WCG Publications http://www.nari.ee.ethz.ch/wireless/pubs/viewpubs.php?group=y WCG Publications Wed, 16 May 2012 23:43:13 +0200 http://www.nari.ee.ethz.ch en On Capacity Scaling of Multi-Antenna Multi-Hop Networks: The Significance of the Relaying Strategy in the “Long Network Limit” http://www.nari.ee.ethz.ch/wireless/pubs/p/TransIT2012 2012-04-01 http://www.nari.ee.ethz.ch/wireless/pubs/p/TransIT2012 Authors Jörg Wagner and Armin Wittneben

Reference

IEEE Transactions on Information Theory, Vol. 58, No. 4, Apr. 2012, to appear.

Keywords

Amplify & forward, capacity scaling, compress & forward, decode & forward, MIMO uplink, multi-hop, multiple-input multiple-output, quantize & forward, random matrix theory, Slepian & Wolf compression


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Copyright Notice: © 2012 J. Wagner and A. Wittneben.

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]]> Affordable Nonlinear MIMO Systems http://www.nari.ee.ethz.ch/wireless/pubs/p/Diss_GP 2011-01-01 http://www.nari.ee.ethz.ch/wireless/pubs/p/Diss_GP Authors Georgios Psaltopoulos

Reference

PhD Thesis, Logos Verlag Berlin, 2011.

Abstract

In this thesis we introduce a new paradigm for low-cost/low power wireless systems: nonlinear MIMO systems. This new type of MIMO systems offers a way to reduce both cost and power consumption of legacy MIMO systems by using nonlinear detection methods, i.e., amplitude and phase detection. Nonlinear MIMO systems have not been considered so far. The nonlinear nature of such systems introduces certain idiosyncrasies: mathematical tractability in nonlinear MIMO systems is not straight-forward anymore and most known results/observations for linear MIMO systems are no more valid. In this inaugural work on nonlinear MIMO systems we explore the fundamental properties and identify the potential of such systems. We develop the theory of nonlinear MIMO systems starting from information theoretic aspects and working towards more realistic systems. First, we show that nonlinear MIMO systems can also exploit the spatial degrees of freedom like MIMO systems, although in a constrained way. This implies that combining multiple antennas with a nonlinear receiver increases the performance with minimal additional cost and power consumption. We then explore ML detection in nonlinear MIMO systems, in conjunction with the achievable receive diversity and spatial multiplexing modulation alphabets. It turns out that nonlinear MIMO systems behave quite different compared to linear MIMO systems. We further develop channel estimation schemes that enable coherent detection in nonlinear MIMO systems, thus completing the basic building blocks required for an operational system. Finally, we demonstrate the validity and potential of nonlinear MIMO systems through a MIMO envelope detection experimental test bed.

This publication is currently not available for download.]]> Efficient Training Phase for Ultra-Wideband based Location Fingerprinting Systems http://www.nari.ee.ethz.ch/wireless/pubs/p/Ieee_TransSP_20 2011-12-01 http://www.nari.ee.ethz.ch/wireless/pubs/p/Ieee_TransSP_20 Authors Christoph Steiner and Armin Wittneben

Reference

IEEE Transactions on Signal Processing, Dec. 2011.

Abstract

Location fingerprinting utilizing ultra-wideband radio frequency 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 non-line-of-sight situations where conventional approaches would fail. The ultra-wide 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.

Keywords

UWB, location fingerprinting, positioning, spatial signal prediction


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]]> Impact of Relays and Supporting Nodes on Locally Restricted Cooperation in Future Cellular Networks http://www.nari.ee.ethz.ch/wireless/pubs/p/ISWCS_2011_MK 2011-11-01 http://www.nari.ee.ethz.ch/wireless/pubs/p/ISWCS_2011_MK Authors Michael Kuhn, Raphael Rolny, and Marc Kuhn

Reference

IEEE International Symposium on Wireless Communication Systems, ISWCS 2011, Aachen, Germany, Nov. 2011.

Abstract

In this paper, we compare different locally restricted cooperation schemes for the downlink of LTE-Advanced. The focus in our investigations is on schemes which are easy to implement and thus have a high level of practical relevance. Two different optimization goals are considered. We first investigate how a target data rate can be achieved with lowest transmit (Tx) power. Reduction of Tx power will lead to reduced electro- magnetic radiation as well as lower total power consumption of the eNodeBs. Furthermore, it will result in reduced interference between adjacent cooperation sets. We secondly maximize the data rate that can be achieved by different schemes for fixed Tx power while considering fairness between the users. Additionally, we consider implementation issues and give an estimation of achievable data rates in case of limited backhaul capacity of practical 4G networks.

