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  • 301.
    Farhadi, Hamed
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ghauch, Hadi
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Pilot-assisted opportunistic user scheduling for wireless multi-cell networks2015In: IEEE International Conference on Communications, IEEE , 2015Conference paper (Refereed)
    Abstract [en]

    We consider downlink transmission in multi-cell wireless networks where in each cell one base station is serving multiple mobile terminals. There is no a priori channel state information (CSI) available at base stations and mobile terminals. We propose a low-complexity pilot-assisted opportunistic user scheduling (PAOUS) scheme. The proposed scheme operates in four subsequent phases: channel training; feedback transmission; user scheduling; and data transmission. We deploy an orthogonal pilot-assisted channel training scheme for acquiring CST at mobile terminals. Consequently, each mobile terminal obtains a noisy estimation of the corresponding local CST (i.e. channel gains from base stations to the mobile terminal). Then, it makes a local decision based on the estimated channel gains of the interfering links (i.e. the links between base stations in neighboring cells and the mobile terminal) and sends a one-bit feedback signal to the base station of the corresponding cell. Each base station schedules one mobile terminal for communication. We compute the achievable rate region and the achievable degrees of freedom (DoF) of the proposed transmission scheme. Our results show that in a multi-cell network with K base stations and coherence time T, the total DoF K-opt (1 - K-opt/T) is achievable given that the number of mobile terminals in each cell scales proportional to signal-to-noise-ratio. Since limited radio resources are available, only a subset of base stations should be activated, where the optimum number of active base stations is K-opt = min {K, T/2}. This recommends that in large networks (K > T/2), select only a subset of the base stations to be active and perform the PAOUS scheme within the cells associated to these base stations. Our results reveal that, even with single antenna at base stations and no a priori CSI at terminals, a non-trivial DoF gain can be achieved. We also investigate the power allocation between channel training and data transmission phases. Our study shows that in large networks (many base stations) more power should be allocated to channel training while in dense networks (many mobile terminals in each cell) more power should be allocated for data transmission.

  • 302.
    Farhadi, Hamed
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Nasiri Khormuji, Majid
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Pilot-assisted ergodic interference alignment for wireless networks2014Conference paper (Refereed)
    Abstract [en]

    This paper considers the ergodic block fading multi-user Gaussian interference channel (IC) in which each source desires to communicate to an intended destination. We assume that there is no CSI a priori available at terminals. We develop achievable rate results and compute the associated degrees of freedom by using a pilot-assisted interference alignment scheme. In this scheme, each source first sends known pilot symbols via which the destinations estimate channel gains,  and the destinations then broadcast the estimated channel gains via orthogonal feedback channels. The estimated channel gains are used to perform interference alignment for data transmission. The pilot transmission power can be different from the data transmission power. By allocating more power to pilot transmission, channel gains can be estimated more accurately which implies less power left for data transmission. We find the optimum power allocation to pilot symbols and data symbols. Our study recommends, in large networks, to allocate more power to channel training instead of data transmission. In addition, our results reveal that for a K-user ergodic IC with a coherence time T, the total degrees of freedom 1/2Kopt(1-Kopt/T) is achievable, where Kopt=min{K,T/2} is the optimum number of users selected to be active in the network. This recommends to perform a user selection in large networks (K>T/2), and apply channel training and interference alignment within the set of selected users.

  • 303.
    Farhadi, Hamed
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Nasiri Khormuji, Majid
    Wang, Chao
    Tongji University, P.R. China.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ergodic interference alignment with noisy channel state information2013In: 2013 IEEE International Symposium on Information Theory Proceedings (ISIT), IEEE conference proceedings, 2013, p. 584-588Conference paper (Refereed)
    Abstract [en]

    We investigate the multi-user time-varying Gaussian interference channel (IC) in which each source desires to communicate to an intended destination. For the ergodic time-varying IC with global perfect CSI at all terminals, it is known that with an interference alignment technique each source-destinationpair can communicate at half of the interference-free achievable rate. In practice, the channel gains are estimated by transmitting known pilot symbols from the sources, and the channel estimation procedure is hence prone to errors. In this paper, we model the channel estimation error at the destinations by an independent additive Gaussian noise and study the behavior of the ergodic interference alignment scheme with the global noisy CSI at all terminals. Toward this end, we present a closed-form innerbound on the achievable rate region by which we conclude that the achievable degrees of freedom with global perfect CSI is preserved, if the variance of channel estimation error is proportional to the inverse of the transmitted power.

  • 304.
    Farhadi, Hamed
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Wang, Chao
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Distributed interference alignment and power control for wireless MIMO interference networks2013In: 2013 IEEE Wireless Communications and Networking Conference (WCNC), IEEE Communications Society, 2013, p. 3077-3082Conference paper (Refereed)
    Abstract [en]

    This paper considers joint transceiver design and power control for K-user multiple-input multiple-output (MIMO) interference networks. Each source intends to communicate with its corresponding destination at a fixed data rate. Only local channel side information (i.e. knowledge related to the channels directly connected to a terminal) is available at each terminal. We propose iterative algorithms to perform power control to guarantee successful communication while designing transmitter beamforming matrices and receiver filtering matrices according to the interference alignment concept. The proposed algorithms can exhibit a substantial performance improvement compared to the conventional orthogonal transmission schemes.

