Armin Wittneben

ETH Zurich, Zürich, Zurich, Switzerland

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Publications (163)47.59 Total impact

  • Y. Hassan · M. Kuhn · A. Wittneben
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    ABSTRACT: Future MIMO terminals are expected to be equipped with a higher number of antennas. A possible intermediary solution between using the optimal but complex SIC decoder and the simple but poor performing MMSE decoder, is to consider different group decoders, namely, group SIC (GSIC) and group parallel decoding (GPD). The performances of such decoders strongly depend on the grouping strategy. In this paper, we introduce a unified framework to handle different group decoders. We use tools from random matrix theory to present a tight approximation of the average sum rate achieved in the case of adopting any kind of these decoders using only statistical CSI. For large number of data streams and fast changing channels, finding the optimal grouping for each channel realization is very complex. We formulate an optimization problem in which we use our developed approximations to find a static grouping which is shown to lead to a performance near to the optimal SIC and much better than the MMSE, especially for high transmit correlation. We also show how the performance depends on different system parameters, such as correlation strength and number of groups.
    No preview · Article · Jul 2015
  • R.T.L. Rolny · M. Kuhn · A. Wittneben
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    ABSTRACT: We consider the downlink of a 'post-cellular' network in which base stations (BSs) are no longer evenly spread in the entire area of service but rather placed where they can easily be installed. Accordingly, the BSs are not necessarily close to the users anymore but have to serve distant mobiles with aggressive spatial multiplexing, possibly with the help of additional low-complexity relays. In such networks, it is important to allow for flexible and dynamic cooperation between different infrastructure nodes to achieve high data rates and coverage. To this end, we develop a framework that optimizes the performance by dynamic BS clustering with joint transmission for one- and two-hop communication under practical conditions such as backhaul rate limitations and power control. The network performance is maximized by an evolutionary algorithm that optimizes the BS clustering, relay routing, and power allocation for a beamforming scheme with closed-form solution. We show that a very high performance can be achieved in an efficient way with small overhead and that high data rates can be delivered to areas without wired backhaul access.
    No preview · Article · Jun 2015
  • Y. Hassan · A. Wittneben
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    ABSTRACT: In this paper we jointly consider the normally distinct worlds of communication system design and circuit theory. We introduce the - up to our knowledge - first algorithm to optimize the uncoupled matching network (UC-MN) at a receiver that uses a linear MMSE equalizer in a MU-MIMO system with compact antenna array at the receiver. We design our adaptive UC-MN in order to either maximize the minimum rate of all users or to maximize the total sum rate. We compare to the conventional matching, which ignores antenna coupling, and to the cases of choosing one of the MNs that either maximizes the achievable rate or maximizes the minimum user rate for joint decoding of all data streams. In all cases, we observe a considerable performance boost. We view our results as an example of the potential of jointly considering circuit theoretical aspects and communication theory, especially for systems adopting large antenna arrays in a confined space.
    No preview · Article · Jun 2015
  • Source
    Zemene Walle Mekonnen · Armin Wittneben
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    ABSTRACT: In this paper, we propose and investigate a self-calibration method which estimates the locations and clock offsets of the anchors based on TOA measurements. The agent locations are not surveyed and hence they can be realized by a single moving agent, which makes the calibration procedure simple and cost effective. Instead of considering a specific clock synchronization scenario, which was the case with previous related works, we systematically classify different clock synchronization cases that may arise in practice and provide a generalized formulation of the self-calibration problem that covers all the synchronization classes. The maximum likelihood (ML) solution of the calibration problem, which jointly estimates all the unknown parameters, is shown to be a non-convex optimization problem. We propose to relax the ML estimator to a semi-definite programming (SDP) problem by applying semi-definite relaxation. To improve the accuracy of the SDP solution, we further refine it with the ML estimator. Simulation results confirm that the proposed method is capable of accurately calibrating TOA based localization systems.
