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1.
  • Abdelaziz, Mahmoud, et al. (författare)
  • Digital Predistortion for Hybrid MIMO Transmitters
  • 2018
  • Ingår i: IEEE Journal on Selected Topics in Signal Processing. - 1932-4553.
  • Tidskriftsartikel (refereegranskat)abstract
    • This article investigates digital predistortion (DPD) linearization of hybrid beamforming large-scale antenna transmitters. We propose a novel DPD processing and learning technique for an antenna sub-array, which utilizes a combined signal of the individual power amplifier (PA) outputs in conjunction with a decorrelation-based learning rule. In effect, the proposed approach results in minimizing the nonlinear distortions in the direction of the intended receiver. This feature is highly desirable, since emissions in other directions are naturally weak due to beamforming. The proposed parameter learning technique requires only a single observation receiver, and therefore supports simple hardware implementation. It is also shown to clearly outperform the current state-of-the-art technique which utilizes only a single PA for learning. Analysis of the feedback network amplitude and phase imbalances reveals that the technique is robust even to high levels of such imbalances. Finally, we also show that the array system out-of-band emissions are well-behaving in all spatial directions, and essentially below those of the corresponding single-antenna transmitter, due to the combined effects of the DPD and beamforming.
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2.
  • Andersson, Maria, et al. (författare)
  • Recognition of Anomalous Motion Patterns in Urban Surveillance
  • 2013
  • Ingår i: IEEE Journal on Selected Topics in Signal Processing. - : IEEE Signal Processing Society. - 1932-4553 .- 1941-0484. ; 7:1, s. 102-110
  • Tidskriftsartikel (refereegranskat)abstract
    • We investigate the unsupervised K-means clustering and the semi-supervised hidden Markov model (HMM) to automatically detect anomalous motion patterns in groups of people (crowds). Anomalous motion patterns are typically people merging into a dense group, followed by disturbances or threatening situations within the group. The application of K-means clustering and HMM are illustrated with datasets from four surveillance scenarios. The results indicate that by investigating the group of people in a systematic way with different K values, analyze cluster density, cluster quality and changes in cluster shape we can automatically detect anomalous motion patterns. The results correspond well with the events in the datasets. The results also indicate that very accurate detections of the people in the dense group would not be necessary. The clustering and HMM results will be very much the same also with some increased uncertainty in the detections.
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3.
  • Čirkić, Mirsad, 1984-, et al. (författare)
  • Allocation of Computational Resources for Soft MIMO Detection
  • 2011
  • Ingår i: IEEE Journal of Selected Topics in Signal Processing. - : IEEE conference proceedings. - 1932-4553. ; 5:8, s. 1451-1461
  • Tidskriftsartikel (refereegranskat)abstract
    • We consider soft MIMO detection for the case of block fading. That is, the transmitted codeword spans over several independent channel realizations and several instances of the detection problem must be solved for each such realization. We develop methods that adaptively allocate computational resources to the detection problems of each channel realization, under a total per-codeword complexity constraint. Our main results are a formulation of the problem as a mathematical optimization problem with a well-defined objective function and constraints, and algorithms that solve this optimization problem efficiently computationally.
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4.
  • Curic, Vladimir, et al. (författare)
  • Salience adaptive structuring elements
  • 2012
  • Ingår i: IEEE Journal on Selected Topics in Signal Processing. - 1932-4553 .- 1941-0484. ; 6:7, s. 809-819
  • Tidskriftsartikel (refereegranskat)abstract
    • Spatially adaptive structuring elements adjust their shape to the local structures in the image, and are often defined by a ball in a geodesic distance or gray-weighted distance metric space. This paper introduces salience adaptive structuring elements as spatially variant structuring elements that modify not only their shape, but also their size according to the salience of the edges in the image. Morphological operators with salience adaptive structuring elements shift edges with high salience to a less extent than those with low salience. Salience adaptive structuring elements are less flexible than morphological amoebas and their shape is less affected by noise in the image. Consequently, morphological operators using salience adaptive structuring elements have better properties.
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5.
  • Engelke, Ulrich, et al. (författare)
  • Psychophysiology-Based QoE Assessment : A Survey
  • 2017
  • Ingår i: IEEE Journal on Selected Topics in Signal Processing. - 1932-4553 .- 1941-0484. ; 11:1, s. 6-21
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a survey of psychophysiology-based assessment for quality of experience (QoE) in advanced multimedia technologies. We provide a classification of methods relevant to QoE and describe related psychological processes, experimental design considerations, and signal analysis techniques. We summarize multimodal techniques and discuss several important aspects of psychophysiology-based QoE assessment, including the synergies with psychophysical assessment and the need for standardized experimental design. This survey is not considered to be exhaustive but serves as a guideline for those interested to further explore this emerging field of research.
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6.
  • Fascista, Alessio, et al. (författare)
  • RIS-aided Joint Localization and Synchronization with a Single-Antenna Receiver: Beamforming Design and Low-Complexity Estimation
  • 2022
  • Ingår i: IEEE Journal on Selected Topics in Signal Processing. - 1941-0484 .- 1932-4553. ; 16:5, s. 1141-1156
  • Tidskriftsartikel (refereegranskat)abstract
    • Reconfigurable intelligent surfaces (RISs) have attracted enormous interest thanks to their ability to overcome line-of-sight blockages in mmWave systems, enabling in turn accurate localization with minimal infrastructure. Less investigated are however the benefits of exploiting RIS with suitably designed beamforming strategies for optimized localization and synchronization performance. In this paper, a novel low-complexity method for joint localization and synchronization based on an optimized design of the base station (BS) active precoding and RIS passive phase profiles is proposed, for the challenging case of a single-antenna receiver. The theoretical position error bound is first derived and used as metric to jointly optimize the BS-RIS beamforming, assuming a priori knowledge of the user position. By exploiting the low-dimensional structure of the solution, a novel codebook-based robust design strategy with optimized beam power allocation is then proposed, which provides low-complexity while taking into account the uncertainty on the user position. Finally, a reduced-complexity maximum-likelihood based estimation procedure is devised to jointly recover the user position and the synchronization offset. Extensive numerical analysis shows that the proposed joint BS-RIS beamforming scheme provides enhanced localization and synchronization performance compared to existing solutions, with the proposed estimator attaining the theoretical bounds even at low signal-to-noise-ratio and in the presence of additional uncontrollable multipath propagation.
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7.
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8.
  • Garcia, F., et al. (författare)
  • Real-time distance-dependent mapping for a hybrid ToF multi-camera rig
  • 2012
  • Ingår i: IEEE Journal on Selected Topics in Signal Processing. - 1932-4553. ; 6, s. 425-436
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
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9.
