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  • 1.
    Abarghouyi, Hadis
    et al.
    IUST, Sch Elect Engn, Tehran 1665973561, Iran.;MTNi Co, Tehran 1665973561, Iran..
    Razavizadeh, S. Mohammad
    IUST, Sch Elect Engn, Tehran 1684613114, Iran..
    Björnson, Emil
    Linköping Univ, Dept Elect Engn ISY, S-58183 Linköping, Sweden..
    QoE-Aware Beamforming Design for Massive MIMO Heterogeneous Networks2018In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 67, no 9, p. 8315-8323Article in journal (Refereed)
    Abstract [en]

    One of the main goals of the future wireless networks is improving the users' quality of experience (QoE). In this paper, we consider the problem of the QoE-based resource allocation in the downlink of a massive multiple-input multiple-output heterogeneous network. The network consists of a macrocell with a number of small cells embedded in it. The small cells' base stations (BSs) are equipped with a few antennas, while the macro BS is equipped with a massive number of antennas. We consider the two services Video and Web Browsing and design the beamforming vectors at the BSs. The objective is to maximize the aggregated mean opinion score (MOS) of the users under constraints on the BSs' powers and the required quality of service of the users. We also consider extra constraints on the QoE of users to more strongly enforce the QoE in the beamforming design. To reduce the complexity of the optimization problem, we suggest suboptimal and computationally efficient solutions. Our results illustrate that increasing the number of antennas at the BSs and also increasing the number of small cells' antennas in the network leads to a higher user satisfaction.

  • 2.
    Abdalmoaty, Mohamed
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Learning Stochastic Nonlinear Dynamical Systems Using Non-stationary Linear Predictors2017Licentiate thesis, monograph (Other academic)
    Abstract [en]

    The estimation problem of stochastic nonlinear parametric models is recognized to be very challenging due to the intractability of the likelihood function. Recently, several methods have been developed to approximate the maximum likelihood estimator and the optimal mean-square error predictor using Monte Carlo methods. Albeit asymptotically optimal, these methods come with several computational challenges and fundamental limitations.

    The contributions of this thesis can be divided into two main parts. In the first part, approximate solutions to the maximum likelihood problem are explored. Both analytical and numerical approaches, based on the expectation-maximization algorithm and the quasi-Newton algorithm, are considered. While analytic approximations are difficult to analyze, asymptotic guarantees can be established for methods based on Monte Carlo approximations. Yet, Monte Carlo methods come with their own computational difficulties; sampling in high-dimensional spaces requires an efficient proposal distribution to reduce the number of required samples to a reasonable value.

    In the second part, relatively simple prediction error method estimators are proposed. They are based on non-stationary one-step ahead predictors which are linear in the observed outputs, but are nonlinear in the (assumed known) input. These predictors rely only on the first two moments of the model and the computation of the likelihood function is not required. Consequently, the resulting estimators are defined via analytically tractable objective functions in several relevant cases. It is shown that, under mild assumptions, the estimators are consistent and asymptotically normal. In cases where the first two moments are analytically intractable due to the complexity of the model, it is possible to resort to vanilla Monte Carlo approximations. Several numerical examples demonstrate a good performance of the suggested estimators in several cases that are usually considered challenging.

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  • 3.
    Abdalmoaty, Mohamed
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Hjalmarsson, Håkan
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    A Simulated Maximum Likelihood Method for Estimation of Stochastic Wiener Systems2016In: 2016 IEEE 55th Conference on Decision and Control, CDC 2016, Institute of Electrical and Electronics Engineers (IEEE), 2016, p. 3060-3065, article id 7798727Conference paper (Refereed)
    Abstract [en]

    This paper introduces a simulation-based method for maximum likelihood estimation of stochastic Wienersystems. It is well known that the likelihood function ofthe observed outputs for the general class of stochasticWiener systems is analytically intractable. However, when the distributions of the process disturbance and the measurement noise are available, the likelihood can be approximated byrunning a Monte-Carlo simulation on the model. We suggest the use of Laplace importance sampling techniques for the likelihood approximation. The algorithm is tested on a simple first order linear example which is excited only by the process disturbance. Further, we demonstrate the algorithm on an FIR system with cubic nonlinearity. The performance of the algorithm is compared to the maximum likelihood method and other recent techniques.

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  • 4.
    Abdalmoaty, Mohamed
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Hjalmarsson, Håkan
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Application of a Linear PEM Estimator to a Stochastic Wiener-Hammerstein Benchmark Problem2018In: 18th IFAC Symposium on System Identification, 2018Conference paper (Refereed)
    Abstract [en]

    The estimation problem of stochastic Wiener-Hammerstein models is recognized to be challenging, mainly due to the analytical intractability of the likelihood function. In this contribution, we apply a computationally attractive prediction error method estimator to a real-data stochastic Wiener-Hammerstein benchmark problem. The estimator is defined using a deterministic predictor that is nonlinear in the input. The prediction error method results in tractable expressions, and Monte Carlo approximations are not necessary. This allows us to tackle several issues considered challenging from the perspective of the current mainstream approach. Under mild conditions, the estimator can be shown to be consistent and asymptotically normal. The results of the method applied to the benchmark data are presentedand discussed.

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    0028.pdf
  • 5.
    Abdalmoaty, Mohamed
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Hjalmarsson, Håkan
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Consistent Estimators of Stochastic MIMO Wiener Models based on Suboptimal Predictors2018Conference paper (Refereed)
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    fulltext
  • 6.
    Abdalmoaty, Mohamed
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Hjalmarsson, Håkan
    KTH, School of Electrical Engineering (EES), Automatic Control.
    On Re-Weighting, Regularization Selection, and Transient in Nuclear Norm Based Identification2015Conference paper (Refereed)
    Abstract [en]

    In this contribution, we consider the classical problem of estimating an Output Error model given a set of input-output measurements. First, we develop a regularization method based on the re-weighted nuclear norm heuristic. We show that the re-weighting improves the estimate in terms of better fit. Second, we suggest an implementation method that helps in eliminating the regularization parameters from the problem by introducing a constant based on a validation criterion. Finally, we develop a method for considering the effect of the transient when the initial conditions are unknown. A simple numerical example is used to demonstrate the proposed method in comparison to classical and another recent method based on the nuclear norm heuristic.