  • 305.
    Farhadi, Hamed
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Wang, Chao
    Tongji University.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Distributed Transceiver Design and Power Control for Wireless MIMO Interference Networks2015In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 14, no 3, p. 1199-1212, article id 7055983Article in journal (Refereed)
    Abstract [en]

    This paper considers distributed transceiver design and power control for K-user multiple-input-multiple-output interference networks. Each source intends to send multiple independent data streams to its corresponding destination where the number of data streams coincides with the degrees of freedom of the network. Each data stream is encoded at a fixed data rate, whereas different streams can be encoded at possibly different rates. We assume that only local channel side information (i.e., knowledge related to channels directly connected to a terminal) can be acquired by each terminal. We propose iterative algorithms to perform both power control and transceiver design. Transmitter beamforming matrices and receiver filtering matrices are designed to maximize signal-to-interference-plus-noise ratio corresponding to each stream, and a power control scheme is performed to assign the minimum power to each encoded data stream such that successful communication can be guaranteed. The proposed algorithms exhibit a substantial performance improvement compared with the conventional orthogonal transmission schemes.

  • 306.
    Farhadi, Hamed
    et al.
    Chalmers University of Technology, Gothenburg, Sweden.
    Wang, Chao
    Tongji University, Shanghai, China.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ergodic Interference Alignment with Limited Feedback: Power Control and Rate Adaptation2015In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 4, no 12, p. 6679-6694Article in journal (Refereed)
    Abstract [en]

    Considering the time-varying K-user single-antenna interference channel (IC), it has been shown that, when terminals have perfect global channel state information (CSI) and they can tolerate asymptotically long delay, applying an ergodic interference alignment (EIA) scheme can achieve half of the interference-free achievable rate. However, in practice obtaining such CSI is challenging, and only a limited delay is acceptable. This paper addresses data transmission over the IC by taking these concerns into account. Specifically, we consider the case that each transmitter attains only quantized CSI via limited feedback signals. This causes imperfect interference alignment and a degraded performance. We propose adaptive schemes to compensate the impact of the CSI uncertainties. We first study a power control problem which concerns how to communicate at fixed rates using minimum transmit powers. A power control algorithm is used to reach the solution. Next, we address a throughput maximization problem when the transmit powers are fixed. Through the analysis of system outage probability, we propose a rate adaptation scheme to maximize throughput. Finally, we quantify the throughput loss in delay-limited systems. Our results show that, even with limited feedback, performing the EIA scheme with proper power control or rate adaptation strategies can still outperform conventional orthogonal transmission approaches.

  • 307.
    Farhadi, Hamed
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Wang, Chao
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Power Control in Wireless Interference Networks with Limited Feedback2012In: International Symposium on Wireless Communication Systems (ISWCS), 2012, IEEE conference proceedings, 2012, p. 671-675Conference paper (Refereed)
    Abstract [en]

    This paper addresses a power control problem in a wireless time-varying K-user interference network. Each transmitter intends to communicate to its desired receiver at afixed rate. Quantized channel gains are globally available through limited feedback signals. To eliminate multi-user interference, interference alignment scheme is performed based on the imperfect channel knowledge. The communication quality is affected by the channel quantization errors and interference leakage. We proposea power control algorithm, aiming to guarantee successful transmissions of each user while minimizing the transmission powerof the network. Our results show that even with limited number of feedback bits, by performing power control the considered interference alignment scheme can outperform the conventional time-division-multiple-access scheme.

  • 308.
    Farhadi, Hamed
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Zaidi, Ali
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Fischione, Carlo
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Wang, Chao
    School of Electronics and Information Engineering, Tongji University, Shanghai, China.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Distributed Interference Alignment and Power Control for Wireless MIMO Interference Networks with Noisy Channel State Information2013In: 2013 First International Black Sea Conference on Communications and Networking (BlackSeaCom), IEEE conference proceedings, 2013, p. 23-27Conference paper (Refereed)
    Abstract [en]

    This paper considers a multi-input multi-output(MIMO) interference network in which each transmitter intendsto communicate with its dedicated receiver at a certain fixed rate. It is known that when perfect CSI is available at each terminal, the interference alignment technique can be applied to align theinterference signals at each receivers in a subspace independent of the desired signal subspace. The impact of interference canhence be eliminated. In practice, however, terminals in general can acquire only noisy CSI. Interference alignment cannot be perfectly performed to avoid interference leakage in the signal subspace. Thus, the quality of each communication link dependson the transmission power of the unintended transmitters. Tosolve this problem, we propose an iterative algorithm to performstochastic power control and transceiver design based on onlynoisy local CSI. The transceiver design is conducted based on the interference alignment concept, and the power control seeks solutions of efficiently assigning transmit powers to provide successful communications for all transmitter-receiver pairs.

  • 309. Farokhi, F.
    et al.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Shames, I.
    Cantoni, M.
    Quadratic Gaussian privacy games2016In: Proceedings of the IEEE Conference on Decision and Control, IEEE conference proceedings, 2016, p. 4505-4510Conference paper (Refereed)
    Abstract [en]

    A game-theoretic model for analysing the effects of privacy on strategic communication between agents is devised. In the model, a sender wishes to provide an accurate measurement of the state to a receiver while also protecting its private information (which is correlated with the state) private from a malicious agent that may eavesdrop on its communications with the receiver. A family of nontrivial equilibria, in which the communicated messages carry information, is constructed and its properties are studied.