  • Ghauch, Hadi, et al. (författare)
  • Subspace Estimation and Decomposition for Large Millimeter-Wave MIMO Systems
  • 2016
  • Ingår i: IEEE Journal on Selected Topics in Signal Processing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1932-4553 .- 1941-0484. ; 10:3, s. 528-542
  • Tidskriftsartikel (refereegranskat)abstract
    • Channel estimation and precoding in hybrid analog-digital millimeter-wave (mmWave) MIMO systems is a fundamental problem that has yet to be addressed, before any of the promised gains can be harnessed. For that matter, we propose a method (based on the well-known Arnoldi iteration) exploiting channel reciprocity in TDD systems and the sparsity of the channel's eigenmodes, to estimate the right (resp. left) singular subspaces of the channel, at the BS (resp. MS). We first describe the algorithm in the context of conventional MIMO systems, and derive bounds on the estimation error in the presence of distortions at both BS and MS. We later identify obstacles that hinder the application of such an algorithm to the hybrid analog-digital architecture, and address them individually. In view of fulfilling the constraints imposed by the hybrid analog-digital architecture, we further propose an iterative algorithm for subspace decomposition, whereby the above estimated subspaces, are approximated by a cascade of analog and digital precoder/combiner. Finally, we evaluate the performance of our scheme against the perfect CSI, fully digital case (i.e., an equivalent conventional MIMO system), and conclude that similar performance can be achieved, especially at medium-to-high SNR (where the performance gap is less than 5%), however, with a drastically lower number of RF chains (similar to 4 to 8 times less).
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10.
  • Gokceoglu, Ahmet, et al. (författare)
  • Spatio-Temporal Waveform Design for Multiuser Massive MIMO Downlink With 1-bit Receivers
  • 2017
  • Ingår i: IEEE Journal on Selected Topics in Signal Processing. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 1932-4553 .- 1941-0484. ; 11:2, s. 347-362
  • Tidskriftsartikel (refereegranskat)abstract
    • Internet-of-Things (IoT) refers to a high-density network of low-cost, low-bitrate terminals and sensors where low energy consumption is also one central feature. As the power budget of classical receiver chains is dominated by the high-resolution analog-to-digital converters (ADCs), there is a growing interest toward deploying receiver architectures with reduced bit or even 1-bit ADCs. In this paper, we study waveform design, optimization, and detection aspects of multiuser massive MIMO downlink, where user terminals adopt very simple 1-bit ADCs with oversampling. In order to achieve spectral efficiency higher than 1 bit/s/Hz per real dimension, and per receiver antenna, we propose a two-stage precoding structure, namely, a novel quantization precoder followed by maximum-ratio transmission or zero-forcing-type spatial channel precoder which jointly form the multiuser multiantenna transmit waveform. The quantization precoder outputs are designed and optimized, under appropriate transmitter and receiver filter bandwidth constraints, to provide controlled intersymbol interference enabling the input symbols to be uniquely detected from 1-bit quantized observations with a low-complexity symbol detector in the absence of noise. An additional optimization constraint is also imposed in the quantization precoder design to increase the robustness against noise and residual interuser interference (IUI). The purpose of the spatial channel precoder, in turn, is to suppress the IUI and provide high beamforming gains such that good symbol error rates can be achieved in the presence of noise and interference. Extensive numerical evaluations illustrate that the proposed spatio-temporal precoder-based multiantenna waveform design can facilitate good multiuser link performance, despite the extremely simple 1-bitADCsin the receivers, hence being one possible enabling technology for the future low-complexity IoT networks.
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11.
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12.
  • Hu, R., et al. (författare)
  • Automotive Squint-forward-looking SAR : High Resolution and Early Warning
  • 2021
  • Ingår i: IEEE Journal on Selected Topics in Signal Processing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1932-4553 .- 1941-0484. ; , s. 1-1
  • Tidskriftsartikel (refereegranskat)abstract
    • Forward-looking automotive radars can sense long-distant targets to enable early warning, but the lateral resolution is limited. Synthetic aperture radar (SAR) techniques can achieve very high azimuth resolution, but cannot resolve targets in the forward direction. As a trade-off, squint-forward-looking SAR (SFL-SAR) can perform 2D imaging on a distant area squint to the moving direction, providing both high resolution and early warning. In this paper, we analyzed and derived the constraints of automotive SFL-SAR to satisfy both required resolution and braking distance. Simulations and imaging results verified the analysis.
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13.
  • Johansson, Håkan (författare)
  • A Polynomial-Based Time-Varying Filter Structure for the Compensation of Frequency-Response Mismatch Errors in Time-Interleaved ADCs
  • 2009
  • Ingår i: IEEE JOURNAL OF SELECTED TOPICS IN SIGNAL PROCESSING. - 1932-4553. ; 3:3, s. 384-396
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper introduces a structure for the compensation of frequency-response mismatch errors in M-channel time-interleaved analog-to-digital converters (ADCs). It makes use of a number of fixed digital filters, approximating differentiators of different orders, and a few variable multipliers that correspond to parameters in polynomial models of the channel frequency responses. Whenever the channel frequency responses change, which occurs from time to time in a practical time-interleaved ADC, it suffices to alter the values of these variable multipliers. In this way, expensive on-line filter design is avoided. The paper includes several design examples that illustrate the properties and capabilities of the proposed structure.
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14.
  • Jorswieck, Eduard A, et al. (författare)
  • Introduction to the Issue on Game Theory in Signal Processing
  • 2012
  • Ingår i: IEEE Journal on Selected Topics in Signal Processing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1932-4553 .- 1941-0484. ; 6:2, s. 73-75
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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15.
  • Kalantari, A., et al. (författare)
  • Directional Modulation Via Symbol-Level Precoding : A Way to Enhance Security
  • 2016
  • Ingår i: IEEE Journal on Selected Topics in Signal Processing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1932-4553 .- 1941-0484. ; 10:8, s. 1478-1493
  • Tidskriftsartikel (refereegranskat)abstract
    • Wireless communication provides a wide coverage at the cost of exposing information to unintended users. As an information-theoretic paradigm, secrecy rate derives bounds for secure transmission when the channel to the eavesdropper is known. However, such bounds are shown to be restrictive in practice and may require exploitation of specialized coding schemes. In this paper, we employ the concept of directional modulation and follow a signal processing approach to enhance the security of multiuser multi-input multioutput (MIMO) communication systems when a multiantenna eavesdropper is present. Security enhancement is accomplished by increasing the symbol error rate at the eavesdropper. Unlike the information-theoretic secrecy rate paradigm, we assume that the legitimate transmitter is not aware of its channel to the eavesdropper, which is a more realistic assumption. We examine the applicability of MIMO receiving algorithms at the eavesdropper. Using the channel knowledge and the intended symbols for the users, we design security enhancing symbol-level precoders for different transmitter and eavesdropper antenna configurations. We transform each design problem to a linearly constrained quadratic program and propose two solutions, namely the iterative algorithm and one based on nonnegative least squares, at each scenario for a computationally efficient modulation. Simulation results verify the analysis and show that the designed precoders outperform the benchmark scheme in terms of both power efficiency and security enhancement.
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16.
