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  • 101. Christopoulos, Dimitrios
    et al.
    Chatzinotas, Symeon
    Krause, Jens
    Ottersten, Björn
    SnT - Security and trust.lu, University of Luxembourg, Luxembourg .
    Multi-User Detection in Multibeam Mobile Satellite Systems: A Fair Performance Evaluation2013In: 2013 IEEE 77th Vehicular Technology Conference: (VTC Spring), 2013Conference paper (Refereed)
    Abstract [en]

    Multi-User Detection (MUD) techniques are currently being examined as promising technologies for the next generation of broadband, interactive, multibeam satellite communication (SatCom) systems. Results in the existing literature have shown that when full frequency and polarization reuse is employed and user signals are jointly processed at the gateway, more than threefold gains in terms of spectral efficiency over conventional systems can be obtained. However, the information theoretic results for the capacity of the multibeam satellite channel are given under ideal assumptions, disregarding the implementation constraints of such an approach. Considering a real system implementation, the adoption of full resource reuse is bound to increase the payload complexity and power consumption. Since these novel techniques require extra payload resources, fairness issues in the comparison among the two approaches arise. The present contribution evaluates in a fair manner, the performance of the return link (RL) of a SatCom system serving mobile users that are jointly decoded at the receiver. In this context, the throughput performance of the assumed system is compared to that of a conventional one, under the constraint of equal physical layer resource utilization; thus the comparison can be regarded as fair. Results show, that even when systems operate under the same payload requirements as the conventional systems, a significant gain can be realized, especially in the high SNR region. Finally, existing analytical formulas are also employed to provide closed form descriptions of the performance of clustered systems, thus introducing insights on how the performance scales with respect to the system parameters.

  • 102.
    Christopoulos, Dimitrios
    et al.
    SnT - securityandtrust.lu, University of Luxembourg.
    Chatzinotas, Symeon
    SnT - securityandtrust.lu, University of Luxembourg.
    Matthaiou, Michail
    Chalmers University of Technology, Gothenburg, Sweden.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Capacity Analysis of Multibeam Joint Decoding over Composite Satellite Channels2011In: Proc. of the 45th Asilomar Conference on Signals, Systems and Computer, 2011Conference paper (Refereed)
    Abstract [en]

    The throughput of current multibeam satellite systemsis limited by self interference. Interference mitigationtechniques have the potential to significantly increase the spectralefficiency of these satellite communication systems. The presentcontribution investigates the ergodic capacity of the return linkof a multibeam satellite system, where full frequency reuse is employedand user signals are jointly processed at the gateway. Theproposed model incorporates correlated satellite antennas overRician channels which represent some inherent characteristics ofsatellite communications. Additionally, the effects of shadowingcaused by user mobility, are modeled via the lognormal distribution.Hence, a composite Rician/lognormal fading channel withfully correlated receive antennas is considered. For this channel, anew lower bound on the ergodic capacity is analytically deducedand verified through simulations.

  • 103.
    Christopoulos, Dimitrios
    et al.
    Univ Luxembourg, Luxembourg.
    Chatzinotas, Symeon
    Univ Luxembourg, Luxembourg.
    Zheng, Gan
    Univ Luxembourg, Luxembourg.
    Grotz, Joel
    SES, Betzdorf, Luxembourg.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Linear and nonlinear techniques for multibeam joint processing in satellite communications2012In: EURASIP Journal on Wireless Communications and Networking, ISSN 1687-1472, E-ISSN 1687-1499, p. 162-Article in journal (Refereed)
    Abstract [en]

    Existing satellite communication standards such as DVB-S2, operate under highly-efficient adaptive coding and modulation schemes thus making significant progress in improving the spectral efficiencies of digital satellite broadcast systems. However, the constantly increasing demand for broadband and interactive satellite links emanates the need to apply novel interference mitigation techniques, striving towards Terabit throughput. In this direction, the objective of the present contribution is to investigate joint multiuser processing techniques for multibeam satellite systems. In the forward link, the performance of linear precoding is investigated with optimal nonlinear precoding (i.e., dirty article coding) acting as the upper performance limit. To this end, the resulting power and precoder design problems are approached through optimization methods. Similarly, in the return link the concept of linear filtering (i.e., linear minimum mean square error) is studied with the optimal successive interference cancelation acting as the performance limit. The derived capacity curves for both scenarios are compared to conventional satellite systems where beams are processed independently and interbeam interference is mitigated through a four color frequency reuse scheme, in order to quantify the potential gain of the proposed techniques.

  • 104.
    Devarakota, Pandu R
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Mirbach, Bruno
    IEE S. A., ZAE Weiergewan, 11, rue Edmond Reuter, L-5326 Contern, Luxembourg.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Confidence estimation in classification decision: A method for detecting unseen patterns2007In: Proceedings of the Sixth International Conference on Advances in Pattern Recognition, SINGAPORE: WORLD SCIENTIFIC PUBL CO PTE LTD , 2007, p. 290-294Conference paper (Other academic)
    Abstract [en]

    The classification task for a real world application shall include a confidence estimation to handle unseen patterns i.e., patterns which were not considered during the learning stage of a classifier. This is important especially for safety critical applications where the goal is to assign these situations as "unknown" before they can lead to a false classification. Several methods were proposed in the past which were based on choosing a threshold on the estimated class membership probability. In this paper we extend the use of Gaussian mixture model (GMM)to estimate the uncertainty of the estimated class membership probability in terms of confidence interval around the estimated class membership probability. This uncertainty measure takes into account the number of training patterns available in the local neighborhood of a test pattern. Accordingly, the lower bound of the confidence interval or the number of training samples around a test pattern, can be used to detect the unseen patterns. Experimental results on a real-world application are discussed.

  • 105.
    Devarakota, Pandu Ranga Rao
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Castillo-Franco, Marta
    IEE S. A., Luxembourg.
    Ginhoux, Romuald
    IEE S. A., Luxembourg.
    Mirbach, Bruno
    IEE S. A., Luxembourg.
    Kater, Serge
    IEE S. A., Luxembourg.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    3-D-Skeleton-Based Head Detection and Tracking Using Range Images2009In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 58, no 8, p. 4064-4077Article in journal (Refereed)
    Abstract [en]

    Vision-based 3-D head detection and tracking systems have been studied in several applications like video surveillance, face-detection systems, and occupant posture analysis. In this paper, we present the development of a topology-based framework using a 3-D skeletal model for the robust detection and tracking of a vehicle occupant's head position from low-resolution range image data for a passive safety system. Unlike previous approaches to head detection, the proposed approach explores the topology information of a scene to detect the position of the head. Among the different available topology representations, the Reeb graph technique is chosen and is adapted to low-resolution 3-D range images. Invariance of the graph under rotations is achieved by using a Morse radial distance function. To cope with the particular challenges such as the noise and the large variations in the density of the data, a voxel neighborhood connectivity notion is proposed. A multiple-hypothesis tracker (MHT) with nearest-neighbor data association and Kalman filter prediction is applied on the endpoints of the Reeb graph to select and filter the correct head candidate out of Reeb graph endpoints. A systematic evaluation of the head detection framework is carried out on full-scale experimental 3-D range images and compared with the ground truth. It is shown that the Reeb graph topology algorithm developed herein allows the correct detection of the head of the occupant with only two head candidates as input to the MHT. Results of the experiments demonstrate that the proposed framework is robust under the large variations of the scene. The processing requirements of the proposed approach are discussed. It is shown that the number of operations is rather low and that real-time processing requirements can be met with the proposed method.

