503 research outputs found
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
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
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
Two-Layered Superposition of Broadcast/Multicast and Unicast Signals in Multiuser OFDMA Systems
We study optimal delivery strategies of one common and independent
messages from a source to multiple users in wireless environments. In
particular, two-layered superposition of broadcast/multicast and unicast
signals is considered in a downlink multiuser OFDMA system. In the literature
and industry, the two-layer superposition is often considered as a pragmatic
approach to make a compromise between the simple but suboptimal orthogonal
multiplexing (OM) and the optimal but complex fully-layered non-orthogonal
multiplexing. In this work, we show that only two-layers are necessary to
achieve the maximum sum-rate when the common message has higher priority than
the individual unicast messages, and OM cannot be sum-rate optimal in
general. We develop an algorithm that finds the optimal power allocation over
the two-layers and across the OFDMA radio resources in static channels and a
class of fading channels. Two main use-cases are considered: i) Multicast and
unicast multiplexing when users with uplink capabilities request both
common and independent messages, and ii) broadcast and unicast multiplexing
when the common message targets receive-only devices and users with uplink
capabilities additionally request independent messages. Finally, we develop a
transceiver design for broadcast/multicast and unicast superposition
transmission based on LTE-A-Pro physical layer and show with numerical
evaluations in mobile environments with multipath propagation that the capacity
improvements can be translated into significant practical performance gains
compared to the orthogonal schemes in the 3GPP specifications. We also analyze
the impact of real channel estimation and show that significant gains in terms
of spectral efficiency or coverage area are still available even with
estimation errors and imperfect interference cancellation for the two-layered
superposition system
On the Gaussian Many-to-One X Channel
In this paper, the Gaussian many-to-one X channel, which is a special case of
general multiuser X channel, is studied. In the Gaussian many-to-one X channel,
communication links exist between all transmitters and one of the receivers,
along with a communication link between each transmitter and its corresponding
receiver. As per the X channel assumption, transmission of messages is allowed
on all the links of the channel. This communication model is different from the
corresponding many-to-one interference channel (IC). Transmission strategies
which involve using Gaussian codebooks and treating interference from a subset
of transmitters as noise are formulated for the above channel. Sum-rate is used
as the criterion of optimality for evaluating the strategies. Initially, a many-to-one X channel is considered and three transmission strategies
are analyzed. The first two strategies are shown to achieve sum-rate capacity
under certain channel conditions. For the third strategy, a sum-rate outer
bound is derived and the gap between the outer bound and the achieved rate is
characterized. These results are later extended to the case. Next,
a region in which the many-to-one X channel can be operated as a many-to-one IC
without loss of sum-rate is identified. Further, in the above region, it is
shown that using Gaussian codebooks and treating interference as noise achieves
a rate point that is within bits from the sum-rate capacity.
Subsequently, some implications of the above results to the Gaussian
many-to-one IC are discussed. Transmission strategies for the many-to-one IC
are formulated and channel conditions under which the strategies achieve
sum-rate capacity are obtained. A region where the sum-rate capacity can be
characterized to within bits is also identified.Comment: Submitted to IEEE Transactions on Information Theory; Revised and
updated version of the original draf
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