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Monich U.J.,TU Berlin | Boche H.,TU Berlin | Boche H.,Fraunhofer German Sino Laboratory for Mobile Communications
Signal Processing

In this paper non-equidistant sampling series are studied for bounded bandlimited signals. We consider sampling patterns that are made of the zeros of sine-type functions and analyze the local and global convergence behavior of the sampling series. It is shown that the series converge locally uniformly for bounded bandlimited signals that vanish at infinity. Moreover, we discuss the influence of oversampling on the global approximation behavior and the convergence speed of the sampling series. © 2010 Elsevier B.V. All rights reserved. Source

Buhler J.,TU Berlin | Wunder G.,Fraunhofer German Sino Laboratory for Mobile Communications
GLOBECOM - IEEE Global Telecommunications Conference

In this paper, we study duality relations for the fading broadcast channel (BC) under additive white Gaussian noise and a strict ordering of the fading distributions without channel state information at the transmitter and the natural corresponding dual fading multiple-access channel (MAC). We show that if the fading distribution for the weaker user is non-deterministic, the achievable rate region using superposition coding and successive decoding and Gaussian signaling, which is conjectured to be the capacity region, is different from the dual MAC region. Duality holds only in the case of one-sided fading, where the fading distribution for the weaker user is deterministic. Despite this lack of duality, we propose to use the dual MAC in order to approximatively solve a non-convex problem for the BC. Specifically, we consider the problem of weighted sum-rate optimization for the BC and give, under some assumptions, upper bounds on the error incurred using this procedure. ©2010 IEEE. Source

Buhler J.,TU Berlin | Wunder G.,Fraunhofer German Sino Laboratory for Mobile Communications
33rd IEEE Sarnoff Symposium 2010, Conference Proceedings

This paper deals with the computation of the boundary of the capacity region for the two-user memoryless multiple-access channel, which is equivalent to solving a difficult non-convex optimization problem. We study properties of the optimality conditions for a relaxation (cooperation) approach suggested in the literature. We give conditions under which a solution to the relaxed problem has the same value as the actual optimal solution and show that these conditions can in some cases be applied to construct solutions for a restricted class of discrete multiple-access channel using convex optimization. Source

Buhler J.,TU Berlin | Wunder G.,Fraunhofer German Sino Laboratory for Mobile Communications
IEEE International Symposium on Information Theory - Proceedings

Duality between multiple-access (MAC) and broadcast channels (BC) is an interesting and useful concept in multiuser information theory. While duality relationships have been established for some Gaussian and deterministic channels, the question to what extent and under which conditions duality holds for the case of discrete memoryless channels still remains open. In this paper, we define the notion of weak duality, closely related to the existing duality definitions. We give a sufficient condition and a necessary condition for a BC to be weakly dual to a discrete MAC of a certain type. Exemplarily, we use these conditions to derive a weak duality relation between the binary symmetric BC and this class of discrete MACs. © 2010 IEEE. Source

Kaliszan M.,Fraunhofer German Sino Laboratory for Mobile Communications | Stanczak S.,Fraunhofer German Sino Laboratory for Mobile Communications
Conference Record - Asilomar Conference on Signals, Systems and Computers

The main design challenge in wireless sensor networks is to achieve satisfactory network lifetimes under scarce energy resources available at the nodes. In this paper we present an optimization framework for maximizing lifetime of a network in which opportunistic routing together with random linear network coding is used. We propose a scheme in which each node attempts to receive transmissions from a given neighbor, and thus consumes energy for receiving, with a certain probability. Optimality conditions are presented and approaches to solving the problem are discussed. We conclude with numerical experiments which confirm performance improvements achieved using our framework. © 2010 IEEE. Source

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