  • 310. Feldbauer, C.
    et al.
    Kubin, G.
    Kleijn, W. Bastiaan
    KTH, School of Electrical Engineering (EES), Sound and Image Processing.
    Anthropomorphic coding of speech and audio: A model inversion approach2005In: EURASTP journal an applied signal processing, ISSN 1110-8657, E-ISSN 1687-0433, Vol. 2005, no 9, p. 1334-1349Article in journal (Refereed)
    Abstract [en]

    Auditory modeling is a well-established methodology that provides insight into human perception and that facilitates the extraction of signal features that are most relevant to the listener. The aim of this paper is to provide a tutorial on perceptual speech and audio coding using an invertible auditory model. In this approach, the audio signal is converted into an auditory representation using an invertible auditory model. The auditory representation is quantized and coded. Upon decoding, it is then transformed back into the acoustic domain. This transformation converts a complex distortion criterion into a simple one, thus facilitating quantization with low complexity. We briefly review past work on auditory models and describe in more detail the components of our invertible model and its inversion procedure, that is, the method to reconstruct the signal from the output of the auditory model. We summarize attempts to use the auditory representation for low-bit-rate coding. Our approach also allows the exploitation of the inherent redundancy of the human auditory system for the purpose of multiple description (joint source-channel) coding.

  • 311.
    Fikos, George
    et al.
    Physics Dept., Aristotle University of Thessaloniki, Greece.
    Nalpantidis, Lazaros
    Physics Dept., Aristotle University of Thessaloniki, Greece.
    Siskos, Stylianos
    Physics Dept., Aristotle University of Thessaloniki, Greece.
    A 32x32 smart photo-array with minimum-size FGMOS for amplification and FPN reduction2005In: SiPS 2005: IEEE Workshop on Signal Processing Systems - Design and Implementation, 2005, Vol. 2005, p. 199-203Conference paper (Refereed)
    Abstract [en]

    A logarithmic response photoarray, incorporating two minimum-sized floating-gate mosfets (FGMOS) in its basic photocell, is presented. Exploiting the same FGMOS as an analog memory element for Fixed Pattern Noise (FPN) reduction, and as an inherent amplifying element, is, to our knowledge, novel. The above features, favored by the use of small control gate capacitors, lead to area reduction. The circuit behavior is analyzed and experimental results of a 32×32 prototype array implemented in AMS 0.6Όm CMOS technology, are presented and discussed.

  • 312.
    Fikos, George
    et al.
    Physics Dept., Aristotle University of Thessaloniki, Greece.
    Nalpantidis, Lazaros
    Physics Dept., Aristotle University of Thessaloniki, Greece.
    Siskos, Stylianos
    Physics Dept., Aristotle University of Thessaloniki, Greece.
    A compact APS with FPN reduction and focusing criterion using FGMOS photocell2008In: Sensors and Actuators A-Physical, ISSN 0924-4247, E-ISSN 1873-3069, Vol. 147, no 2, p. 419-424Article in journal (Refereed)
    Abstract [en]

    Prior implementations of CMOS photoarrays with floating-gate MOS (FGMOS), substituted one MOS with a FGMOS in, otherwise, well-established photocell structures. Bipolar manipulation of the floating-gate's charge requires special structures to achieve fixed pattern noise (FPN) suppression. The control capacitor accompanying the FGMOS, needed to be quite larger than the MOS parasitic capacitances, resulting in increased area. Also, output amplification was dealt separately, by additional amplification cells. The proposed logarithmic CMOS photoarray, carefully incorporates two FGMOS in each photocell, favoring the use of minimum control-gate capacitance, achieving area reduction. Unipolar manipulation of floating-gate charge is achieved without special circuitry, preserving FPN suppression. Simultaneously, output amplification is achieved by exploiting the same FGMOS's inherent processing capabilities. A very simple circuit providing a focusing function was also incorporated and successfully tested. Additionally, global normalization towards the average photocurrent, make the circuit ideal preprocessor for image recognition tasks. Experimental results from a 32 × 32 array in AMS 0.6 Όm CMOS technology support the theoretical analysis. © 2008 Elsevier B.V. All rights reserved.

  • 313.
    Fikos, George
    et al.
    Physics Dept., Aristotle University of Thessaloniki, Greece.
    Nalpantidis, Lazaros
    Physics Dept., Aristotle University of Thessaloniki, Greece.
    Siskos, Stylianos
    Physics Dept., Aristotle University of Thessaloniki, Greece.
    A low-voltage, analog power-law function generator2006In: 2006 IEEE INTERNATIONAL SYMPOSIUM ON CIRCUITS AND SYSTEMS, VOLS 1-11, PROCEEDINGS, NEW YORK: IEEE , 2006, p. 3818-3821Conference paper (Refereed)
    Abstract [en]

    A simple low voltage circuit topology able to generate any positive real number power-law function is presented. The proposed circuit exploits BJTs and is based on piecewise linear approximation of the nonlinear function to be generated. An in-depth mathematical analysis is deployed. The instances of a squarer, a cube-law, a square rooting and cube rooting circuit are thoroughly examined through simulation. The obtained results verify the theoretical calculations.

  • 314. Flam, J. T.
    et al.
    Zachariah, Dave
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Vehkaperä, mikko
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Chatterjee, Saikat
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    The linear model under mixed gaussian inputs: Designing the transfer matrix2013In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 61, no 21, p. 5247-5259Article in journal (Refereed)
    Abstract [en]

    Suppose a linear model Y = Hx+n, where inputs x, n are independent Gaussian mixtures. The problem is to design the transfer matrix so as to minimize the mean square error (MSE) when estimating x from . This problem has important applications, but faces at least three hurdles. Firstly, even for a fixed H, the minimum MSE (MMSE) has no analytical form. Secondly, theMMSE is generally not convex in . Thirdly, derivatives of the MMSEw.r.t. are hard to obtain. This paper casts theproblemas a stochastic program and invokes gradient methods. The study is motivated by two applications in signal processing. One concerns the choice of error-reducing precoders; the other deals with selection of pilot matrices for channel estimation. In either setting, our numerical results indicate improved estimation accuracy-markedly better than those obtained by optimal design based on standard linear estimators. Some implications of the non-convexities of the MMSE are noteworthy, yet, to our knowledge, not well known. For example, there are cases in which more pilot power is detrimental for channel estimation. This paper explains why.