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    fulltext
  • 7.
    Abdalmoaty, Mohamed
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Hjalmarsson, Håkan
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Simulated Pseudo Maximum Likelihood Identification of Nonlinear Models2017In: The 20th IFAC World Congress, Elsevier, 2017, Vol. 50, p. 14058-14063Conference paper (Refereed)
    Abstract [en]

    Nonlinear stochastic parametric models are widely used in various fields. However, for these models, the problem of maximum likelihood identification is very challenging due to the intractability of the likelihood function. Recently, several methods have been developed to approximate the analytically intractable likelihood function and compute either the maximum likelihood or a Bayesian estimator. These methods, albeit asymptotically optimal, are computationally expensive. In this contribution, we present a simulation-based pseudo likelihood estimator for nonlinear stochastic models. It relies only on the first two moments of the model, which are easy to approximate using Monte-Carlo simulations on the model. The resulting estimator is consistent and asymptotically normal. We show that the pseudo maximum likelihood estimator, based on a multivariate normal family, solves a prediction error minimization problem using a parameterized norm and an implicit linear predictor. In the light of this interpretation, we compare with the predictor defined by an ensemble Kalman filter. Although not identical, simulations indicate a close relationship. The performance of the simulated pseudo maximum likelihood method is illustrated in three examples. They include a challenging state-space model of dimension 100 with one output and 2 unknown parameters, as well as an application-motivated model with 5 states, 2 outputs and 5 unknown parameters.

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  • 8.
    Abdalmoaty, Mohamed
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Hjalmarsson, Håkan
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Wahlberg, Bo
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    The Gaussian MLE versus the Optimally weighted LSE2020In: IEEE signal processing magazine (Print), ISSN 1053-5888, E-ISSN 1558-0792, Vol. 37, no 6, p. 195-199Article in journal (Refereed)
    Abstract [en]

    In this note, we derive and compare the asymptotic covariance matrices of two parametric estimators: the Gaussian Maximum Likelihood Estimator (MLE), and the optimally weighted Least-Squares Estimator (LSE). We assume a general model parameterization where the model's mean and variance are jointly parameterized, and consider Gaussian and non-Gaussian data distributions.

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  • 9.
    Abdalmoaty, Mohamed
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Rojas, Cristian R.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Hjalmarsson, Håkan
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Identication of a Class of Nonlinear Dynamical Networks2018Conference paper (Refereed)
    Abstract [en]

    Identifcation of dynamic networks has attracted considerable interest recently. So far the main focus has been on linear time-invariant networks. Meanwhile, most real-life systems exhibit nonlinear behaviors; consider, for example, two stochastic linear time-invariant systems connected in series, each of which has a nonlinearity at its output. The estimation problem in this case is recognized to be challenging, due to the analytical intractability of both the likelihood function and the optimal one-step ahead predictors of the measured nodes. In this contribution, we introduce a relatively simple prediction error method that may be used for the estimation of nonlinear dynamical networks. The estimator is defined using a deterministic predictor that is nonlinear in the known signals. The estimation problem can be defined using closed-form analytical expressions in several non-trivial cases, and Monte Carlo approximations are not necessarily required. We show, that this is the case for some block-oriented networks with no feedback loops and where all the nonlinear modules are polynomials. Consequently, the proposed method can be applied in situations considered challenging by current approaches. The performance of the estimation method is illustrated on a numerical simulation example.

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    0131.pdf
  • 10. Abdu, Tedros Salih
    et al.
    Kisseleff, Steven
    Lagunas, Eva
    Chatzinotas, Symeon
    Ottersten, Björn
    Interdisciplinary Centre for Security, Reliability and Trust, University of Luxembourg, Luxembourg, Luxembourg.
    Demand and Interference Aware Adaptive Resource Management for High Throughput GEO Satellite Systems2022In: IEEE Open Journal of the Communications Society, E-ISSN 2644-125X, Vol. 3, p. 759-775Article in journal (Refereed)
    Abstract [en]

    The scarce spectrum and power resources, the inter-beam interference, together with the high traffic demand, pose new major challenges for the next generation of Very High Throughput Satellite (VHTS) systems. Accordingly, future satellites are expected to employ advanced resource/interference management techniques to achieve high system spectrum efficiency and low power consumption while ensuring user demand satisfaction. This paper proposes a novel demand and interference aware adaptive resource management for geostationary (GEO) VHTS systems. For this, we formulate a multi-objective optimization problem to minimize the total transmit power consumption and system bandwidth usage while matching the offered capacity with the demand per beam. In this context, we consider resource management for a system with full-precoding, i.e., all beams are precoded; without precoding, i.e., no precoding is applied to any beam; and with partial precoding, i.e., only some beams are precoded. The nature of the problem is non-convex and we solve it by jointly using the Dinkelbach and Successive Convex Approximation (SCA) methods. The simulation results show that the proposed method outperforms the benchmark schemes. Specifically, we show that the proposed method requires low resource consumption, low computational time, and simultaneously achieves a high demand satisfaction.

