3,615 research outputs found
A New Coding Paradigm for the Primitive Relay Channel
We consider the primitive relay channel, where the source sends a message to
the relay and to the destination, and the relay helps the communication by
transmitting an additional message to the destination via a separate channel.
Two well-known coding techniques have been introduced for this setting:
decode-and-forward and compress-and-forward. In decode-and-forward, the relay
completely decodes the message and sends some information to the destination;
in compress-and-forward, the relay does not decode, and it sends a compressed
version of the received signal to the destination using Wyner-Ziv coding. In
this paper, we present a novel coding paradigm that provides an improved
achievable rate for the primitive relay channel. The idea is to combine
compress-and-forward and decode-and-forward via a chaining construction. We
transmit over pairs of blocks: in the first block, we use compress-and-forward;
and in the second block, we use decode-and-forward. More specifically, in the
first block, the relay does not decode, it compresses the received signal via
Wyner-Ziv, and it sends only part of the compression to the destination. In the
second block, the relay completely decodes the message, it sends some
information to the destination, and it also sends the remaining part of the
compression coming from the first block. By doing so, we are able to strictly
outperform both compress-and-forward and decode-and-forward. Note that the
proposed coding scheme can be implemented with polar codes. As such, it has the
typical attractive properties of polar coding schemes, namely, quasi-linear
encoding and decoding complexity, and error probability that decays at
super-polynomial speed. As a running example, we take into account the special
case of the erasure relay channel, and we provide a comparison between the
rates achievable by our proposed scheme and the existing upper and lower
bounds.Comment: 10 pages, 4 figures, in Proc. of ISIT'18 (short version) and in
Algorithms (full version
Distributed Information Bottleneck for a Primitive Gaussian Diamond MIMO Channel
This paper considers the distributed information bottleneck (D-IB) problem for a primitive Gaussian diamond channel with two relays and MIMO Rayleigh fading. The channel state is an independent and identically distributed (i.i.d.) process known at the relays but unknown to the destination. The relays are oblivious, i.e., they are unaware of the codebook and treat the transmitted signal as a random process with known statistics. The bottleneck constraints prevent the relays to communicate the channel state information (CSI) perfectly to the destination. To evaluate the bottleneck rate, we provide an upper bound by assuming that the destination node knows the CSI and the relays can cooperate with each other, and also two achievable schemes with simple symbol-by-symbol relay processing and compression. Numerical results show that the lower bounds obtained by the proposed achievable schemes can come close to the upper bound on a wide range of relevant system parameters
Distributed Detection and Estimation in Wireless Sensor Networks
In this article we consider the problems of distributed detection and
estimation in wireless sensor networks. In the first part, we provide a general
framework aimed to show how an efficient design of a sensor network requires a
joint organization of in-network processing and communication. Then, we recall
the basic features of consensus algorithm, which is a basic tool to reach
globally optimal decisions through a distributed approach. The main part of the
paper starts addressing the distributed estimation problem. We show first an
entirely decentralized approach, where observations and estimations are
performed without the intervention of a fusion center. Then, we consider the
case where the estimation is performed at a fusion center, showing how to
allocate quantization bits and transmit powers in the links between the nodes
and the fusion center, in order to accommodate the requirement on the maximum
estimation variance, under a constraint on the global transmit power. We extend
the approach to the detection problem. Also in this case, we consider the
distributed approach, where every node can achieve a globally optimal decision,
and the case where the decision is taken at a central node. In the latter case,
we show how to allocate coding bits and transmit power in order to maximize the
detection probability, under constraints on the false alarm rate and the global
transmit power. Then, we generalize consensus algorithms illustrating a
distributed procedure that converges to the projection of the observation
vector onto a signal subspace. We then address the issue of energy consumption
in sensor networks, thus showing how to optimize the network topology in order
to minimize the energy necessary to achieve a global consensus. Finally, we
address the problem of matching the topology of the network to the graph
describing the statistical dependencies among the observed variables.Comment: 92 pages, 24 figures. To appear in E-Reference Signal Processing, R.
Chellapa and S. Theodoridis, Eds., Elsevier, 201
Using quantum key distribution for cryptographic purposes: a survey
The appealing feature of quantum key distribution (QKD), from a cryptographic
viewpoint, is the ability to prove the information-theoretic security (ITS) of
the established keys. As a key establishment primitive, QKD however does not
provide a standalone security service in its own: the secret keys established
by QKD are in general then used by a subsequent cryptographic applications for
which the requirements, the context of use and the security properties can
vary. It is therefore important, in the perspective of integrating QKD in
security infrastructures, to analyze how QKD can be combined with other
cryptographic primitives. The purpose of this survey article, which is mostly
centered on European research results, is to contribute to such an analysis. We
first review and compare the properties of the existing key establishment
techniques, QKD being one of them. We then study more specifically two generic
scenarios related to the practical use of QKD in cryptographic infrastructures:
1) using QKD as a key renewal technique for a symmetric cipher over a
point-to-point link; 2) using QKD in a network containing many users with the
objective of offering any-to-any key establishment service. We discuss the
constraints as well as the potential interest of using QKD in these contexts.
We finally give an overview of challenges relative to the development of QKD
technology that also constitute potential avenues for cryptographic research.Comment: Revised version of the SECOQC White Paper. Published in the special
issue on QKD of TCS, Theoretical Computer Science (2014), pp. 62-8
Sign-Compute-Resolve for Random Access
We present an approach to random access that is based on three elements:
physical-layer network coding, signature codes and tree splitting. Upon
occurrence of a collision, physical-layer network coding enables the receiver
to decode the sum of the information that was transmitted by the individual
users. For each user this information consists of the data that the user wants
to communicate as well as the user's signature. As long as no more than
users collide, their identities can be recovered from the sum of their
signatures. A splitting protocol is used to deal with the case that more than
users collide. We measure the performance of the proposed method in terms
of user resolution rate as well as overall throughput of the system. The
results show that our approach significantly increases the performance of the
system even compared to coded random access, where collisions are not wasted,
but are reused in successive interference cancellation.Comment: Accepted for presentation at 52nd Annual Allerton Conference on
Communication, Control, and Computin
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