Fraunhofer German Sino Laboratory for Mobile Communications

Berlin, Germany

Fraunhofer German Sino Laboratory for Mobile Communications

Berlin, Germany
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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 | Year: 2010

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.


Goldenbaum 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 | Year: 2010

The paper deals with the problem of data transmission and function computation of the sensed data in wireless sensor networks, in which multiple sensor nodes transmit their data to one sink node over a wireless multiple-access channel. We focus on the problem of computing the geometric mean at the sink node by merging the data transmission and function computation into one step via an explicit utilization of channel collisions caused by simultaneous transmissions of sensor nodes. The paper provides the analysis of the estimation error and compares the scheme with traditional time division multiple-access based schemes to indicate potential for significant performance gains. © 2010 IEEE.


Stanczak S.,Fraunhofer German Sino Laboratory for Mobile Communications | Stanczak S.,TU Berlin | Feistel A.,TU Berlin | Wiczanowski M.,Fraunhofer German Sino Laboratory for Mobile Communications | And 2 more authors.
Wireless Networks | Year: 2010

This paper addresses the issue of incorporating QoS requirements expressed in terms of some minimum SIR targets into the traditional utility-based power control problem. As suitable projection methods seem to be not amenable to distributed implementation, we first focus on a primal-dual algorithm to solve the utility-based power control problem subject to the SIR requirements. We prove a global convergence of the algorithm for a large class of utility functions and show that it can be implemented in a distributed wireless environment. However, the approach has an important drawback: An optimal solution may not exist as the SIR targets may be infeasible due to, for instance, channel effects. This motivates a reformulation of the problem so that an optimal solution always exists. We consider the possibility of using a barrier method to closely approach the desired SIRs of the users and combine this approach with the conventional utility-based power control problem to incorporate best effort users. We prove relevant properties of optimal solutions and propose a distributed recursive algorithm with global convergence. Finally, the performance of the proposed approaches is verified by simulations. © 2009 Springer Science+Business Media, LLC.


Monich U.J.,TU Berlin | Boche H.,TU Berlin | Boche H.,Fraunhofer German Sino Laboratory for Mobile Communications
Signal Processing | Year: 2010

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.


Buhler J.,TU Berlin | Wunder G.,Fraunhofer German Sino Laboratory for Mobile Communications
GLOBECOM - IEEE Global Telecommunications Conference | Year: 2010

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.


Tomecki D.,Fraunhofer German Sino Laboratory for Mobile Communications | Stanczak S.,Fraunhofer German Sino Laboratory for Mobile Communications
ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings | Year: 2010

In this paper, we address the problem of the feasible SNR region for a multicast MIMO downlink channel. We characterize the feasible SNR region for a multicast group consisting of two mobile users. Based on this characterization, we propose solving the maxmin SNR problem over the smallest convex and downward comprehensive superset of the feasible SNR region. We show, that the maxmin SNR transmit beamformer is achievable via maximization of a weighted sum of SNRs. Both transmitter and the receivers are equipped with multiple antenna elements. The receive beamformers are fixed but arbitrary and each transmission is a single-mode transmission (no multiplexing and parallel transmissions of symbols). ©2010 IEEE.


Goldenbaum M.,Fraunhofer German Sino Laboratory for Mobile Communications | Stanczak S.,Fraunhofer German Sino Laboratory for Mobile Communications
ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings | Year: 2010

We view a wireless sensor network as a collection of sensor nodes that observe sources of information, process the picked up data and send it to a sink node, with the goal of computing a desired function of the measurements. To this end, we consider a previously proposed coding scheme that exploits the underlying fading multiple-access channel (MAC) to efficiently estimate the function values. The main problem addressed in this paper is how much channel state information (CSI) is needed at the sensor nodes to obtain sufficiently good estimates? First we show that there is no performance loss, independent of fading distributions, if, instead of perfect CSI, each sensor node has only access to the modulus of its channel coefficient. In the case of multiple antenna elements at the sink node and specific independent distributed fading environments, it is shown that CSI at sensor nodes is not necessary and a very simple correction of fading effects can be performed at the sink based on some statistical channel knowledge. In many cases, fading improves the estimation accuracy due to the multiple-access nature of the channel. ©2010 IEEE.


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

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.


Buhler J.,Fraunhofer German Sino Laboratory for Mobile Communications | Wunder G.,Fraunhofer German Sino Laboratory for Mobile Communications
IEEE Transactions on Communications | Year: 2010

This paper studies the problem of admission control and air interface (AI) selection in heterogeneous network environments. The statistics of random user arrivals, channel conditions and service durations are considered for the optimization of heterogeneous access management strategies with respect to minimizing the expected mean cost for blocking events. Based on state aggregation in a semi-Markov decision process formulation, an efficient approximation algorithm using state aggregation for policy optimization is proposed. Though this solution is suboptimal, it still offers considerable performance gains in comparison to simpler heuristic strategies, which is demonstrated by simulations in a heterogeneous GSM-EDGE (Global System for Mobile Communications Enhanced Data Rate)/UMTS (Universal Mobile Telecommunications System) scenario. Furthermore, structural properties of optimal user assignment policies are studied, proving certain monotonicity properties for a specific type of systems. © 2010 IEEE.


Buhler J.,TU Berlin | Wunder G.,Fraunhofer German Sino Laboratory for Mobile Communications
IEEE International Symposium on Information Theory - Proceedings | Year: 2010

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.

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