  • Kammoun, Abla, et al. (författare)
  • Linear Precoding Based on Polynomial Expansion : Large-Scale Multi-Cell MIMO Systems
  • 2014
  • Ingår i: IEEE Journal on Selected Topics in Signal Processing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1932-4553 .- 1941-0484. ; 8:5, s. 861-875
  • Tidskriftsartikel (refereegranskat)abstract
    • Large-scale MIMO systems can yield a substantial improvements in spectral efficiency for future communication systems. Due to the finer spatial resolution and array gain achieved by a massive number of antennas at the base station, these systems have shown to be robust to inter-user interference and the use of linear precoding appears to be asymptotically optimal. However, from a practical point of view, most precoding schemes exhibit prohibitively high computational complexity as the system dimensions increase. For example, the near-optimal regularized zero forcing (RZF) precoding requires the inversion of a large matrix. To solve this issue, we propose in this paper to approximate the matrix inverse by a truncated polynomial expansion (TPE), where the polynomial coefficients are optimized to maximize the system performance. This technique has been recently applied in single cell scenarios and it was shown that a small number of coefficients is sufficient to reach performance similar to that of RZF, while it was not possible to surpass RZF. In a realistic multi-cell scenario involving large-scale multi-user MIMO systems, the optimization of RZF precoding has, thus far, not been feasible. This is mainly attributed to the high complexity of the scenario and the non-linear impact of the necessary regularizing parameters. On the other hand, the scalar coefficients in TPE precoding give hope for possible throughput optimization. To this end, we exploit random matrix theory to derive a deterministic expression of the asymptotic signal-to-interference-and-noise ratio for each user based on channel statistics. We also provide an optimization algorithm to approximate the coefficients that maximize the network-wide weighted max-min fairness. The optimization weights can be used to mimic the user throughput distribution of RZF precoding. Using simulations, we compare the network throughput of the proposed TPE precoding with that of the suboptimal RZF scheme and show that our scheme can achieve higher throughput using a TPE order of only 5.
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17.
  • Kant, Shashi, et al. (författare)
  • Federated Learning Using Three-Operator ADMM
  • 2023
  • Ingår i: IEEE Journal on Selected Topics in Signal Processing. - : IEEE Signal Processing Society. - 1932-4553 .- 1941-0484. ; 17:1, s. 205-221
  • Tidskriftsartikel (refereegranskat)abstract
    • Federated learning (FL) has emerged as an instance of distributed machine learning paradigm that avoids the transmission of data generated on the users' side. Although data are not transmitted, edge devices have to deal with limited communication bandwidths, data heterogeneity, and straggler effects due to the limited computational resources of users' devices. A prominent approach to overcome such difficulties is FedADMM, which is based on the classical two-operator consensus alternating direction method of multipliers (ADMM). The common assumption of FL algorithms, including FedADMM, is that they learn a global model using data only on the users' side and not on the edge server. However, in edge learning, the server is expected to be near the base station and has often direct access to rich datasets. In this paper, we argue that it is much more beneficial to leverage the rich data on the edge server then utilizing only user datasets. Specifically, we show that the mere application of FL with an additional virtual user node representing the data on the edge server is inefficient. We propose FedTOP-ADMM, which generalizes FedADMM and is based on a three-operator ADMM-type technique that exploits a smooth cost function on the edge server to learn a global model in parallel to the edge devices. Our numerical experiments indicate that FedTOP-ADMM has substantial gain up to 33% in communication efficiency to reach a desired test accuracy with respect to FedADMM, including a virtual user on the edge server.
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18.
  • Keskin, Furkan, 1988, et al. (författare)
  • MIMO-OFDM Joint Radar-Communications: Is ICI Friend or Foe
  • 2021
  • Ingår i: IEEE Journal on Selected Topics in Signal Processing. - 1941-0484 .- 1932-4553. ; 15:6, s. 1393-1408
  • Tidskriftsartikel (refereegranskat)abstract
    • Inter-carrier interference (ICI) poses a significant challenge for OFDM joint radar-communications (JRC) systems in high-mobility scenarios. In this paper, we propose a novel ICI-aware sensing algorithm for MIMO-OFDM JRC systems to detect the presence of multiple targets and estimate their delay-Doppler-angle parameters. First, leveraging the observation that spatial covariance matrix is independent of target delays and Dopplers, we perform angle estimation via the MUSIC algorithm. For each estimated angle, we next formulate the radar delay-Doppler estimation as a joint carrier frequency offset (CFO) and channel estimation problem via an APES (amplitude and phase estimation) spatial filtering approach by transforming the delay-Doppler parameterized radar channel into an unstructured form. To account for the presence of multiple targets at a given angle, we devise an iterative interference cancellation based orthogonal matching pursuit (OMP) procedure, where at each iteration the generalized likelihood ratio test (GLRT) detector is employed to form decision statistics, providing as by-products the maximum likelihood estimates (MLEs) of radar channels and CFOs. In the final step, target detection is performed in delay-Doppler domain using target-specific, ICI-decontaminated channel estimates over time and frequency, where CFO estimates are utilized to resolve Doppler ambiguities, thereby turning ICI from foe to friend. The proposed algorithm can further exploit the ICI effect to introduce an additional dimension (namely, CFO) for target resolvability, which enables resolving targets located at the same delay-Doppler-angle cell. Simulation results illustrate the ICI exploitation capability of the proposed approach and showcase its superior detection and estimation performance in high-mobility scenarios over conventional methods.
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19.
  • Keykhosravi, Kamran, 1990, et al. (författare)
  • RIS-Enabled SISO Localization under User Mobility and Spatial-Wideband Effects
  • 2022
  • Ingår i: IEEE Journal on Selected Topics in Signal Processing. - 1941-0484 .- 1932-4553. ; 16:5, s. 1125-1140
  • Tidskriftsartikel (refereegranskat)abstract
    • Reconfigurable intelligent surface (RIS) is a promising technological enabler for the 6th generation (6G) of wireless systems with applications in localization and communication. In this paper, we consider the problem of positioning a single-antenna user in 3D space based on the received signal from a single-antenna base station and reflected signal from an RIS by taking into account the mobility of the user and spatial-wideband (WB) effects. To do so, we first derive the spatial-WB channel model under the far-field assumption, for orthogonal frequency-division multiplexing signal transmission with the user having a constant velocity. We derive the Cram\'er Rao bounds to serve as a benchmark. Furthermore, we devise a low-complexity estimator that attains the bounds in high signal-to-noise ratios. Our estimator neglects the spatial-WB effects and deals with the user mobility by estimating the radial velocities and compensating for their effects in an iterative fashion. We show that the spatial-WB effects can degrade the localization accuracy for large RIS sizes and large signal bandwidths as the direction of arrival or departure deviate from the RIS normal. In particular, for a 64 $\times$ 64 RIS, the proposed estimator is resilient against the spatial-WB effects up to 140 MHz bandwidth. Regarding user mobility, our results suggest that the velocity of the user influences neither the bounds nor the accuracy of our estimator. Specifically, we observe that the state of the user with a high speed (42 m/s) can be estimated virtually with the same accuracy as a static user.
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20.
