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  • 1. Abu-Shaban, Z.
    et al.
    Bhavani Shankar Mysore, R.
    Mehrpouyan, H.
    Ottersten, Björn
    SnT - Univ. of Luxembourg, Luxembourg, Luxembourg.
    Enhanced List-based Group-wise overloaded receiver with application to satellite reception2014In: 2014 IEEE International Conference on Communications (ICC), IEEE conference proceedings, 2014, p. 5616-5621Conference paper (Refereed)
    Abstract [en]

    The market trends towards the use of smaller dish antennas for TV satellite receivers, as well as the growing density of broadcasting satellites in orbit require the application of robust adjacent satellite interference (ASI) cancellation algorithms at the receivers. The wider beamwidth of a small size dish and the growing number of satellites in orbit impose an overloaded scenario, i.e., a scenario where the number of transmitting satellites exceeds the number of receiving antennas. For such a scenario, we present a two stage receiver to enhance signal detection from the satellite of interest, i.e., the satellite that the dish is pointing to, while reducing interference from neighboring satellites. Towards this objective, we propose an enhanced List-based Group-wise Search Detection (LGSD) receiver architecture that takes into account the spatially correlated additive noise and uses the signal-to-interference-plus-noise ratio (SINR) maximization criterion to improve detection performance. Simulations show that the proposed receiver structure enhances the performance of satellite systems in the presence of ASI when compared to existing methods.

  • 2. Abu-Shaban, Z.
    et al.
    Mehrpouyan, H.
    Grotz, J.
    Ottersten, Björn
    SnT - University of Luxembourg, Luxembourg .
    Overloaded satellite receiver using SIC with hybrid beamforming and ML detection2013In: 2013 IEEE 14th Workshop on Signal Processing Advances in Wireless Communications (SPAWC), New York: IEEE , 2013, p. 450-454Conference paper (Refereed)
    Abstract [en]

    In this paper, a new receiver structure that is intended to detect the signals from multiple adjacent satellites in the presence of other interfering satellites is proposed. We tackle the worst case interference conditions, i.e., it is assumed that uncoded signals that fully overlap in frequency arrive at a multiple-element small-size parabolic antenna in a spatially correlated noise environment. The proposed successive interference cancellation (SIC) receiver, denoted by SIC Hy/ML, employs hybrid beamforming and disjoint maximum likelihood (ML) detection. Depending on the individual signals spatial position, the proposed SIC Hy/ML scheme takes advantage of two types of beamformers: a maximum ratio combining (MRC) beamformer and a compromised array response (CAR) beamformer. The performance of the proposed receiver is compared to an SIC receiver that uses only MRC beamforming scheme with ML detection for all signals, a joint ML detector, and a minimum mean square error detector. It is found that SIC Hy/ML outperforms the other schemes by a large margin.

  • 3. Afzal, H.
    et al.
    Aouada, D.
    Font, D.
    Mirbach, B.
    Ottersten, Björn
    RGB-D multi-view system calibration for full 3D scene reconstruction2014In: 2014 22nd International Conference on Pattern Recognition, IEEE conference proceedings, 2014, p. 2459-2464Conference paper (Refereed)
    Abstract [en]

    One of the most crucial requirements for building a multi-view system is the estimation of relative poses of all cameras. An approach tailored for a RGB-D cameras based multi-view system is missing. We propose BAICP+ which combines Bundle Adjustment (BA) and Iterative Closest Point (ICP) algorithms to take into account both 2D visual and 3D shape information in one minimization formulation to estimate relative pose parameters of each camera. BAICP+ is generic enough to take different types of visual features into account and can be easily adapted to varying quality of 2D and 3D data. We perform experiments on real and simulated data. Results show that with the right weighting factor BAICP+ has an optimal performance when compared to BA and ICP used independently or sequentially.

  • 4. Al Ismaeil, K.
    et al.
    Aouada, D.
    Mirbach, B.
    Ottersten, Björn
    Interdisciplinary Centre for Security, Reliability and Trust, Universtity of Luxembourg, Luxembourg.
    Depth super-resolution by enhanced shift and add2013In: Computer Analysis of Images and Patterns: 15th International Conference, CAIP 2013, York, UK, August 27-29, 2013, Proceedings, Part II, Springer, 2013, Vol. 8048 LNCS, no PART 2, p. 100-107Conference paper (Refereed)
    Abstract [en]

    We use multi-frame super-resolution, specifically, Shift & Add, to increase the resolution of depth data. In order to be able to deploy such a framework in practice, without requiring a very high number of observed low resolution frames, we improve the initial estimation of the high resolution frame. To that end, we propose a new data model that leads to a median estimation from densely upsampled low resolution frames. We show that this new formulation solves the problem of undefined pixels and further allows to improve the performance of pyramidal motion estimation in the context of super-resolution without additional computational cost. As a consequence, it increases the motion diversity within a small number of observed frames, making the enhancement of depth data more practical. Quantitative experiments run on the Middlebury dataset show that our method outperforms state-of-the-art techniques in terms of accuracy and robustness to the number of frames and to the noise level.

