495 research outputs found
Asymptotic Capacity of Large Fading Relay Networks with Random Node Failures
To understand the network response to large-scale physical attacks, we
investigate the asymptotic capacity of a half-duplex fading relay network with
random node failures when the number of relays is infinitely large. In this
paper, a simplified independent attack model is assumed where each relay node
fails with a certain probability. The noncoherent relaying scheme is
considered, which corresponds to the case of zero forward-link channel state
information (CSI) at the relays. Accordingly, the whole relay network can be
shown equivalent to a Rayleigh fading channel, where we derive the
-outage capacity upper bound according to the multiple access (MAC)
cut-set, and the -outage achievable rates for both the
amplify-and-forward (AF) and decode-and-forward (DF) strategies. Furthermore,
we show that the DF strategy is asymptotically optimal as the outage
probability goes to zero, with the AF strategy strictly suboptimal
over all signal to noise ratio (SNR) regimes. Regarding the rate loss due to
random attacks, the AF strategy suffers a less portion of rate loss than the DF
strategy in the high SNR regime, while the DF strategy demonstrates more robust
performance in the low SNR regime.Comment: 24 pages, 5 figures, submitted to IEEE Transactions on Communication
Asymptotic Capacity of Large Relay Networks with Conferencing Links
In this correspondence, we consider a half-duplex large relay network, which
consists of one source-destination pair and relay nodes, each of which is
connected with a subset of the other relays via signal-to-noise ratio
(SNR)-limited out-of-band conferencing links. The asymptotic achievable rates
of two basic relaying schemes with the "-portion" conferencing strategy are
studied: For the decode-and-forward (DF) scheme, we prove that the DF rate
scales as ; for the amplify-and-forward (AF) scheme, we
prove that it asymptotically achieves the capacity upper bound in some
interesting scenarios as goes to infinity.Comment: submitted to IEEE Transactions on Communication
Packet Travel Times in Wireless Relay Chains under Spatially and Temporally Dependent Interference
We investigate the statistics of the number of time slots that it takes a
packet to travel through a chain of wireless relays. Derivations are performed
assuming an interference model for which interference possesses spatiotemporal
dependency properties. When using this model, results are harder to arrive at
analytically, but they are more realistic than the ones obtained in many
related works that are based on independent interference models.
First, we present a method for calculating the distribution of . As the
required computations are extensive, we also obtain simple expressions for the
expected value and variance . Finally, we
calculate the asymptotic limit of the average speed of the packet. Our
numerical results show that spatiotemporal dependence has a significant impact
on the statistics of the travel time . In particular, we show that, with
respect to the independent interference case, and
increase, whereas the packet speed decreases
Diversity analysis, code design, and tight error rate lower bound for binary joint network-channel coding
Joint network-channel codes (JNCC) can improve the performance of communication in wireless networks, by combining, at the physical layer, the channel codes and the network code as an overall error-correcting code. JNCC is increasingly proposed as an alternative to a standard layered construction, such as the OSI-model. The main performance metrics for JNCCs are scalability to larger networks and error rate. The diversity order is one of the most important parameters determining the error rate. The literature on JNCC is growing, but a rigorous diversity analysis is lacking, mainly because of the many degrees of freedom in wireless networks, which makes it very hard to prove general statements on the diversity order. In this article, we consider a network with slowly varying fading point-to-point links, where all sources also act as relay and additional non-source relays may be present. We propose a general structure for JNCCs to be applied in such network. In the relay phase, each relay transmits a linear transform of a set of source codewords. Our main contributions are the proposition of an upper and lower bound on the diversity order, a scalable code design and a new lower bound on the word error rate to assess the performance of the network code. The lower bound on the diversity order is only valid for JNCCs where the relays transform only two source codewords. We then validate this analysis with an example which compares the JNCC performance to that of a standard layered construction. Our numerical results suggest that as networks grow, it is difficult to perform significantly better than a standard layered construction, both on a fundamental level, expressed by the outage probability, as on a practical level, expressed by the word error rate
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
Principles of Physical Layer Security in Multiuser Wireless Networks: A Survey
This paper provides a comprehensive review of the domain of physical layer
security in multiuser wireless networks. The essential premise of
physical-layer security is to enable the exchange of confidential messages over
a wireless medium in the presence of unauthorized eavesdroppers without relying
on higher-layer encryption. This can be achieved primarily in two ways: without
the need for a secret key by intelligently designing transmit coding
strategies, or by exploiting the wireless communication medium to develop
secret keys over public channels. The survey begins with an overview of the
foundations dating back to the pioneering work of Shannon and Wyner on
information-theoretic security. We then describe the evolution of secure
transmission strategies from point-to-point channels to multiple-antenna
systems, followed by generalizations to multiuser broadcast, multiple-access,
interference, and relay networks. Secret-key generation and establishment
protocols based on physical layer mechanisms are subsequently covered.
Approaches for secrecy based on channel coding design are then examined, along
with a description of inter-disciplinary approaches based on game theory and
stochastic geometry. The associated problem of physical-layer message
authentication is also introduced briefly. The survey concludes with
observations on potential research directions in this area.Comment: 23 pages, 10 figures, 303 refs. arXiv admin note: text overlap with
arXiv:1303.1609 by other authors. IEEE Communications Surveys and Tutorials,
201
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