6,558 research outputs found
A New Outer Bound and the Noisy-Interference Sum-Rate Capacity for Gaussian Interference Channels
A new outer bound on the capacity region of Gaussian interference channels is
developed. The bound combines and improves existing genie-aided methods and is
shown to give the sum-rate capacity for noisy interference as defined in this
paper. Specifically, it is shown that if the channel coefficients and power
constraints satisfy a simple condition then single-user detection at each
receiver is sum-rate optimal, i.e., treating the interference as noise incurs
no loss in performance. This is the first concrete (finite signal-to-noise
ratio) capacity result for the Gaussian interference channel with weak to
moderate interference. Furthermore, for certain mixed (weak and strong)
interference scenarios, the new outer bounds give a corner point of the
capacity region.Comment: 20 pages, 8 figures, submitted to IEEE Trans. Inform. Theory
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
On Code Design for Interference Channels
abstract: There has been a lot of work on the characterization of capacity and achievable rate regions, and rate region outer-bounds for various multi-user channels of interest. Parallel to the developed information theoretic results, practical codes have also been designed for some multi-user channels such as multiple access channels, broadcast channels and relay channels; however, interference channels have not received much attention and only a limited amount of work has been conducted on them. With this motivation, in this dissertation, design of practical and implementable channel codes is studied focusing on multi-user channels with special emphasis on interference channels; in particular, irregular low-density-parity-check codes are exploited for a variety of cases and trellis based codes for short block length designs are performed.
Novel code design approaches are first studied for the two-user Gaussian multiple access channel. Exploiting Gaussian mixture approximation, new methods are proposed wherein the optimized codes are shown to improve upon the available designs and off-the-shelf point-to-point codes applied to the multiple access channel scenario. The code design is then examined for the two-user Gaussian interference channel implementing the Han-Kobayashi encoding and decoding strategy. Compared with the point-to-point codes, the newly designed codes consistently offer better performance. Parallel to this work, code design is explored for the discrete memoryless interference channels wherein the channel inputs and outputs are taken from a finite alphabet and it is demonstrated that the designed codes are superior to the single user codes used with time sharing. Finally, the code design principles are also investigated for the two-user Gaussian interference channel employing trellis-based codes with short block lengths for the case of strong and mixed interference levels.Dissertation/ThesisDoctoral Dissertation Electrical Engineering 201
Capacity Analysis for Gaussian and Discrete Memoryless Interference Networks
Interference is an important issue for wireless communication systems where multiple
uncoordinated users try to access to a common medium. The problem is even more
crucial for next-generation cellular networks where frequency reuse becomes ever more
intense, leading to more closely placed co-channel cells. This thesis describes our attempt to understand the impact of interference on communication performance as well as optimal ways to handle interference. From the theoretical point of view, we examine how interference affects the fundamental performance limits, and provide insights on how interference should be treated for various channel models under different operating
conditions. From the practical design point of view, we provide solutions to improve the
system performance under unknown interference using multiple independent receptions
of the same information.
For the simple two-user Gaussian interference channel, we establish that the simple
Frequency Division Multiplexing (FDM) technique suffices to provide the optimal sum-
rate within the largest computable subregion of the general achievable rate region for a
certain interference range.
For the two-user discrete memoryless interference channels, we characterize different
interference regimes as well as the corresponding capacity results. They include one-
sided weak interference and mixed interference conditions. The sum-rate capacities are
derived in both cases. The conditions, capacity expressions, as well as the capacity achieving schemes are analogous to those of the Gaussian channel model. The study
also leads to new outer bounds that can be used to resolve the capacities of several new
discrete memoryless interference channels.
A three-user interference up-link transmission model is introduced. By examining how
interference affects the behavior of the performance limits, we capture the differences
and similarities between the traditional two-user channel model and the channel model
with more than two users. If the interference is very strong, the capacity region is just
a simple extension of the two-user case. For the strong interference case, a line segment
on the boundary of the capacity region is attained. When there are links with weak
interference, the performance limits behave very differently from that of the two-user
case: there is no single case that is found of which treating interference as noise is
optimal. In particular, for a subclass of Gaussian channels with mixed interference, a
boundary point of the capacity region is determined. For the Gaussian channel with
weak interference, sum capacities are obtained under various channel coefficients and
power constraint conditions. The optimalities in all the cases are obtained by decoding
part of the interference.
Finally, we investigate a topic that has practical ramifications in real communication
systems. We consider in particular a diversity reception system where independently
copies of low density parity check (LDPC) coded signals are received. Relying only on
non-coherent reception in a highly dynamic environment with unknown interference, soft-decision combining is achieved whose performance is shown to improve significantly over existing approaches that rely on hard decision combining
A New Capacity Result for the Z-Gaussian Cognitive Interference Channel
This work proposes a novel outer bound for the Gaussian cognitive
interference channel in strong interference at the primary receiver based on
the capacity of a multi-antenna broadcast channel with degraded message set. It
then shows that for the Z-channel, i.e., when the secondary receiver
experiences no interference and the primary receiver experiences strong
interference, the proposed outer bound not only is the tightest among known
bounds but is actually achievable for sufficiently strong interference. The
latter is a novel capacity result that from numerical evaluations appears to be
generalizable to a larger (i.e., non-Z) class of Gaussian channels
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