  • 5. Al Ismaeil, K.
    et al.
    Aouada, D.
    Mirbach, B.
    Ottersten, Björn
    Advanced Engineering - IEE S.A., Luxembourg .
    Dynamic super resolution of depth sequences with non-rigid motions2013In: 2013 IEEE International Conference on Image Processing, ICIP 2013 - Proceedings, IEEE Signal Processing Society, 2013, p. 660-664Conference paper (Refereed)
    Abstract [en]

    We enhance the resolution of depth videos acquired with low resolution time-of-flight cameras. To that end, we propose a new dedicated dynamic super-resolution that is capable to accurately super-resolve a depth sequence containing one or multiple moving objects without strong constraints on their shape or motion, thus clearly outperforming any existing super-resolution techniques that perform poorly on depth data and are either restricted to global motions or not precise because of an implicit estimation of motion. The proposed approach is based on a new data model that leads to a robust registration of all depth frames after a dense upsampling. The textureless nature of depth images allows to robustly handle sequences with multiple moving objects as confirmed by our experiments.

  • 6. Al Ismaeil, K.
    et al.
    Aouada, D.
    Mirbach, B.
    Ottersten, Björn
    SnT - Universtity of Luxembourg, Luxembourg .
    Multi-frame super-resolution by enhanced shift & add2013In: 2013 8th International Symposium on Image and Signal Processing and Analysis (ISPA), IEEE , 2013, p. 171-176Conference paper (Refereed)
    Abstract [en]

    A critical step in multi-frame super-resolution is the registration of frames based on their motion. We improve the performance of current state-of-the-art super-resolution techniques by proposing a more robust and accurate registration as early as in the initialization stage of the high resolution estimate. Indeed, we solve the limitations on scale and motion inherent to the classical Shift & Add approach by upsampling the low resolution frames up to the super-resolution factor prior to estimating motion or to median filtering. This is followed by an appropriate selective optimization, leading to an enhanced Shift & Add. Quantitative and qualitative evaluations have been conducted at two levels; the initial estimation and the final optimized superresolution. Results show that the proposed algorithm outperforms existing state-of-art methods.

  • 7. Al Ismaeil, Kassem
    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.
    Bilateral Filter Evaluation Based on Exponential Kernels2012Conference paper (Refereed)
    Abstract [en]

    The well-known bilateral filter is used to smooth noisy images while keeping their edges. This filter is commonly used with Gaussian kernel functions without real justification. The choice of the kernel functions has a major effect on the filter behavior. We propose to use exponential kernels with L1 distances instead of Gaussian ones. We derive Stein's Unbiased Risk Estimate to find the optimal parameters of the new filter and compare its performance with the conventional one. We show that this new choice of the kernels has a comparable smoothing effect but with sharper edges due to the faster, smoothly decaying kernels.

  • 8. Alodeh, M.
    et al.
    Chatzinotas, S.
    Ottersten, Björn
    A multicast approach for constructive interference precoding in MISO downlink channel2014In: 2014 IEEE International Symposium on Information Theory, IEEE conference proceedings, 2014, p. 2534-2538Conference paper (Refereed)
    Abstract [en]

    This paper studies the concept of jointly utilizing the data information (DI) and channel state information (CSI) in order to design symbol-level precoders for a multiple input and single output (MISO) downlink channel. In this direction, the interference among the simultaneous data streams is transformed to useful signal that can improve the signal to interference noise ratio (SINR) of the downlink transmissions. We propose a maximum ratio transmissions (MRT) based algorithm that jointly exploits DI and CSI to gain the benefits from these useful signals. In this context, a novel framework to minimize the power consumption is proposed by formalizing the duality between the constructive interference downlink channel and the multicast channels. The numerical results have shown that the proposed schemes outperform other state of the art techniques.

  • 9. Alodeh, M.
    et al.
    Chatzinotas, S.
    Ottersten, Björn
    Joint channel estimation and pilot allocation in underlay cognitive MISO networks2014In: 2014 International Wireless Communications and Mobile Computing Conference (IWCMC), IEEE conference proceedings, 2014, p. 797-802Conference paper (Refereed)
    Abstract [en]

    Cognitive radios have been proposed as agile technologies to boost the spectrum utilization. This paper tackles the problem of channel estimation and its impact on downlink transmissions in an underlay cognitive radio scenario. We consider primary and cognitive base stations, each equipped with multiple antennas and serving multiple users. Primary networks often suffer from the cognitive interference, which can be mitigated by deploying beamforming at the cognitive systems to spatially direct the transmissions away from the primary receivers. The accuracy of the estimated channel state information (CSI) plays an important role in designing accurate beamformers that can regulate the amount of interference. However, channel estimate is affected by interference. Therefore, we propose different channel estimation and pilot allocation techniques to deal with the channel estimation at the cognitive systems, and to reduce the impact of contamination at the primary and cognitive systems. In an effort to tackle the contamination problem in primary and cognitive systems, we exploit the information embedded in the covariance matrices to successfully separate the channel estimate from other users' channels in correlated cognitive single input multiple input (SIMO) channels. A minimum mean square error (MMSE) framework is proposed by utilizing the second order statistics to separate the overlapping spatial paths that create the interference. We validate our algorithms by simulation and compare them to the state of the art techniques.