  • 11. Abdu, Tedros Salih
    et al.
    Kisseleff, Steven
    Lagunas, Eva
    Grotz, Joel
    Chatzinotas, Symeon
    Ottersten, Björn
    Interdisciplinary Centre for Security, Reliability and Trust (SnT), University of Luxembourg, Luxembourg, Luxembourg.
    Demand-Aware Onboard Payload Processor Management for High Throughput NGSO Satellite Systems2023In: IEEE Transactions on Aerospace and Electronic Systems, ISSN 00189251, p. 1-18Article in journal (Refereed)
    Abstract [en]

    High-Throughput Satellite (HTS) systems with digital payload technology have been identified as a key enabler to support 5G/6G high-data connectivity with wider coverage area. The satellite community has extensively explored resource allocation methods to achieve this target. Typically, these methods do not consider the intrinsic architecture of the flexible satellite digital payload, which consists of multiple processors responsible for receiving, processing, and transmitting the signals. This paper presents a demand-aware onboard processor management scheme for broadband Non-Geostationary (NGSO) satellites. In this context, we formulate an optimization problem to minimize the number of active on-board processors while meeting the system constraints and user requirements. As the problem is non-convex, we solve it in two steps. First, we transform the problem into demand-driven bandwidth allocation while fixing the number of processors. Second, using the bandwidth allocation solution, we determine the required number of processors with two methods: 1) sequential optimization with the Branch & Bound method and 2) Bin Packing with Next Fit, First Fit, and Best Fit methods. Finally, we demonstrate the proposed methods with extensive numerical results. It is shown that the Branch & Bound, Best Fit, and First Fit methods manage the processors better than the Next Fit method. Furthermore, Branch & Bound requires fewer processors than the above methods.

  • 12. Abdullah, Zaid
    et al.
    Kisseleff, Steven
    Alves Martins, Wallace
    Chen, Gaojie
    Sanguinetti, Luca
    Ntontin, Konstantinos
    Papazafeiropoulos, Anastasios
    Chatzinotas, Symeon
    Ottersten, Björn
    University of Luxembourg, Luxembourg.
    Cooperative Hybrid Networks with Active Relays and RISs for B5G: Applications, Challenges, and Research Directions2022In: IEEE Wireless Communications, ISSN 15361284, p. 1-7Article in journal (Refereed)
    Abstract [en]

    Among the recent advances and innovations in wireless technologies, reconfigurable intelligent surfaces (RISs) have received much attention and are envisioned to be one of the enabling technologies for beyond 5G (B5G) networks. On the other hand, active (or classical) cooperative relays have played a key role in providing reliable and power-efficient communications in previous wireless generations. In this article, we focus on hybrid network architectures that amalgamate both active relays and RISs. The operation concept and protocols of each technology are first discussed. Subsequently, we present multiple use cases of cooperative hybrid networks where both active relays and RISs can coexist harmoniously for enhanced rate performance. Furthermore, a case study is provided which demonstrates the achievable rate performance of a communication network assisted by either an active relay, an RIS, or both, and with different relaying protocols. Finally, we provide the reader with the challenges and key research directions in this area.

  • 13.
    Abdullah, Zaid
    et al.
    Interdisciplinary Centre for Security, Reliability and Trust (Sn T), University of Luxembourg, L-1855, Luxembourg..
    Papazafeiropoulos, Anastasios
    Communications and Intelligent Systems Research Group, University of Hertfordshire, Hatfield AL10 9AB, U.K., and also with the SnT, University of Luxembourg, Luxembourg..
    Kisseleff, Steven
    Interdisciplinary Centre for Security, Reliability and Trust (Sn T), University of Luxembourg, L-1855, Luxembourg..
    Chatzinotas, Symeon
    Interdisciplinary Centre for Security, Reliability and Trust (Sn T), University of Luxembourg, L-1855, Luxembourg..
    Ottersten, Björn
    Interdisciplinary Centre for Security, Reliability and Trust (Sn T), University of Luxembourg, L-1855, Luxembourg..
    Impact of Phase-Noise and Spatial Correlation on Double-RIS-Assisted Multiuser MISO Networks2022In: IEEE Wireless Communications Letters, ISSN 2162-2337, E-ISSN 2162-2345, p. 1-1Article in journal (Refereed)
  • 14.
    Abedan Kondori, Farid
    et al.
    Department of Applied Physics and Electronics, Umeå University, Umea, Sweden.
    Yousefi, Shahrouz
    Department of Applied Physics and Electronics, Umeå University, Umea, Sweden.
    Smart Baggage in Aviation2011In: Proceedings - 2011 IEEE International Conferences on Internet of Things and Cyber, Physical and Social Computing, 2011Conference paper (Refereed)
    Abstract [en]

    Nowadays, the Internet has dramatically changed the way people take the normal course of actions. By the recent growth of the Internet, connecting different objects to users through mobile phones and computers is no longer a dream. Aviation industry is one of the areas which have a strong potential to benefit from the Internet of Things. Among many problems related to air travel, delayed and lost luggage are the most common and irritating. Therefore, this paper suggests anew baggage control system, where users can simply track their baggage at the airport to avoid losing them. Attaching a particular pattern on the bag, which can be detected and localized from long distance by an ordinary camera, users are able to track their baggage. The proposed system is much cheaper than previous implementations and does not require sophisticated equipment.

  • 15. Abedan Kondori, Farid
    et al.
    Yousefi, Shahrouz
    KTH, School of Computer Science and Communication (CSC), Media Technology and Interaction Design, MID.
    Li, Haibo
    KTH, School of Computer Science and Communication (CSC), Media Technology and Interaction Design, MID.
    Direct Head Pose Estimation Using Kinect-type Sensors2014In: Electronics Letters, ISSN 0013-5194, E-ISSN 1350-911XArticle in journal (Refereed)
  • 16. Abedan Kondori, Farid
    et al.
    Yousefi, Shahrouz
    KTH, School of Computer Science and Communication (CSC), Media Technology and Interaction Design, MID.
    Liu, Li
    Li, Haibo
    KTH, School of Computer Science and Communication (CSC), Media Technology and Interaction Design, MID. Nanjing University of Posts and Telecommunications, Nanjing, China .
    Head Operated Electric Wheelchair2014In: Proceedings of the IEEE Southwest Symposium on Image Analysis and Interpretation, 2014, p. 53-56Conference paper (Refereed)
    Abstract [en]

    Currently, the most common way to control an electric wheelchair is to use joystick. However, there are some individuals unable to operate joystick-driven electric wheelchairs due to sever physical disabilities, like quadriplegia patients. This paper proposes a novel head pose estimation method to assist such patients. Head motion parameters are employed to control and drive an electric wheelchair. We introduce a direct method for estimating user head motion, based on a sequence of range images captured by Kinect. In this work, we derive new version of the optical flow constraint equation for range images. We show how the new equation can be used to estimate head motion directly. Experimental results reveal that the proposed system works with high accuracy in real-time. We also show simulation results for navigating the electric wheelchair by recovering user head motion.