  • 315.
    Flierl, Markus
    et al.
    Stanford University.
    Girod, Bernd
    Stanford University.
    Multiview Video Compression: Exploiting Inter-Image Similarities2007In: IEEE signal processing magazine (Print), ISSN 1053-5888, E-ISSN 1558-0792, Vol. 24, no 6, p. 66-76Article in journal (Refereed)
    Abstract [en]

    Due to the vast raw bit rate of multiview video, efficient compression techniques are essential for 3D scene communication. As the video data originate from the same scene, the inherent similarities of the multiview imagery are exploited for efficient compression. These similarities can be classified into two types, inter-view similarity between adjacent camera views and temporal similarity between temporally successive images of each video.

  • 316.
    Flierl, Markus
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Girod, Bernd
    Stanford University.
    Vandergheynst, Pierre
    EPFL.
    Image transform for video coding2006Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    A method is disclosed for decomposing a set of even and odd pictures into low-band and high-band pictures respectively in a image decomposing unit, in which the even picture is used by at least two prediction motion compensators on which the output signal of each prediction motion compensator is scaled according to the number of prediction motion compensators. The method includes calculating the high-band picture by subtracting from the odd picture the scaled motion-compensated signals and using the high-band picture in the at least two update motion compensators, the output signal of each update motion compensator being scaled according to the number of update motion compensators. Finally, the low-band picture is calculated by adding the scaled update motion-compensated signals to the even picture.

  • 317.
    Flierl, Markus
    et al.
    KTH, School of Electrical Engineering (EES), Sound and Image Processing.
    Vandergheynst, Pierre
    EPFL.
    Method for spatially scalable video coding2004Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    A method for decomposing a digital image at resolution R and MR into a set of spatial sub-bands of resolution R and MR where MR>R and where the high-band at resolution MR is calculated by subtracting the filtered and up-sampled image at resolution R from the image at resolution MR and where the spatial low-band at resolution R is calculated by adding the filtered and down-sampled spatial high-band to the image at resolution R and where a rational factor for up-and down-sampling M is determined by the resolution ratio.

  • 318. Floor, P. A.
    et al.
    Kim, A.
    Ramstad, T.
    Balasingham, I.
    Wernersson, N.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Transmitting multiple correlated gaussian sources over a Gaussian MAC using delay-free mappings2011In: ISABEL '11 Proceedings of the 4th International Symposium on Applied Sciences in Biomedical and Communication Technologies, 2011Conference paper (Refereed)
    Abstract [en]

    In this paper, we study the problem of communicating multiple correlated Gaussian memoryless sources over a Gaussian Multiple Access Channel (GMAC). We focus on distributed delay-free, low complexity, joint source-channel coding (JSCC) solutions to the problem. Theoretical performance bounds are derived and linear and nonlinear JSCC schemes are evaluated. The main contribution is a nonlinear hybrid discrete-analog mapping based on distributed quantization and a linear continuous mapping named Distributed Quantizer Linear Coder (DQLC). The proposed scheme shows promising performance which improve with increasing correlation and is robust against variations in noise level.

  • 319. Flåm, John
    et al.
    Jaldén, Joakim
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Chatterjee, Saikat
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Gaussian mixture modeling for source localization2011In: ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings, 2011, p. 2604-2607Conference paper (Refereed)
    Abstract [en]

    Exploiting prior knowledge, we use Bayesian estimation to localize a source heard by a fixed sensor network. The method has two main aspects: Firstly, the probability density function (PDF) of a function of the source location is approximated by a Gaussian mixture model (GMM). This approximation can theoretically be made arbitrarily accurate, and allows a closed form minimum mean square error (MMSE) estimator for that function. Secondly, the source location is retrieved by minimizing the Euclidean distance between the function and its MMSE estimate using a gradient method. Our method avoids the issues of a numerical MMSE estimator but shows comparable accuracy.

  • 320. Flåm, John
    et al.
    Vehkaperä, Mikko
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Zachariah, Dave
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Tsakonas, Efthymios
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Mean square error reduction by precoding of mixed Gaussian input2012In: 2012 International Symposium on Information Theory and Its Applications, ISITA 2012, 2012, p. 81-85Conference paper (Refereed)
    Abstract [en]

    Suppose a vector of observations y = Hx + n stems from independent inputs x and n, both of which are Gaussian Mixture (GM) distributed, and that H is a fixed and known matrix. This work focuses on the design of a precoding matrix, F, such that the model modifies to z = HFx + n. The goal is to design F such that the mean square error (MSE) when estimating x from z is smaller than when estimating x from y. We do this under the restriction E[(Fx)TFx] ≤ PT, that is, the precoder cannot exceed an average power constraint. Although the minimum mean square error (MMSE) estimator, for any fixed F, has a closed form, the MMSE does not under these settings. This complicates the design of F. We investigate the effect of two different precoders, when used in conjunction with the MMSE estimator. The first is the linear MMSE (LMMSE) precoder. This precoder will be mismatched to the MMSE estimator, unless x and n are purely Gaussian variates. We find that it may provide MMSE gains in some setting, but be harmful in others. Because the LMMSE precoder is particularly simple to obtain, it should nevertheless be considered. The second precoder we investigate, is derived as the solution to a stochastic optimization problem, where the objective is to minimize the MMSE. As such, this precoder is matched to the MMSE estimator. It is derived using the KieferWolfowitz algorithm, which moves iteratively from an initially chosen F0 to a local minimizer F*. Simulations indicate that the resulting precoder has promising performance.

