4,568 research outputs found
The Benefit of Encoder Cooperation in the Presence of State Information
In many communication networks, the availability of channel state information
at various nodes provides an opportunity for network nodes to work together, or
"cooperate." This work studies the benefit of cooperation in the multiple
access channel with a cooperation facilitator, distributed state information at
the encoders, and full state information available at the decoder. Under
various causality constraints, sufficient conditions are obtained such that
encoder cooperation through the facilitator results in a gain in sum-capacity
that has infinite slope in the information rate shared with the encoders. This
result extends the prior work of the authors on cooperation in networks where
none of the nodes have access to state information.Comment: Extended version of paper presented at ISIT 2017 in Aachen. 20 pages,
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The Relay-Eavesdropper Channel: Cooperation for Secrecy
This paper establishes the utility of user cooperation in facilitating secure
wireless communications. In particular, the four-terminal relay-eavesdropper
channel is introduced and an outer-bound on the optimal rate-equivocation
region is derived. Several cooperation strategies are then devised and the
corresponding achievable rate-equivocation region are characterized. Of
particular interest is the novel Noise-Forwarding (NF) strategy, where the
relay node sends codewords independent of the source message to confuse the
eavesdropper. This strategy is used to illustrate the deaf helper phenomenon,
where the relay is able to facilitate secure communications while being totally
ignorant of the transmitted messages. Furthermore, NF is shown to increase the
secrecy capacity in the reversely degraded scenario, where the relay node fails
to offer performance gains in the classical setting. The gain offered by the
proposed cooperation strategies is then proved theoretically and validated
numerically in the additive White Gaussian Noise (AWGN) channel.Comment: 33 pages, submitted to IEEE Transactions on Information Theor
Multiple Access Channels with States Causally Known at Transmitters
It has been recently shown by Lapidoth and Steinberg that strictly causal
state information can be beneficial in multiple access channels (MACs).
Specifically, it was proved that the capacity region of a two-user MAC with
independent states, each known strictly causally to one encoder, can be
enlarged by letting the encoders send compressed past state information to the
decoder. In this work, a generalization of the said strategy is proposed
whereby the encoders compress also the past transmitted codewords along with
the past state sequences. The proposed scheme uses a combination of
long-message encoding, compression of the past state sequences and codewords
without binning, and joint decoding over all transmission blocks. The proposed
strategy has been recently shown by Lapidoth and Steinberg to strictly improve
upon the original one. Capacity results are then derived for a class of
channels that include two-user modulo-additive state-dependent MACs. Moreover,
the proposed scheme is extended to state-dependent MACs with an arbitrary
number of users. Finally, output feedback is introduced and an example is
provided to illustrate the interplay between feedback and availability of
strictly causal state information in enlarging the capacity region.Comment: Accepted by IEEE Transactions on Information Theory, November 201
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
Degraded Broadcast Diamond Channels with Non-Causal State Information at the Source
A state-dependent degraded broadcast diamond channel is studied where the
source-to-relays cut is modeled with two noiseless, finite-capacity digital
links with a degraded broadcasting structure, while the relays-to-destination
cut is a general multiple access channel controlled by a random state. It is
assumed that the source has non-causal channel state information and the relays
have no state information. Under this model, first, the capacity is
characterized for the case where the destination has state information, i.e.,
has access to the state sequence. It is demonstrated that in this case, a joint
message and state transmission scheme via binning is optimal. Next, the case
where the destination does not have state information, i.e., the case with
state information at the source only, is considered. For this scenario, lower
and upper bounds on the capacity are derived for the general discrete
memoryless model. Achievable rates are then computed for the case in which the
relays-to-destination cut is affected by an additive Gaussian state. Numerical
results are provided that illuminate the performance advantages that can be
accrued by leveraging non-causal state information at the source.Comment: Submitted to IEEE Transactions on Information Theory, Feb. 201
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