2,340 research outputs found
Dependence Balance Based Outer Bounds for Gaussian Networks with Cooperation and Feedback
We obtain new outer bounds on the capacity regions of the two-user multiple
access channel with generalized feedback (MAC-GF) and the two-user interference
channel with generalized feedback (IC-GF). These outer bounds are based on the
idea of dependence balance which was proposed by Hekstra and Willems [1]. To
illustrate the usefulness of our outer bounds, we investigate three different
channel models. We first consider a Gaussian MAC with noisy feedback (MAC-NF),
where transmitter , , receives a feedback , which is the
channel output corrupted with additive white Gaussian noise . As the
feedback noise variances become large, one would expect the feedback to become
useless, which is not reflected by the cut-set bound. We demonstrate that our
outer bound improves upon the cut-set bound for all non-zero values of the
feedback noise variances. Moreover, in the limit as , , our outer bound collapses to the capacity region of the
Gaussian MAC without feedback. Secondly, we investigate a Gaussian MAC with
user-cooperation (MAC-UC), where each transmitter receives an additive white
Gaussian noise corrupted version of the channel input of the other transmitter
[2]. For this channel model, the cut-set bound is sensitive to the cooperation
noises, but not sensitive enough. For all non-zero values of cooperation noise
variances, our outer bound strictly improves upon the cut-set outer bound.
Thirdly, we investigate a Gaussian IC with user-cooperation (IC-UC). For this
channel model, the cut-set bound is again sensitive to cooperation noise
variances but not sensitive enough. We demonstrate that our outer bound
strictly improves upon the cut-set bound for all non-zero values of cooperation
noise variances.Comment: Submitted to IEEE Transactions on Information Theor
The Capacity of the Gaussian Cooperative Two-user Multiple Access Channel to within a Constant Gap
The capacity region of the cooperative two-user Multiple Access Channel (MAC)
in Gaussian noise is determined to within a constant gap for both the
Full-Duplex (FD) and Half-Duplex (HD) case. The main contributions are: (a) for
both FD and HD: unilateral cooperation suffices to achieve capacity to within a
constant gap where only the user with the strongest link to the destination
needs to engage in cooperation, (b) for both FD and HD: backward joint decoding
is not necessary to achieve capacity to within a constant gap, and (c) for HD:
time sharing between the case where the two users do not cooperate and the case
where the user with the strongest link to the destination acts as pure relay
for the other user suffices to achieve capacity to within a constant gap. These
findings show that simple achievable strategies are approximately optimal for
all channel parameters with interesting implications for practical cooperative
schemes.Comment: Submitted to the 2013 IEEE International Conference on Communications
(ICC 2013
Capacity Bounds For Multi-User Channels With Feedback, Relaying and Cooperation
Recent developments in communications are driven by the goal of
achieving high data rates for wireless communication devices. To
achieve this goal, several new phenomena need to be investigated
from an information theoretic perspective. In this dissertation,
we focus on three of these phenomena: feedback, relaying and
cooperation. We study these phenomena for various multi-user
channels from an information theoretic point of view.
One of the aims of this dissertation is to study the performance
limits of simple wireless networks, for various forms of feedback
and cooperation. Consider an uplink communication system, where
several users wish to transmit independent data to a base-station.
If the base-station can send feedback to the users, one can expect
to achieve higher data-rates since feedback can enable cooperation
among the users. Another way to improve data-rates is to make use
of the broadcast nature of the wireless medium, where the users
can overhear each other's transmitted signals. This particular
phenomenon has garnered much attention lately, where users can
help in increasing each other's data-rates by utilizing the
overheard information. This overheard information can be
interpreted as a generalized form of feedback.
To take these several models of feedback and cooperation into
account, we study the two-user multiple access channel and the
two-user interference channel with generalized feedback. For all
these models, we derive new outer bounds on their capacity
regions. We specialize these results for noiseless feedback,
additive noisy feedback and user-cooperation models and show
strict improvements over the previously known bounds.
Next, we study state-dependent channels with rate-limited state
information to the receiver or to the transmitter. This
state-dependent channel models a practical situation of fading,
where the fade information is partially available to the receiver
or to the transmitter. We derive new bounds on the capacity of
such channels and obtain capacity results for a special sub-class
of such channels.
We study the effect of relaying by considering the parallel relay
network, also known as the diamond channel. The parallel relay
network considered in this dissertation comprises of a cascade of
a general broadcast channel to the relays and an orthogonal
multiple access channel from the relays to the receiver. We
characterize the capacity of the diamond channel, when the
broadcast channel is deterministic. We also study the diamond
channel with partially separated relays, and obtain capacity
results when the broadcast channel is either semi-deterministic or
physically degraded. Our results also demonstrate that feedback to
the relays can strictly increase the capacity of the diamond
channel.
In several sensor network applications, distributed lossless
compression of sources is of considerable interest. The presence
of adversarial nodes makes it important to design compression
schemes which serve the dual purpose of reliable source
transmission to legitimate nodes while minimizing the information
leakage to the adversarial nodes. Taking this constraint into
account, we consider information theoretic secrecy, where our aim
is to limit the information leakage to the eavesdropper. For this
purpose, we study a secure source coding problem with coded side
information from a helper to the legitimate user. We derive the
rate-equivocation region for this problem. We show that the helper
node serves the dual purpose of reducing the source transmission
rate and increasing the uncertainty at the adversarial node. Next,
we considered two different secure source coding models and
provide the corresponding rate-equivocation regions
Capacity Theorems for the Fading Interference Channel with a Relay and Feedback Links
Handling interference is one of the main challenges in the design of wireless
networks. One of the key approaches to interference management is node
cooperation, which can be classified into two main types: relaying and
feedback. In this work we consider simultaneous application of both cooperation
types in the presence of interference. We obtain exact characterization of the
capacity regions for Rayleigh fading and phase fading interference channels
with a relay and with feedback links, in the strong and very strong
interference regimes. Four feedback configurations are considered: (1) feedback
from both receivers to the relay, (2) feedback from each receiver to the relay
and to one of the transmitters (either corresponding or opposite), (3) feedback
from one of the receivers to the relay, (4) feedback from one of the receivers
to the relay and to one of the transmitters. Our results show that there is a
strong motivation for incorporating relaying and feedback into wireless
networks.Comment: Accepted to the IEEE Transactions on Information Theor
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