  • 321.
    Folkesson, John
    KTH, School of Computer Science and Communication (CSC), Centres, Centre for Autonomous Systems, CAS. KTH, School of Computer Science and Communication (CSC), Computer Vision and Active Perception, CVAP.
    Robustness of the Quadratic Antiparticle Filter forRobot Localization2011In: European Conference on Mobile Robots / [ed] Achim J. Lilienthal and Tom Duckett, 2011, p. 297-302Conference paper (Refereed)
    Abstract [en]

    Robot localization using odometry and feature measurementsis a nonlinear estimation problem. An efficient solutionis found using the extended Kalman filter, EKF. The EKFhowever suffers from divergence and inconsistency when thenonlinearities are significant. We recently developed a new typeof filter based on an auxiliary variable Gaussian distributionwhich we call the antiparticle filter AF as an alternative nonlinearestimation filter that has improved consistency and stability. TheAF reduces to the iterative EKF, IEKF, when the posterior distributionis well represented by a simple Gaussian. It transitions to amore complex representation as required. We have implementedan example of the AF which uses a parameterization of the meanas a quadratic function of the auxiliary variables which we callthe quadratic antiparticle filter, QAF. We present simulationof robot feature based localization in which we examine therobustness to bias, and disturbances with comparison to the EKF.

  • 322.
    Folkesson, John
    KTH, School of Computer Science and Communication (CSC), Centres, Centre for Autonomous Systems, CAS. KTH, School of Computer Science and Communication (CSC), Computer Vision and Active Perception, CVAP.
    The Antiparticle Filter: an Adaptive Nonlinear Estimator2011In: International Symposium of Robotics Research, 2011Conference paper (Refereed)
    Abstract [en]

    We introduce the antiparticle filter, AF, a new type of recursive Bayesian estimator that is unlike either the extended Kalman Filter, EKF, unscented Kalman Filter, UKF or the particle filter PF. We show that for a classic problem of robot localization the AF can substantially outperform these other filters in some situations. The AF estimates the posterior distribution as an auxiliary variable Gaussian which gives an analytic formula using no random samples. It adaptively changes the complexity of the posterior distribution as the uncertainty changes. It is equivalent to the EKF when theuncertainty is low while being able to represent non-Gaussian distributions as the uncertainty increases. The computation time can be much faster than a particle filter for the same accuracy. We have simulated comparisons of two types of AF to the EKF, the iterative EKF, the UKF, an iterative UKF, and the PF demonstrating that AF can reduce the error to a consistent accurate value.

  • 323.
    Fosgerau, Mogens
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Centres, Centre for Transport Studies, CTS. Technical University of Denmark, Denmark.
    Borjesson, Maria
    KTH, School of Architecture and the Built Environment (ABE), Centres, Centre for Transport Studies, CTS.
    Manipulating a stated choice experiment2015In: Journal of Choice Modelling, ISSN 1755-5345, E-ISSN 1755-5345, Vol. 16, p. 43-49Article in journal (Refereed)
    Abstract [en]

    This paper considers the design of a stated choice experiment intended to measure the marginal rate of substitution (MRS) between cost and an attribute such as time using a conventional logit model. Focusing the experimental design on some target MRS will bias estimates towards that value. The paper shows why this happens. The resulting estimated MRS can then be manipulated by adapting the target MRS in the experimental design.

  • 324. Freni, A.
    et al.
    Lindmark, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Maci, S.
    Mariottini, F.
    The european school of antennas: A new model of distributed PhD school2005Conference paper (Refereed)
  • 325.
    Friberg, Anders
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Speech, Music and Hearing, TMH.
    Lindeberg, Tony
    KTH, School of Electrical Engineering and Computer Science (EECS), Computational Science and Technology (CST).
    Hellwagner, Martin
    KTH, School of Electrical Engineering and Computer Science (EECS), Speech, Music and Hearing, TMH.
    Helgason, Pétur
    KTH, School of Electrical Engineering and Computer Science (EECS), Speech, Music and Hearing, TMH.
    Salomão, Gláucia Laís
    KTH, School of Electrical Engineering and Computer Science (EECS), Speech, Music and Hearing, TMH.
    Elovsson, Anders
    KTH, School of Electrical Engineering and Computer Science (EECS), Speech, Music and Hearing, TMH.
    Lemaitre, Guillaume
    Institute for Research and Coordination in Acoustics and Music, Paris, France.
    Ternström, Sten
    KTH, School of Electrical Engineering and Computer Science (EECS), Speech, Music and Hearing, TMH.
    Prediction of three articulatory categories in vocal sound imitations using models for auditory receptive fields2018In: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 144, no 3, p. 1467-1483Article in journal (Refereed)
    Abstract [en]

    Vocal sound imitations provide a new challenge for understanding the coupling between articulatory mechanisms and the resulting audio. In this study, we have modeled the classification of three articulatory categories, phonation, supraglottal myoelastic vibrations, and turbulence from audio recordings. Two data sets were assembled, consisting of different vocal imitations by four professional imitators and four non-professional speakers in two different experiments. The audio data were manually annotated by two experienced phoneticians using a detailed articulatory description scheme. A separate set of audio features was developed specifically for each category using both time-domain and spectral methods. For all time-frequency transformations, and for some secondary processing, the recently developed Auditory Receptive Fields Toolbox was used. Three different machine learning methods were applied for predicting the final articulatory categories. The result with the best generalization was found using an ensemble of multilayer perceptrons. The cross-validated classification accuracy was 96.8 % for phonation, 90.8 % for supraglottal myoelastic vibrations, and 89.0 % for turbulence using all the 84 developed features. A final feature reduction to 22 features yielded similar results.