  • 106.
    Devarakota, Pandu Ranga Rao
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Castillo-Franco, Marta
    IEE S.A., ZAE Weiergewan, 5326 Contern, Luxembourg.
    Ginhoux, Romuald
    IEE S.A., ZAE Weiergewan, 5326 Contern, Luxembourg.
    Mirbach, Bruno
    IEE S.A., ZAE Weiergewan, 5326 Contern, Luxembourg.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Occupant classification using range images2007In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 56, no 4, p. 1983-1993Article in journal (Refereed)
    Abstract [en]

    Static occupant classification is an important requirement in designing so-called smart airbags. Systems for this purpose can be either based on pressure sensors or vision sensors. Vision-based systems are advantageous over pressure-sensor-based systems as they can provide additional functionalities like dynamic occupant-position analysis or child-seat orientation detection. The focus of this paper is to evaluate and analyze static occupant classification using a low-resolution range sensor, which is based on the time-of-flight principle. This range sensor is advantageous, since it provides directly a dense range image that is independent of the ambient illumination conditions and object textures. Herein, the realization of an occupant-classification system, using a novel low-resolution range image sensor, is described, methods for extracting robust features from the range images are investigated, and different classification methods are evaluated for classifying occupants. Bayes quadratic classifier, Gaussian mixture-model classifier, and polynomial classifier are compared to a clustering-based linear-regression classifier using a polynomial kernel. The latter one shows improved results compared to the first-three classification methods. Full-scale tests have been conducted on a wide range of realistic situations with different adults and child seats in various postures and positions. The results prove the feasibility of low-resolution range images for the current application.

  • 107.
    Devarakota, Pandu Ranga Rao
    et al.
    IEE S. A., Zone Industrielle, 2b Route de Tr`eves L-2632 Findel, Luxembourg..
    Mirbach, Bruno
    IEE S. A., Zone Industrielle, 2b Route de Tr`eves L-2632 Findel, Luxembourg..
    Castillo-Franco, Marta
    IEE S. A., Zone Industrielle, 2b Route de Tr`eves L-2632 Findel, Luxembourg..
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing.
    3-D vision technology for occupant detection and classification2005In: Fifth International Conference on 3-D Digital Imaging and Modeling, Proceedings, LOS ALAMITOS: IEEE COMPUTER SOC , 2005, p. 72-79Conference paper (Refereed)
    Abstract [en]

    This paper describes a 3-D vision system based on a new 3-D sensor technology for the detection and classification of occupants in a car New generation of so-called "smart airbags" require the information about the occupancy type and position of the occupant. This information allows a distinct control of the airbag inflation. In order to reduce the risk of injuries due to airbag deployment, the airbag can be suppressed completely in case of a child seat oriented in reward direction. In this paper we propose a 3-D vision system based on a 3-D optical time-of-flight (TOF) sensor for the detection and classification of the occupancy on the passenger seat. Geometrical shape features are extracted from the 3-D image sequences. Polynomial classifier is considered for the classification task. A comparison of classifier performance with principle components (eigen-images) is presented. This paper also discuss the robustness of the features with variation of the data. The full scale tests have been conducted on a wide range of realistic situations (adults/children/child seats etc.) which may occur in a vehicle.

  • 108.
    Devarakota, Pandu Ranga Rao
    et al.
    IEE S.A., Zone Industrielle, 2b, Route de Tr`eves L-2632 Findel, Luxembourg.
    Mirbach, Bruno
    IEE S.A., Zone Industrielle, 2b, Route de Tr`eves L-2632 Findel, Luxembourg.
    Castillo-Franco, Marta
    IEE S.A., Zone Industrielle, 2b, Route de Tr`eves L-2632 Findel, Luxembourg.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Classification of vehicle occupants using 3D image sequences2005In: 2005 IEEE INTERNATIONAL CONFERENCE ON ACOUSTICS, SPEECH, AND SIGNAL PROCESSING, IEEE , 2005, p. 717-720Conference paper (Refereed)
    Abstract [en]

    The deployment of vehicle airbags for maximum protection requires information about the occupant's position, movement, weight, size etc. Specifically it is desirable to discriminate between adults, children, front- or rear faced child seats, objects put on the seat or simply empty seats. 2D images lack depth information about the object and are very sensitive to illumination conditions. Herein, occupant position classification techniques are developed based on low resolution 3D image sequences. The proposed methods are of low complexity and high reliability allowing real time implementation and meeting the rigorous requirements for passenger safety systems. Features are extracted from the 3D image sequences and a Sequential Forward Search (SFS) feature subset selection algorithm is employed to reduce the size of the feature set. Two classification techniques are evaluated, the B ayes quadratic classifier and the polynomial classifier. We present the classification results based on a large set of measurements from the low resolution 3D image sequences. The full scale tests have been conducted on a wide rance of realistic situations (adults/children/child seats etc.) which may occur in a vehicle.

  • 109.
    Devarakota, Pandu Ranga Rao
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Mirbach, Bruno
    IEE S.A., ZAE Weiergewan, 5326 Contern, Luxembourg.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Reliability estimation of a statistical classifier2008In: Pattern Recognition Letters, ISSN 0167-8655, E-ISSN 1872-7344, Vol. 29, no 3, p. 243-253Article in journal (Refereed)
    Abstract [en]

    Statistical pattern classification techniques have been successfully applied to many practical classification problems. In real-world applications, the challenge is often to cope with patterns that lead to unreliable classification decisions. These situations occur either due to unexpected patterns, i.e., patterns which occur in the regions far from the training data or due to patterns which occur in the overlap region of classes. This paper proposes a method for estimating the reliability of a classifier to cope with these situations. While existing methods for quantifying the reliability are often solely based on the class membership probability estimated on global approximations, in this paper, the reliability is quantified in terms of a confidence interval on the class membership probability. The size of the confidence interval is calculated explicitly based on the local density of training data in the neighborhood of a test pattern. A synthetic example is given to illustrate the various aspects of the proposed approach. In addition, experimental evaluation on real data sets is conducted to demonstrate the effectiveness of the proposed approach to detect unexpected patterns. The lower bound of the confidence interval is used to detect the unexpected patterns. By comparing the performance with the state-of-the-art methods, we show our approach is well-founded.