  • Kilic, Yakup, et al. (författare)
  • Device-Free Person Detection and Ranging in UWB Networks
  • 2014
  • Ingår i: IEEE Journal on Selected Topics in Signal Processing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1941-0484 .- 1932-4553. ; 8:1, s. 43-54
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a novel device-free stationary person detection and ranging method, that is applicable to ultra-wide bandwidth (UWB) networks. The method utilizes a fixed UWB infrastructure and does not require a training database of template waveforms. Instead, the method capitalizes on the fact that a human presence induces small low-frequency variations that stand out against the background signal, which is mainly affected by wideband noise. We analyze the detection probability, and validate our findings with numerical simulations and experiments with off-the-shelf UWB transceivers in an indoor environment.
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21.
  • Landström, Anders, et al. (författare)
  • Morphology-based crack detection for steel slabs
  • 2012
  • Ingår i: IEEE Journal on Selected Topics in Signal Processing. - 1932-4553 .- 1941-0484. ; 6:7, s. 866-875
  • Tidskriftsartikel (refereegranskat)abstract
    • Continuous casting is a highly efficient process used to produce most of the world steel production tonnage, but can cause cracks in the semi-finished steel product output. These cracks may cause problems further down the production chain, and detecting them early in the process would avoid unnecessary and costly processing of the defective goods. In order for a crack detection system to be accepted in industry, however, false detection of cracks in non-defective goods must be avoided. This is further complicated by the presence of scales; a brittle, often cracked, top layer originating from the casting process. We present an approach for an automated on-line crack detection system, based on 3D profile data of steel slab surfaces, utilizing morphological image processing and statistical classification by logistic regression.The initial segmentation successfully extracts 80\% of the crack length present in the data, while discarding most potential pseudo-defects (non-defect surface features similar to defects). The subsequent statistical classification individually has a crack detection accuracy of over 80\% (with respect to total segmented crack length), while discarding all remaining manually identified pseudo-defects. Taking more ambiguous regions into account gives a worst-case false classification of 131~mm within the 30~600~mm long sequence of 150~mm wide regions used as validation data. The combined system successfully identifies over 70\% of the manually identified (unambiguous) crack length, while missing only a few crack regions containing short crack segments.The results provide proof-of-concept for a fully automated crack detection system based on the presented method.
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22.
  • Lei, Wanlu, et al. (författare)
  • Joint Beam Training and Data Transmission Control for mmWave Delay-Sensitive Communications : A Parallel Reinforcement Learning Approach
  • 2022
  • Ingår i: IEEE Journal of Selected Topics in Signal Processing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1932-4553. ; 16:3, s. 447-459
  • Tidskriftsartikel (refereegranskat)abstract
    • Future communication networks call for new solutions to support their capacity and delay demands by leveraging potentials of the millimeter wave (mmWave) frequency band. However, the beam training procedure in mmWave systems incurs significant overhead as well as huge energy consumption. As such, deriving an adaptive control policy is beneficial to both delay-sensitive and energy-efficient data transmission over mmWave networks. To this end, we investigate the problem of joint beam training and data transmission control for mmWave delay-sensitive communications in this paper. Specifically, the considered problem is firstly formulated as a constrained Markov Decision Process (MDP), which aims to minimize the cumulative energy consumption over the whole considered period of time under delay constraint. By introducing a Lagrange multiplier, we transform the constrained MDP into an unconstrained one, which is then solved via a parallel-rollout-based reinforcement learning method in a data-driven manner. Our numerical results demonstrate that the optimized policy via parallel-rollout significantly outperforms other baseline policies in both energy consumption and delay performance.
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23.
  • Lenz, Reiner (författare)
  • Generalized Pareto Distributions-Application to Autofocus in Automated Microscopy
  • 2016
  • Ingår i: IEEE Journal on Selected Topics in Signal Processing. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 1932-4553 .- 1941-0484. ; 10:1, s. 92-
  • Tidskriftsartikel (refereegranskat)abstract
    • Dihedral filters correspond to the Fourier transform of functions defined on square grids. For gray value images there are six pairs of dihedral edge-detector pairs on 5 5 windows. In low-level image statistics the Weibull-or the generalized extreme value distributions are often used as statistical distributions modeling such filter results. Since only points with high filter magnitudes are of interest we argue that the generalized Pareto distribution is a better choice. Practically this also leads to more efficient algorithms since only a fraction of the raw filter results have to be analyzed. The generalized Pareto distributions with a fixed threshold form a Riemann manifold with the Fisher information matrix as a metric tensor. For the generalized Pareto distributions we compute the determinant of the inverse Fisher information matrix as a function of the shape and scale parameters and show that it is the product of a polynomial in the shape parameter and the squared scale parameter. We then show that this determinant defines a sharpness function that can be used in autofocus algorithms. We evaluate the properties of this sharpness function with the help of a benchmark database of microscopy images with known ground truth focus positions. We show that the method based on this sharpness function results in a focus estimation that is within the given ground truth interval for a vast majority of focal sequences. Cases where it fails are mainly sequences with very poor image quality and sequences with sharp structures in different layers. The analytical structure given by the Riemann geometry of the space of probability density functions can be used to construct more efficient autofocus methods than other methods based on empirical moments.
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24.
  • Li, Zuxing, et al. (författare)
  • Privacy-Aware Distributed Bayesian Detection
  • 2015
  • Ingår i: IEEE Journal on Selected Topics in Signal Processing. - 1932-4553 .- 1941-0484. ; 9:7, s. 1345-1357
  • Tidskriftsartikel (refereegranskat)abstract
    • We study the eavesdropping problem in the remotely distributed sensing of a privacy-sensible hypothesis from the Bayesian detection perspective. We consider a parallel distributed detection network where remote decision makers independently make local decisions defined on finite domains and forward them to the fusion center which makes the final decision. An eavesdropper is assumed to intercept a specific set of local decisions to make also a guess on the hypothesis. We propose a novel Bayesian detection-operational privacy metric given by the minimal achievable Bayesian risk of the eavesdropper. Further, we introduce two privacy-aware distributed Bayesian detection formulations, namely the privacy-constrained distributed Bayesian detection problem and the privacy-concerned distributed Bayesian detection problem where the detection performance is optimized under a privacy guarantee constraint and a weighted sum objective of the detection performance and privacy risk is minimized respectively. For an optimal privacy-aware distributed Bayesian detection design, the optimal decision strategy of employing a deterministic likelihood test or a randomized strategy thereof is identified. Further, it is shown that equivalent problems of different formulations always exist and lead to the same optimal privacy-aware distributed Bayesian detection design. The results are illustrated and discussed by numerical examples. The idea of privacy-aware distributed Bayesian detection design provides a novel solution to realize future trustworthy Internet of Things applications.
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25.
