810 research outputs found
State-Dependent Relay Channel with Private Messages with Partial Causal and Non-Causal Channel State Information
In this paper, we introduce a discrete memoryless State-Dependent Relay
Channel with Private Messages (SD-RCPM) as a generalization of the
state-dependent relay channel. We investigate two main cases: SD-RCPM with
non-causal Channel State Information (CSI), and SD-RCPM with causal CSI. In
each case, it is assumed that partial CSI is available at the source and relay.
For non-causal case, we establish an achievable rate region using
Gel'fand-Pinsker type coding scheme at the nodes informed of CSI, and
Compress-and-Forward (CF) scheme at the relay. Using Shannon's strategy and CF
scheme, an achievable rate region for causal case is obtained. As an example,
the Gaussian version of SD-RCPM is considered, and an achievable rate region
for Gaussian SD-RCPM with non-causal perfect CSI only at the source, is
derived. Providing numerical examples, we illustrate the comparison between
achievable rate regions derived using CF and Decode-and-Forward (DF) schemes.Comment: 5 pages, 2 figures, to be presented at the IEEE International
Symposium on Information Theory (ISIT 2010), Austin, Texas, June 201
Capacity of a Class of State-Dependent Orthogonal Relay Channels
The class of orthogonal relay channels in which the orthogonal channels
connecting the source terminal to the relay and the destination, and the relay
to the destination, depend on a state sequence, is considered. It is assumed
that the state sequence is fully known at the destination while it is not known
at the source or the relay. The capacity of this class of relay channels is
characterized, and shown to be achieved by the partial
decode-compress-and-forward (pDCF) scheme. Then the capacity of certain binary
and Gaussian state-dependent orthogonal relay channels are studied in detail,
and it is shown that the compress-and-forward (CF) and
partial-decode-and-forward (pDF) schemes are suboptimal in general. To the best
of our knowledge, this is the first single relay channel model for which the
capacity is achieved by pDCF, while pDF and CF schemes are both suboptimal.
Furthermore, it is shown that the capacity of the considered class of
state-dependent orthogonal relay channels is in general below the cut-set
bound. The conditions under which pDF or CF suffices to meet the cut-set bound,
and hence, achieve the capacity, are also derived.Comment: This paper has been accepted by IEEE Transactions on Information
Theor
Iterative Slepian-Wolf Decoding and FEC Decoding for Compress-and-Forward Systems
While many studies have concentrated on providing theoretical analysis for the relay assisted compress-and-forward systems little effort has yet been made to the construction and evaluation of a practical system. In this paper a practical CF system incorporating an error-resilient multilevel Slepian-Wolf decoder is introduced and a novel iterative processing structure which allows information exchanging between the Slepian-Wolf decoder and the forward error correction decoder of the main source message is proposed. In addition, a new quantization scheme is incorporated as well to avoid the complexity of the reconstruction of the relay signal at the final decoder of the destination. The results demonstrate that the iterative structure not only reduces the decoding loss of the Slepian-Wolf decoder, it also improves the decoding performance of the main message from the source
The Three Node Wireless Network: Achievable Rates and Cooperation Strategies
We consider a wireless network composed of three nodes and limited by the
half-duplex and total power constraints. This formulation encompasses many of
the special cases studied in the literature and allows for capturing the common
features shared by them. Here, we focus on three special cases, namely 1) Relay
Channel, 2) Multicast Channel, and 3) Conference Channel. These special cases
are judicially chosen to reflect varying degrees of complexity while
highlighting the common ground shared by the different variants of the three
node wireless network. For the relay channel, we propose a new cooperation
scheme that exploits the wireless feedback gain. This scheme combines the
benefits of decode-and-forward and compress-and-forward strategies and avoids
the idealistic feedback assumption adopted in earlier works. Our analysis of
the achievable rate of this scheme reveals the diminishing feedback gain at
both the low and high signal-to-noise ratio regimes. Inspired by the proposed
feedback strategy, we identify a greedy cooperation framework applicable to
both the multicast and conference channels. Our performance analysis reveals
several nice properties of the proposed greedy approach and the central role of
cooperative source-channel coding in exploiting the receiver side information
in the wireless network setting. Our proofs for the cooperative multicast with
side-information rely on novel nested and independent binning encoders along
with a list decoder.Comment: 52 page
Cooperation with an Untrusted Relay: A Secrecy Perspective
