44,272 research outputs found
The Network Design Problem with Relays
Cataloged from PDF version of article.The network design problem with relays (NDPR) is defined on an undirected graph G = (V,E,K), where V = {1,...,n} is
a vertex set, E = {(i,j):i,j 2 V,i < j} is an edge set. The set K = {(o(k),d(k))} is a set of communication pairs (or commodities):
o(k) 2 V and d(k) 2 V denote the origin and the destination of the kth commodity, respectively. With each edge (i,j)
are associated a cost cij and a length dij. With vertex i is associated a fixed cost fi of locating a relay at i. The NDPR consists
of selecting a subset E of edges of E and of locating relays at a subset V of vertices of V in such a way that: (1) the sum Q of
edge costs and relay costs is minimized; (2) there exists a path linking the origin and the destination of each commodity in
which the length between the origin and the first relay, the last relay and the destination, or any two consecutive relays does
not exceed a preset upper bound k. This article develops a lower bound procedure and four heuristics for the NPDR. These
are compared on several randomly generated instances with |V| 6 1002 and |E| 6 1930.
2006 Elsevier B.V. All rights reserved
An Algebraic Coding Scheme for Wireless Relay Networks With Multiple-Antenna Nodes
We consider the problem of coding over a half-duplex wireless relay network where both the transmitter and the receiver have respectively several transmit and receive antennas, whereas each relay is a small device with only a single antenna. Since, in this scenario, requiring the relays to decode results in severe rate hits, we propose a full rate strategy where the relays do a simple operation before forwarding the signal, based on the idea of distributed space-time coding. Our scheme relies on division algebras, an algebraic object which allows the design of fully diverse matrices. The code construction is applicable to systems with any number of transmit/receive antennas and relays, and has better performance than random code constructions, with much less encoding complexity. Finally, the robustness of the proposed distributed space-time codes to node failures is considered
Rank-Two Beamforming and Power Allocation in Multicasting Relay Networks
In this paper, we propose a novel single-group multicasting relay beamforming
scheme. We assume a source that transmits common messages via multiple
amplify-and-forward relays to multiple destinations. To increase the number of
degrees of freedom in the beamforming design, the relays process two received
signals jointly and transmit the Alamouti space-time block code over two
different beams. Furthermore, in contrast to the existing relay multicasting
scheme of the literature, we take into account the direct links from the source
to the destinations. We aim to maximize the lowest received quality-of-service
by choosing the proper relay weights and the ideal distribution of the power
resources in the network. To solve the corresponding optimization problem, we
propose an iterative algorithm which solves sequences of convex approximations
of the original non-convex optimization problem. Simulation results demonstrate
significant performance improvements of the proposed methods as compared with
the existing relay multicasting scheme of the literature and an algorithm based
on the popular semidefinite relaxation technique
Generating Probability Distributions using Multivalued Stochastic Relay Circuits
The problem of random number generation dates back to von Neumann's work in
1951. Since then, many algorithms have been developed for generating unbiased
bits from complex correlated sources as well as for generating arbitrary
distributions from unbiased bits. An equally interesting, but less studied
aspect is the structural component of random number generation as opposed to
the algorithmic aspect. That is, given a network structure imposed by nature or
physical devices, how can we build networks that generate arbitrary probability
distributions in an optimal way? In this paper, we study the generation of
arbitrary probability distributions in multivalued relay circuits, a
generalization in which relays can take on any of N states and the logical
'and' and 'or' are replaced with 'min' and 'max' respectively. Previous work
was done on two-state relays. We generalize these results, describing a duality
property and networks that generate arbitrary rational probability
distributions. We prove that these networks are robust to errors and design a
universal probability generator which takes input bits and outputs arbitrary
binary probability distributions
A fault-tolerant relay placement algorithm for ensuring k vertex-disjoint shortest paths in wireless sensor networks
Wireless sensor networks (WSNs) are prone to failures. To be robust to failures, the network topology should provide alternative routes to the sinks so when failures occur the routing protocol can still offer reliable delivery. Our contribution is a solution that enables fault-tolerant WSN deployment planning by judicious use of a minimum number of additional relays. A WSN is robust if at least one route with an acceptable length to a sink is available for each sensor node after the failure of any nodes. In this paper, we define the problem for increasing WSN reliability by deploying a number of additional relays to ensure that each sensor node in the initial design has k length-bounded vertex-disjoint shortest paths to the sinks. To identify the maximum k such that each node has k vertex-disjoint shortest paths, we propose Counting-Paths and its dynamic programming variant. Then, we introduce GRASP-ARP, a centralised offline algorithm that uses Counting-Paths to minimise the number of deployed relays. Empirically, it deploys 35% fewer relays with reasonable runtime compared to the closest approach. Using network simulation, we show that GRASP-ARP’s designs offer a substantial improvement over the original topologies, maintaining connectivity for twice as many surviving nodes after 10% of the original nodes have failed
Iterative transceiver design for MIMO AF relay networks with multiple sources
This paper addresses the problem of transceiver design for an amplify-and-forward relay network with multiple sources, multiple relays and multiple destinations. Each node in the network is assumed to be equipped with multiple antennas. A general iterative algorithm is proposed based on convex quadratic optimization theory to minimize mean-square-error of the recovered signals at the destinations. Its convergence and extensions to other scenarios are also discussed. Finally, the effectiveness of the proposed iterative algorithm is demonstrated by computer simulations. ©2010 IEEE.published_or_final_versionThe IEEE Military Communications Conference (MILCOM 2010), San Jose, CA., 31 October-3 November 2010. In Proceedings of MILCOM, 2010, p. 369-37
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