  • Lindsten, Fredrik, et al. (författare)
  • Rao–Blackwellized particle smoothers for conditionally linear Gaussian models
  • 2016
  • Ingår i: IEEE Journal on Selected Topics in Signal Processing. - : IEEE. - 1932-4553 .- 1941-0484. ; 10:2, s. 353-365
  • Tidskriftsartikel (refereegranskat)abstract
    • Sequential Monte Carlo (SMC) methods, such as the particle filter, are by now one of the standard computational techniques for addressing the filtering problem in general state-space models. However, many applications require post-processing of data offline. In such scenarios the smoothing problem-in which all the available data is used to compute state estimates-is of central interest. We consider the smoothing problem for a class of conditionally linear Gaussian models. We present a forward-backward-type Rao-Blackwellized particle smoother (RBPS) that is able to exploit the tractable substructure present in these models. Akin to the well known Rao-Blackwellized particle filter, the proposed RBPS marginalizes out a conditionally tractable subset of state variables, effectively making use of SMC only for the “intractable part” of the model. Compared to existing RBPS, two key features of the proposed method are: 1) it does not require structural approximations of the model, and 2) the aforementioned marginalization is done both in the forward direction and in the backward direction.
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26.
  • Lundgren, Malin, 1979, et al. (författare)
  • A CPHD Filter for Tracking With Spawning Models
  • 2013
  • Ingår i: IEEE Journal on Selected Topics in Signal Processing. - 1941-0484 .- 1932-4553. ; 7:3, s. 496-507
  • Tidskriftsartikel (refereegranskat)abstract
    • In some applications of multi-target tracking, appearing targets are suitably modeled as spawning from existing targets. However, in the original formulation of the cardinalized probability hypothesis density (CPHD) filter, this type of model is not supported; instead appearing targets are modeled by spontaneous birth only. In this paper we derive the necessary equations for a CPHD filter for the case when the process model also includes target spawning. For this generalized filter, the cardinality prediction formula might become computationally intractable for general spawning models. However, when the cardinality distribution of the spawning targets is either Bernoulli or Poisson, we derive expressions that are practical and computationally efficient. Simulations show that the proposed filter responds faster to a change in target number due to spawned targets than the original CPHD filter. In addition, the performance of the filter, considering the optimal subpattern assignment (OSPA), is improved when having an explicit spawning model.
  •  
27.
  • Lundquist, Christian, 1978-, et al. (författare)
  • An Extended Target CPHD Filter and a Gamma Gaussian Inverse Wishart Implementation
  • 2013
  • Ingår i: IEEE Journal on Selected Topics in Signal Processing. - : IEEE Signal Processing Society. - 1932-4553 .- 1941-0484. ; 7:3, s. 472-483
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper presents a cardinalized probability hypothesis density (CPHD) filter for extended targets that can result in multiple measurements at each scan. The probability hypothesis density (PHD) filter for such targets has been derived by Mahler, and different implementations have been proposed recently. To achieve better estimation performance this work relaxes the Poisson assumptions of the extended target PHD filter in target and measurement numbers. A gamma Gaussian inverse Wishart mixture implementation, which is capable of estimating the target extents and measurement rates as well as the kinematic state of the target, is proposed, and it is compared to its PHD counterpart in a simulation study. The results clearly show that the CPHD filter has a more robust cardinality estimate leading to smaller OSPA errors, which confirms that the extended target CPHD filter inherits the properties of its point target counterpart.
  •  
28.
  • Ma, Teng, et al. (författare)
  • Integrated Sensing and Communication for Wireless Extended Reality (XR) With Reconfigurable Intelligent Surface
  • 2023
  • Ingår i: IEEE Journal on Selected Topics in Signal Processing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1932-4553 .- 1941-0484. ; 17:5, s. 980-994
  • Tidskriftsartikel (refereegranskat)abstract
    • Future wireless networks will witness ubiquitous human-machine interactions, where extended reality (XR) is expected to be a key scenario in next-generation mobile systems. In this article, we examine the integrated sensing and communication (ISAC) framework in XR, where a reconfigurable intelligent surface (RIS) may assist user (UE) positioning and communication. Specifically, a practical positioning algorithm based on multiple signal classification (MUSIC) with the aid of specially designed RIS configurations is conceived. Furthermore, we formulate the joint optimization of the UE beamformer and RIS phase shifter to maximize the channel capacity under Cramer-Rao lower bound (CRLB) constraints, which is solved by alternating optimization with gradient projection and manifold optimization. Finally, we use simulation results to demonstrate the feasibility of the conceived positioning algorithm and corroborate the effectiveness of the proposed optimization approach.
  •  
29.
  • Ma, Wing-Kin, et al. (författare)
  • The Equivalence of Semidefinite Relaxation MIMO Detectors for Higher-Order QAM
  • 2009
  • Ingår i: IEEE Journal on Selected Topics in Signal Processing. - 1932-4553. ; 3:6, s. 1038-1052
  • Tidskriftsartikel (refereegranskat)abstract
    • In multi-input multi-output (MIMO) detection, semidefinite relaxation (SDR) has been shown to be an efficient high-performance approach. For BPSK and QPSK, it has been found that SDR can provide near-optimal bit error probability performance. This has stimulated a number of recent research endeavors that aim to apply SDR to the high-order QAM cases. These independently developed SDRs are different in concept, structure and complexity, and presently no serious analysis has been given to compare these methods. This paper analyzes the relationship of three such SDR methods, namely the polynomial-inspired SDR (PI-SDR) by Wiesel et al., the bound-constrained SDR (BC-SDR) by Sidiropoulos and Luo, and the virtually-antipodal SDR (VA-SDR) by Mao et al. Rather unexpectedly, we prove that the three SDRs are equivalent in the following sense: The three SDRs yield the same optimal objective values, and their optimal solutions have strong correspondences. Specifically, we establish this solution equivalence between BC-SDR and VA-SDR for any 4(q)-QAM constellations, and that between BC-SDR and PI-SDR for 16-QAM and 64-QAM. Moreover, the equivalence result holds for any channel, problem size, and signal-to-noise ratio. Our theoretical findings are confirmed by simulations, where the three SDRs offer identical symbol error probabilities. Additional simulation results are also provided to demonstrate the effectiveness of SDR compared to some other MIMO detectors, in terms of complexity and symbol error performance.
  •  
30.
  • Magnusson, Sindri, et al. (författare)
  • Communication Complexity of Dual Decomposition Methods for Distributed Resource Allocation Optimization
  • 2018
  • Ingår i: IEEE Journal on Selected Topics in Signal Processing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1932-4553 .- 1941-0484. ; 12:4, s. 717-732
  • Tidskriftsartikel (refereegranskat)abstract
    • Dual decomposition methods are among the most prominent approaches for finding primal/dual saddle point solutions of resource allocation optimization problems. To deploy these methods in the emerging Internet of things networks, which will often have limited data rates, it is important to understand the communication overhead they require. Motivated by this, we introduce and explore twomeasures of communication complexity of dual decomposition methods to identify the most efficient communication among these algorithms. The first measure is epsilon-complexity, which quantifies the minimal number of bits needed to find an epsilon-accurate solution. The second measure is b-complexity, which quantifies the best possible solution accuracy that can be achieved from communicating b bits. We find the exact epsilon -and b-complexity of a class of resource allocation problems where a single supplier allocates resources to multiple users. For both the primal and dual problems, the epsilon-complexity grows proportionally to log(2) (1/epsilon) and the b-complexity proportionally to 1/2(b). We also introduce a variant of the epsilon- and b-complexity measures where only algorithms that ensure primal feasibility of the iterates are allowed. Such algorithms are often desirable because overuse of the resources can overload the respective systems, e.g., by causing blackouts in power systems. We provide upper and lower bounds on the convergence rate of these primal feasible complexity measures. In particular, we show that the b-complexity cannot converge at a faster rate than O(1/b). Therefore, the results demonstrate a tradeoff between fast convergence and primal feasibility. We illustrate the result by numerical studies.