Keywords

4G, relaying, CoMP, BS cooperation, cellular networks, supporting nodes

This publication is currently not available for download.]]> Multiuser Precoding for UWB Sensor Networks http://www.nari.ee.ethz.ch/wireless/pubs/p/iswcs2011 2011-11-01 http://www.nari.ee.ethz.ch/wireless/pubs/p/iswcs2011 Authors Heinrich Luecken and Armin Wittneben

Reference

IEEE International Symposium on Wireless Communication Systems, ISWCS 2011, Aachen, Germany, pp. 156-160, Nov. 2011.

Abstract

We consider the downlink of an Ultra-Wideband (UWB) sensor network, i.e. communication from a central unit to many sensor nodes. The key to achieve low-complexity, low-power and low-cost sensor nodes are non-coherent receivers. Conventionally, their detection performance strongly suffers from inter-symbol interference due to multipath, which substantially limits the data rate or requires expensive receiver post-processing. To overcome this problem, we propose a novel precoding scheme to transmit to several nodes simultaneously. This way the sum data rate can be increased, while low complexity of sensor nodes is maintained. Specifically, we consider nodes with generalized energy detection receivers and transmission of pulse position modulated data. First, precoding optimization is derived from a Signal-to-Interference-plus-Noise Ratio (SINR) expression for this setup based on full channel state information. To achieve the best sensor network coverage, the minimum SINR of all nodes is maximized. In a second step, optimization is extended to statistical channel knowledge, which depends on the position of the nodes. Performance evaluation based on an extensive measurement campaign shows that multiple nodes can efficiently be served simultaneously. Only marginal increase in transmit power is necessary compared to time-multiplexing.


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]]> sMILE: The first MIMO Envelope Detection Testbed http://www.nari.ee.ethz.ch/wireless/pubs/p/VTC11_psaltopg 2011-09-01 http://www.nari.ee.ethz.ch/wireless/pubs/p/VTC11_psaltopg Authors Georgios Psaltopoulos, Christoph Sulser, and Armin Wittneben

Reference

IEEE Vehicular Technology Conference, VTC Fall, San Francisco, Sept. 2011.

Abstract

We present the first implementation of a MIMO envelope detection system. Such systems have so far been theoretically studied in the framework of nonlinear MIMO. The design considered employs an envelope detector on each receive antenna. The simplicity of the receiver enables extreme low-cost low-power implementations, making such systems attractive for wireless sensor networks and alike applications. The test bed presented here is a first implementation of such a system and demonstrates detection of spatially multiplexed data streams using envelope detectors.


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]]> The Potential of Restricted PHY Cooperation for the Downlink of LTE-Advanced http://www.nari.ee.ethz.ch/wireless/pubs/p/vtc2011fall_MK 2011-09-01 http://www.nari.ee.ethz.ch/wireless/pubs/p/vtc2011fall_MK Authors Marc Kuhn, Raphael Rolny, Armin Wittneben, Michael Kuhn, and Thomas Zasowski

Reference

IEEE Vehicular Technology Conference, VTC Fall, San Francisco, Sept. 2011.

Abstract

We investigate the potential of restricted PHY co- operation for the downlink of 4G networks. The cooperation is restricted to a cluster of eNodeBs. We distinguish between low and high mobility users, and propose two appropriate cooperation methods. The goal is to guarantee high user rates even on cell edges. We present a simulation study to analyze the spectral efficiency achieved by cooperation methods for urban micro cells. To investigate their influence on coordinated multipoint (CoMP), we consider different frequency allocation strategies and different sector orientations in a cell. In addition, we compare CoMP transmission to Multiuser MIMO and investigate how cooperation can improve power allocation. Based on the results, we provide important insights into future cell planing aspects.

Keywords

cooperative communications, 4G, LTE-advanced, CoMP, basestation cooperation


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]]> UWB Radar Imaging based Multipath Delay Prediction for NLOS Position Estimation http://www.nari.ee.ethz.ch/wireless/pubs/p/icuwb2011 2011-09-01 http://www.nari.ee.ethz.ch/wireless/pubs/p/icuwb2011 Authors Heinrich Luecken and Armin Wittneben

Reference

IEEE International Conference on Ultra-Wideband, ICUWB 2011, Bologna, Italy, pp. 101-105, Sept. 2011