  • 110. Devarakota, Pandu RangaRao
    et al.
    Castillo-Franco, Marta
    Ginhoux, Romuald
    Mirbach, Bruno
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Application of the reeb graph technique to vehicle occupant's head detection in low-resolution range images2007In: 2007 IEEE CONFERENCE ON COMPUTER VISION AND PATTERN RECOGNITION, 2007, p. 3426-3433Conference paper (Refereed)
    Abstract [en]

    In [3], a low-resolution range sensor was investigated for an occupant classification system that distinguish person from child seats or an empty seat. The optimal deployment of vehicle airbags for maximum protection moreover requires information about the occupant's size and position. The detection of occupant's position involves the detection and localization of occupant's head. This is a challenging problem as the approaches based on local shape analysis (in 2D or 3D) alone are not robust enough as other parts of the person's body like shoulders, knee may have similar shapes as the head. This paper discusses and investigate the potential of a Reeb graph approach to describe the topology of vehicle occupants in terms of a skeleton. The essence of the proposed approach is that an occupant sitting in a vehicle has a typical topology which leads to different branches of a Reeb Graph and the possible location of the occupant's head are thus the end points of the Reeb graph. The proposed method is applied on real 3D range images and is compared to Ground truth information. Results show the feasibility of using topological information to identify the position of occupant's

  • 111. Garcia, F.
    et al.
    Aouada, D.
    Abdella, H. K.
    Solignac, T.
    Mirbach, B.
    Ottersten, Björn
    Depth enhancement by fusion for passive and active sensing2012In: Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics), 2012, Vol. 7585 LNCS, p. 506-515Conference paper (Refereed)
    Abstract [en]

    This paper presents a general refinement procedure that enhances any given depth map obtained by passive or active sensing. Given a depth map, either estimated by triangulation methods or directly provided by the sensing system, and its corresponding 2-D image, we correct the depth values by separately treating regions with undesired effects such as empty holes, texture copying or edge blurring due to homogeneous regions, occlusions, and shadowing. In this work, we use recent depth enhancement filters intended for Time-of-Flight cameras, and adapt them to alternative depth sensing modalities, both active using an RGB-D camera and passive using a dense stereo camera. To that end, we propose specific masks to tackle areas in the scene that require a special treatment. Our experimental results show that such areas are satisfactorily handled by replacing erroneous depth measurements with accurate ones

  • 112. Garcia, F.
    et al.
    Aouada, D.
    Mirbach, B.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Real-time distance-dependent mapping for a hybrid ToF multi-camera rig2012In: IEEE Journal on Selected Topics in Signal Processing, ISSN 1932-4553, Vol. 6, p. 425-436Article in journal (Refereed)
    Abstract [en]

    We propose a real-time mapping procedure for data matching to deal with hybrid time-of-flight (ToF) multi-camera rig data fusion. Our approach takes advantage of the depth information provided by the ToF camera to calculate the distance-dependent disparity between the two cameras that constitute the system. As a consequence, the not co-centric binocular system behaves as a co-centric system with co-linear optical axes between their sensors. The association between mapped and non-mapped image coordinates can be described by a set of look-up tables. This, in turn, reduces the complexity of the whole process to a simple indexing step, and thus, performs in real-time. The experimental results show that in addition to being straightforward and easy to compute, our proposed data matching approach is highly accurate which facilitates further fusion operations.

  • 113. Garcia, F.
    et al.
    Aouada, D.
    Solignac, T.
    Mirbach, B.
    Ottersten, Björn
    Interdisciplinary Centre for Security, Reliability and Trust, University of Luxembourg, L-1359, Luxembourg.
    Real-time depth enhancement by fusion for RGB-D cameras2013In: IET Computer Vision, ISSN 1751-9632, Vol. 7, no 5Article in journal (Refereed)
    Abstract [en]

    This study presents a real-time refinement procedure for depth data acquired by RGB-D cameras. Data from RGB-Dcameras suffer from undesired artefacts such as edge inaccuracies or holes owing to occlusions or low object remission. In thiswork, the authors use recent depth enhancementfilters intended for time-of-flight cameras, and extend them to structured light-based depth cameras, such as the Kinect camera. Thus, given a depth map and its corresponding two-dimensional image, wecorrect the depth measurements by separately treating its undesired regions. To that end, the authors propose specificconfidence maps to tackle areas in the scene that require a special treatment. Furthermore, in the case offiltering artefacts, theauthors introduce the use of RGB images as guidance images as an alternative to real-time state-of-the-art fusionfilters thatuse greyscale guidance images. The experimental results show that the proposed fusionfilter provides dense depth maps withcorrected erroneous or invalid depth measurements and adjusted depth edges. In addition, the authors propose a mathematicalformulation that enables to use thefilter in real-time applications.

  • 114. Garcia, F.
    et al.
    Ottersten, Björn
    CPU-based real-time surface and solid voxelization for incomplete point cloud2014In: 2014 22nd International Conference on Pattern Recognition, 2014, p. 2757-2762Conference paper (Refereed)
    Abstract [en]

    This paper presents a surface and solid voxelization approach for incomplete point cloud datasets. Voxelization stands for a discrete approximation of 3-D objects into a volumetric representation, a process which is commonly employed in computer graphics and increasingly being used in computer vision. In contrast to surface voxelization, solid voxelization not only set those voxels related to the object surface but also those voxels considered to be inside the object. To that end, we first approximate the given point set, usually describing the external object surface, to an axis-aligned voxel grid. Then, we slice-wise construct a shell containing all surface voxels along each grid-axis pair. Finally, voxels inside the constructed shell are set. Solid voxelization results from the combination of all slices, resulting in a watertight and gap-free representation of the object. The experimental results show a high performance when voxelizing point cloud datasets, independently of the object's complexity, robust to noise, and handling large portions of data missing.

  • 115.
    Garcia, Frederic
    et al.
    Advanced Engineering Department, IEE S.A..
    Aouada, Djamila
    Interdisciplinary Centre for Security, Reliability and Trust, University of Luxembourg.
    Mirbach, Bruno
    Advanced Engineering Department, IEE S.A..
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    A new 1-D colour model and its application to image filtering2011In: ISPA 2011 - 7th International Symposium on Image and Signal Processing and Analysis, 2011, p. 134-138Conference paper (Refereed)
    Abstract [en]

    This paper introduces a new 1-D model to encodecoloured images for an efficient subsequent processing. Thisrepresentation is equivalent to, but more compact than, the 3-DHCL conical representation. It consists in gathering all the hue,chroma and luminance information in one component, namely,the cumulative spiral angle, where the spirals in question aredefined as a sampling of the solid HCL cone. We use theproposed model for joint bilateral upsampling of low-resolutiondepth maps. The results show that, in addition to preserving theperceptual properties of the HCL colour representation, usingthe proposed model leads to a solution that is more accuratethan when using grayscale images.

  • 116. Garcia, Frederic
    et al.
    Aouada, Djamila
    Mirbach, Bruno
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Spatio-Temporal ToF Data Enhancement by Fusion2012Conference paper (Refereed)
  • 117.
    Garcia, Frederic
    et al.
    IEE S.A., Luxembourg, Luxembourg; University of Luxembourg, Luxembourg.
    Aouada, Djamila
    University of Luxembourg, Luxembourg.
    Mirbach, Bruno
    IEE S.A., Luxembourg.
    Ottersten, Björn
    University of Luxembourg, Luxembourg.
    Spiral colour model: reduction from 3-D to 2-D2011In: 2011 IEEE INTERNATIONAL CONFERENCE ON ACOUSTICS, SPEECH, AND SIGNAL PROCESS, IEEE , 2011, p. 1305-1308Conference paper (Refereed)
    Abstract [en]

    We define a new reduced model to represent coloured images. We propose to use two components for a full definition of a colour instead of three. To that end we take advantage of the geometrical structure of the HCL conical colour space and approximate its circular base by a spiral. We thus write chroma as a function of hue. The resulting spiral is therefore defined by one parameter only. This parameter is then combined with luminance in order to represent all the colour information. Our experiments show that our proposed model ensures an accurate representation of coloured digital images. Further more, it preserves the perceptual properties of the original HCL representation.