We consider the communication scenario where a source-destination pair wishes
to keep the information secret from a relay node despite wanting to enlist its
help. For this scenario, an interesting question is whether the relay node
should be deployed at all. That is, whether cooperation with an untrusted relay
node can ever be beneficial. We first provide an achievable secrecy rate for
the general untrusted relay channel, and proceed to investigate this question
for two types of relay networks with orthogonal components. For the first
model, there is an orthogonal link from the source to the relay. For the second
model, there is an orthogonal link from the relay to the destination. For the
first model, we find the equivocation capacity region and show that answer is
negative. In contrast, for the second model, we find that the answer is
positive. Specifically, we show by means of the achievable secrecy rate based
on compress-and-forward, that, by asking the untrusted relay node to relay
information, we can achieve a higher secrecy rate than just treating the relay
as an eavesdropper. For a special class of the second model, where the relay is
not interfering itself, we derive an upper bound for the secrecy rate using an
argument whose net effect is to separate the eavesdropper from the relay. The
merit of the new upper bound is demonstrated on two channels that belong to
this special class. The Gaussian case of the second model mentioned above
benefits from this approach in that the new upper bound improves the previously
known bounds. For the Cover-Kim deterministic relay channel, the new upper
bound finds the secrecy capacity when the source-destination link is not worse
than the source-relay link, by matching with the achievable rate we present.Comment: IEEE Transactions on Information Theory, submitted October 2008,
revised October 2009. This is the revised versio
Computation Alignment: Capacity Approximation without Noise Accumulation
Consider several source nodes communicating across a wireless network to a
destination node with the help of several layers of relay nodes. Recent work by
Avestimehr et al. has approximated the capacity of this network up to an
additive gap. The communication scheme achieving this capacity approximation is
based on compress-and-forward, resulting in noise accumulation as the messages
traverse the network. As a consequence, the approximation gap increases
linearly with the network depth.
This paper develops a computation alignment strategy that can approach the
capacity of a class of layered, time-varying wireless relay networks up to an
approximation gap that is independent of the network depth. This strategy is
based on the compute-and-forward framework, which enables relays to decode
deterministic functions of the transmitted messages. Alone, compute-and-forward
is insufficient to approach the capacity as it incurs a penalty for
approximating the wireless channel with complex-valued coefficients by a
channel with integer coefficients. Here, this penalty is circumvented by
carefully matching channel realizations across time slots to create
integer-valued effective channels that are well-suited to compute-and-forward.
Unlike prior constant gap results, the approximation gap obtained in this paper
also depends closely on the fading statistics, which are assumed to be i.i.d.
Rayleigh.Comment: 36 pages, to appear in IEEE Transactions on Information Theor
A Unified Approach for Network Information Theory
In this paper, we take a unified approach for network information theory and
prove a coding theorem, which can recover most of the achievability results in
network information theory that are based on random coding. The final
single-letter expression has a very simple form, which was made possible by
many novel elements such as a unified framework that represents various network
problems in a simple and unified way, a unified coding strategy that consists
of a few basic ingredients but can emulate many known coding techniques if
needed, and new proof techniques beyond the use of standard covering and
packing lemmas. For example, in our framework, sources, channels, states and
side information are treated in a unified way and various constraints such as
cost and distortion constraints are unified as a single joint-typicality
constraint.
Our theorem can be useful in proving many new achievability results easily
and in some cases gives simpler rate expressions than those obtained using
conventional approaches. Furthermore, our unified coding can strictly
outperform existing schemes. For example, we obtain a generalized
decode-compress-amplify-and-forward bound as a simple corollary of our main
theorem and show it strictly outperforms previously known coding schemes. Using
our unified framework, we formally define and characterize three types of
network duality based on channel input-output reversal and network flow
reversal combined with packing-covering duality.Comment: 52 pages, 7 figures, submitted to IEEE Transactions on Information
theory, a shorter version will appear in Proc. IEEE ISIT 201
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