  • 17.
    Abtahi, Farhad
    KTH, School of Technology and Health (STH), Medical Engineering, Medical sensors, signals and systems.
    Aspects of Electrical Bioimpedance Spectrum Estimation2014Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Electrical bioimpedance spectroscopy (EBIS) has been used to assess the status or composition of various types of tissue, and examples of EBIS include body composition analysis (BCA) and tissue characterisation for skin cancer detection. EBIS is a non-invasive method that has the potential to provide a large amount of information for diagnosis or monitoring purposes, such as the monitoring of pulmonary oedema, i.e., fluid accumulation in the lungs. However, in many cases, systems based on EBIS have not become generally accepted in clinical practice. Possible reasons behind the low acceptance of EBIS could involve inaccurate models; artefacts, such as those from movements; measurement errors; and estimation errors. Previous thoracic EBIS measurements aimed at pulmonary oedema have shown some uncertainties in their results, making it difficult to produce trustworthy monitoring methods. The current research hypothesis was that these uncertainties mostly originate from estimation errors. In particular, time-varying behaviours of the thorax, e.g., respiratory and cardiac activity, can cause estimation errors, which make it tricky to detect the slowly varying behaviour of this system, i.e., pulmonary oedema.

    The aim of this thesis is to investigate potential sources of estimation error in transthoracic impedance spectroscopy (TIS) for pulmonary oedema detection and to propose methods to prevent or compensate for these errors.   This work is mainly focused on two aspects of impedance spectrum estimation: first, the problems associated with the delay between estimations of spectrum samples in the frequency-sweep technique and second, the influence of undersampling (a result of impedance estimation times) when estimating an EBIS spectrum. The delay between frequency sweeps can produce huge errors when analysing EBIS spectra, but its effect decreases with averaging or low-pass filtering, which is a common and simple method for monitoring the time-invariant behaviour of a system. The results show the importance of the undersampling effect as the main estimation error that can cause uncertainty in TIS measurements.  The best time for dealing with this error is during the design process, when the system can be designed to avoid this error or with the possibility to compensate for the error during analysis. A case study of monitoring pulmonary oedema is used to assess the effect of these two estimation errors. However, the results can be generalised to any case for identifying the slowly varying behaviour of physiological systems that also display higher frequency variations.  Finally, some suggestions for designing an EBIS measurement system and analysis methods to avoid or compensate for these estimation errors are discussed.

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    Thesis
  • 18. 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.

  • 19. 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.

  • 20. Abu-Shaban, Zohair
    et al.
    Mehrpouyan, Hani
    M. R., Bhavani Shankar
    Ottersten, Björn
    Interdisciplinary Centre for Security, Reliability and Trust at the University of Luxembourg, Luxembourg.
    Reduced complexity satellite broadcast receiver with interference mitigation in correlated noise2018In: International Journal of Satellite Communications And Networking, ISSN 1542-0973, E-ISSN 1542-0981, Vol. 36, no 5, p. 402-415Article in journal (Refereed)
    Abstract [en]

    The recent commercial trends towards using smaller dish antennas for satellite receivers and the growing density of broadcasting satellites necessitate the application of robust adjacent satellite interference cancellation schemes. This orbital density growth along with the wider beamwidth of a smaller dish have imposed an overloaded scenario at the satellite receiver, where the number of transmitting satellites exceeds the number of receiving elements at the dish antenna. To ensure successful operation in this practical scenario, we propose a satellite receiver that enhances signal detection from the desired satellite by mitigating the interference from neighboring satellites. Towards this objective, we propose an enhanced list-based group-wise search detection (E-LGSD) receiver under the assumption of spatially correlated additive noise. To further enhance detection performance, the proposed satellite receiver utilizes a newly designed whitening filter to remove the spatial correlation among the noise parameters, while also applying a preprocessor that maximizes the signal-to-interference-plus-noise ratio. We exploit the structure of this filter and propose a reduced complexity LGSD (RC-LGSD) receiver. Extensive simulations under practical scenarios show that the proposed receiver enhances the performance of satellite broadcast systems in the presence of adjacent satellite interference compared with existing methods. Also, under pointing error, RC-LGSD exhibits similar behavior to that of the optimum receiver

  • 21.
    Adler, Jonas
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Mathematics (Div.). Elekta, Box 7593, 103 93 Stockholm, Sweden.
    Ringh, Axel
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Öktem, Ozan
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Mathematics (Div.).
    Karlsson, Johan
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Learning to solve inverse problems using Wasserstein lossManuscript (preprint) (Other academic)
    Abstract [en]

    We propose using the Wasserstein loss for training in inverse problems. In particular, we consider a learned primal-dual reconstruction scheme for ill-posed inverse problems using the Wasserstein distance as loss function in the learning. This is motivated by miss-alignments in training data, which when using standard mean squared error loss could severely degrade reconstruction quality. We prove that training with the Wasserstein loss gives a reconstruction operator that correctly compensates for miss-alignments in certain cases, whereas training with the mean squared error gives a smeared reconstruction. Moreover, we demonstrate these effects by training a reconstruction algorithm using both mean squared error and optimal transport loss for a problem in computerized tomography.

  • 22. 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.