  • 10. Alodeh, M.
    et al.
    Chatzinotas, S.
    Ottersten, Björn
    Spatial DCT-based least square estimation in multi-antenna multi-cell interference channels2014In: 2014 IEEE International Conference on Communications (ICC), IEEE conference proceedings, 2014, p. 4729-4734Conference paper (Refereed)
    Abstract [en]

    Interference management techniques in multicell multiple input multiple output (MIMO) networks require accurate channel state information (CSI). A popular technique for acquiring this CSI in time division duplex (TDD) systems is uplink training by exploiting the reciprocity of the wireless medium. Recently, the pilot contamination problem has been identified as one of the limiting factors for such kind of CSI acquisition. In an effort to tackle the problem of contamination, we utilize the compression capability of discrete cosine transform (DCT) and covariance matrices to spatially separate the estimate for the scenario of correlated single input multiple input (SIMO) channels. A least square estimation framework is proposed by utilizing the DCT to separate the overlapping spatial paths that create the interference. The spatial domain is thus exploited to mitigate the contamination which is able to discriminate across the interfering users. We validate our algorithms by simulation and compare them to the state of the art techniques.

  • 11. Alodeh, Maha
    et al.
    Chatzinotas, Symeon
    Ottersten, Björn E.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Spatial DCT-Based Channel Estimation in Multi-Antenna Multi-Cell Interference Channels2015In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 63, no 6, p. 1404-1418Article in journal (Refereed)
    Abstract [en]

    This work addresses channel estimation in multiple antenna multicell interference-limited networks. Channel state information (CSI) acquisition is vital for interference mitigation. Wireless networks often suffer from multicell interference, which can be mitigated by deploying beamforming to spatially direct the transmissions. The accuracy of the estimated CSI plays an important role in designing accurate beamformers that can control the amount of interference created from simultaneous spatial transmissions to mobile users. Therefore, a new technique based on the structure of the spatial covariance matrix and the discrete cosine transform (DCT) is proposed to enhance channel estimation in the presence of interference. Bayesian estimation and least squares estimation frameworks are introduced by utilizing the DCT to separate the overlapping spatial paths that create the interference. The spatial domain is thus exploited to mitigate the contamination which is able to discriminate across interfering users. Gains over conventional channel estimation techniques are presented in our simulations which are also valid for a small number of antennas.

  • 12. Aouada, D.
    et al.
    Al Ismaeil, K.
    Idris, K. K.
    Ottersten, Björn
    Surface UP-SR for an improved face recognition using low resolution depth cameras2014In: 2014 11th IEEE International Conference on Advanced Video and Signal Based Surveillance (AVSS), IEEE conference proceedings, 2014, p. 107-112Conference paper (Refereed)
    Abstract [en]

    We address the limitation of low resolution depth cameras in the context of face recognition. Considering a face as a surface in 3-D, we reformulate the recently proposed Upsampling for Precise Super-Resolution algorithm as a new approach on three dimensional points. This reformulation allows an efficient implementation, and leads to a largely enhanced 3-D face reconstruction. Moreover, combined with a dedicated face detection and representation pipeline, the proposed method provides an improved face recognition system using low resolution depth cameras. We show experimentally that this system increases the face recognition rate as compared to directly using the low resolution raw data.1.

  • 13.
    Arapoglou, Pantelis-Daniel
    et al.
    University of Luxembourg, Luxembourg.
    Shankar, M. R. Bhavani
    University of Luxembourg, Luxembourg.
    Panagopoulos, Athanasios
    University of Luxembourg, Luxembourg.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Gateway Diversity Strategies in Q/V Band Feeder Links2011In: Proceedings 17th Ka and Broadband Communications Conference, 2011Conference paper (Refereed)
  • 14. Aravanis, Alexis
    et al.
    Shankar Bhavani, M.R.
    Danoy, Gregoire
    Arapoglou, Pantelis-Daniel
    Cottis, Panayotis
    Ottersten, Björn
    Multi-objective Optimization Approach to Power Allocation in Multibeam Systems2012Conference paper (Refereed)
  • 15. Aravanis, Alexis
    et al.
    Shankar Bhavani, M.R.
    Danoy, Gregoire
    Arapoglou, Pantelis-Daniel
    Cottis, Panayotis
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Power allocation in multibeam satellites: A hybrid-genetic algorithm approach2012Conference paper (Refereed)
  • 16. Arnau, J.
    et al.
    Christopoulos, D.
    Chatzinotas, S.
    Mosquera, C.
    Ottersten, Björn
    Performance of the multibeam satellite return link with correlated rain attenuation2014In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 13, no 11, p. 6286-6299Article in journal (Refereed)
    Abstract [en]