    Full-text · Conference Paper · Jun 2015
  • T. Rüegg · M. Kuhn · Armin Wittneben
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    ABSTRACT: In this paper we propose a decentralized target rate precoding for multi-user multiple-input multiple-output downlink setups. It is well suited for joint transmission and works for arbitrary cooperation sets. The precoding is optimized for each link separately with respect to the transmit and leakage power. This allows to control the interference into the network and to design the precoding flexibly with respect to energy efficiency and outage minimization. A closed form solution for the optimization problem is presented and the trade-off between the used transmit power and generated leakage power is discussed. Based on the proposed target rate precoding, different strategies for the iterative optimization of a network are presented and evaluated in numerical simulations.
    No preview · Article · Apr 2015
  • Y. Hassan · A. Wittneben · T. Ruegg
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    ABSTRACT: With the two conflicting demands of increasing the number of antennas in terminals and decreasing the devices sizes, considering compact MIMO systems became inevitable. Such systems suffer from both antenna coupling and noise correlation. This has led to the observation that the impedance matching network fundamentally affects the performance of such MIMO enabled communications systems. In this paper we consider a multi-user MIMO system, for which we design the matching network at the receiver given that it uses the optimal successive interference cancellation receiver. For the two cases of time sharing and no time sharing we design the matching network to alter the capacity region in order to maximize the minimum user rate. We compare to both the conventional matching, which ignores antenna coupling, and to the case of choosing the matching network such that the achievable rate is maximized. In both cases we observe a performance enhancement. We view our results as a new step in connecting the two worlds of information theory and circuit theory. Such results are of very relevant practical interest to wireless communication systems that adopt a large number of antennas while maintaining a small size.
    No preview · Article · Apr 2015
  • Y. Hassan · A. Wittneben
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    ABSTRACT: Compact arrays are known to be associated with antenna coupling and noise correlation. The noise can be either antenna noise, LNA noise or downstream noise. Due to these effects, it was shown that the matching network affects the performance of MIMO systems with coupled receiver antennas. Since the optimal multiport matching network is of very high complexity as well as very narrow operation bandwidth, development of single-port (SP) matching networks that boost the performance became inevitable. In this paper we develop a gradient-search algorithm to design the matching network for achievable rate maximization of multi user MIMO systems. For any combination of noise sources, we rigorously derive the exact gradient of the achievable rate with respect to the components of the matching network. We assume either full knowledge of the spatial channel or knowing its statistical properties. In the later case we optimize the matching network to maximize the Jensen's bound. Substantial performance enhancement is shown when our algorithms are used. Significant reduction in the array area is gained in comparison to the often used λ/2 antenna spacing without taking coupling into account. This can be vital for future wireless systems adopting massive MIMO arrays. Via eigenvalues distribution simulations at different SNR regimes, we show an intuitive link to the communication theory.
    No preview · Article · Nov 2014
  • T. Ruegg · A.U.T. Amah · A. Wittneben
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    ABSTRACT: In this paper, we study the interdependency between leakage reduction and transmit power control for rate maximization in leakage based precoding (LBP) for a multi user multiple-input multiple-output (MU-MIMO) scenario. We propose a LBP scheme which provides the rate optimal precoding for each MIMO link under a joint leakage and transmit power constraint and derive an iterative closed form solution for it. Depending on the constraints and the strength of the leakage power, the leakage power and/or the transmit power needs to be adjusted. Any leakage level between the egoistic case, where the leakage is not reduced at all, and the altruistic case, where the leakage is minimized, can be achieved. This allows to optimize the network performance in a MU-MIMO setup by optimally choosing the trade-off between leakage power and transmit power constraints. Using numerical simulations, we show the interdependency between the leakage power and the transmit power and demonstrate the gain we can achieve with the optimal trade-off.
    No preview · Article · Oct 2014
  • R.T.L. Rolny · C. Dunner · A. Wittneben
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    ABSTRACT: We consider a cellular network in which the base stations (BSs) are supported by a large amount of very low-complexity relays that are spread over the entire area, like a carpet. This carpet of relays enables massive antenna arrays and sophisticated multi-user MIMO transmission at the BSs, as they see only the static relays as the nodes they communicate with. On the other hand, the communication via the small relay cells allows to improve coverage and data rates by distributed signal processing. In order to control the residual interference caused by the massively deployed relay nodes, we apply power control to either minimize the transmit power at the BSs and relays required to achieve desired user rates, to maximize the minimum rate, or to minimize the outage probability. The proposed schemes are all of low complexity and show that the relay carpet is a promising concept for communication in future cellular networks.