  • 23. Afzal, Hassan
    et al.
    Aouada, Djamila
    Mirbach, Bruno
    Ottersten, Björn
    University of Luxembourg, Interdisciplinary Centre for Security, Reliability and Trust (SnT), Luxembourg, L-1855, Luxembourg.
    Full 3D Reconstruction of Non-Rigidly Deforming Objects2018In: ACM Transactions on Multimedia Computing, Communications, and Applications (TOMCCAP), ISSN 1551-6857, E-ISSN 1551-6865, Vol. 14, no 1s, article id A24Article in journal (Refereed)
    Abstract [en]

    In this article, we discuss enhanced full 360 degrees 3D reconstruction of dynamic scenes containing non-rigidly deforming objects using data acquired from commodity depth or 3D cameras. Several approaches for enhanced and full 3D reconstruction of non-rigid objects have been proposed in the literature. These approaches suffer from several limitations due to requirement of a template, inability to tackle large local deformations and topology changes, inability to tackle highly noisy and low-resolution data, and inability to produce online results. We target online and template-free enhancement of the quality of noisy and low-resolution full 3D reconstructions of dynamic non-rigid objects. For this purpose, we propose a view-independent recursive and dynamic multi-frame 3D super-resolution scheme for noise removal and resolution enhancement of 3D measurements. The proposed scheme tracks the position and motion of each 3D point at every timestep by making use of the current acquisition and the result of the previous iteration. The effects of system blur due to per-point tracking are subsequently tackled by introducing a novel and efficient multi-level 3D bilateral total variation regularization. These characteristics enable the proposed scheme to handle large deformations and topology changes accurately. A thorough evaluation of the proposed scheme on both real and simulated data is carried out. The results show that the proposed scheme improves upon the performance of the state-of-the-art methods and is able to accurately enhance the quality of low-resolution and highly noisy 3D reconstructions while being robust to large local deformations.

  • 24.
    Agevik, Niklas
    et al.
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    Fransson, Henrik
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    Grunell, Henrik
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    Jakiel, Patrick
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    Lundin, Henrik
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    On Loudspeaker Linearization Using Pre-Distortion2004In: European DSP Education & Research Symposium (EDERS), 2004Conference paper (Refereed)
    Abstract [en]

    In this paper we present a system for linearizing the combined output of a stereo amplifier and loudspeaker through pre-distortion. Removal of room cancellation effects is also discussed. The system uses white noise to estimate an FIR model with the Recursive Least Squares algorithm and experiments show that this can significantly improve the linearity of the sound system. We show that the system can be extended with a nonlinear model and that this indeed can be implemented on a TexasInstruments TMS320C6701 DSP with excellent performance.

  • 25. Ahmed, Zakir
    et al.
    Bhardwaj, Krishna
    Krishnan, Ramesh
    Yajnanarayana, Vijaya
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Estimation of Sample Clock Frequency Offset Using Error Vector Magnitude2011Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    A low complexity system and method for operating a receiver in order to estimate an offset between the actual sample clock rate 1/TS' of a receiver and an intended sample clock rate 1/TS. The receiver captures samples of a received baseband signal at the rate 1/TS', operates on the captured samples to generate an estimate for the clock rate offset, and fractionally resamples the captured samples using the clock rate offset. The resampled data represents an estimate of baseband symbols transmitted by the transmitter. The action of operating on the captured samples involves computing an error vector signal and then estimating the clock rate offset using the error vector signal. The error vector signal may be computed in different ways depending on whether or not carrier frequency offset and carrier phase offset are assumed to be present in the received baseband signal.

    Download full text (pdf)
    fulltext
  • 26. Ahmed, Zakir
    et al.
    Yajnanarayana, Vijaya
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Blind mechanism for the joint estimation of frequency offset and phase offset for QAM modulated signals2010Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    A mechanism for jointly correcting carrier phase and carrier frequency errors in a demodulated signal. A computer system may receive samples of a baseband input signal (resulting from QAM demodulation). The computer system may compute values of a cost function J over a grid in a 2D angle-frequency space. A cost function value J(theta,omega) is computed for each point (theta,omega) in the grid by (a) applying a phase adjustment of angle theta and a frequency adjustment of frequency omega to the input signal; (b) performing one or more iterations of the K-means algorithm on the samples of the adjusted signal; (c) generated a sum on each K-means cluster; and (d) adding the sums. The point (thetae,omegae) in the 2D angle-frequency space that minimizes the cost function J serves an estimate for the carrier phase error and carrier frequency error.; The estimated errors may be used to correct the input signal.

    Download full text (pdf)
    fulltext
  • 27. Ahmed, Zakir
    et al.
    Yajnanarayana, Vijaya
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Maximizing the Viterbi Winning Path Metric to Estimate Carrier Frequency and Phase Offsets in Continuous Phase Modulated Signals2012Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    A system and method for estimating carrier frequency offset Δf and carrier phase offset φ0 inherent in a received CPM signal. Samples of a continuous phase modulated (CPM) signal are received. A maximum of an objective function J is determined over a two-dimensional region parameterized by frequency offset v and phase offset w. The coordinates vmax and wmax of a maximizing point in the region represent estimates of the carrier frequency offset Δf and the carrier phase offset φ0. To evaluate the objective function J at a point (v, w), apply a frequency shift of amount −v and a phase shift of amount −w to the received samples to obtain modified samples, and perform Viterbi demodulation on the modified samples to obtain a winning path metric value at a final time. The winning path metric value is the objective function value J(v, w). 

    Download full text (pdf)
    fulltext
  • 28.
    Ahmed, Zakir
    et al.
    Motorola India Electron. Ltd., Bangalore .
    Yajnanarayana, Vijaya
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Sancheti, Nirmal Kumar
    A time domain based efficient block decision algorithm for audio coders2007In: International Symposium on Communications and Information Technologies, 2007. ISCIT '07, IEEE Press, 2007, p. 1077-1081Conference paper (Refereed)
    Abstract [en]

    In typical audio encoders the block decision is done either using time-domain techniques like energy computation or frequency domain techniques like temporal noise shaping (TNS) [1], [2]. The time-domain energy computation based decisions are less effective for detecting many of the stringent scenarios presented by test cases like castanets and fatboy. The frequency domain based algorithms have better decision making capabilities, however they are inherently complex as they require the computation of the FFT, additionally in case of TNS the computation of LPC (Linear Prediction coding) in the frequency domain. An improved time-domain technique with better block decision capability compared to TNS and with lesser computational complexity is proposed in this paper.