  • 118.
    Garcia, Frederic
    et al.
    Advanced Engineering Department, IEE S.A., Luxembourg; Universtity of Luxembourg, Luxembourg, Luxembourg .
    Aouada, Djamila
    SnT - Universtity of Luxembourg, Luxembourg.
    Mirbach, Bruno
    Advanced Engineering Department, IEE S.A..
    Solignac, Thomas
    Advanced Engineering Department, IEE S.A., Luxembourg .
    Ottersten, Björn
    Universtity of Luxembourg, Luxembourg.
    A new multi-lateral filter for real-time depth enhancement2011In: 2011 8th IEEE International Conference on Advanced Video and Signal Based Surveillance, AVSS 2011, IEEE , 2011, p. 42-47Conference paper (Refereed)
    Abstract [en]

    We present an adaptive multi-lateral filter for real-time low-resolution depth map enhancement. Despite the great advantages of Time-of-Flight cameras in 3-D sensing, there are two main drawbacks that restricts their use in a wide range of applications; namely, their fairly low spatial resolution, compared to other 3-D sensing systems, and the high noise level within the depth measurements. We therefore propose a new data fusion method based upon a bilateral filter. The proposed filter is an extension the pixel weighted average strategy for depth sensor data fusion. It includes a new factor that allows to adaptively consider 2-D data or 3-D data as guidance information. Consequently, unwanted artefacts such as texture copying get almost entirely eliminated, outperforming alternative depth enhancement filters. In addition, our algorithm can be effectively and efficiently implemented for real-time applications.

  • 119.
    Garcia, Frederic
    et al.
    University of Luxembourg, Luxembourg; Advanced Engineering Department, IEE S.A., Luxembourg.
    Aouada, Djamila
    University of Luxembourg, Luxembourg.
    Mirbach, Bruno
    Advanced Engineering Department, IEE S.A., Luxembourg.
    Solignac, Thomas
    Advanced Engineering Department, IEE S.A., Luxembourg.
    Ottersten, Björn
    University of Luxembourg, Luxembourg.
    Real-time hybrid ToF multi-camera rig fusion system for depth map enhancement2011In: IEEE Computer Society Conference on Computer Vision and Pattern Recognition Workshops, IEEE , 2011Conference paper (Refereed)
    Abstract [en]

    We present a full real-time implementation of a multilateral filtering system for depth sensor data fusion with 2-D data. For such a system to perform in real-time, it is necessary to have a real-time implementation of the filter, but also a real-time alignment of the data to be fused. To achieve an automatic data mapping, we express disparity as a function of the distance between the scene and the cameras, and simplify the matching procedure to a simple indexation procedure. Our experiments show that this implementation ensures the fusion of 3-D data and 2-D data in real-time and with high accuracy.

  • 120.
    Garcia, Frederic
    et al.
    Advanced Engineering - IEE S.A., Luxembourg.
    Mirbach, Bruno
    Advanced Engineering - IEE S.A., Luxembourg.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Grandidier, Frédéric
    Advanced Engineering - IEE S.A., Luxembourg.
    Cuesta, Ángel
    Advanced Engineering - IEE S.A., Luxembourg.
    Pixel Weighted Average Strategy for Depth Sensor Data Fusion2010In: 2010 IEEE INTERNATIONAL CONFERENCE ON IMAGE PROCESSING, 2010, p. 2805-2808Conference paper (Refereed)
    Abstract [en]

    This paper introduces a new multi-lateral filter to fuse low-resolution depth maps with high-resolution images. The goal is to enhance the resolution of Time-of-Flight sensors and, at the same time, reduce the noise level in depth measurements. Our approach is based on the joint bilateral upsampling, extended by a new factor that considers the low reliability of depth measurements along the low-resolution depth map edges. Our experimental results show better performances than alternative depth enhancing data fusion techniques.

  • 121. Gerbracht, Sabrina
    et al.
    Jorswieck, Eduard A.
    Zheng, Gan
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Non-regenerative two-hop wiretap channels using interference neutralization2012Conference paper (Other academic)
    Abstract [en]

    In this paper, we analyze the achievable secrecy rates in the two-hop wiretap channel with four nodes, where the transmitter and the receiver have multiple antennas while the relay and the eavesdropper have only a single antenna each. The relay is operating in amplify-and-forward mode and all the channels between the nodes are known perfectly by the transmitter. We discuss different transmission and protection schemes like artificial noise (AN). Furthermore, we introduce interference neutralization (IN) as a new protection scheme. We compare the different schemes regarding the high-SNR slope and the high-SNR power offset and illustrate the performance by simulation results. It is shown analytically as well as by numerical simulations that the high SNR performance of the proposed IN scheme is better than the one of AN.

  • 122.
    Gershman, Alex B.
    et al.
    Darmstadt University of Technology, Germany.
    Sidiropoulos, Nicholas D.
    Technical University of Crete, Greece.
    Shahbazpanahi, Shahram
    University of Ontario Institute of Technology, Oshawa, Canada.
    Bengtsson, Mats
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Signal Processing.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Convex Optimization-Based Beamforming: From Receive to Transmit and Network Designs2010In: IEEE signal processing magazine (Print), ISSN 1053-5888, E-ISSN 1558-0792, Vol. 27, no 3, p. 62-75Article in journal (Refereed)
    Abstract [en]

    In this article, an overview of advanced convex optimization approaches to-multisensor beamforming is presented, and connections are drawn between different types of optimization-based beamformers that apply to a broad class of receive, transmit, and network beamformer design problems. It is demonstrated that convex optimization provides an indispensable set of tools for beamforming, enabling rigorous formulation and effective solution of both long-standing and emerging design problems.

  • 123. Gharanjik, A.
    et al.
    Shankar, M. R. B.
    Soltanalian, M.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Max-min transmit beamforming via iterative regularization2017In: Conference Record - Asilomar Conference on Signals, Systems and Computers, IEEE Computer Society, 2017, p. 1437-1441Conference paper (Refereed)
    Abstract [en]

    This paper introduces an iterative optimization framework to tackle the multi-group multicast Max-Min transmit beamforming problem. In each iteration, the optimization problem is decomposed into four sub-problems, all of which can be solved using computationally efficient algorithms. The advantage of proposed method lies in its ability to handle different types of signal constraints like total power and unimodularity; a feature not exhibited by other techniques. The proposed technique outperforms the well-known semidefinite relaxation method in terms of quality of solutions.