    No preview · Article · Oct 2014
  • Source
    Zemene Walle Mekonnen · Armin Wittneben
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    ABSTRACT: In this paper, we address the problem of sensor network localization based on Time-of-Arrival (TOA) measurements under the presence of anchor location errors. We consider the practically appealing setup where the agents are low-complexity transmit-only nodes whose clocks' are not synchronized with that of the anchors. The maximum likelihood (ML) solution of the localization problem is formulated and shown to be a non-convex optimization problem. The relaxation of the ML solution to a convex optimization problem based on semi-definite programming (SDP) is proposed. The proposed localization method is compared with the Cramér Rao lower bound (CRLB) and an existing related approach. Simulation results show that the proposed localization method outperforms the existing scheme, notably when the anchor location uncertainties are the dominant source of errors.
    Full-text · Conference Paper · Sep 2014
  • Raphael T. L. Rolny · Tim Rüegg · Marc Kuhn · Armin Wittneben
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    ABSTRACT: We consider the up- as well as downlink of a cellular network in which base stations (BSs) are supported by a large amount of relays spread over the entire area like a carpet. The BSs only see the static relays as the nodes they communicate with, which enables large antenna arrays at the BSs with sophisticated multi-user MIMO transmission. Together with a simple form of BS cooperation, the communication via the small relay cells allows to improve the data rates by distributed interference management and to reduce the complexity at the terminals. We investigate different types of relays as well as different relaying strategies for this relay carpet and compare them with respect to complexity, required channel state information (CSI), and performance in the interference-limited environment of dense cellular networks. The robustness of the different schemes with respect to channel estimation errors is studied and we conclude that especially relays of very low complexity are not sensitive to CSI imperfections. Relays can thus be applied in large numbers and enable massive MIMO at the BSs. The relay carpet proves thereby to be an efficient approach to enhance future generations of cellular networks significantly.
    No preview · Article · Sep 2014 · International Journal of Wireless Information Networks
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    Eric Slottke · Armin Wittneben
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    ABSTRACT: We consider the problem of locating a sensor in a network of nodes which use inductive coupling as means of interaction. Conventional approaches in this setting require the located node to have a power supply or complex circuitry. By analysis of the circuit model underlying inductive coupling, we develop a localization method which allows for passive nodes with a simple layout. The proposed method reconstructs the unknown position from measurements of the input impedance at a set of reference nodes via the Nelder-Mead simplex algorithm. We show that the accuracy of the localization depends highly on the initialization value used for optimization, and provide a heuristic grid search algorithm to increase the quality of the initial position and thus of the localization process. A lower bound on the performance is provided for a two-dimensional setup; it can be closely met by the proposed localization algorithms in a realistic setup. The results show that the discussed approach can provide very high localization accuracy with a low-complexity node configuration.
    Full-text · Conference Paper · May 2014
  • Aditya Umbu Tana Amah · Armin Wittneben
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    ABSTRACT: In this paper, we consider relay-aided wireless multicasting where one source transmits the same information to multiple destinations. We assume that there is a half-duplex regenerative relay station (RS) which may cooperatively assist the source. Our underlying problems are two-fold: when and how should the source and the RS cooperate to improve the multicast rate? Firstly, we show the required conditions for using the RS for wireless multicasting and propose opportunistic relaying strategies where the RS, when in use, forwards only partial information of the source. Thus, the proposed opportunistic relaying strategies lead to an efficient use of the RS. Secondly, we explain how we can maximise the multicast rate by optimising both the source transmission rate and the time sharing between the source and the RS. It is shown that the proposed opportunistic relaying strategies improve the multicast rate of one-hop (direct links only) wireless multicasting and they outperform other benchmarked relaying strategies.