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  • 29. Ahnström, Ulrika
    et al.
    Falk, Johan
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    Händel, Peter
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Wikström, Maria
    Detection and direction-finding of spread spectrum signals using correlation and narrowband interference rejection2003In: Nordic Matlab Conference 2003, 2003Conference paper (Refereed)
    Abstract [en]

    An algorithm for correlation-based detection of direct sequence spread spectrum signals with direction finding, including direction-filtering and narrow-band interference rejection, is implemented and evaluated in MATLAB. An analog noise-free signal is generated and sampled by a test-bed system. Numerical simulations are run based on data corrupted by mutually uncorrelated white Gaussian noise sequences, and also with recorded noise from two spatially separated HF radio receivers. The simulations and measurements show promising results for detection and direction-finding of covert wideband signals in low SNR and in presence of narrowband interferers. Direction filtering is shown to improve the results.

  • 30. Ai, Yun
    et al.
    Pereira de Figueiredo, Felipe Augusto
    Kong, Long
    Cheffena, Michael
    Chatzinotas, Symeon
    Ottersten, Björn
    University of Luxembourg, Esch-sur-Alzette, Luxembourg.
    Secure Vehicular Communications through Reconfigurable Intelligent Surfaces2021In: IEEE Transactions on Vehicular Technology, ISSN 00189545, Vol. 70, no 7, p. 7272-7276Article in journal (Refereed)
  • 31.
    Ainomäe, Ahti
    KTH, School of Electrical Engineering (EES), Information Science and Engineering.
    Distributed Detection in Cognitive Radio Networks2017Licentiate thesis, monograph (Other academic)
    Abstract [en]

    One of the problems with the modern radio communication is the lack of availableradio frequencies. Recent studies have shown that, while the available licensed radiospectrum becomes more occupied, the assigned spectrum is significantly underutilized.To alleviate the situation, cognitive radio (CR) technology has been proposedto provide an opportunistic access to the licensed spectrum areas. Secondary CRsystems need to cyclically detect the presence of a primary user by continuouslysensing the spectrum area of interest. Radiowave propagation effects like fading andshadowing often complicate sensing of spectrum holes. When spectrum sensing isperformed in a cooperative manner, then the resulting sensing performance can beimproved and stabilized.

    In this thesis, two fully distributed and adaptive cooperative Primary User (PU)detection solutions for CR networks are studied.

    In the first part of this thesis we study a distributed energy detection schemewithout using any fusion center. Due to reduced communication such a topologyis more energy efficient. We propose the usage of distributed, diffusion least meansquare (LMS) type of power estimation algorithms with different network topologies.We analyze the resulting energy detection performance by using a commonframework and verify the theoretical findings through simulations.

    In the second part of this thesis we propose a fully distributed detection scheme,based on the largest eigenvalue of adaptively estimated correlation matrices, assumingthat the primary user signal is temporally correlated. Different forms of diffusionLMS algorithms are used for estimating and averaging the correlation matrices overthe CR network. The resulting detection performance is analyzed using a commonframework. In order to obtain analytic results on the detection performance, theadaptive correlation matrix estimates are approximated by a Wishart distribution.The theoretical findings are verified through simulations.

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    Ahti_Ainomae_LicTech_040917
  • 32.
    Ainomäe, Ahti
    et al.
    KTH, School of Electrical Engineering (EES), Information Science and Engineering. Tallinn University of Technology, Estonia.
    Trump, T.
    Bengtsson, Mats
    KTH, School of Electrical Engineering (EES), Information Science and Engineering.
    Distributed largest eigenvalue detection2017In: 2017 IEEE International Conference on Acoustics, Speech, and Signal Processing, ICASSP 2017, Institute of Electrical and Electronics Engineers (IEEE), 2017, p. 3519-3523, article id 7952811Conference paper (Refereed)
    Abstract [en]

    Cognitive radio (CR) systems need to detect the presence of a primary user (PU) signal by continuously sensing the spectrum area of interest. Radiowave propagation effects like fading and shadowing often complicate sensing of spectrum holes because the PU signal can be weak in a particular area. Cooperative spectrum sensing is seen as a prospective solution to enhance the detection of PU signals. In this paper we study distributed spectrum sensing, based on the largest eigenvalue of adaptively estimated correlation matrices (CMs) of received signals. The PU signal is assumed to be temporally correlated. In this paper an Combine and Adapt (CTA) least Mean Square (LMS) diffusion based mean vector estimation scheme is proposed. No fusion center (FC) for estimation or detection is used. We analyse the resulting detection performance and verify the theoretical findings through simulations.

  • 33.
    Ainomäe, Ahti
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. Tallinn Univ. of Technol., Tallinn, Estonia.
    Trump, Tõnu
    Tallinn Univ. of Technol., Tallinn, Estonia.
    Bengtsson, Mats
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Distributed Diffusion LMS based Energy Detection2014In: Proceedings of 6th International Congress on Ultra Modern Telecommunications and Control Systems and Workshops (ICUMT), 2014, 2014, p. 176-183Conference paper (Refereed)
    Abstract [en]

    Cognitive radio (CR) is seen as a promising technology to make radio spectrum usage more effective by providing an opportunistic access for secondary users to the licensed spectrum areas. CR systems need to detect the presence of a primary user (PU) signal by continuously sensing the spectrum area of interest. Radiowave propagation effects like fading and shadowing often complicate sensing of spectrum holes because the PU signal can be weak in a particular area. Cooperative spectrum sensing is seen as a prospective solution to enhance the detection of PU signals. This paper studies distributed spectrum sensing in a cognitive radio context. We investigate distributed energy detection schemes without using any fusion center. We propose the usage of distributed, diffusion least mean square (LMS) type of power estimation algorithms. In this paper an Adapt and Combine (ATC) diffusion based power estimation scheme is proposed and the performance is compared with the Combine and Adapt (CTA) and ring-around schemes in a common framework. The PU signal is assumed to be slowly fading. We analyse the resulting energy detection performance and verify the theoretical findings through simulations.