  • 124.
    Gharanjik, Ahmad
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. University of Luxembourg.
    Bhavani Shankar, M. R.
    Arapoglou, P. D.
    Bengtsson, Mats
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Robust precoding design for multibeam downlink satellite channel with phase uncertainty2015In: ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings, IEEE conference proceedings, 2015, p. 3083-3087Conference paper (Refereed)
    Abstract [en]

    n this work, we study the design of a precoder on the user downlink of a multibeam satellite channel. The variations in channel due to phase noise introduced by on-board oscillators and the long round trip delay result in outdated channel information at the transmitter. The phase uncertainty is modelled and a robust design framework is formulated based on availability and power constraints. The optimization problem is cast into the convex paradigm after approximations and the benefits of the resulting precoder are highlighted.

  • 125.
    Gharanjik, Ahmad
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. Univ Luxembourg, Luxembourg.
    Bhavani Shankar, M. R.
    Arapoglou, Pantelis-Daniel
    Bengtsson, Mats
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. Univ Luxembourg, Luxembourg.
    Precoding design and user selection for multibeam satellite channels2015In: IEEE Workshop on Signal Processing Advances in Wireless Communications, SPAWC, IEEE conference proceedings, 2015, p. 420-424Conference paper (Refereed)
    Abstract [en]

    Precoding for the downlink of a multibeam satellite system has been recently shown, under ideal conditions, to be promising technique towards employing aggressive frequency reuse gainfully. However, time varying phase uncertainties imposed by the components and the channel, combined with delayed feedback perturbs the channel state information at the transmitter (CSIT). In this paper, we consider a power constrained robust formulation of the downlink precoding problem to counter the phase uncertainties. In particular it considers imposing conditions on the average signal to interference plus noise ratio (SINR), to deal with imperfect CSIT. In addition to the robust formulation, the primacy of user selection is highlighted and a new approach exploiting the satellite system design is proposed. Performance of the derived robust precoder in conjunction with the proposed location based user selection is then evaluated and the gains are tabulated.

  • 126. Gharanjik, Ahmad
    et al.
    Rao, Bhavani Shankar Mysore Rama
    Arapoglou, Pantelis-Daniel
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. University of Luxembourg, Luxembourg.
    Gateway Switching in Q/V Band Satellite Feeder Links2013In: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 17, no 7, p. 1384-1387Article in journal (Refereed)
    Abstract [en]

    A main challenge towards realizing the next generation Terabit/s broadband satellite communications (SatCom) is the limited spectrum available in the Ka band. An attractive solution is to move the feeder link to the higher Q/V band, where more spectrum is available. When utilizing the Q/V band, due to heavy rain attenuation, gateway diversity is considered a necessity to ensure the required feeder link availability. Although receive site diversity has been studied in the past for SatCom, there is much less maturity in terms of transmit diversity techniques. In this paper, a modified switch and stay combining scheme is proposed for a Q/V band feeder link, but its performance is also evaluated over an end-to-end satellite link. The proposed scheme is pragmatic and has close to optimal performance with notably lower complexity.

  • 127.
    Gharanjik, Ahmad
    et al.
    Interdisciplinary Cen tre for Security, Reliability and Tru st (SnT), University of Luxembourg.
    Rao, Bhavani Shankar Mysore Rama
    Interdisciplinary Cen tre for Security, Reliability and Tru st (SnT), University of Luxembourg.
    Arapoglou, Pantelis-Daniel
    Ottersten, Björn
    Interdisciplinary Cen tre for Security, Reliability and Tru st (SnT), University of Luxembourg.
    Large scale transmit diversity in Q/V band feeder link with multiple gateways2013In: 2013 IEEE 24th International Symposium on Personal Indoor and Mobile Radio Communications (PIMRC), 2013, p. 766-770Conference paper (Refereed)
    Abstract [en]

    Exploiting transmit diversity amid a high number of multiple gateways (GW) is a new research challenge in Q/V band satellite communication providing data rates of hundreds of Gbit/s. In this paper, we propose a practical switching strategy in a scenario with N+P GWs (N active and P redundant GWs) towards achieving GW transmit diversity. Differently from other works, the treatment in this paper is analytical and explores two key factors: outage performance and switching rate in detail. Further, the interplay between the number of redundant and active GWs on the availability is illustrated highlighting the contribution of the work towards system sizing.

  • 128.
    Gharanjik, Ahmad
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. University of Luxembourg, Luxembourg.
    Shankar, B.
    Soltanalian, M.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. University of Luxembourg, Luxembourg.
    An iterative approach to nonconvex QCQP with applications in signal processing2016In: Proceedings of the IEEE Sensor Array and Multichannel Signal Processing Workshop, IEEE, 2016Conference paper (Refereed)
    Abstract [en]

    This paper introduces a new iterative approach to solve or to approximate the solutions of the nonconvex quadratically constrained quadratic programs (QCQP). First, this constrained problem is transformed to an unconstrained problem using a specialized penalty-based method. A tight upper-bound for the alternative unconstrained objective is introduced. Then an efficient minimization approach to the alternative unconstrained objective is proposed and further studied. The proposed approach involves power iterations and minimization of a convex scalar function in each iteration, which are computationally fast. The important design problem of multigroup multicast beamforming is formulated as a nonconvex QCQP and solved using the proposed method.

  • 129.
    Gharanjik, Ahmad
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Shankar, Bhavani M. R.
    Arapoglou, Pantelis-Daniel
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Multiple Gateway Transmit Diversity in Q/V Band Feeder Links2015In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 63, no 3, p. 916-926Article in journal (Refereed)
    Abstract [en]

    Design of high bandwidth and reliable feeder links are central toward provisioning new services on the user link of a multibeam satellite communication system. Toward this, utilization of the Q/V band and an exploitation of multiple gateways (GWs) as a transmit diversity measure for overcoming severe propagation effects are being considered. In this context, this contribution deals with the design of a feeder link comprising N + P GWs (N active and P redundant GWs). Toward provisioning the desired availability, a novel switching scheme is analyzed and practical aspects such as prediction-based switching and switching rate are discussed. Unlike most relevant works, a dynamic rain attenuation model is used to analytically derive average outage probability in the fundamental 1 + 1 GW case. Building on this result, an analysis for the N + P scenario leading to a quantification of the end-to-end performance is provided. This analysis aids system sizing by illustrating the interplay between the number of active and redundant GWs on the chosen metrics: average outage and average switching rate.

  • 130.
    Gorokhov, A.
    et al.
    Telecome Paris, 46 rue Barrault, 75634 Paris Cedex 13.
    Kristensson, Martin
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Youssefmir, M.
    ArrayComm Inc., San Jose, CA 95134, USA.
    Some Results on Blind Deconvolution Applied to Digital Communication Signals1997In: Proceedings of DSP 97, 1997, p. 107-110Conference paper (Refereed)
    Abstract [en]

    Blind deconvolution techniques applied to spatially and/or temporally oversampled signals have recentlyattracted much interest in the research community. This contribution contains an analysis of experimental data collected from an antenna array in a suburban environment. The Noise Subspace (NS) technique of [1] and the Linear Prediction(LP) method of [2, 4] are examined. The real data examples presented demonstrate a case where joint spatial and temporal deconvolution has clear benefits as compared to decoupled processing.