    Rain attenuation is among the major impairments for satellite systems operating in the K-band and above. In this paper, we investigate the impact of spatially correlated rain attenuation on the performance of a multibeam satellite return link. For a comprehensive assessment, an analytical model for the antenna pattern that generates the beams is also proposed. We focus on the outage capacity of the link and obtain analytical approximations at high and low signal-to-noise ratio. The derived approximations provide insights into the effect of key system parameters such as the interuser distance, the satellite beam radius, or the rain intensity, and simulation results show that it fits tightly with the Monte Carlo results. Additionally, the derived expressions can be easily particularized for the single-user case, providing some novel insights.

  • 17.
    Astély, David
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Constrained Complexity Spatio-Temporal Interference Rejection Combining1999In: Proceedings of SPAWC’99, Signal Processing Advances in Wireless Communications, IEEE , 1999, p. 110-113Conference paper (Refereed)
    Abstract [en]

    Space-time processing for co-channel interference (CCI) rejection and equalization with antenna arrays may provide large gains over space-only processing, especially in interference limited scenarios. However, taking thetemporal correlation of the noise and CCI process into account leads to sequence detection with highercomplexity as compared to space-only processing that neglects this correlation. We propose the use of the generalized Viterbi algorithm for sequence detection with lower complexity. Special cases include the M-algorithm and the delayed decision feedback sequence estimator. A relevant comparison between spatial andspatio-temporal processing with sequence detectors of the same complexity may thus be performed. Numerical examples show substantial gains for spatio-temporal processing as compared to space-only processing also in this case when the optimality of the sequence detector is traded for interference rejection.

  • 18.
    Astély, David
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    MLSE and Spatio-Temporal Interference Rejection Combining with Antenna Arrays1998In: Proceedings of Eusipco-98, Ninth European Signal Processing Conference, Island of Rhodes, Greece, 1998, p. 1341-1344Conference paper (Refereed)
  • 19.
    Astély, David
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    On Spatio-Temporal Interference Rejection Combining with Antenna Arrays1998Other (Refereed)
  • 20.
    Astély, David
    et al.
    Ericsson Research.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Spatio-Temporal Interference Rejection Combining2005In: Smart Antennas - State-of-the-Art / [ed] Kaiser, Thomas, Hindawi Publishing Corporation , 2005, p. 5-26Chapter in book (Other academic)
  • 21.
    Astély, David
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    The effects of local scattering on direction of arrival estimation with MUSIC1999In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 47, no 12, p. 3220-3234Article in journal (Refereed)
    Abstract [en]

    In wireless communication scenarios, multipath propagation may cause angular spreading as seen from a base station antenna array. Environments where most energy incident on the array is from scatterers local to the mobile transmitters are considered, and the effects on direction of arrival (DOA) estimation with the MUSIC algorithm are studied. Previous work has studied rapidly time-varying channels and concluded that local scattering has a minor effect on DOA estimation in such scenarios. In this work, a channel that is time-invariant during the observation period is considered, and under the assumption of small angular spread, an approximate distribution for the DOA estimates is derived. The results show that local scattering has a significant impact on DOA estimation in the time invariant case. Numerical examples are included to illustrate the analysis and to demonstrate that the results may be used to formulate a simple estimator of angular spread. An extension to more general Rayleigh and Ricean fading channels is also included, In addition, results from processing experimental data collected in suburban environments are presented. Good agreement with the derived distributions is obtained.

  • 22.
    Astély, David
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Swindlehurst, Andrew Lee
    Department of Electrical and Computer Engineering, Brigham Young University, Provo, UT 84602 USA.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Spatial signature estimation for uniform linear arrays with unknown receiver gains and phases1999In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 47, no 8, p. 2128-2138Article in journal (Refereed)
    Abstract [en]

    The problem of spatial signature estimation using a uniform linear array (ULA) with unknown receiver gain and phase responses is studied. Sufficient conditions for identifying the spatial signatures are derived, and a closed-Form ESPRIT-like estimator is proposed, The performance of the method is investigated by means of simulations and on experimental data collected with an antenna array in a suburban environment. The results show that the absence of receiver calibration is not critical for uplink signal waveform estimation using a plane wave model.