    No preview · Conference Paper · Sep 2013
  • Raphael T.L. Rolny · Marc Kuhn · Armin Wittneben
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    ABSTRACT: We consider the up- as well as downlink of a cellular network with multi-user multiple-input multiple-output (MIMO) communication and propose to turn the entire network into a two-hop network where a large amount of relays assist the bidirectional communication. To this end, many two-way relays are spread over the entire area of the network. In addition to introducing the concept of ubiquitous relaying, different two-way relaying protocols are developed, for amplify-and-forward (AF) as well as decode-and-forward (DF) relays. The goal is to efficiently apply two-way relaying to interference limited cellular networks. To achieve this, relaying is combined with a simple form of base station (BS) cooperation that allows canceling some interference terms. The relays are used to reduce the complexity at the terminal nodes and to improve the overall performance by distributed interference management. Our results show that the proposed concept can offer significant gains compared to a conventional multi-user MIMO strategy without relays.
    No preview · Conference Paper · Sep 2013
  • Yahia Hassan · Raphael T.L. Rolny · Armin Wittneben
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    ABSTRACT: It is well known that compact arrays introduce spatial channel correlation, antenna coupling, superdirectivity and noise correlation. While these effects have been thoroughly investigated for point to point MIMO, only isolated results are available on the effect of such phenomena on performance of relaying systems. This paper tries to fill part of this void. Specifically we study the impact of lossless and lossy compact antenna arrays on multiuser amplify and forward (AF) relaying in the presence of different noise sources. We optimize the gain allocation for sum rate maximization under a dissipated power constraint. For compact arrays this constraint is more relevant than the commonly used radiated power constraint. We provide an extensive insight-oriented discussion of our results, some of which may appear counterintuitive at first glance. We show that for compact MIMO relaying the standard model, considering only channel correlation but ignoring antenna coupling and noise correlation, is insufficient and may lead to a wrong system characterization.
    No preview · Conference Paper · Jan 2013
  • R.T.L. Rolny · M. Kuhn · A. Amah · A. Wittneben
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    ABSTRACT: We consider two-way communication between multiple MIMO transceiver pairs that is assisted by non-regenerative half-duplex two-way relays. A generalized system model is formulated in which an arbitrary number of multi-antenna relays can make use of symbol extensions in frequency, e.g. OFDM subcarriers. In contrast to conventional approaches, the relays can forward arbitrary linear combinations of their receive symbols in the spatial as well as frequency domain. We apply a closed form zero-forcing approach to orthogonalize the different transceiver pairs and compare simple heuristic power allocation with numerically optimized relay gain allocation schemes. Based on simulation results, we study the advantages of cooperation between subcarriers to improve the sum rate of two-way relaying. Furthermore, we show how such a two-way relaying scheme can beneficially be implemented in a cellular network.
    No preview · Article · Jan 2013
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    Heinrich Luecken · Christoph Steiner · Armin Wittneben
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    ABSTRACT: Future wireless networks based on Ultra-Wideband (UWB) will offer localization capabilities with centimeter accuracy. We propose to use this inherently obtainable location knowledge to adapt the transceiver to the multipath channel conditions. This saves overhead for channel estimation and dissemination and enables low cost, low complexity and low power data transmission. In particular, we study the location-aware adaptation of generalized energy detection receivers for UWB impulse radio communication with binary pulse position modulation. Conventionally, these receivers are very vulnerable to narrowband interference. Therefore, we derive transmitter and receiver optimization schemes based on the Signal-to-Interference-plus-Noise-Ratio (SINR): First, we present the SINR optimization based on full channel knowledge. The location knowledge is then incorporated by means of a statistical channel model, which depends on the position of the nodes. Performance evaluation based on a simple channel model is used to give insight about the fundamental behavior of the derived optimization schemes. Moreover, an extensive measurement campaign in a rich scattering environment proves that location information can improve the data transmission and helps to successfully suppress narrowband interference. Performance gains of 2 to 5 dB compared to conventional energy detection can be obtained.