  • 326.
    Frid, Emma
    et al.
    KTH, School of Computer Science and Communication (CSC), Media Technology and Interaction Design, MID.
    Moll, Jonas
    Uppsala University.
    Bresin, Roberto
    KTH, School of Computer Science and Communication (CSC), Media Technology and Interaction Design, MID.
    Sallnäs Pysander, Eva-Lotta
    KTH, School of Computer Science and Communication (CSC), Media Technology and Interaction Design, MID.
    Haptic feedback combined with movement sonification using a friction sound improves task performance in a virtual throwing task2018In: Journal on Multimodal User Interfaces, ISSN 1783-7677, E-ISSN 1783-8738Article in journal (Refereed)
    Abstract [en]

    In this paper we present a study on the effects of auditory- and haptic feedback in a virtual throwing task performed with a point-based haptic device. The main research objective was to investigate if and how task performance and perceived intuitiveness is affected when interactive sonification and/or haptic feedback is used to provide real-time feedback about a movement performed in a 3D virtual environment. Emphasis was put on task solving efficiency and subjective accounts of participants’ experiences of the multimodal interaction in different conditions. The experiment used a within-subjects design in which the participants solved the same task in different conditions: visual-only, visuohaptic, audiovisual and audiovisuohaptic. Two different sound models were implemented and compared. Significantly lower error rates were obtained in the audiovisuohaptic condition involving movement sonification based on a physical model of friction, compared to the visual-only condition. Moreover, a significant increase in perceived intuitiveness was observed for most conditions involving haptic and/or auditory feedback, compared to the visual-only condition. The main finding of this study is that multimodal feedback can not only improve perceived intuitiveness of an interface but that certain combinations of haptic feedback and movement sonification can also contribute with performance-enhancing properties. This highlights the importance of carefully designing feedback combinations for interactive applications.

  • 327. Frid, Henrik
    et al.
    Jonsson, B. Lars G.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Compensation of radome effects in small airborne monopulse arrays by convex optimization2018In: IET Conference Publications, Institution of Engineering and Technology , 2018, no CP741Conference paper (Refereed)
    Abstract [en]

    The quality of small array antennas in airborne monopulse systems can be significantly reduced by the radome. We therefore present a convex optimization approach to minimize radome effects in monopulse arrays. This is achieved by using active element patterns in the optimization to determine the excitation weights. Simulation results for a BoR array with 48 elements and an extended hemispherical radome are presented. We demonstrate that it is possible to reduce the side-lobe level by 3.5 dB by taking radome effects into account in the optimization. This approach also results in an increased gain, particularly at large scan angles. Furthermore, the presented approach allows the monopulse slope to be indirectly specified as a design parameter. It is shown that the trade-off between the monopulse slope coefficient and the side-lobe level is approximately linear.

  • 328.
    Gaiarin, Simone
    et al.
    DTU Fotonik, Technical University of Denmark, Kgs. Lyngby, 2800, Denmark.
    Pang, Xiaodan
    Acreo Swedish ICT AB, Isafjordsgatan 22, Kista, 164 40, Sweden.
    Ozolins, Oskars
    Acreo Swedish ICT AB, Isafjordsgatan 22, Kista, 164 40, Sweden.
    Jones, Rasmus T
    DTU Fotonik, Technical University of Denmark, Kgs. Lyngby, 2800, Denmark.
    Da Silva, Edson Porto
    DTU Fotonik, Technical University of Denmark, Kgs. Lyngby, 2800, Denmark.
    Schatz, Richard
    KTH, School of Engineering Sciences (SCI), Applied Physics, Photonics.
    Westergren, Urban
    KTH, School of Engineering Sciences (SCI), Applied Physics, Photonics.
    Popov, Sergei
    KTH, School of Engineering Sciences (SCI), Applied Physics, Photonics.
    Jacobsen, Gunnar
    Acreo Swedish ICT AB, Isafjordsgatan 22, Kista, 164 40, Sweden.
    Zibar, Darko
    DTU Fotonik, Technical University of Denmark, Kgs. Lyngby, 2800, Denmark.
    High speed PAM-8 optical interconnects with digital equalization based on neural network2016In: Asia Communications and Photonics Conference, Optical Society of America, 2016Conference paper (Refereed)
    Abstract [en]

    We experimentally evaluate a high-speed optical interconnection link with neural network equalization. Enhanced equalization performances are shown comparing to standard linear FFE for an EML-based 32 GBd PAM-8 signal after 4-km SMF transmission.

  • 329. 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

  • 330. 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.

  • 331. 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.

  • 332. 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.

  • 333.
    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.

  • 334. 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)
  • 335.
    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.

  • 336.
    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.