  • 131.
    Gorokhov, Alexei
    et al.
    Ecole Sup ́rieure d’Electricit ́, 91192 Gif-sur-Yvette, France..
    Kristensson, Martin
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Robust Blind Second Order Deconvolution of Multiple FIR Channels1998In: Proceedings IEEE Global Telecommunications Conference, 1998. GLOBECOM 98. The Bridge to Global Integration., IEEE , 1998, p. 2062-2067Conference paper (Refereed)
    Abstract [en]

    Second order blind deconvolution of single input multiple output (SIMO) FIR channels is considered herein. A major drawback of several blind diversity techniques using antenna arrays/temporal-oversampling is high sensitivity to the choice of model order. In this article, a robust method using only the second order statistics is described. It provides high estimation accuracy even for a limited sample size and an unknown model order. In contrast to other suggested approaches, that often exploit properties valid only in the large sample case, the proposed method is applicable both in the large sample and high signal-to-noise ratio (SNR) scenario; it also enjoys a simple implementation.

  • 132.
    Gorokhov, Alexei
    et al.
    Ecole Sup ́ rieure d’Electricit ́, 91192 Gif-sur-Yvette, France..
    Kristensson, Martin
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Robust Blind Second-Order Deconvolution1999In: IEEE Signal Processing Letters, ISSN 1070-9908, Vol. 6, no 1, p. 13-16Article in journal (Refereed)
    Abstract [en]

    Second-order blind deconvolution of single input multiple output (SIMO) finite impulse response (FIR) channels is considered. A major drawback of several blind diversity techniques using antenna arrays/temporal-oversampling is high sensitivity to the choice of the model order. In this contribution, a robust method using only the second-order statistics is described. It provides high and robust estimation accuracy even for a limited sample size and an unknown model order. In contrast to other suggested approaches, that often exploit properties valid only in the large sample case, the proposed method is applicable both in the large sample and high signal-to-noise ratio (SNR) scenario.

  • 133.
    Grotz, Joel
    et al.
    SES ASTRA, L-6815 Betzdorf, Luxembourg.
    Krause, Jens
    SES ASTRA, L-6815 Betzdorf, Luxembourg.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Decision-directed interference cancellation applied to satellite broadcast reception: 2005 IEEE 62ND VEHICULAR TECHNOLOGY CONFERENCE, 1-4, PROCEEDINGS2005In: VTC2005-FALL, 2005, p. 903-906Conference paper (Refereed)
    Abstract [en]

    This paper investigates the usage of established interference cancellation techniques applied to the simultaneous reception of geostationary satellite broadcast signals from two or more satellites. In particular the reduction of interference from adjacent satellites is of interest, which would allow a reduction of the antenna size and the requirements on the directivity of the installation. The rejection of unwanted adjacent satellite interferers can imply a large equivalent parabolic reflector size to achieve the required spatial separation of the signals. The usage of small and cheap reception antennas at the end-user premises can be facilitated by the reduction of the requirements on the antenna characteristics in terms of adjacent satellite interference rejection, in particular for the joint reception of signals from two or more simultaneous geostationary orbital locations. In this study the novel approach of using simple decision directed interference reduction techniques at the symbol detection level is considered to relax the requirements on the reception system front-end.

  • 134.
    Grotz, Joel
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Krause, Jens
    SES ASTRA, L-6815 Betzdorf, Luxembourg, Europe.
    Applicability Of Interference Processing To DTH Reception2006In: Ninth International Workshop on Signal Processing for Space Communications, September 2006, 2006Conference paper (Other academic)
    Abstract [en]

    Today fixed satellite broadcast reception has to compete efficiently with other means of broadcast content delivery to end-users. The ease of reception is essential to maintain a high penetration rate under more competitive conditions. The introduction of DVB-S2 increases efficiency and allows for a higher throughput or a reduction of the reception equipment requirements. This means that a robust broadcast reception is conceivable with a reduced direct-to-home (DTH) antenna size. The current interference situation at common geostationary broadcast positions dictates the spatial discrimination requirements of common direct-to-home (DTH) reception antennas. A more robust coding rate or a relaxation of the frequency coordination constraints would obviously relax the requirements on the reception front-end but only at the expense of a reduced aggregate efficiency. The use of known interference processing schemes for DTH reception has been investigated under dual reception path scenarios, see [1]. The present work extends the concept by introducing linear pre-processing (LPP) to combine coherent reception paths. These mechanisms will only be practical if the transmitted broadcast signals are compliant with established standards (ie. DVB-S [5] or DVB-S2 [4]). The maximization of the efficiency is a main objective under given reception environments. We show how multi-user detection techniques can increase efficiency and allow reduced antenna size under realistic conditions.

  • 135.
    Grotz, Joel
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Krause, Jens
    Systems Engineering, SES ASTRA, L-6815 Betzdorf, Luxembourg.
    Data-aided frequency synchronization under interference limited conditions2005In: 2005 IEEE 61ST VEHICULAR TECHNOLOGY CONFERENCE, IEEE , 2005, p. 2683-2686Conference paper (Refereed)
    Abstract [en]

    Data-aided multi-user burst frequency synchronization under interference limited conditions is analyzed. It is assumed that a unique-word based synchronization mechanism is used to achieve synchronization. In a first approach this unique-word is assumed to be located at the beginning of the burst structure. The interference represents frequency-adjacent bursts that are coarsely time synchronous. This corresponds to a typical multi frequency (MF) TDMA system with co-channel interference (CCI) limited minimal frequency separation. A novel approach is analyzed to reduce the interference impact of the carrier offset estimation, applying interference cancellation iteratively to increase the estimation accuracy. We demonstrate improved frequency synchronization with this novel approach of iterative burst synchronization.

  • 136.
    Grotz, Joel
    et al.
    SES ASTRA, Chateau de Betzdorf, Betzdorf, L-6815 Luxembourg.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Signal Processing.
    Krause, Jens
    SES ASTRA, Chateau de Betzdorf, Betzdorf, L-6815 Luxembourg.
    Joint channel synchronization under interference limited conditions2007In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 6, no 10, p. 3781-3789Article in journal (Refereed)
    Abstract [en]

    Spectral efficiency is of great concern in the return channel of satellite based broadband systems. In [1] the feasibility of increased efficiency by reducing channel spacing below the Symbol Rate was demonstrated using joint detection and decoding for a synchronized system. We extend this work by addressing the critical synchronization problem in the presence of adjacent channel interference (ACI) which limits performance as carrier spacing is reduced. A pilot sequence aided joint synchronization scheme for a multi-frequency time division multiple access (MF-TDMA) system is proposed. Based on a maximum likelihood (ML) criterion, the channel parameters, including frequency, time and phase are jointly estimated for the channel of interest and the adjacent channels. The impact of ACI on the synchronization and detection performance is investigated. It is shown that joint channel parameter estimation outperforms single carrier synchronization with reasonable additional computational complexity in the receiver. Based on the proposed synchronization scheme in conjunction with an appropriate joint detection mechanism, see [1], carrier spacing can be reduced significantly compared to current systems providing a substantial increase in spectral efficiency.