  •  
31.
  • Mai, Vien V., et al. (författare)
  • Wireless Power Transfer for Distributed Estimation in Sensor Networks
  • 2017
  • Ingår i: IEEE Journal on Selected Topics in Signal Processing. - : IEEE. - 1932-4553 .- 1941-0484. ; 11:3, s. 549-562
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper studies power allocation for distributed estimation of an unknown scalar random source in sensor networks with a multiple-antenna fusion center (FC), where wireless sensors are equipped with radio-frequency-based energy harvesting technology. The sensors' observation is locally processed by using an uncoded amplify-and-forward scheme. The processed signals are then sent to the FC, and are coherently combined at the FC, at which the best linear unbiased estimator (BLUE) is adopted for reliable estimation. We aim to solve the following two power allocation problems: 1) minimizing distortion under various power constraints; and 2) minimizing total transmit power under distortion constraints, where the distortion is measured in terms of mean-squared error of the BLUE. Two iterative algorithms are developed to solve the nonconvex problems, which converge at least to a local optimum. In particular, the above algorithms are designed to jointly optimize the amplification coefficients, energy beamforming, and receive filtering. For each problem, a suboptimal design, a single-antenna FC scenario, and a common harvester deployment for collocated sensors, are also studied. Using the powerful semidefinite relaxation framework, our result is shown to be valid for any number of sensors, each with different noise power, and for an arbitrarily number of antennas at the FC.
  •  
32.
  •  
33.
  • Mochaourab, Rami, et al. (författare)
  • Exchange economy in two-user multiple-input single-output interference channels
  • 2012
  • Ingår i: IEEE Journal on Selected Topics in Signal Processing. - : IEEE. - 1932-4553. ; 6:2, s. 151-164
  • Tidskriftsartikel (refereegranskat)abstract
    • We study the conflict between two links in a multiple- input single-output interference channel. This setting is strictly competitive and can be related to perfectly competitive market models. In such models, general equilibrium theory is used to determine equilibrium measures that are Pareto optimal. First, we consider the links to be consumers that can trade goods within themselves. The goods in our setting correspond to beamforming vectors. We utilize the conflict representation of the consumers in the Edgeworth box, a graphical tool that depicts the allocation of the goods for the two consumers, to provide closed-form solution to all Pareto optimal outcomes. Afterwards, we model the situation between the links as a competitive market which additionally defines prices for the goods. The equilibrium in this economy is called Walrasian and corresponds to the prices that equate the demand to the supply of goods. We calculate the unique Walrasian equilibrium and propose a coordination process that is realized by an arbitrator which distributes the Walrasian prices to the consumers. The consumers then calculate in a decentralized manner their optimal demand corresponding to beamforming vectors that achieve the Walrasian equilibrium. This outcome is Pareto optimal and dominates the noncooperative outcome of the systems. Thus, based on the game theoretic model and solution concept, an algorithm for a distributed implementation of the beamforming problem in multiple-input single-output interference channels is provided.
  •  
34.
  • Mohammed, Saif K., et al. (författare)
  • High-Rate Space-Time Coded Large-MIMO Systems : Low-Complexity Detection and Channel Estimation
  • 2009
  • Ingår i: IEEE Journal on Selected Topics in Signal Processing. - 1932-4553 .- 1941-0484. ; 3:6, s. 958-974
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper, we present a low-complexity algorithm for detection in high-rate, non-orthogonal space-time block coded (STBC) large-multiple-input multiple-output (MIMO) systems that achieve high spectral efficiencies of the order of tens of bps/Hz. We also present a training-based iterative detection/channel estimation scheme for such large STBC MIMO systems. Our simulation results show that excellent bit error rate and nearness-to-capacity performance are achieved by the proposed multistage likelihood ascent search (M-LAS) detector in conjunction with the proposed iterative detection/channel estimation scheme at low complexities. The fact that we could show such good results for large STBCs like 16 X 16 and 32 X 32 STBCs from Cyclic Division Algebras (CDA) operating at spectral efficiencies in excess of 20 bps/Hz (even after accounting for the overheads meant for pilot based training for channel estimation and turbo coding) establishes the effectiveness of the proposed detector and channel estimator. We decode perfect codes of large dimensions using the proposed detector. With the feasibility of such a low-complexity detection/channel estimation scheme, large-MIMO systems with tens of antennas operating at several tens of bps/Hz spectral efficiencies can become practical, enabling interesting high data rate wireless applications.
  •  
35.
  • Mueller, Ralf R., et al. (författare)
  • Blind Pilot Decontamination
  • 2014
  • Ingår i: IEEE Journal on Selected Topics in Signal Processing. - 1932-4553 .- 1941-0484. ; 8:5, s. 773-786
  • Tidskriftsartikel (refereegranskat)abstract
    • A subspace projection to improve channel estimation in massive multi-antenna systems is proposed and analyzed. Together with power-controlled hand-off, it can mitigate the pilot contamination problem without the need for coordination among cells. The proposed method is blind in the sense that it does not require pilot data to find the appropriate subspace. It is based on the theory of large random matrices that predicts that the eigenvalue spectra of large sample covariance matrices can asymptotically decompose into disjoint bulks as the matrix size grows large. Random matrix and free probability theory are utilized to predict under which system parameters such a bulk decomposition takes place. Simulation results are provided to confirm that the proposed method outperforms conventional linear channel estimation if bulk separation occurs.
  •  
36.
  •  
37.
  • Qian, Liangxin, et al. (författare)
  • Distributed Learning for Wireless Communications : Methods, Applications and Challenges
  • 2022
  • Ingår i: IEEE Journal on Selected Topics in Signal Processing. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 1932-4553 .- 1941-0484. ; 16:3, s. 326-342
  • Tidskriftsartikel (refereegranskat)abstract
    • With its privacy-preserving and decentralized features, distributed learning plays an irreplaceable role in the era of wireless networks with a plethora of smart terminals, an explosion of information volume and increasingly sensitive data privacy issues. There is a tremendous increase in the number of scholars investigating how distributed learning can be employed to emerging wireless network paradigms in the physical layer, media access control layer and network layer. Nonetheless, research on distributed learning for wireless communications is still in its infancy. In this paper, we review the contemporary technical applications of distributed learning for wireless communications. We first introduce the typical frameworks and algorithms for distributed learning. Examples of applications of distributed learning frameworks in emerging wireless network paradigms are then provided. Finally, main research directions and challenges of distributed learning for wireless communications are discussed.
