants
in the mc-TIN and mc-CTIN regimes, yet scales logarithmically with the number
of cells in the mc-SLS regime.Comment: Accepted for publication in the IEEE Transactions on Information
Theor
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