  • 34.
    Ainomäe, Ahti
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. Department of Radio and Telecommunication Engineering, Tallinn University of Technology, Tallinn, Estonia .
    Trump, Tõnu
    Tallin University of Technology.
    Bengtsson, Mats
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Distributed Recursive Energy Detection2014In: Proceedings of Wireless Communications and Networking Conference (WCNC), 2014, IEEE Communications Society, 2014, p. 1242-1247Conference paper (Refereed)
    Abstract [en]

    Recent studies have shown that, while the available licensed radio spectrum becomes more occupied, the assigned spectrum is significantly underutilized. To alleviate the situation, cognitive radio (CR) technology has been proposed to provide an opportunistic access to the licensed spectrum areas. CR systems are able to serve the secondary users for detecting and utilizing so called spectrum holes by sensing and adapting to the environment without causing harmful effects or interference to the licensed primary users (PU). CR systems need to detect the presence of a primary user by continuously sensing the spectrum area of interest. Radiowave propagation effects like fading and shadowing often complicate sensing of spectrum holes because the PU signal can be weak in a particular area. Cooperative spectrum sensing is seen as a prospective solution to enhance the detection of PU signals. This paper studies distributed spectrum sensing in a cognitive radio context. We investigate a distributed energy detection scheme without using any fusion center. Due to reduced communication such a topology is more energy efficient. The PU signal is assumed to be in slow fading. A recursive distributed power estimation and detection scheme is proposed. The theoretical findings are verified through simulations.

  • 35.
    Akbar, Noman
    et al.
    Australian Natl Univ, Res Sch Engn, GPO Box 4, Acton, ACT 2601, Australia..
    Björnson, Emil
    Linköping Univ, Dept Elect Engn ISY, Linköping, Sweden..
    Larsson, Erik G.
    Linköping Univ, Dept Elect Engn ISY, Linköping, Sweden..
    Yang, Nan
    Australian Natl Univ, Res Sch Engn, GPO Box 4, Acton, ACT 2601, Australia..
    Downlink Power Control in Massive MIMO Networks with Distributed Antenna Arrays2018In: 2018 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS (ICC), IEEE , 2018Conference paper (Refereed)
    Abstract [en]

    In this paper, we investigate downlink power control in massive multiple-input multiple-output (MIMO) networks with distributed antenna arrays. The base station (BS) in each cell consists of multiple antenna arrays, which are deployed in arbitrary locations within the cell. Due to the spatial separation between antenna arrays, the large-scale propagation effect is different from a user to different antenna arrays in a cell, which makes power control a challenging problem as compared to conventional massive MIMO. We assume that the BS in each cell obtains the channel estimates via uplink pilots. Based on the channel estimates, the BSs perform maximum ratio transmission for the downlink. We then derive a closed-form spectral efficiency (SE) expression, where the channels are subject to correlated fading. Utilizing the derived expression, we propose a max-min power control algorithm to ensure that each user in the network receives a uniform quality of service. Numerical results demonstrate that, for the network considered in this work, optimizing for max-min SE through the max-min power control improves the sum SE of the network as compared to the equal power allocation.

  • 36.
    Akbar, Noman
    et al.
    Australian Natl Univ, Res Sch Engn, Canberra, ACT 2600, Australia..
    Björnson, Emil
    Linköping Univ, Dept Elect Engn ISY, S-58183 Linköping, Sweden..
    Yang, Nan
    Australian Natl Univ, Res Sch Engn, Canberra, ACT 2600, Australia..
    Larsson, Erik G.
    Linköping Univ, Dept Elect Engn ISY, S-58183 Linköping, Sweden..
    Max-Min Power Control in Downlink Massive MIMO With Distributed Antenna Arrays2021In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 69, no 2, p. 740-751Article in journal (Refereed)
    Abstract [en]

    In this paper, we investigate optimal downlink power allocation in massive multiple-input multiple-output (MIMO) networks with distributed antenna arrays (DAAs) under correlated and uncorrelated channel fading. In DAA massive MIMO, a base station (BS) consists of multiple antenna sub-arrays. Notably, the antenna sub-arrays are deployed in arbitrary locations within a DAA massive MIMO cell. Consequently, the distance-dependent large-scale propagation coefficients are different from a user to these different antenna sub-arrays, which makes power control a challenging problem. We assume that the network operates in time-division duplex mode, where each BS obtains the channel estimates via uplink pilots. Based on the channel estimates, the BSs perform maximum-ratio transmission in the downlink. We then derive a closed-form signal-to-interference-plus-noise ratio (SINR) expression, where the channels are subject to correlated fading. Based on the SINR expression, we propose a network-wide max-min power control algorithm to ensure that each user in the network receives a uniform quality of service. Numerical results demonstrate the performance advantages offered by DAA massive MIMO. For some specific scenarios, DAA massive MIMO can improve the average per-user throughput up to 55%. Furthermore, we demonstrate that channel fading covariance is an important factor in determining the performance of DAA massive MIMO.

  • 37.
    Akbarnejad, Shahin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Kennedy, M. W.
    Fritzsch, R.
    Aune, R. E.
    An investigation on permeability of ceramic foam filters (CFF)2015In: TMS Light Metals, 2015, p. 949-954Conference paper (Refereed)
    Abstract [en]

    CFFs are used to filter liquid metal in the aluminum industry. CFFs are classified in grades or pores per inch (PPI), ranging from 10-100 PPI. Their properties vary in everything from pore and strut size to window size. CFFs of 80-100 PPI are generally not practical for use by industry, as priming of the filters by gravitational forces requires an excessive metal head. Recently, co-authors have invented a method to prime such filters using electromagnetic Lorentz forces, thus allowing filters to be primed with a low metal head. In the continuation of this research work, an improved experimental setup was developed in the present study to validate previous results and to measure the permeability of different filters, as well as a stack of filters. The study of permeability facilitates estimation of the required pressure drop to prime the filters and the head required to generate a given casting rate.