  •  
38.
  • Rahal, Moustafa, et al. (författare)
  • RIS-Enabled NLoS Near-Field Joint Position and Velocity Estimation under User Mobility
  • 2024
  • Ingår i: IEEE Journal on Selected Topics in Signal Processing. - 1941-0484 .- 1932-4553. ; In Press
  • Tidskriftsartikel (refereegranskat)abstract
    • In the context of single-(BS) nonline- of-sight (NLoS) single-epoch localization with the aid of a reflective (RIS), this paper introduces a novel three-step algorithm that jointly estimates the position and velocity of a mobile (UE), while compensating for the Doppler effects observed in (NF) at the (RIS) elements over the short transmission duration of a sequence of (DL) pilot symbols. First, a low-complexity initialization procedure is proposed, relying in part on (FF) approximation and a static user assumption. Then, an alternating optimization procedure is designed to iteratively refine the velocity and position estimates, as well as the channel gain. %, at every step along the way. The refinement routines leverage small angle approximations and the linearization of the (RIS) response, accounting for both NF and mobility effects. We evaluate the performance of the proposed algorithm through extensive simulations under diverse operating conditions with regard to (SNR), (UE) mobility, uncontrolled multipath and (RIS)-(UE) distance. %We evaluate the performance of the proposed algorithm by means of simulations in a canonical scenario and Our results reveal remarkable performance improvements over the (SoTA) mobility-agnostic benchmark algorithm, while indicating convergence of the proposed algorithm to respective theoretical bounds on position and velocity estimation. %[BD: I remember we had this discussion with CHAL about the use of Algo1 as a variant of an existing algo (in 1st approximation). Does it still hold?], illustrating the dominating impact of the distance to the (RIS), as well as of (UE) velocity.
  •  
39.
  • Rana, Pravin Kumar, et al. (författare)
  • Probabilistic Multiview Depth Image Enhancement Using Variational Inference
  • 2015
  • Ingår i: IEEE Journal on Selected Topics in Signal Processing. - 1932-4553 .- 1941-0484. ; 9:3, s. 435-448
  • Tidskriftsartikel (refereegranskat)abstract
    • An inference-based multiview depth image enhancement algorithm is introduced and investigated in this paper. Multiview depth imagery plays a pivotal role in free-viewpoint television. This technology requires high-quality virtual view synthesis to enable viewers to move freely in a dynamic real world scene. Depth imagery of different viewpoints is used to synthesize an arbitrary number of novel views. Usually, the depth imagery is estimated individually by stereo-matching algorithms and, hence, shows inter-view inconsistency. This inconsistency affects the quality of view synthesis negatively. This paper enhances the multiview depth imagery at multiple viewpoints by probabilistic weighting of each depth pixel. First, our approach classifies the color pixels in the multiview color imagery. Second, using the resulting color clusters, we classify the corresponding depth values in the multiview depth imagery. Each clustered depth image is subject to further subclustering. Clustering based on generative models is used for assigning probabilistic weights to each depth pixel. Finally, these probabilistic weights are used to enhance the depth imagery at multiple viewpoints. Experiments show that our approach consistently improves the quality of virtual views by 0.2 dB to 1.6 dB, depending on the quality of the input multiview depth imagery.
  •  
40.
  •  
41.
  • Rydell, Joakim, et al. (författare)
  • Bilateral Filtering of fMRI Data
  • 2008
  • Ingår i: IEEE JOURNAL OF SELECTED TOPICS IN SIGNAL PROCESSING. - 1932-4553. ; 2:6, s. 891-896
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a class of adaptive filtering techniques of functional magnetic resonance imaging (fMRI) data related to bilateral filtering. This class of methods average activities in consistent regions rather than regions that maximize correlation with a BOLD model. Similarity measures based on signal similarity and anatomical similarity are discussed and compared experimentally to standard linear low pass filtering. It is demonstrated that adaptive filtering provides improved detection of activated regions.
  •  
42.
  • Sadanandan, Sajith Kecheril, et al. (författare)
  • Segmentation and Track-Analysis in Time-Lapse Imaging of Bacteria
  • 2016
  • Ingår i: IEEE Journal on Selected Topics in Signal Processing. - : IEEE Communications Society. - 1932-4553 .- 1941-0484. ; 10:1, s. 174-184
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper, we have developed tools to analyze prokaryotic cells growing in monolayers in a microfluidic device. Individual bacterial cells are identified using a novel curvature based approach and tracked over time for several generations. The resulting tracks are thereafter assessed and filtered based on track quality for subsequent analysis of bacterial growth rates. The proposed method performs comparable to the state-of-the-art methods for segmenting phase contrast and fluorescent images, and we show a 10-fold increase in analysis speed.
  •  
43.
  • Sahmoudi, Mohamed, et al. (författare)
  • Introduction to the Issue on Advanced Signal Processing for GNSS and Robust Navigation
  • 2009
  • Ingår i: IEEE Journal on Selected Topics in Signal Processing. - : IEEE. - 1932-4553 .- 1941-0484. ; 3:5, s. 737-739
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • The 13 papers int his issue fall into three main areas, namely aided Global Navigation Satellite Systems (GNSS) positioning, non-GNSS geolocalization technologies, and robust algorithms for filtering and positioning in severe environments.
  •  
44.
  • Senel, Kamil, et al. (författare)
  • What Role can NOMA Play in Massive MIMO?
  • 2019
  • Ingår i: IEEE Journal on Selected Topics in Signal Processing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1932-4553 .- 1941-0484. ; 13:3, s. 597-611
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper seeks to answer a simple but fundamental question: what role can non-orthogonal multiple access (NOMA) play in massive multi-in multi-out (MIMO)? It is well established that power-domain NOMA schemes can outperform conventional orthogonal multiple access schemes in cellular networks. However, this fact does not imply that NOMA is the most efficient way to communicate in massive MIMO setups, where the base stations have many more antennas than there are users in the cell. These setups are becoming the norm in future networks and are usually studied by assuming spatial multiplexing of the users using linear multi-user beamforming. To answer the above-mentioned question, we analyze and compare the performance achieved by NOMA and multi-user beamforming in both non-line-of-sight and line-of-sight scenarios. We reveal that the latter scheme gives the highestaverage sum rate in massive MIMO setups. We also identify specific cases where NOMA is the better choice in massive MIMO and explain how NOMA plays an essential role in creating a hybrid of NOMA and multi-user beamforming that is shown to perform better than two standalone schemes do.
  •  
45.