  • 23.
    Asztély, David
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Bengtsson, Mats
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Kristensson, Martin
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Spatio-Temporal Processing for Wireless Communications1998In: First Annual UCSD Conference on Wireless Communications, 1998Conference paper (Refereed)
  • 24.
    Asztély, David
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Modified Array Manifold for Signal Waveform Estimation in Wireless Communications1996In: 30:th Asilomar Conference on Signals, Systems & Computers, IEEE , 1996, p. 738-741Conference paper (Refereed)
    Abstract [en]

    In wireless communication scenarios, local scatterers in the vicinity of the sources cause angular spreading. A parameterization of the spatial signature in the presence of local scattering is presented which applies to uniform linear arrays (ULAs). The spatial signature is shown to be approximately a Vandermonde vector for a ULA inenvironments with small angular spread. An estimator of the spatial signature is formulated based on ESPRIT. Fora simple signal waveform estimator the gain may be considerable in scenarios with multiple sources, as compared with using the ideal manifold parameterized by direction of arrival (DOA).

  • 25.
    Asztély, David
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    The Effects of Local Scattering on Direction of Arrival Estimation with MUSIC and ESPRIT1998In: Acoustics, Speech and Signal Processing, ICASSP 98., IEEE , 1998, p. 3333-3336Conference paper (Refereed)
    Abstract [en]

    In wireless communication scenarios, multipath propagation from local scatterers in the vicinity of mobile sources may cause angular spreading as seen from a base station antenna array. This paper studies the effects of suchlocal scattering on direction of arrival (DOA) estimation with the MUSIC and ESPRIT algorithms. Previous work has considered rapidly time-varying scenarios, and concluded that local scattering has a minor effect on DOAestimation in such scenarios. This work considers the case in which the channel is time-invariant during theobservation period. The distribution of the DOA estimates is derived, and the results show that local scatteringhas a significant impact on DOA estimation in the time-invariant case. In addition, numerical examples are included to illustrate the analysis, and to demonstrate that the results may be used to formulate simple estimators of angular spread.

  • 26.
    Asztély, David
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Swindlehurst, Andrew Lee
    Department of Electrical and Computer Engineering, Brigham Young University, Provo, UT 84602 USA.
    Generalised Array Manifold Model for Wireless Communication Channels with Local Scattering1998In: IEE Proceedings Radar, Sonar and Navigation, ISSN 1350-2395, Vol. 145, no 1, p. 51-57Article in journal (Refereed)
    Abstract [en]

    The authors propose the use of a generalised array manifold for parameterised spatial signature estimation in wireless communication channels with local scattering. The array manifold commonly used for point sources is generalised to include linear combinations of the nominal array response vectors and their derivatives. The motivation behind this idea is to obtain better estimates of the spatial signatures for direction of arrival (DOA) based signal waveform estimation. The estimators proposed exploit the orthogonality between the so-called noise and signal subspaces, leading to a separable solution for the derivative coefficients. As a result, a search is required for the DOAs only. For uniform linear arrays, the spatial signatures are shown to be approximately Vandermonde vectors with damped modes, and a closed-form estimator such as ESPRIT may be used in this case. Simulation examples are included to compare the signal estimation performance obtained using the proposed generalised manifold and the conventional array manifold.

  • 27.
    Asztély, David
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Swindlehurst, Andrew Lee
    Department of Electrical and Computer Engineering, Brigham Young University, Provo, UT 84602 USA.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    A Generalized Array Manifold Model for Local Scattering in Wireless Communications1997In: Proceedings of IEEE International Conference on Acoustics, Speech, and Signal Processing. ICASSP-97, IEEE , 1997, p. 4021-4024Conference paper (Refereed)
    Abstract [en]

    In wireless communication scenarios, local scatterers in the vicinity of the mobile sources cause angular spreading. As a result, the spatial signatures will not belong to the conventional array manifold parameterized by direction of arrival (DOA) alone. A parameterized model for spatial signatures applicable in scenarios with localscattering is presented. Several algorithms that exploit this model are proposed, and the performance of signal waveform estimators using the model is investigated via simulations. It is demonstrated that considerable gain may result as compared with using the conventional plane wave model.

  • 28.
    Asztély, David
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Swindlehurst, Andrew Lee
    Brigham Young University, Utah ,US.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Auto Calibration for Signal Separation with Uniform Linear Arrays1997Conference paper (Refereed)
    Abstract [en]

    In this paper, the problem of signal waveform estimation using a uniform linear array with unknown receiver gain and phase responses is considered. As is well known, it is not possible to uniquely estimate directions-of-arrival(DOAs) and receiver gain and phase simultaneously. For steering vector and signal separation this ambiguity is notcritical. An ESPRIT-like solution is presented, and the proposed method is examined on data collected with an antenna array in a suburban environment.

  • 29. Bahnsen, A. C.
    et al.
    Aouada, D.
    Ottersten, Björn
    Example-dependent cost-sensitive logistic regression for credit scoring2014In: 2014 13th International Conference on Machine Learning and Applications, IEEE conference proceedings, 2014, p. 263-269Conference paper (Refereed)
    Abstract [en]

    Several real-world classification problems are example-dependent cost-sensitive in nature, where the costs due to misclassification vary between examples. Credit scoring is a typical example of cost-sensitive classification. However, it is usually treated using methods that do not take into account the real financial costs associated with the lending business. In this paper, we propose a new example-dependent cost matrix for credit scoring. Furthermore, we propose an algorithm that introduces the example-dependent costs into a logistic regression. Using two publicly available datasets, we compare our proposed method against state-of-the-art example-dependent cost-sensitive algorithms. The results highlight the importance of using real financial costs. Moreover, by using the proposed cost-sensitive logistic regression, significant improvements are made in the sense of higher savings.