  • 337. Garcia, Frederic
    et al.
    Aouada, Djamila
    Mirbach, Bruno
    Solignac, Thomas
    Ottersten, Björn
    Interdisciplinary Centre for Security, Reliability and Trust, University of Luxembourg, Luxembourg.
    Unified multi-lateral filter for real-time depth map enhancement2015In: Image and Vision Computing, ISSN 0262-8856, E-ISSN 1872-8138, Vol. 41, p. 26-41Article in journal (Refereed)
    Abstract [en]

    This paper proposes a unified multi-lateral filter to efficiently increase the spatial resolution of low-resolution and noisy depth maps in real-time. Time-of-Flight (ToF) cameras have become a very promising alternative to stereo-based range sensing systems as they provide depth measurements at a high frame rate. However, there are actually two main drawbacks that restrict their use in a wide range of applications; namely, their fairly low spatial resolution as well as the amount of noise within the depth estimation. In order to address these drawbacks, we propose a new approach based on sensor fusion. That is, we couple a ToF camera of low-resolution with a 2-D camera of higher resolution to which the low-resolution depth map will be efficiently upsampled. In this paper, we first review the existing depth map enhancement approaches based on sensor fusion and discuss their limitations. We then propose a unified multi-lateral filter that accounts for the inaccuracy of depth edges position due to the low-resolution ToF depth maps. By doing so, unwanted artefacts such as texture copying and edge blurring are almost entirely eliminated. Moreover, the proposed filter is configurable to behave as most of the alternative depth enhancement approaches. Using a convolution-based formulation and data quantization and downsampling, the described filter has been effectively and efficiently implemented for dynamic scenes in real-time applications. The experimental results show a sensitive qualitative as well as quantitative improvement on raw depth maps, outperforming state-of-the-art multi-lateral filters. © 2015 Elsevier B.V. All rights reserved.

  • 338.
    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.

  • 339. Garcia-Garcia, L.
    et al.
    Lindmark, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Jaldén, Niklas
    KTH, School of Electrical Engineering (EES), Signal Processing.
    De Haro, L.
    Multi-user MIMO capacity from measurements in indoor environment with in- and outdoor base stations2007In: 2nd European Conference on Antennas and Propagation (EuCAP 2007), 2007, no 11961Conference paper (Refereed)
    Abstract [en]

    MIMO systems have been widely studied in recent years, and several characteristics of the radio channel have been studied and analysed. One aspect of great interest is the analysis and optimization of parameters regarding the base station when multiple antennas are used at the receiver and the transmitter. Moreover, when not only the link-level but also the system- level is to be studied, the system performance when multiple users are considered is of importance. By using the channel measurements obtained with different base station locations and multiple routes in an indoor scenario, we present in this paper the results for a multi-user MIMO system when different possibilities in location and signal combination or cooperation for base stations are compared. Results are shown in terms of sum-capacity, which is evaluated for different transmit methods (with and without CSI) and base station locations, and it is compared with the capacity in a single user system (with and without interference).

  • 340. Gautam, S.
    et al.
    Lagunas, E.
    Chatzinotas, S.
    Ottersten, Björn
    Relay Selection and Resource Allocation for SWIPT in Multi-User OFDMA Systems2019In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 18, no 5, p. 2493-2508Article in journal (Refereed)
  • 341. Gautam, S.
    et al.
    Vu, T. X.
    Chatzinotas, S.
    Ottersten, Björn
    Cache-Aided Simultaneous Wireless Information and Power Transfer (SWIPT) With Relay Selection2019In: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008, Vol. 37, no 1, p. 187-201Article in journal (Refereed)
  • 342.
    Georgakis, Apostolos
    et al.
    Ericsson.
    Rana, Pravin Kumar
    KTH, School of Electrical Engineering (EES), Sound and Image Processing.
    Radulovic, Ivana
    Ericsson.
    3DTV Exploration Experiments (EE1 & EE4) on the Lovebird1 Data Set2009Report (Other (popular science, discussion, etc.))
    Abstract [en]

    This contribution describes the results to two sets of 3DTV exploration experiments undertaken by Ericsson using the Lovebird 1 sequence defined in the last MPEG meeting in London (see w10720). These sets cover both EE1 for depth estimation and view synthesis and EE4 for coding efficiency.

  • 343. 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.

  • 344.
    Gerkmann, Timo
    KTH, School of Electrical Engineering (EES), Sound and Image Processing.
    Cepstral Weighting for Speech Dereverberation Without Musical Noise2011In: Proceedings European Signal Processing Conference, 2011, p. 2309-2313Conference paper (Refereed)
    Abstract [en]

    We present an effective way to reduce musical noise in binaural speech dereverberation algorithms based on an instantaneous weighting of the cepstrum. We propose this instantaneous technique, as temporal smoothing techniques result ina smearing of the signal over time and are thus expected to reduce the dereverberation performance. For the instantaneousweighting function we compute the a posteriori probabilitythat a cepstral coefficient represents the speech spectral structure. The proposed algorithm incorporates a priori knowledge about the speech spectral structure by training the parameters of the respective likelihood function offline using aspeech database. The proposed algorithm employs neither avoiced/unvoiced detection nor a fundamental period estimator and is shown to outperform an algorithm without cepstralprocessing in terms of a higher signal-to-interference ratio, alower bark spectral distortion, and a lower log kurtosis ratio, indicating a reduction of musical noise.