DOI: 10.1109/ICUWB.2011.6058804

Abstract

Conventional Time-of-Arrival (ToA) based Ultra-Wideband (UWB) positioning suffers strongly from multipath. Harsh propagation environments or non-line-of-sight (NLOS) situations lead to biased position estimates with high estimation errors. To overcome this problem, we propose a radar imaging based method to predict delays of dominant propagation paths. This is done in a three-step approach: First, a radar image of the environment is created using measured training data. We generate a scattering coefficient map with the large synthetic aperture of distributed and moving antennas. The training data can easily be obtained from channel estimates of a UWB communication system with mobile nodes. Second, the radar image is used to reconstruct path gains and path delays. Thus, the channel response is predicted for arbitrary transmitter and receiver positions. Finally, dominant multipath delays are extracted using WRELAX. The proposed algorithm is validated by anechoic chamber measurements with controlled reflectors. Moreover, an extensive measurement campaign in a laboratory/office environment shows that strong paths can be predicted with nanosecond accuracy in a real world scenario.


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]]> Performance Analysis of Distributed Cluster-Based MAC Protocol for Multiuser MIMO Wireless Networks http://www.nari.ee.ethz.ch/wireless/pubs/p/ae_eurasip2011 2011-07-01 http://www.nari.ee.ethz.ch/wireless/pubs/p/ae_eurasip2011 Authors Azadeh Ettefagh, Marc Kuhn, Celal Esli, and Armin Wittneben

Reference

EURASIP Journal on Wireless Communications and Networking, July 2011.

Abstract

It is known that multiuser MIMO communication can enhance the performance of wireless networks. It can substantially increase the spectral efficiency of wireless networks by utilising multiuser interference rather than avoiding it. This paradigm shift has most impact on the medium access control (MAC) protocol because most existing MAC protocols are designed to reduce the interference. In this paper, we propose a novel cluster-based carrier sense multiple access with collision avoidance (CB-CSMA/CA) scheme. The proposed scheme enables multiuser MIMO transmissions in WLANs by utilising the multiuser interference cancellation capability of the physical layer. In this paper we focus on the performance analysis of CB-CSMA/CA. We investigate saturation throughput applying optimum backoff parameters and in the presence of synchronisation errors. Furthermore, we study the impact of different clustering methods on non-saturation throughput. We show that CB-CSMA/CA improves throughput significantly compared to the CSMA/CA scheme used in the IEEE 802.11 system. It is a promising approach for a variety of network configurations including typical infrastructure WLANs as well as many other wireless cooperative networks.

Keywords

Cluster-based CSMA/CA, cooperative wireless networks, MIMO, WLAN, infrastructure network, clustering


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Copyright Notice: © 2011 A. Ettefagh, M. Kuhn, C. Esli, and A. Wittneben.

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]]> Localization via Taylor Series Approximation for UWB based Human Motion Tracking http://www.nari.ee.ethz.ch/wireless/pubs/p/WPNC2011 2011-04-01 http://www.nari.ee.ethz.ch/wireless/pubs/p/WPNC2011 Authors Zemene Walle Mekonnen and Armin Wittneben

Reference

8th Workshop on Positioning, Navigation and Communication (WPNC), Dresden, Germany, Apr. 2011.

Abstract

In this paper, we propose and investigate a low-complexity human motion tracking system which is based on ultra-wideband (UWB) radio nodes. The maximum likelihood (ML) solution of the localization problem that arises in such a system has been presented in [1]. However, the ML solution has a computational complexity that prohibits cost-effective real-time human motion tracking. In this paper, an iterative solution of the localization problem, which is based on the first order Taylor series (TS) approximation of the ranges between the anchors and the agents, is presented. The localization algorithm can handle range measurements with unknown offsets which arise due to the asynchronism between the clock of the agents and the anchors. By means of computer simulations, it is shown that the TS based approximate solution performs close to the ML solution within a few number of iterations if it is started with a “good” initial guess of the agents position. With the a priori knowledge of the agents trajectory and position estimates in the previous time-steps, the position in the next time-step can be predicted. It has been shown that using these predicted positions as an initial guess for the TS based approximation scheme greatly improves performance.

Keywords

localization, human motion tracking, biased range measurement


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Copyright Notice: © 2011 Z. W. Mekonnen and A. Wittneben.

This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.

]]> Analysis and Design of Communications Techniques in Spectrally Efficient Wireless Relaying Systems http://www.nari.ee.ethz.ch/wireless/pubs/p/Diss_JZ 2010-01-01 http://www.nari.ee.ethz.ch/wireless/pubs/p/Diss_JZ Authors Jian Zhao

Reference

PhD Thesis, Logos Verlag Berlin, 2010.

This publication is currently not available for download.]]> Coherent Cooperative Relaying in Low Mobility Wireless Multiuser Networks http://www.nari.ee.ethz.ch/wireless/pubs/p/Diss_SB 2010-01-01 http://www.nari.ee.ethz.ch/wireless/pubs/p/Diss_SB Authors Stefan Berger

Reference

PhD Thesis, Logos Verlag Berlin, 2010.