    Preview · Article · Sep 2012 · IEEE Transactions on Wireless Communications
  • Jörg Wagner · Armin Wittneben
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    ABSTRACT: The sum-capacity $C$ of a static uplink channel with $n$ single-antenna sources and an $n$-antenna destination is known to scale linearly in $n$, if the random channel matrix fulfills the conditions for the Marcenko-Pastur law: if each source transmits at power $P/n$, there exists a positive $c_{0}$, such that $\lim_{n \ura{} \infty}C/n=c_{0}$ almost surely. This paper addresses the question to which extent this result carries over to multi-hop networks. Specifically, an $L+1$-hop network with $n$ non-cooperative source antennas, $n$ fully cooperative destination antennas, and $L$ relay stages of $n_{\cal R}$ (cooperative or non-cooperative) relay antennas each is considered. Four relaying strategies are assessed based on the interrelationship between two sequences. For each considered strategy ${\rm XF}$, there exists a sequence $(c_{L}^{\rm XF})_{L=0}^{\infty}$ , such that $c_{L}^{\rm XF}=\lim_{n \ura{} \infty}R^{\rm XF}_{L}/n$ almost surely, where $R^{\rm XF}_{L}$ denotes the supremum of the set of sum-rates that are achievable by the strategy over $L\!+\!1$ hops. This sequence depends on the sequence $(P_{L})_{L=0}^{\infty}$ , where $P_{L}$ corresponds to the power of the source stage and each of the relay stages in an $L\!+\!1$-hop network. Results are summarized as follows: Decode & forward (DF): For $n_{\cal R}=n$, $c^{\rm DF}_{L}$ is constant with respect to $L$, if also $P_{L}$ is constant with respect to $L$.
    No preview · Article · Apr 2012 · IEEE Transactions on Information Theory
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    E. Slottke · R. Rolny · A. Wittneben
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    ABSTRACT: We propose a method for enabling complex computations in a network of low-complexity wireless devices. By utilizing multihop relaying, such devices can form the wireless equivalent of an artificial neural network (ANN). We provide a method for programming the network functionality in a decentralized fashion and demonstrate the robustness of wireless ANNs against node failures and imperfections. Applications of this scheme exist in low-complexity sensor networks, where elaborate calculations can be carried out in a distributed fashion, or for creating powerful ANNs with very high degrees of interconnectivity realized by the wireless medium.
    Full-text · Conference Paper · Jan 2012
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    Christoph Steiner · Armin Wittneben
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    ABSTRACT: Location fingerprinting utilizing ultrawideband (UWB) radio frequency (RF) signals is an attractive alternative to conventional positioning concepts based on range, angle, or received signal strength estimates. Such a location fingerprinting method proves particularly beneficial in indoor environments with dense multipath propagation and nonline-of-sight situations where conventional approaches would fail. The ultrawide bandwidth allows for location fingerprints with many degrees of freedom and thus gives the important advantage that a single anchor suffices for good localization performance. The downside is that a large amount of training data is usually required, which makes the training phase time-consuming and tedious. In this paper, we propose and study a novel and efficient training method which is based on the idea of spatial signal prediction. We develop a regional channel model which supports spatial signal prediction in the vicinity of a reference point. We show that the parameters of this regional channel model can be estimated from very few measured received signals with known transmitter and receiver positions. The prediction accuracy and the location fingerprinting performance are evaluated with measured channel impulse responses obtained in an anechoic chamber and in a typical office environment.
    Preview · Article · Jan 2012 · IEEE Transactions on Signal Processing

Publication Stats

4k Citations
47.59 Total Impact Points

Institutions

  • 2007-2012
    • ETH Zurich
      Zürich, Zurich, Switzerland
  • 2011
    • Evangelische Hochschule Darmstadt
      Darmstadt, Hesse, Germany
  • 2010
    • Eawag: Das Wasserforschungs-Institut des ETH-Bereichs
      Duebendorf, Zurich, Switzerland
  • 2002
    • Universität des Saarlandes
      Saarbrücken, Saarland, Germany