  • 30. Bahnsen, Alejandro
    et al.
    Stojanovic, Aleksandar
    Aouada, Djamila
    Ottersten, Björn
    University of Luxembourg, Luxembourg.
    Cost sensitive credit card fraud detection using bayes minimum risk2013In: Proceedings - 2013 12th International Conference on Machine Learning and Applications, ICMLA 2013, IEEE Computer Society, 2013, p. 333-338Conference paper (Refereed)
    Abstract [en]

    Credit card fraud is a growing problem that affects card holders around the world. Fraud detection has been an interesting topic in machine learning. Nevertheless, current state of the art credit card fraud detection algorithms miss to include the real costs of credit card fraud as a measure to evaluate algorithms. In this paper a new comparison measure that realistically represents the monetary gains and losses due to fraud detection is proposed. Moreover, using the proposed cost measure a cost sensitive method based on Bayes minimum risk is presented. This method is compared with state of the art algorithms and shows improvements up to 23% measured by cost. The results of this paper are based on real life transactional data provided by a large European card processing company.

  • 31.
    Bengtsson, Mats
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Astély, David
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Measurements of Spatial Characteristics and Polarization with a Dual Polarized Antenna Array1999In: Proceedings IEEE Vehicular Technology Conference, IEEE , 1999, p. 366-370Conference paper (Refereed)
    Abstract [en]

    We consider antenna arrays equipped with cross-polarized antenna elements. The multipath propagation will affect both the spatial characteristics and the polarization of the received signals which will influence the performance of the system in terms of, for example, bit error rate or direction estimation. In this paper, we present results from field measurement data recorded at the 1800 MHz band, provided by Ericsson Radio Systems AB. The study is divided into two main parts. In the first part we introduce a diversity gain measure related to the BER of an MRC receiver. The polarization diversity introduced by the radio channel is studied, and compared to the spatial diversity. In the second part we use a parameterized model of the received polarized radio waves and illustrate the typical behavior of the estimated polarization parameters

  • 32.
    Bengtsson, Mats
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Martin, Cristoff
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ben Slimane, Slimane
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Zetterberg, Per
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Recent Advances on MIMO Processing in the SATURN Project2002In: Proc. IST Mobile Communications Summit, 2002, p. 309-313Conference paper (Other academic)
    Abstract [en]

    We highlight some recent results on the theory and algorithms for  MIMO systems, obtained at the Royal Institute of  Technology (KTH) within the SATURN project.   The paper includes a a new approximate expression for the ergodic  channel capacity of a MIMO system with correlated fading, algorithms  for MIMO beamforming under EIRP (equivalent isotropic radiated  power) constraints and a low-complexity algorithm for MIMO channel  estimation in OFDM systems. Also, we show how transmit and  beamformers can be determined in a decentralized fashion without  explicitly estimating the channel response.

  • 33.
    Bengtsson, Mats
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Martin, Cristoff
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Slimane, Ben
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Zetterberg, Per
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Recent Advances on MIMO Processing in the SATURN Project2002In: Proc. IST Mobile Communications Summit, 2002Conference paper (Refereed)
    Abstract [en]

    We highlight some recent results on the theory and algorithmsfor MIMO systems, obtained at the Royal Instituteof Technology (KTH) within the SATURN project.The paper includes a a new approximate expression forthe ergodic channel capacity of a MIMO system with correlatedfading, algorithms for MIMO beamforming underEIRP (equivalent isotropic radiated power) constraintsand a low-complexity algorithm for MIMO channel estimationin OFDM systems. Also, we show how transmitand beamformers can be determined in a decentralizedfashion without explicitly estimating the channel response.

  • 34.
    Bengtsson, Mats
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing.
    A generalization of weighted subspace fitting to full-rank models2001In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 49, no 5, p. 1002-1012Article in journal (Refereed)
    Abstract [en]

    The idea of subspace fitting provides a popular framework for different applications of parameter estimation and system identification. Previously, some algorithms have been suggested based on similar ideas, for a sensor array processing problem where the underlying data model is not low rank. We show that two of these algorithms (DSPE and DISPARE) fail to give consistent estimates and introduce a general class of subspace fitting-like algorithms for consistent estimation of parameters from a possibly full-rank data model. The asymptotic performance is analyzed, and an optimally weighted algorithm is derived. The result gives a lower bound on the estimation performance for any estimator based on a low-rank approximation of the linear space spanned by the sample data. We show that in general, for full-rank data models, no subspace-based method can reach the Cramer-Rao lower bound (CRB)