This publication is currently not available for download.]]> Design and Optimization of Distributed Multiuser Cooperative Wireless Networks http://www.nari.ee.ethz.ch/wireless/pubs/p/Diss_CE 2010-01-01 http://www.nari.ee.ethz.ch/wireless/pubs/p/Diss_CE Authors Celal Esli

Reference

PhD Thesis, Logos Verlag Berlin, 2010.

This publication is currently not available for download.]]> Location Fingerprinting for Ultra-Wideband Systems - The Key to Efficient and Robust Localization http://www.nari.ee.ethz.ch/wireless/pubs/p/Diss_CS 2010-01-01 http://www.nari.ee.ethz.ch/wireless/pubs/p/Diss_CS Authors Christoph Steiner

Reference

PhD Thesis, Logos Verlag Berlin, 2010.

This publication is currently not available for download.]]> Distributed Gain Allocation in Non-Regenerative Multiuser Multihop MIMO Networks http://www.nari.ee.ethz.ch/wireless/pubs/p/Asilomar10rr 2010-11-25 http://www.nari.ee.ethz.ch/wireless/pubs/p/Asilomar10rr Authors Raphael Rolny, Jörg Wagner, and Armin Wittneben

Reference

Asilomar Conference on Signals, Systems, and Computers, Pacific Grove, CA, USA, Nov. 2010, (invited paper).

Abstract

In this work, we study distributed gain allocation to maximize the achievable sum-rate in non-regenerative multihop networks with multiple users and multi-antenna nodes. The source and relay nodes are constrained to forward linear transformations of their input and calculate their transformation matrices based on locally available channel state information and limited feedback from the destination. We relax the optimization problem by imposing a norm constraint instead of a power constraint on each node, and devise a gain allocation scheme that is based on an approximation of the gradient of the sum-rate. By means of computer simulations, we show that the proposed algorithm achieves close to optimal solutions, if a good initialization is provided. This makes the scheme particularly useful for channel tracking in slow fading environments.


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]]> A Hierarchical AF Protocol for Distributed Orthogonalization in Multiuser Relay Networks http://www.nari.ee.ethz.ch/wireless/pubs/p/esli_tvt_2010 2010-10-01 http://www.nari.ee.ethz.ch/wireless/pubs/p/esli_tvt_2010 Authors Celal Esli and Armin Wittneben

Reference

IEEE Transactions on Vehicular Technology, Oct. 2010.

Abstract

We consider distributed orthogonalization of multiple source-destination terminal pairs through coherent amplify-and-forward (AF) relaying. When an excess number of relays is available in the network, additional gains of diversity and sum rate are known to be attained through efficient gain allocation schemes. The common requirement of these schemes is global dissemination of local channel state information (CSI) of each relay. Consequently, as the number of relays grows, the CSI dissemination overhead may diminish the aforementioned gains in practice. We propose a novel hierarchical relaying protocol where relays with different amounts of CSI knowledge can coexist within the same network. In the lower level of hierarchy, each relay employs only local CSI to compute its gain factor, and hence, is cost-free in terms of CSI dissemination overhead. However, the relays in the higher level of hierarchy have further channel information which allows them to determine the gain factors enabling distributed orthogonalization of multiple pairs. We study sufficient conditions for achieving full spatial multiplexing, the required channel knowledge per hierarchical level, the corresponding relay gain allocations, and power allocation strategies among hierarchical levels. We finally identify relay selection for different hierarchical levels as an efficient means to recover outage (diversity) and sum rate gains. It is shown that with drastically reduced CSI dissemination overhead, the hierarchical protocol combined with relay selection approaches to the performance of conventional multiuser relaying which requires global CSI at all relay nodes.

This publication is currently not available for download.]]> Constrained Maximum Likelihood Positioning for UWB Based Human Motion Tracking http://www.nari.ee.ethz.ch/wireless/pubs/p/ipin2010 2010-09-01 http://www.nari.ee.ethz.ch/wireless/pubs/p/ipin2010 Authors Zemene Walle Mekonnen, Eric Slottke, Heinrich Luecken, Christoph Steiner, and Armin Wittneben

Reference

International Conference on Indoor Positioning and Indoor Navigation, IPIN 2010, Zurich, Switzerland, pp. 1-10, Sept. 2010