  • 38.
    Akhlaghpasand, Hossein
    et al.
    Iran Univ Sci & Technol, Sch Elect Engn, Tehran 1684613114, Iran..
    Björnson, Emil
    Linköping Univ, Dept Elect Engn, S-58183 Linköping, Sweden..
    Razavizadeh, S. Mohammad
    Iran Univ Sci & Technol, Sch Elect Engn, Tehran 1684613114, Iran..
    Jamming Suppression in Massive MIMO Systems2020In: IEEE Transactions on Circuits and Systems - II - Express Briefs, ISSN 1549-7747, E-ISSN 1558-3791, Vol. 67, no 1, p. 182-186Article in journal (Refereed)
    Abstract [en]

    In this brief, we propose a framework for protecting the uplink transmission of a massive multiple-input multiple-output (mMIMO) system from a jamming attack. Our framework includes a novel minimum mean-squared error-based jamming suppression (MMSE-JS) estimator for channel training and a linear zero-forcing jamming suppression (ZFJS) detector for uplink combining. The MMSE-JS exploits some intentionally unused pilots to reduce the pilot contamination caused by the jammer. The ZFJS suppresses the jamming interference during the detection of the legitimate users' data symbols. The proposed framework is implementable, since the complexities of computing the MMSE-JS and the ZFJS are linear (not exponential) with respect to the number of antennas at the base station and can be fabricated using 28-nm fully depleted silicon on insulator technology and for the mMIMO systems. Our analysis shows that the jammer cannot dramatically affect the performance of an mMIMO system equipped with the combination of MMSE-JS and ZFJS. Numerical results confirm our analysis.

  • 39.
    Akhlaghpasand, Hossein
    et al.
    Iran Univ Sci & Technol, Sch Elect Engn, Tehran 1684613114, Iran..
    Björnson, Emil
    Linköping Univ, Dept Elect Engn, S-58183 Linköping, Sweden..
    Razavizadeh, S. Mohammad
    Iran Univ Sci & Technol, Sch Elect Engn, Tehran 1684613114, Iran..
    Jamming-Robust Uplink Transmission for Spatially Correlated Massive MIMO Systems2020In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 68, no 6, p. 3495-3504Article in journal (Refereed)
    Abstract [en]

    In this paper, we consider how the uplink transmission of a spatially correlated massive multiple-input multiple-output (MIMO) system can be protected from a jamming attack. To suppress the jamming, we propose a novel framework including a new optimal linear estimator in the training phase and a bilinear equalizer in the data phase. The proposed estimator is optimal in the sense of maximizing the spectral efficiency of the legitimate system attacked by a jammer, and its implementation needs the statistical knowledge about the jammer's channel. We derive an efficient algorithm to estimate the jamming information needed for implementation of the proposed framework. Furthermore, we demonstrate that optimized power allocation at the legitimate users can improve the performance of the proposed framework regardless of the jamming power optimization. Our proposed framework can be exploited to combat jamming in scenarios with either ideal or non-ideal hardware at the legitimate users and the jammer. Numerical results reveal that using the proposed framework, the jammer cannot dramatically affect the performance of the legitimate system.

  • 40.
    Akhlaghpasand, Hossein
    et al.
    Iran Univ Sci & Technol, Sch Elect Engn, Tehran 1684613114, Iran..
    Razavizadeh, S. Mohammad
    Iran Univ Sci & Technol, Sch Elect Engn, Tehran 1684613114, Iran..
    Björnson, Emil
    Linköping Univ, Dept Elect Engn ISY, S-58183 Linköping, Sweden..
    Do, Tan Tai
    Ericsson AB, Ericsson Res, S-22362 Lund, Sweden..
    Jamming Detection in Massive MIMO Systems2018In: IEEE Wireless Communications Letters, ISSN 2162-2337, E-ISSN 2162-2345, Vol. 7, no 2, p. 242-245Article in journal (Refereed)
    Abstract [en]

    This letter considers the physical layer security of a pilot-based massive multiple-input multiple-output (MaMIMO) system in presence of a multi-antenna jammer. We propose a new jamming detection method that makes use of a generalized likelihood ratio test over some coherence blocks. Our proposed method utilizes intentionally unused pilots in the network. The performance of the proposed detector improves by increasing the number of antennas at the base station, the number of unused pilots and also by the number of the coherence blocks that are utilized. Simulation results show that in the MaMIMO regime, perfect detection is achievable even with a small number of unused pilots.

  • 41. 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.

  • 42. 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.

  • 43. 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.

  • 44. 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.

  • 45. Alaee-Kerahroodi, M.
    et al.
    Bhavani Shankar, M. R.
    Mishra, K. V.
    Ottersten, Björn
    SnT - Interdisciplinary Centre for Security, Reliability and Trust, University of Luxembourg, LUXEMBOURG.
    Meeting the lower bound on designing set of unimodular sequences with small aperiodic/periodic ISL2019Conference paper (Refereed)
  • 46. Alaee-Kerahroodi, M.
    et al.
    Imani, S.
    Bhavani Shankar, M. R.
    Nayebi, M. M.
    Ottersten, Björn
    Interdisciplinary Centre for Security, University of Luxembourg.
    A coordinate descent framework to joint design of MPSK sequences and receive filter weights in MIMO radar systems2019Conference paper (Refereed)
  • 47. Alaee-Kerahroodi, M.
    et al.
    Mishra, K. V.
    Bhavani Shankar, M. R.
    Ottersten, Björn
    SnT - Interdisciplinary Centre for Security, Reliability and Trust, University of Luxembourg, Luxembourg.
    Discrete-Phase Sequence Design for Coexistence of MIMO Radar and MIMO Communications2019Conference paper (Refereed)
  • 48. Alaee-Kerahroodi, M.
    et al.
    Modarres-Hashemi, M.
    Naghsh, M. M.
    Bhavani Shankar, M. R.
    Ottersten, Björn
    Interdisciplinary Centre for Security, Reliability and Trust (SnT), University of Luxembourg.
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    Bhavani Shankar, M. R.
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    Interdisciplinary Centre for Security, Reliability and Trust (SnT), University of Luxembourg.
    Designing (In)finite-alphabet Sequences via Shaping the Radar Ambiguity Function2019Conference paper (Refereed)
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    Bhavani, S. M. R.
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    Ottersten, Björn
    SnT - Interdisciplinary Centre for Security, University of Luxembourg.
    Information Theoretic Approach for Waveform Design in Coexisting MIMO Radar and MIMO Communications2020Conference paper (Refereed)
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