  • 137.
    Grotz, Joel
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Krause, Jens
    SES ASTRA, Luxembourg.
    Signal Detection and Synchronization for Interference Overloaded Satellite Broadcast Reception2010In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 9, no 10, p. 3052-3063Article in journal (Refereed)
    Abstract [en]

    We address fixed satellite broadcast reception with the goal of decreasing the aperture of the receiving antenna. The front-end antenna size is commonly determined by the presence of interference from adjacent satellites. A small antenna aperture leads to interference from neighboring satellites utilizing the same frequency bands. We propose a reception system with. M multiple input elements and with subsequent joint detection of desired and interfering signals that provides reliable communication in the presence of multiple interfering signals. An iterative least squares technique is adopted combining spatial and temporal processing and achieving robustness against pointing errors. Simulation results show how the proposed joint spatial and temporal adapted mechanism outperforms the simple combination of existing techniques under interference overloaded conditions. Also, we demonstrate how to accurately synchronize the signals as part of the detection procedure. The technique is evaluated in a realistic simulation study representing the conditions encountered in a DVB-S2 broadcast scenario.

  • 138.
    Göransson, Bo
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Jansson, Magnus
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Spatial and Temporal Frequency Estimation of Uncorrelated Signals Using Subspace Fitting1996In: IEEE Signal Processing Workshop on Statistical Signal and Array Processing, 1996, p. 94-96Conference paper (Refereed)
    Abstract [en]

    We present a novel method for spatial and temporal frequency estimation in the case of uncorrelated sources. By imposing the diagonal structure given in the signal covariance matrix, it is possible to improve the performance of subspace based estimators. The proposed method combines ideas from subspace and covariance matching methods to yield a non-iterative frequency estimation algorithm. In a numerical example we show that the estimator has a lower small sample resolution threshold than root-MUSIC and similar large sample performance.

  • 139.
    Göransson, Bo
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Direction estimation in partially unknown noise fields1999In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 47, no 9, p. 2375-2385Article in journal (Refereed)
    Abstract [en]

    The problem of direction of arrival estimation in the presence of colored noise with unknown covariance is considered, The unknown noise covariance is assumed to obey a linear parametric model. Using this model, the maximum likelihood directions parameter estimate is derived, and a large sample approximation is formed. It is shown that a priori information on the source signal correlation structure is easily incorporated into this approximate ML (AML) estimator. Furthermore, a closed-form expression of the Cramer-Rao bound on the direction parameter is provided. A perturbation analysis with respect to a small error in the assumed noise model is carried out, and an expression of the asymptotic bias due to the model mismatch is given. Computer simulations and an application of the proposed technique to a full-scale passive sonar experiment is provided to illustrate the results.

  • 140.
    Göransson, Bo
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Efficient Direction Estimation of Uncorrelated Sources Using Polynomial Rooting1997In: Proceedings of 13th International Conference on Digital Signal Processing, IEEE , 1997, p. 935-938Conference paper (Refereed)
    Abstract [en]

    This paper presents a novel technique for estimating directions of arrival of uncorrelated narrowband sources. It is also shown that, if a uniform linear array is assumed, the estimation can be performed by a computationally attractive rooting technique. It is further shown that the asymptotic covariance of the estimation error attains the proper Cramer-Rao lower bound. The theoretical results presented are compared to computer simulations.

  • 141.
    Hammarwall, David
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Bengtsson, Mats
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Acquiring partial CSI for spatially selective transmission by instantaneous channel norm feedback2008In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 56, no 3, p. 1188-1204Article in journal (Refereed)
    Abstract [en]

    In the design of next-generation multiuser communication systems, multiple-antenna transmission is an essential part providing additional spatial degrees of freedom and allowing efficient use of resources. A major limiting factor in the resource allocation is the amount of channel state information (CSI) available at the transmitter, particularly in multiuser systems where the feedback from each user terminal must be limited. Herein, we show that the Euclidean norm of the instantaneous channel, when combined with long-term channel statistics provides sufficient information for the transmitter to efficiently utilize multiuser diversity in time, frequency, and space. We consider the downlink of a communication system where the base station has multiple transmit antennas whereas each user terminal has a single receive antenna. The CSI provided by channel statistics and feedback of the norm of the instantaneous channel vector is studied in depth for correlated Rayleigh and Ricean fading channels, within a minimum mean-square error (MMSE) estimation framework. An asymptotic analysis (high instantaneous SNR) is presented which shows that channel realizations with large channel norm provide additional spatial CSI at the transmitter. This makes the proposed scheme ideal for multiuser diversity transmission schemes, where resources are only allocated to users experiencing favorable channel conditions.

  • 142.
    Hammarwall, David
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Bengtsson, Mats
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Beamforming and user selection in SDMA systems utilizing channel statistics and instantaneous SNR feedback2007In: 2007 IEEE International Conference on Acoustics, Speech, and Signal Processing, IEEE , 2007, p. 113-116Conference paper (Refereed)
    Abstract [en]

    Spatial division multiple access (SDMA) systems efficiently take advantage of the spatial dimensions of the channel to increase the performance of the system. A major difficulty, common to all SDMA systems, is the requirement of channel knowledge at the transmitter to enable transmission of multiple streams without catastrophic interference. Herein we show that, in wide area scenarios, statistical channel information combined with the Euclidean norm of the channel realization, fed back from the users, provide sufficient information for SDMA systems to efficiently allocate users in time and space. A joint beamforming and scheduling algorithm is proposed for the downlink, which extends the proportional fair scheduling criterion to an SDMA setting, resulting in a weighted sum rate maximization.

  • 143.
    Hammarwall, David
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Bengtsson, Mats
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    On downlink beamforming with indefinite shaping constraints2006In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 54, no 9, p. 3566-3580Article in journal (Refereed)
    Abstract [en]

    Beamforming schemes have been proposed to exploit the spatial characteristics of multiple-input single-output (MISO) wireless radio channels. Several algorithms are available for optimal joint beamforming and power control for the downlink. Such optimal beamforming minimizes the total transmission power, while ensuring an individual target quality of service (QoS) for each user; alternatively the weakest QoS is maximized, subject to a power constraint. Herein, we consider both formulations and some of the available algorithms are generalized to enable indefinite quadratic shaping constraints on the beamformers. By imposing such additional constraints, the QoS measure can be extended to take other factors than the customary signal-to-interference-and-noise ratio (SINR) into account. Alternatively, other limitations such as interference requirements or physical constraints may be handled within the optimization. We also consider a more general SINR expression than previously analyzed, which allows for more accurate modeling, e.g., of nonzero self-interference in code-division multiple-access (CDMA) systems. Several applications for indefinite equality or inequality constraints are suggested and evaluated. For example, it is shown how such constraints may be used to ensure a minimum level of path diversity in a CDMA system. Other applications include limiting intercell interference in decentralized systems

  • 144.
    Hammarwall, David
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Bengtsson, Mats
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Utilizing the spatial information provided by channel norm feedback in SDMA systems2008In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 56, no 7, p. 3278-3293Article in journal (Refereed)
    Abstract [en]

    To achieve high performance, in terms of reliability and throughput, in future multiple-antenna communication systems, it is essential to fully exploit the spatial dimensions of the wireless propagation channel. In multiuser communication systems, the throughput can be significantly increased by simultaneously transmitting to several users in the same time-frequency slot by means of spatial-division multi-access (SDMA). A major limiting factor for downlink SDMA transmission is the amount of channel-state information (CSI) that is available at the transmitter. In most cases, CSI can be measured/estimated only at the user terminals and must be fed back to the base station. This procedure typically constrains the amount of CSI that can be conveyed to the base station. Herein, we develop several low-complexity, as well as optimized, SDMA downlink resource-allocation schemes that are particularly suitable for systems utilizing statistical channel information and partial CSI feedback. A framework is proposed for combining statistical channel information with a class of instantaneous channel norms. It is shown that, in wide-area scenarios, the feedback of such a scalar norm provides sufficient information for the proposed resource-allocation algorithms to perform efficient SDMA beamforming (BF) and scheduling.