DOI: 10.1109/IPIN.2010.5647912

Abstract

In this paper, the problem of human motion tracking with ultra-wideband radio nodes is addressed. We provide a general maximum likelihood formulation of the positioning problem based on range measurements which can handle synchronous and asynchronous agents. Geometrical constraints on the node topology, which are imposed by the human body, are also taken into account. For a Gaussian ranging error model and the specific problem of arm motion tracking, we derive the maximum likelihood estimation rule and calculate an analytical expression for the unconstrained and constrained Cramér-Rao Lower Bound. With these results, we study analytically and via computer simulations under what circumstances the geometrical constraints lead to performance gains. It is found that the largest benefits are obtained in case of asynchronous agents and for certain arm positions. Intuitive reasons for this phenomenon are given. Finally, we verify these findings and evaluate the position location performance experimentally with range estimates obtained from measured ultra-wideband channel impulse responses including the impact of the human body.


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Copyright Notice: © 2010 Z. W. Mekonnen, E. Slottke, H. Luecken, C. Steiner, and A. Wittneben.

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]]> Comparison of Channel Estimation Protocols for Coherent AF Relaying Networks in the Presence of Additive Noise and LO Phase Noise http://www.nari.ee.ethz.ch/wireless/pubs/p/Eurasip_10 2010-06-01 http://www.nari.ee.ethz.ch/wireless/pubs/p/Eurasip_10 Authors Stefan Berger and Armin Wittneben

Reference

EURASIP Journal on Wireless Communications and Networking, June 2010.

Abstract

In this work channel estimation protocols for wireless two-hop networks with amplify-and-forward (AF) relays are compared. We consider multiuser relaying networks, where the gain factors are chosen such that the signals from all relays add up coherently at the destinations. While the destinations require channel knowledge in order to decode, our focus lies on the channel estimates that are used to calculate the relay gains. Since knowledge of the compound two-hop channels is generally not sufficient to do this, the protocols considered here measure all single-hop coefficients in the network. We start from the observation that the direction in which the channels are measured determines 1) the number of channel uses required to estimate all coefficient and 2) the need for global carrier phase reference. Four protocols are identified that differ in the direction in which the first-hop and the second-hop channels are measured. We derive a sensible measure for the accuracy of the channel estimates in the presence of additive noise and phase noise and compare the protocols based on this measure. Finally, we provide a quantitative performance comparison for a simple single-user application example. It is important to note that the results can be used to compare the channel estimation protocols for any two-hop network configuration and gain allocation scheme.

Keywords

Cooperative relaying, channel estimation, amplify-and-forward, phase synchronization

This publication is currently not available for download.]]> Asymmetric Data Rate Transmission in Two-Way Relaying Systems With Network Coding http://www.nari.ee.ethz.ch/wireless/pubs/p/ICC2010 2010-05-01 http://www.nari.ee.ethz.ch/wireless/pubs/p/ICC2010 Authors Jian Zhao, Marc Kuhn, Armin Wittneben, and Gerhard Bauch

Reference

IEEE International Conference on Communications (ICC), Cape Town, South Africa, May 2010.

Abstract

We propose a novel transmission scheme for the broadcast phase of two-way relaying systems. The proposed scheme employs network coding at the relay and is able to transmit with asymmetric data rates to the receivers according to their individual link qualities. The idea is that the weaker link receiver exploits a priori bit information in each transmit symbol, so that it only needs to decode on a subset of the transmit signal constellation. Subject to the same bit error rate constraint, the weaker link receiver can decode at lower signal-to-noise ratio compared to the stronger link. The signal labeling used for mapping bits to symbols at the relay is shown to be crucial for the performance at the receivers, and we provide the criterion and method for finding the optimized labeling schemes. Simulations show that the proposed transmission scheme can be applied to practical scenarios with asymmetric channel qualities, and the optimized labeling greatly outperforms conventional ones at both receivers.


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]]> Channel Estimation for Very Low Power MIMO Envelope Detectors http://www.nari.ee.ethz.ch/wireless/pubs/p/ICC10_psaltopg 2010-05-26 http://www.nari.ee.ethz.ch/wireless/pubs/p/ICC10_psaltopg Authors Georgios Psaltopoulos and Armin Wittneben

Reference

IEEE International Conference on Communications, ICC 2010, Cape Town, May 2010.

Abstract

We consider a MIMO system for very low-power applications, e.g, sensor networks, where the receiver employs an envelope detector at each receive antenna. Properties of such systems have been studied in [1], [2] and [3], where the channel was considered to be perfectly known at the receiver, or a linear channel estimation model was used. In this paper we propose a very simple channel estimation scheme, which allows the non-coherent MIMO envelope detector to estimate all required channel knowledge necessary for maximum likelihood detection. In contrast to linear MIMO system, complete knowledge of the channel coefficients is not required.


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]]>