  • 35.
    Bengtsson, Mats
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Downlink Beamformer Design Using Semidefinite Optimization1999In: RadioVetenskap och Kommunikation (RVK), 1999, p. 289-293Conference paper (Other academic)
  • 36.
    Bengtsson, Mats
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Low Complexity Estimation of Angular Spread with an Antenna Array1997In: Proceedings of 11th IFAC Symposium on System Identification, 1997, p. 535-540Conference paper (Refereed)
  • 37.
    Bengtsson, Mats
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Low-complexity estimators for distributed sources2000In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 48, no 8, p. 2185-2194Article in journal (Refereed)
    Abstract [en]

    In antenna array applications, the propagation environment is often more complicated than the ordinarily assumed model of plane wavefronts. Here, a low-complexity algorithm is suggested for estimating both the DOA and the spread angle of a source subject to local scattering, using a uniform linear array. The parameters are calculated from the estimates obtained using a standard algorithm such as root-MUSIC to fit a two-ray model to the data. The algorithm is shown to give consistent estimates, and the statistical performance is studied analytically and through simulations

  • 38.
    Bengtsson, Mats
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    On Approximating a Spatially Scattered Source with Two Point Sources1998In: Proceedings Nordic Signal Processing Symposium (NORSIG'98), 1998, p. 45-48Conference paper (Other academic)
  • 39.
    Bengtsson, Mats
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Optimal and Suboptimal Transmit Beamforming2001In: Handbook of Antennas in Wireless Communications / [ed] Lal C. Godara, CRC Press , 2001, p. 18-1-18-33Chapter in book (Other academic)
  • 40.
    Bengtsson, Mats
    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), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Signal Processing.
    Optimal Downlink BeamformingUsing Semidefinite Optimization1999In: Proc. of 37th Annual Allerton Conference on Communication,Control, and Computing, 1999, p. 987-996Conference paper (Other academic)
    Abstract [en]

    When using antenna arrays at the base station of a cellular system, one critical aspectis the transmission strategy. An optimal choice of beamformers for simultaneous transmissionto several co-channel users must be solved jointly for all users and base stations in anarea. We formulate an optimal transmit strategy and show how the solution can be calculatedefficiently using interior point methods for semidefinite optimization. The algorithmminimizes the total transmitted power under certain constraints to guarantee a specificquality of service. The method provides large flexibility in the choice of constraints andcan be extended to be robust to channel perturbations.

  • 41.
    Bengtsson, Mats
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Rooting Techniques for Estimation of Angular Spread with an Antenna Array1997In: Proceedings of IEEE 47th Vehicular Technology Conference. VTC 97, IEEE , 1997, p. 1158-1162Conference paper (Refereed)
    Abstract [en]

    When antenna arrays are used in mobile communications systems, multipath propagation effects must be taken into account. Local scattering around each signal source causes angular spreading. One important parameter foroptimal transmit and receive algorithms is the width of the angular spread of each scattered source signal. We present a new principle for consistent estimation of direction of arrival as well as angular spread using standardrooting techniques such as root MUSIC, MODE or ESPRIT. The computational complexity is much lower than forpreviously suggested algorithms.

  • 42.
    Bengtsson, Mats
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Signal Waveform Estimation from Array Data in Angular Spread Environment1996In: 30:th Asilomar Conference on Signals, Systems & Computers, IEEE , 1996, p. 355-359Conference paper (Refereed)
    Abstract [en]

    We analyze different direction based signal copy algorithms for a model of angular spread caused by local scattering around each signal source. Optimal algorithms, in terms of signal to interference and noise ratio, are derived for both rapidly and slowly time varying angular spread and a low complexity an-hoc algorithm is suggested. Simulations show that these algorithms outperform traditional signal copy algorithms in terms of signalto interference and noise ratio as well as outage probability.

  • 43.
    Bengtsson, Mats
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Uplink and Downlink Beamforming for Fading Channels1999In: Proceedings of SPAWC’99, Signal Processing Advances in Wireless Communications, IEEE , 1999, p. 350-353Conference paper (Refereed)
    Abstract [en]

    We highlight some issues in the design of beamformers for transmission and reception in communications systems with antenna arrays at the base stations. We assume a radio channel characterized by frequency flat Rayleighfading which is correlated (but not coherent) from antenna element to antenna element. Different design criteria are considered and we show the relationship between downlink and uplink formulations and solutions. The resulting beamformers are typically given by quadratically constrained optimization problems which could be expected to give increased robustness to signal cancellation. Unfortunately, signal cancellation is still present, but diagonal loading can be introduced to minimize the problem.