  • 345.
    Gerkmann, Timo
    et al.
    KTH, School of Electrical Engineering (EES).
    Hendriks, Richard
    Delft University of Technology.
    Noise Power Estimation Based on the Probability of Speech Presence2011In: Proceedings IEEE Workshop on Applications of Signal Processing to Audio and Acoustics, 2011, p. 145-148Conference paper (Refereed)
    Abstract [en]

    In this paper, we analyze the minimum mean square error (MMSE) based spectral noise power estimator [1] and present an improve-ment. We will show that the MMSE based spectral noise powerestimate is only updated when the a posteriori signal-to-noise ratio (SNR) is lower than one. This threshold on the a posteriori SNRcan be interpreted as a voice activity detector (VAD).We propose in this work to replace the hard decision of theVAD by a soft speech presence probability (SPP). We show thatby doing so, the proposed estimator does not require a bias cor-rection and safety-net as is required by the MMSE estimator pre-sented in [1]. At the same time, the proposed estimator maintainsthe quick noise tracking capability which is characteristic for theMMSE noise tracker, results in less noise power overestimation andis computationally less expensive.

  • 346.
    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.

  • 347.
    Ghadimi, Euhanna
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Accelerating Convergence of Large-scale Optimization Algorithms2015Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Several recent engineering applications in multi-agent systems, communication networks, and machine learning deal with decision problems that can be formulated as optimization problems. For many of these problems, new constraints limit the usefulness of traditional optimization algorithms. In some cases, the problem size is much larger than what can be conveniently dealt with using standard solvers. In other cases, the problems have to be solved in a distributed manner by several decision-makers with limited computational and communication resources. By exploiting problem structure, however, it is possible to design computationally efficient algorithms that satisfy the implementation requirements of these emerging applications.

    In this thesis, we study a variety of techniques for improving the convergence times of optimization algorithms for large-scale systems. In the first part of the thesis, we focus on multi-step first-order methods. These methods add memory to the classical gradient method and account for past iterates when computing the next one. The result is a computationally lightweight acceleration technique that can yield significant improvements over gradient descent. In particular, we focus on the Heavy-ball method introduced by Polyak. Previous studies have quantified the performance improvements over the gradient through a local convergence analysis of twice continuously differentiable objective functions. However, the convergence properties of the method on more general convex cost functions has not been known. The first contribution of this thesis is a global convergence analysis of the Heavy- ball method for a variety of convex problems whose objective functions are strongly convex and have Lipschitz continuous gradient. The second contribution is to tailor the Heavy- ball method to network optimization problems. In such problems, a collection of decision- makers collaborate to find the decision vector that minimizes the total system cost. We derive the optimal step-sizes for the Heavy-ball method in this scenario, and show how the optimal convergence times depend on the individual cost functions and the structure of the underlying interaction graph. We present three engineering applications where our algorithm significantly outperform the tailor-made state-of-the-art algorithms.

    In the second part of the thesis, we consider the Alternating Direction Method of Multipliers (ADMM), an alternative powerful method for solving structured optimization problems. The method has recently attracted a large interest from several engineering communities. Despite its popularity, its optimal parameters have been unknown. The third contribution of this thesis is to derive optimal parameters for the ADMM algorithm when applied to quadratic programming problems. Our derivations quantify how the Hessian of the cost functions and constraint matrices affect the convergence times. By exploiting this information, we develop a preconditioning technique that allows to accelerate the performance even further. Numerical studies of model-predictive control problems illustrate significant performance benefits of a well-tuned ADMM algorithm. The fourth and final contribution of the thesis is to extend our results on optimal scaling and parameter tuning of the ADMM method to a distributed setting. We derive optimal algorithm parameters and suggest heuristic methods that can be executed by individual agents using local information. The resulting algorithm is applied to distributed averaging problem and shown to yield substantial performance improvements over the state-of-the-art algorithms. 

  • 348.
    Ghadimi, Euhanna
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Shames, Iman
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Multi-Step Gradient Methods for Networked Optimization2013In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 61, no 21, p. 5417-5429Article in journal (Refereed)
    Abstract [en]

    We develop multi-step gradient methods for network-constrained optimization of strongly convex functions with Lipschitz-continuous gradients. Given the topology of the underlying network and bounds on the Hessian of the objective function, we determine the algorithm parameters that guarantee the fastest convergence and characterize situations when significant speed-ups over the standard gradient method are obtained. Furthermore, we quantify how uncertainty in problem data at design-time affects the run-time performance of the gradient method and its multi-step counterpart, and conclude that in most cases the multi-step method outperforms gradient descent. Finally, we apply the proposed technique to three engineering problems: resource allocation under network-wide budget constraint, distributed averaging, and Internet congestion control. In all cases, our proposed algorithms converge significantly faster than the state-of-the art.

  • 349. 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.

  • 350. Gharanjik, A.
    et al.
    Shankar, M. R. B.
    Zimmer, F.
    Ottersten, Björn
    Interdisciplinary Centre for Security, Reliability and Trust, University of Luxembourg.
    Centralized Rainfall Estimation Using Carrier to Noise of Satellite Communication Links2018In: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008, Vol. 36, no 5, p. 1065-1073Article in journal (Refereed)
    Abstract [en]

    In this paper, we present a centralized method for real-time rainfall estimation using carrier-to-noise power ratio ( C/N ) measurements from broadband satellite communication networks. The C/N data of both forward link and return link are collected by the gateway station from the user terminals in the broadband satellite communication network and stored in a database. The C/N for such Ka-band scenarios is impaired mainly by the rainfall. Using signal processing and machine learning techniques, we develop an algorithm for real-time rainfall estimation. Extracting relevant features from C/N , we use artificial neural network in order to distinguish the rain events from dry events. We then determine the signal attenuation corresponding to the rain events and examine an empirical relationship between rainfall rate and signal attenuation. Experimental results are promising and prove the high potential of satellite communication links for real environment monitoring, particularly rainfall estimation. © 1983-2012 IEEE.

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