  • 145.
    Hammarwall, David
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Exploiting the spatial information provided by channel statistics and SNR feedback2006In: 2006 IEEE 7th Workshop on Signal Processing Advances in Wireless Communications, NEW YORK: IEEE , 2006, p. 164-168Conference paper (Refereed)
    Abstract [en]

    A major limiting factor in communication systems utilizing multiantenna transmission is the amount of spatial channel information available at the transmitter. Since the channel realizations, in most cases, can only be estimated at the receiver, such information must be fed back to the transmitter. In multiuser systems the amount of feedback must be kept minimal, which seriously limits the information that can be fed back. Herein it is shown that the feedback of a scalar signal to noise ratio (SNR), together with knowledge of the statistical properties of the channel, provides substantial spatial information about the current channel realization. The spatial information is particularly good for strong channel realizations, i.e. for users that are candidates for scheduling. Previous results are extended to the Ricean channel model and the impact of the non-zero expected value is shown to further improve the spatial information.

  • 146.
    Hammarwall, David
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Spatial transmit processing using long-term channel statistics and pilot signaling on selected antennas2006In: 2006 Fortieth Asilomar Conference on Signals, Systems and Computers, 2006, p. 762-766Conference paper (Refereed)
    Abstract [en]

    In wireless high performance systems utilizing smart antenna transmission techniques, increased pilot signaling becomes problematic when more transmit antennas are added. Herein, we propose a scheme where the pilot signaling is restricted to a subset of the transmit antennas, and the total signal strength of these antennas is fed back to the transmitter. This potentially reduces the required pilot signaling and feedback so it becomes comparable to that of single antenna systems. By combining the feedback with channel statistics, known to the transmitter, substantial spatial information is gained. Herein, this information is used to develop elaborate scheduling and beamforming techniques.

  • 147.
    Hari, K. V. S.
    et al.
    Department of Electrical Communication Engineering, Indian Institute of Science, Bangalore 560 012, India.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Parameter Estimation Using a Sensor Array in a Ricean Fading Channel1998In: Sadhana-Academy Proceedings in Engineering Sciences, Vol. 23, no 1, p. 5-15Article in journal (Refereed)
    Abstract [en]

    The estimation of the Direction-Of-Arrival (DOA) and the variance of the angular spread, using an array of sensors in the case of a Ricean channel is considered, using the Maximum- Likelihood, Least-Squares and Weighted Least Squares criteria. The Cramer-Rao bound is also obtained for the problem of interest. Simplification of the cost functions to reduce the dimension of the problem has been carried out and the performance of the methods has been studied based on numerical experiments.

  • 148.
    Hari, K. V. S.
    et al.
    Department of Electrical Communication Engineering, Indian Institute of Science , Bangalore 560012, India .
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Parameter Estimation Using a Sensor Array in a Ricean Fading Channel1997In: Proc. SPCDM 97, 1997Conference paper (Refereed)
    Abstract [en]

    The estimation of the Direction-Of-Arrival (DOA) and the variance of the angular spread, using an array of sensors in the case of a Ricean channel is considered, using the Maximum-Likelihood, Least-Squares and Weighted Least Squares criteria. The Cramér-Rao bound is also obtained for the problem of interest. Simplification of the cost functions to reduce the dimension of the problem has been carried out and the performance of the methods has been studied based on numerical experiments.

  • 149. He, Shiwen
    et al.
    Huang, Yongming
    Yang, Luxi
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Coordinated Multicell Multiuser Precoding for Maximizing Weighted Sum Energy Efficiency2014In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 62, no 3, p. 741-751Article in journal (Refereed)
    Abstract [en]

    Energy efficiency optimization of wireless systems has become urgently important due to its impact on the global carbon footprint. In this paper we investigate energy efficient multicell multiuser precoding design and consider a new criterion of weighted sum energy efficiency, which is defined as the weighted sum of the energy efficiencies of multiple cells. This objective is more general than the existing methods and can satisfy heterogeneous requirements from different kinds of cells, but it is hard to tackle due to its sum-of-ratio form. In order to address this non-convex problem, the user rate is first formulated as a polynomial optimization problem with the test conditional probabilities to be optimized. Based on that, the sum-of-ratio form of the energy efficient precoding problem is transformed into a parameterized polynomial form optimization problem, by which a solution in closed form is achieved through a two-layer optimization. We also show that the proposed iterative algorithm is guaranteed to converge. Numerical results are finally provided to confirm the effectiveness of our energy efficient beamforming algorithm. It is observed that in the low signal-to-noise ratio (SNR) region, the optimal energy efficiency and the optimal sum rate are simultaneously achieved by our algorithm; while in the middle-high SNR region, a certain performance loss in terms of the sum rate is suffered to guarantee the weighed sum energy efficiency.

  • 150. He, Shiwen
    et al.
    Huang, Yongming
    Yang, Luxi
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. University of Luxembourg, Luxembourg.
    Hong, Wei
    Energy Efficient Coordinated Beamforming for Multicell System: Duality-Based Algorithm Design and Massive MIMO Transition2015In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 63, no 12, p. 4920-4935Article in journal (Refereed)
    Abstract [en]

    In this paper, we investigate joint beamforming and power allocation in multicell multiple-input single-output (MISO) downlink networks. Our goal is to maximize the utility function defined as the ratio between the system weighted sum rate and the total power consumption subject to the users' quality of service requirements and per-base-station (BS) power constraints. The considered problem is nonconvex and its objective is in a fractional form. To circumvent this problem, we first resort to an virtual uplink formulations of the the primal problem by introducing an auxiliary variable and applying the uplink-downlink duality theory. By exploiting the analytic structure of the optimal beamformers in the dual uplink problem, an efficient algorithm is then developed to solve the considered problem. Furthermore, to reduce further the exchange overhead between coordinated BSs in a large-scale antenna system, an effective coordinated power allocation solution only based on statistical channel state information is reached by deriving the asymptotic optimization problem, which is used to obtain the power allocation in a long-term timescale. Numerical results validate the effectiveness of our proposed schemes and show that both the spectral efficiency and the energy efficiency can be simultaneously improved over traditional downlink coordinated schemes, especially in the middle-high transmit power region.

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