  • 44.
    Bengtsson, Mats
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Yu, Kai
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    D523, Part 1. Single and Dual Multi-Sensor Channel Characterisation - Analysis and Models: Stochastic Models2001Report (Other academic)
  • 45.
    Bergman, Svante
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Järmyr, Simon
    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.
    Jorswieck, E.
    Optimization with skewed majorization constraints: Application to MIMO systems2008Conference paper (Refereed)
    Abstract [en]

    This paper considers the problem of optimizing a Schur-convex objective under a linearly shifted, or skewed, majorization constraint. Similar to the case with a regular majorization constraint, the solution is found to be the same for the entire class of cost functions. Furthermore, it is shown that the problem is equivalent to identifying the convex hull under a simple polygon defined by the constraint parameters. This leads to an algorithm that produces the exact optimum with linear computational complexity. As an application, we present a novel precoder design for a multi-input multi-output communication system with heterogeneous signal constellations utilizing decision feedback detection at the receiver.

  • 46.
    Bergman, Svante
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Martin, Cristoff
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Bit and power loading for spatial multiplexing using partial channel state information2004In: 2004 ITG: WORKSHOP ON SMART ANTENNAS, PROCEEDINGS, NEW YORK: IEEE , 2004, p. 152-159Conference paper (Other academic)
    Abstract [en]

    Using information about the channel at the transmitter can improve the performance of Multi-Input Multi-Output (MIMO) communication systems. When perfect Channel State Information (CSI) is available at the transmitter, data can be multiplexed and optimized over independent spatial channels. However, when the available channel information is imperfect or partial, crosstalk between the spatial channels is inevitable, complicating the design of the transmitted data. This paper presents a novel practical bit and power loading algorithm, Spatial Loading based on Incomplete Channel Estimates (SLICE), that enables the use of partial CSI for spatial multiplexing. An approximation for the Bit Error Rate (BER) of the spatial channels is derived that facilitates the loading. Numerical experiments demonstrate performance improvements compared with methods that do not consider the partial information available.

  • 47.
    Bergman, Svante
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Adaptive spatial bit loading using imperfect channel state information2005In: Proceedings of International Workshop on Optical and Electronic Device Technology for Access Networks, Aalborg, Denmark, 2005Conference paper (Refereed)
    Abstract [en]

    Using information about the channel at the transmitter can improve the performance of multi-input multi-output (MIMO) communication systems. When perfect channel state information (CSI) is available, data can be multiplexed and optimized over independent spatial channels. When the available channel information is imperfect or partial, crosstalk between the spatial channels is inevitable complicating the design since the performance of the spatial streams has to be considered jointly. In this paper an efficient algorithm for bit and power loading on the spatial channels is presented. Focus is on maximizing the data rate at fixed bit error rate and reasonable computational complexity.

  • 48.
    Bergman, Svante
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Design of robust linear dispersion codes based on imperfect2006In: Proceedings European Signal Processing Conference, 2006Conference paper (Refereed)
    Abstract [en]

    This paper concerns the design of codes for multiple-input multiple-output communication systems. The transmission scheme utilizes imperfect channel state information (CSI) in the design, assuming that maximum-likelihood detection is employed at the receiver. It is argued that channel diagonalizing codes are not robust to imperfections in the CSI. A robust non-diagonalizing code with good minimum distance separation between received codewords is proposed. The design is very suitable for systems operating at high data rates since the complexity scales nicely with the number of antennas. Numerical results show that the proposed code outperforms a state-of-the-art diagonalizing precoder.

  • 49.
    Bergman, Svante
    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.
    Lattice based linear precoding for MIMO block codes2007In: 2007 IEEE International Conference on Acoustics, Speech, and Signal Processing, IEEE , 2007, p. 329-332Conference paper (Refereed)
    Abstract [en]

    Herein, the design of linear dispersion codes for block based multiple-input multiple-output communication systems is investigated. The receiver as well as the transmitter are assumed to have perfect knowledge of the channel, and the receiver is assumed to employ maximum likelihood detection. We propose to use linear precoding and lattice invariant operations to transform the channel matrix into a lattice with large coding gain. With appropriate approximations, it is shown that this corresponds to selecting lattices with good sphere packing properties. Lattice invariant transformations are then used to minimize the power consumption. An algorithm for this power minimization is presented along with a lower bound on the optimization. Numerical results indicate that there is a potential gain of several dB by using the method compared to channel inversion with adaptive bit loading.

  • 50.
    Bergman, Svante
    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.
    Lattice-based linear precoding for MIMO channels with transmitter CSI2008In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 56, no 7, p. 2902-2914Article in journal (Refereed)
    Abstract [en]

    Herein, the design of linear dispersion codes for multiple-input multiple-output communication systems is investigated. The receiver as well as the transmitter are assumed to have perfect knowledge of the channel, and the receiver is assumed to employ maximum likelihood detection. We propose to use linear precoding and lattice invariant operations to transform the channel matrix into a lattice generator matrix with large minimum distance separation. With appropriate approximations, it is shown that this corresponds to selecting lattices with good sphere-packing properties. Lattice invariant transformations are then used to minimize the power consumption. An algorithm for this power minimization is presented along with a lower bound on the optimization. Numerical results indicate significant gains by using the proposed method compared to channel diagonalization with adaptive bit loading.

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