5,086 research outputs found
Inner and Outer Bounds for the Gaussian Cognitive Interference Channel and New Capacity Results
The capacity of the Gaussian cognitive interference channel, a variation of
the classical two-user interference channel where one of the transmitters
(referred to as cognitive) has knowledge of both messages, is known in several
parameter regimes but remains unknown in general. In this paper we provide a
comparative overview of this channel model as we proceed through our
contributions: we present a new outer bound based on the idea of a broadcast
channel with degraded message sets, and another series of outer bounds obtained
by transforming the cognitive channel into channels with known capacity. We
specialize the largest known inner bound derived for the discrete memoryless
channel to the Gaussian noise channel and present several simplified schemes
evaluated for Gaussian inputs in closed form which we use to prove a number of
results. These include a new set of capacity results for the a) "primary
decodes cognitive" regime, a subset of the "strong interference" regime that is
not included in the "very strong interference" regime for which capacity was
known, and for the b) "S-channel" in which the primary transmitter does not
interfere with the cognitive receiver. Next, for a general Gaussian cognitive
interference channel, we determine the capacity to within one bit/s/Hz and to
within a factor two regardless of channel parameters, thus establishing rate
performance guarantees at high and low SNR, respectively. We also show how
different simplified transmission schemes achieve a constant gap between inner
and outer bound for specific channels. Finally, we numerically evaluate and
compare the various simplified achievable rate regions and outer bounds in
parameter regimes where capacity is unknown, leading to further insight on the
capacity region of the Gaussian cognitive interference channel.Comment: submitted to IEEE transaction of Information Theor
The Approximate Capacity Region of the Gaussian Z-Interference Channel with Conferencing Encoders
A two-user Gaussian Z-Interference Channel (GZIC) is considered, in which
encoders are connected through noiseless links with finite capacities. In this
setting, prior to each transmission block the encoders communicate with each
other over the cooperative links. The capacity region and the sum-capacity of
the channel are characterized within 1.71 bits per user and 2 bits in total,
respectively. It is also established that properly sharing the total limited
cooperation capacity between the cooperative links may enhance the achievable
region, even when compared to the case of unidirectional transmitter
cooperation with infinite cooperation capacity. To obtain the results,
genie-aided upper bounds on the sum-capacity and cut-set bounds on the
individual rates are compared with the achievable rate region. In the
interference-limited regime, the achievable scheme enjoys a simple type of
Han-Kobayashi signaling, together with the zero-forcing, and basic relaying
techniques. In the noise-limited regime, it is shown that treating interference
as noise achieves the capacity region up to a single bit per user.Comment: 25 pages, 6 figures, submitted to IEEE Transactions on Information
Theor
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
Interference Mitigation in Large Random Wireless Networks
A central problem in the operation of large wireless networks is how to deal
with interference -- the unwanted signals being sent by transmitters that a
receiver is not interested in. This thesis looks at ways of combating such
interference.
In Chapters 1 and 2, we outline the necessary information and communication
theory background, including the concept of capacity. We also include an
overview of a new set of schemes for dealing with interference known as
interference alignment, paying special attention to a channel-state-based
strategy called ergodic interference alignment.
In Chapter 3, we consider the operation of large regular and random networks
by treating interference as background noise. We consider the local performance
of a single node, and the global performance of a very large network.
In Chapter 4, we use ergodic interference alignment to derive the asymptotic
sum-capacity of large random dense networks. These networks are derived from a
physical model of node placement where signal strength decays over the distance
between transmitters and receivers. (See also arXiv:1002.0235 and
arXiv:0907.5165.)
In Chapter 5, we look at methods of reducing the long time delays incurred by
ergodic interference alignment. We analyse the tradeoff between reducing delay
and lowering the communication rate. (See also arXiv:1004.0208.)
In Chapter 6, we outline a problem that is equivalent to the problem of
pooled group testing for defective items. We then present some new work that
uses information theoretic techniques to attack group testing. We introduce for
the first time the concept of the group testing channel, which allows for
modelling of a wide range of statistical error models for testing. We derive
new results on the number of tests required to accurately detect defective
items, including when using sequential `adaptive' tests.Comment: PhD thesis, University of Bristol, 201
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