2,628 research outputs found
On the Capacity Region of the Two-user Interference Channel with a Cognitive Relay
This paper considers a variation of the classical two-user interference
channel where the communication of two interfering source-destination pairs is
aided by an additional node that has a priori knowledge of the messages to be
transmitted, which is referred to as the it cognitive relay. For this
Interference Channel with a Cognitive Relay (ICCR) In particular, for the class
of injective semi-deterministic ICCRs, a sum-rate upper bound is derived for
the general memoryless ICCR and further tightened for the Linear Deterministic
Approximation (LDA) of the Gaussian noise channel at high SNR, which disregards
the noise and focuses on the interaction among the users' signals. The capacity
region of the symmetric LDA is completely characterized except for the regime
of moderately weak interference and weak links from the CR to the destinations.
The insights gained from the analysis of the LDA are then translated back to
the symmetric Gaussian noise channel (GICCR). For the symmetric GICCR, an
approximate characterization (to within a constant gap) of the capacity region
is provided for a parameter regime where capacity was previously unknown. The
approximately optimal scheme suggests that message cognition at a relay is
beneficial for interference management as it enables simultaneous over the air
neutralization of the interference at both destinations
Capacity Bounds for a Class of Interference Relay Channels
The capacity of a class of Interference Relay Channels (IRC) -the Injective
Semideterministic IRC where the relay can only observe one of the sources- is
investigated. We first derive a novel outer bound and two inner bounds which
are based on a careful use of each of the available cooperative strategies
together with the adequate interference decoding technique. The outer bound
extends Telatar and Tse's work while the inner bounds contain several known
results in the literature as special cases. Our main result is the
characterization of the capacity region of the Gaussian class of IRCs studied
within a fixed number of bits per dimension -constant gap. The proof relies on
the use of the different cooperative strategies in specific SNR regimes due to
the complexity of the schemes. As a matter of fact, this issue reveals the
complex nature of the Gaussian IRC where the combination of a single coding
scheme for the Gaussian relay and interference channel may not lead to a good
coding scheme for this problem, even when the focus is only on capacity to
within a constant gap over all possible fading statistics.Comment: 23 pages, 6 figures. Submitted to IEEE Transactions on Information
Theory (revised version
Cooperative Strategies for Simultaneous and Broadcast Relay Channels
Consider the \emph{simultaneous relay channel} (SRC) which consists of a set
of relay channels where the source wishes to transmit common and private
information to each of the destinations. This problem is recognized as being
equivalent to that of sending common and private information to several
destinations in presence of helper relays where each channel outcome becomes a
branch of the \emph{broadcast relay channel} (BRC). Cooperative schemes and
capacity region for a set with two memoryless relay channels are investigated.
The proposed coding schemes, based on \emph{Decode-and-Forward} (DF) and
\emph{Compress-and-Forward} (CF) must be capable of transmitting information
simultaneously to all destinations in such set.
Depending on the quality of source-to-relay and relay-to-destination
channels, inner bounds on the capacity of the general BRC are derived. Three
cases of particular interest are considered: cooperation is based on DF
strategy for both users --referred to as DF-DF region--, cooperation is based
on CF strategy for both users --referred to as CF-CF region--, and cooperation
is based on DF strategy for one destination and CF for the other --referred to
as DF-CF region--. These results can be seen as a generalization and hence
unification of previous works. An outer-bound on the capacity of the general
BRC is also derived. Capacity results are obtained for the specific cases of
semi-degraded and degraded Gaussian simultaneous relay channels. Rates are
evaluated for Gaussian models where the source must guarantee a minimum amount
of information to both users while additional information is sent to each of
them.Comment: 32 pages, 7 figures, To appear in IEEE Trans. on Information Theor
On Two-Pair Two-Way Relay Channel with an Intermittently Available Relay
When multiple users share the same resource for physical layer cooperation
such as relay terminals in their vicinities, this shared resource may not be
always available for every user, and it is critical for transmitting terminals
to know whether other users have access to that common resource in order to
better utilize it. Failing to learn this critical piece of information may
cause severe issues in the design of such cooperative systems. In this paper,
we address this problem by investigating a two-pair two-way relay channel with
an intermittently available relay. In the model, each pair of users need to
exchange their messages within their own pair via the shared relay. The shared
relay, however, is only intermittently available for the users to access. The
accessing activities of different pairs of users are governed by independent
Bernoulli random processes. Our main contribution is the characterization of
the capacity region to within a bounded gap in a symmetric setting, for both
delayed and instantaneous state information at transmitters. An interesting
observation is that the bottleneck for information flow is the quality of state
information (delayed or instantaneous) available at the relay, not those at the
end users. To the best of our knowledge, our work is the first result regarding
how the shared intermittent relay should cooperate with multiple pairs of users
in such a two-way cooperative network.Comment: extended version of ISIT 2015 pape
The Multi-way Relay Channel
The multiuser communication channel, in which multiple users exchange
information with the help of a relay terminal, termed the multi-way relay
channel (mRC), is introduced. In this model, multiple interfering clusters of
users communicate simultaneously, where the users within the same cluster wish
to exchange messages among themselves. It is assumed that the users cannot
receive each other's signals directly, and hence the relay terminal in this
model is the enabler of communication. In particular, restricted encoders,
which ignore the received channel output and use only the corresponding
messages for generating the channel input, are considered. Achievable rate
regions and an outer bound are characterized for the Gaussian mRC, and their
comparison is presented in terms of exchange rates in a symmetric Gaussian
network scenario. It is shown that the compress-and-forward (CF) protocol
achieves exchange rates within a constant bit offset of the exchange capacity
independent of the power constraints of the terminals in the network. A finite
bit gap between the exchange rates achieved by the CF and the
amplify-and-forward (AF) protocols is also shown. The two special cases of the
mRC, the full data exchange model, in which every user wants to receive
messages of all other users, and the pairwise data exchange model which
consists of multiple two-way relay channels, are investigated in detail. In
particular for the pairwise data exchange model, in addition to the proposed
random coding based achievable schemes, a nested lattice coding based scheme is
also presented and is shown to achieve exchange rates within a constant bit gap
of the exchange capacity.Comment: Revised version of our submission to the Transactions on Information
Theor
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