770 research outputs found
On the Corner Points of the Capacity Region of a Two-User Gaussian Interference Channel
This work considers the corner points of the capacity region of a two-user
Gaussian interference channel (GIC). In a two-user GIC, the rate pairs where
one user transmits its data at the single-user capacity (without interference),
and the other at the largest rate for which reliable communication is still
possible are called corner points. This paper relies on existing outer bounds
on the capacity region of a two-user GIC that are used to derive informative
bounds on the corner points of the capacity region. The new bounds refer to a
weak two-user GIC (i.e., when both cross-link gains in standard form are
positive and below 1), and a refinement of these bounds is obtained for the
case where the transmission rate of one user is within of the
single-user capacity. The bounds on the corner points are asymptotically tight
as the transmitted powers tend to infinity, and they are also useful for the
case of moderate SNR and INR. Upper and lower bounds on the gap (denoted by
) between the sum-rate and the maximal achievable total rate at the two
corner points are derived. This is followed by an asymptotic analysis analogous
to the study of the generalized degrees of freedom (where the SNR and INR
scalings are coupled such that ), leading to an asymptotic characterization of this gap which is
exact for the whole range of . The upper and lower bounds on
are asymptotically tight in the sense that they achieve the exact asymptotic
characterization. Improved bounds on are derived for finite SNR and
INR, and their improved tightness is exemplified numerically.Comment: Submitted to the IEEE Trans. on Information Theory in July 17, 2014,
and revised in April 5, 2015. Presented in part at Allerton 2013, and also
presented in part with improved results at ISIT 201
Capacity Regions and Sum-Rate Capacities of Vector Gaussian Interference Channels
The capacity regions of vector, or multiple-input multiple-output, Gaussian
interference channels are established for very strong interference and aligned
strong interference. Furthermore, the sum-rate capacities are established for Z
interference, noisy interference, and mixed (aligned weak/intermediate and
aligned strong) interference. These results generalize known results for scalar
Gaussian interference channels.Comment: 33 pages, 1 figure, submitted to IEEE trans. on Information theor
On the Capacity Region of the Two-User Interference Channel
One of the key open problems in network information theory is to obtain the
capacity region for the two-user Interference Channel (IC). In this paper, new
results are derived for this channel. As a first result, a noisy interference
regime is given for the general IC where the sum-rate capacity is achieved by
treating interference as noise at the receivers. To obtain this result, a
single-letter outer bound in terms of some auxiliary random variables is first
established for the sum-rate capacity of the general IC and then those
conditions under which this outer bound is reduced to the achievable sum-rate
given by the simple treating interference as noise strategy are specified. The
main benefit of this approach is that it is applicable for any two-user IC
(potentially non-Gaussian). For the special case of Gaussian channel, our
result is reduced to the noisy interference regime that was previously
obtained. Next, some results are given on the Han-Kobayashi (HK) achievable
rate region. The evaluation of this rate region is in general difficult. In
this paper, a simple characterization of the HK rate region is derived for some
special cases, specifically, for a novel very weak interference regime. As a
remarkable characteristic, it is shown that for this very weak interference
regime, the achievable sum-rate due to the HK region is identical to the one
given by the simple treating interference as noise strategy.Comment: 12 pages. In this paper a noisy interference regime is identified for
any two-user interference channel (potentially non-Gaussian). For conference
publicatio
On the High-SNR Capacity of the Gaussian Interference Channel and New Capacity Bounds
The best outer bound on the capacity region of the two-user Gaussian
Interference Channel (GIC) is known to be the intersection of regions of
various bounds including genie-aided outer bounds, in which a genie provides
noisy input signals to the intended receiver. The Han and Kobayashi (HK) scheme
provides the best known inner bound. The rate difference between the best known
lower and upper bounds on the sum capacity remains as large as 1 bit per
channel use especially around , where is the symmetric power
constraint and is the symmetric real cross-channel coefficient. In this
paper, we pay attention to the \emph{moderate interference regime} where
. We propose a new upper-bounding technique
that utilizes noisy observation of interfering signals as genie signals and
applies time sharing to the genie signals at the receivers. A conditional
version of the worst additive noise lemma is also introduced to derive new
capacity bounds. The resulting upper (outer) bounds on the sum capacity
(capacity region) are shown to be tighter than the existing bounds in a certain
range of the moderate interference regime. Using the new upper bounds and the
HK lower bound, we show that characterizes the capacity of the symmetric real
GIC to within bit per channel use in the moderate interference regime
at any signal-to-noise ratio (SNR). We further establish a high-SNR
characterization of the symmetric real GIC, where the proposed upper bound is
at most bit far from a certain HK achievable scheme with Gaussian
signaling and time sharing for . In particular,
is achievable at high SNR by the proposed HK scheme and turns out to be the
high-SNR capacity at least at .Comment: Submitted to IEEE Transactions on Information Theory on June 2015,
revised on November 2016, and accepted for publication on Feb. 28, 201
Accessible Capacity of Secondary Users
A new problem formulation is presented for the Gaussian interference channels
(GIFC) with two pairs of users, which are distinguished as primary users and
secondary users, respectively. The primary users employ a pair of encoder and
decoder that were originally designed to satisfy a given error performance
requirement under the assumption that no interference exists from other users.
In the scenario when the secondary users attempt to access the same medium, we
are interested in the maximum transmission rate (defined as {\em accessible
capacity}) at which secondary users can communicate reliably without affecting
the error performance requirement by the primary users under the constraint
that the primary encoder (not the decoder) is kept unchanged. By modeling the
primary encoder as a generalized trellis code (GTC), we are then able to treat
the secondary link and the cross link from the secondary transmitter to the
primary receiver as finite state channels (FSCs). Based on this, upper and
lower bounds on the accessible capacity are derived. The impact of the error
performance requirement by the primary users on the accessible capacity is
analyzed by using the concept of interference margin. In the case of
non-trivial interference margin, the secondary message is split into common and
private parts and then encoded by superposition coding, which delivers a lower
bound on the accessible capacity. For some special cases, these bounds can be
computed numerically by using the BCJR algorithm. Numerical results are also
provided to gain insight into the impacts of the GTC and the error performance
requirement on the accessible capacity.Comment: 42 pages, 12 figures, 2 tables; Submitted to IEEE Transactions on
Information Theory on December, 2010, Revised on November, 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
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