337 research outputs found
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
Secrecy Capacity Region of Some Classes of Wiretap Broadcast Channels
This work investigates the secrecy capacity of the Wiretap Broadcast Channel
(WBC) with an external eavesdropper where a source wishes to communicate two
private messages over a Broadcast Channel (BC) while keeping them secret from
the eavesdropper. We derive a non-trivial outer bound on the secrecy capacity
region of this channel which, in absence of security constraints, reduces to
the best known outer bound to the capacity of the standard BC. An inner bound
is also derived which follows the behavior of both the best known inner bound
for the BC and the Wiretap Channel. These bounds are shown to be tight for the
deterministic BC with a general eavesdropper, the semi-deterministic BC with a
more-noisy eavesdropper and the Wiretap BC where users exhibit a less-noisiness
order between them. Finally, by rewriting our outer bound to encompass the
characteristics of parallel channels, we also derive the secrecy capacity
region of the product of two inversely less-noisy BCs with a more-noisy
eavesdropper. We illustrate our results by studying the impact of security
constraints on the capacity of the WBC with binary erasure (BEC) and binary
symmetric (BSC) components.Comment: 19 pages, 8 figures, To appear in IEEE Trans. on Information Theor
Broadcasting over the Relay Channel with Oblivious Cooperative Strategy
This paper investigates the problem of information transmission over the
simultaneous relay channel with two users (or two possible channel outcomes)
where for one of them the more suitable strategy is Decode-and-Forward (DF)
while for the other one is Compress-and-Forward (CF). In this setting, it is
assumed that the source wishes to send common and private informations to each
of the users (or channel outcomes). This problem is relevant to: (i) the
transmission of information over the broadcast relay channel (BRC) with
different relaying strategies and (ii) the transmission of information over the
conventional relay channel where the source is oblivious to the coding strategy
of relay. A novel coding that integrates simultaneously DF and CF schemes is
proposed and an inner bound on the capacity region is derived for the case of
general memoryless BRCs. As special case, the Gaussian BRC is studied where it
is shown that by means of the suggested broadcast coding the common rate can be
improved compared to existing strategies. Applications of these results arise
in broadcast scenarios with relays or in wireless scenarios where the source
does not know whether the relay is collocated with the source or with the
destination.Comment: 6 pages, presented at Allerton 201
Capacity of a Class of Broadcast Relay Channels
Consider the broadcast relay channel (BRC) which consists of a source sending
information over a two user broadcast
channel in presence of two relay nodes that help the transmission to the
destinations. Clearly, this network with
five nodes involves all the problems encountered in relay and broadcast
channels. New inner bounds on the capacity
region of this class of channels are derived. These results can be seen as a
generalization and hence unification of
previous work in this topic. Our bounds are based on the idea of
recombination of message bits and various effective
coding strategies for relay and broadcast channels. Capacity result is
obtained for the semi-degraded BRC-CR, where
one relay channel is degraded while the other one is reversely degraded. An
inner and upper bound is also presented
for the degraded BRC with common relay (BRC-CR), where both the relay and
broadcast channel are degraded which is
the capacity for the Gaussian case. Application of these results arise in the
context of opportunistic cooperation
of cellular networks.Comment: 5 pages, to appear in proc. IEEE ISIT, June 201
Secure Lossy Source Coding with Side Information at the Decoders
This paper investigates the problem of secure lossy source coding in the
presence of an eavesdropper with arbitrary correlated side informations at the
legitimate decoder (referred to as Bob) and the eavesdropper (referred to as
Eve). This scenario consists of an encoder that wishes to compress a source to
satisfy the desired requirements on: (i) the distortion level at Bob and (ii)
the equivocation rate at Eve. It is assumed that the decoders have access to
correlated sources as side information. For instance, this problem can be seen
as a generalization of the well-known Wyner-Ziv problem taking into account the
security requirements. A complete characterization of the
rate-distortion-equivocation region for the case of arbitrary correlated side
informations at the decoders is derived. Several special cases of interest and
an application example to secure lossy source coding of binary sources in the
presence of binary and ternary side informations are also considered. It is
shown that the statistical differences between the side information at the
decoders and the presence of non-zero distortion at the legitimate decoder can
be useful in terms of secrecy. Applications of these results arise in a variety
of distributed sensor network scenarios.Comment: 7 pages, 5 figures, 1 table, to be presented at Allerton 201
Secure Multiterminal Source Coding with Side Information at the Eavesdropper
The problem of secure multiterminal source coding with side information at
the eavesdropper is investigated. This scenario consists of a main encoder
(referred to as Alice) that wishes to compress a single source but
simultaneously satisfying the desired requirements on the distortion level at a
legitimate receiver (referred to as Bob) and the equivocation rate --average
uncertainty-- at an eavesdropper (referred to as Eve). It is further assumed
the presence of a (public) rate-limited link between Alice and Bob. In this
setting, Eve perfectly observes the information bits sent by Alice to Bob and
has also access to a correlated source which can be used as side information. A
second encoder (referred to as Charlie) helps Bob in estimating Alice's source
by sending a compressed version of its own correlated observation via a
(private) rate-limited link, which is only observed by Bob. For instance, the
problem at hands can be seen as the unification between the Berger-Tung and the
secure source coding setups. Inner and outer bounds on the so called
rates-distortion-equivocation region are derived. The inner region turns to be
tight for two cases: (i) uncoded side information at Bob and (ii) lossless
reconstruction of both sources at Bob --secure distributed lossless
compression. Application examples to secure lossy source coding of Gaussian and
binary sources in the presence of Gaussian and binary/ternary (resp.) side
informations are also considered. Optimal coding schemes are characterized for
some cases of interest where the statistical differences between the side
information at the decoders and the presence of a non-zero distortion at Bob
can be fully exploited to guarantee secrecy.Comment: 26 pages, 16 figures, 2 table
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
Multiple Access Channel with States Known Noncausally at One Encoder and Only Strictly Causally at the Other Encoder
We consider a two-user state-dependent multiaccess channel in which the
states of the channel are known non-causally to one of the encoders and only
strictly causally to the other encoder. Both encoders transmit a common message
and, in addition, the encoder that knows the states non-causally transmits an
individual message. We study the capacity region of this communication model.
In the discrete memoryless case, we establish inner and outer bounds on the
capacity region. Although the encoder that sends both messages knows the states
fully, we show that the strictly causal knowledge of these states at the other
encoder can be beneficial for this encoder, and in general enlarges the
capacity region. Furthermore, we find an explicit characterization of the
capacity in the case in which the two encoders transmit only the common
message. In the Gaussian case, we characterize the capacity region for the
model with individual message as well. Our converse proof in this case shows
that, for this model, strictly causal knowledge of the state at one of the
encoders does not increase capacity if the other is informed non-causally, a
result which sheds more light on the utility of conveying a compressed version
of the state to the decoder in recent results by Lapidoth and Steinberg on a
multiacess model with only strictly causal state at both encoders and
independent messages.Comment: 5 pages, to appear in the 2011 IEEE International Symposium on
Information Theor
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