  • Shang, Xiaolei, et al. (författare)
  • Weighted SPICE Algorithms for Range-Doppler Imaging Using One-Bit Automotive Radar
  • 2021
  • Ingår i: IEEE Journal on Selected Topics in Signal Processing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1932-4553 .- 1941-0484. ; 15:4, s. 1041-1054
  • Tidskriftsartikel (refereegranskat)abstract
    • We consider the problem of range-Doppler imaging using one-bit automotive LFMCW1 or PMCW radar that utilizes one-bit ADC sampling with time-varying thresholds at the receiver. The one-bit sampling technique can significantly reduce the cost as well as the power consumption of automotive radar systems. We formulate the one-bit LFMCW/PMCW radar range-Doppler imaging problem as one-bit sparse parameter estimation. The recently proposed hyperparameter-free (and hence user friendly) weighted SPICE algorithms, including SPICE, LIKES, SLIM and IAA, achieve excellent parameter estimation performance for data sampled with high precision. However, these algorithms cannot be used directly for one-bit data. In this paper we first present a regularized minimization algorithm, referred to as 1bSLIM, for accurate range-Doppler imaging using one-bit radar systems. Then, we describe how to extend the SPICE, LIKES and IAA algorithms to the one-bit data case, and refer to these extensions as 1bSPICE, 1bLIKES and 1bIAA. These one-bit hyperparameter-free algorithms are unified within the one-bit weighted SPICE framework. Moreover, efficient implementations of the aforementioned algorithms are investigated that rely heavily on the use of FFTs. Finally, both simulated and experimental examples are provided to demonstrate the effectiveness of the proposed algorithms for range-Doppler imaging using one-bit automotive radar systems.
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46.
  • Shariati, Nafiseh, et al. (författare)
  • Low-Complexity Polynomial Channel Estimation in Large-Scale MIMO with Arbitrary Statistics
  • 2014
  • Ingår i: IEEE Journal on Selected Topics in Signal Processing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1932-4553 .- 1941-0484. ; 8:5, s. 815-830
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper considers pilot-based channel estimation in large-scale multiple-input multiple-output (MIMO) communication systems, also known as “massive MIMO”, where there are hundreds of antennas at one side of the link. Motivated by the fact that computational complexity is one of the main challenges in such systems, a set of low-complexity Bayesian channel estimators, coined Polynomial ExpAnsion CHannel (PEACH) estimators, are introduced for arbitrary channel and interference statistics. While the conventional minimum mean square error (MMSE) estimator has cubic complexity in the dimension of the covariance matrices, due to an inversion operation, our proposed estimators significantly reduce this to square complexity by approximating the inverse by a L-degree matrix polynomial. The coefficients of the polynomial are optimized to minimize the mean square error (MSE) of the estimate. We show numerically that near-optimal MSEs are achieved with low polynomial degrees. We also derive the exact computational complexity of the proposed estimators, in terms of the floating-point operations (FLOPs), by which we prove that the proposed estimators outperform the conventional estimators in large-scale MIMO systems of practical dimensions while providing a reasonable MSEs. Moreover, we show that L needs not scale with the system dimensions to maintain a certain normalized MSE. By analyzing different interference scenarios, we observe that the relative MSE loss of using the low-complexity PEACH estimators is smaller in realistic scenarios with pilot contamination. On the other hand, PEACH estimators are not well suited for noise-limited scenarios with high pilot power; therefore, we also introduce the low-complexity diagonalized estimator that performs well in this regime. Finally, we also investigate numerically how the estimation performance is affected by having imperfect statistical knowledge. High robustness is achieved for large-dimensional matrices by us- ng a new covariance estimate which is an affine function of the sample covariance matrix and a regularization term.
  •  
47.
  • Stavrou, Photios A., et al. (författare)
  • Zero-Delay Rate Distortion via Filtering for Vector-Valued Gaussian Sources
  • 2018
  • Ingår i: IEEE Journal on Selected Topics in Signal Processing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1932-4553 .- 1941-0484. ; 12:5, s. 841-856
  • Tidskriftsartikel (refereegranskat)abstract
    • We deal with zero-delay source coding of a vector-valued Gauss-Markov source subject to a mean-squared error (MSE) fidelity criterion characterized by the operational zero-delay vector-valued Gaussian rate distortion function (RDF). We address this problem by considering the nonanticipative RDF (NRDF), which is a lower bound to the causal optimal performance theoretically attainable function (or simply causal RDF) and operational zero-delay RDF. We recall the realization that corresponds to the optimal "test-channel" of the Gaussian NRDF, when considering a vector Gauss-Markov source subject to a MSE distortion in the finite time horizon. Then, we introduce sufficient conditions to show existence of solution for this problem in the infinite time horizon (or asymptotic regime). For the asymptotic regime, we use the asymptotic characterization of the Gaussian NRDF to provide a new equivalent realization scheme with feedback, which is characterized by a resource allocation (reverse-waterfilling) problem across the dimension of the vector source. We leverage the new realization to derive a predictive coding scheme via lattice quantization with subtractive dither and joint memoryless entropy coding. This coding scheme offers an upper bound to the operational zero-delay vector-valued Gaussian RDF. When we use scalar quantization, then for r active dimensions of the vector Gauss-Markov source the gap between the obtained lower and theoretical upper bounds is less than or equal to 0.254r + 1 bits/vector. However, we further show that it is possible when we use vector quantization, and assume infinite dimensional Gauss-Markov sources to make the previous gap to be negligible, i.e., Gaussian NRDF approximates the operational zero-delay Gaussian RDF. We also extend our results to vector-valued Gaussian sources of any finite memory under mild conditions. Our theoretical framework is demonstrated with illustrative numerical experiments.
  •  
48.
  • Ström, Marie, 1984, et al. (författare)
  • Wideband Waveform and Receiver Filter Bank Design for Clutter Suppression
  • 2015
  • Ingår i: IEEE Journal on Selected Topics in Signal Processing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1941-0484 .- 1932-4553. ; 9:8, s. 1366-1376
  • Tidskriftsartikel (refereegranskat)abstract
    • Modern wideband radar systems with long integration time, equipped with arbitrarily waveform generators, raise a demand for advanced signaling transmission schemes. In this paper, we propose two algorithms to select transmit waveforms and receiver filters. The techniques are based on a clutter suppression criterion. For the first algorithm, we employ an optimized filter bank, and for the second algorithm, we use a matched filter bank. Clutter suppression is achieved by minimizing the correlation between receiver filters and interfering clutter echoes. The algorithm, for the optimized filter bank, is extended to adapt the transmission scheme and receiver filters to a time-evolving scenario. Adaptation parameters are based on estimates of a clutter map and detected target characteristics. To estimate the clutter map we propose a Kalman filter, whereas target parameters are calculated using a least-squares fit to data. The efficiency of the algorithms and the adaptation scheme are visualized through a numerical simulation.
  •  
49.
  • Thurley, Matthew J., et al. (författare)
  • Fast morphological image processing open-source extensions for GPU processing with CUDA
  • 2012
  • Ingår i: IEEE Journal on Selected Topics in Signal Processing. - 1932-4553 .- 1941-0484. ; 6:7, s. 849-855
  • Tidskriftsartikel (refereegranskat)abstract
    • GPU architectures offer a significant opportunity for faster morphological image processing, and the NVIDIA CUDA architecture offers a relatively inexpensive and powerful framework for performing these operations. However, the generic morphological erosion and dilation operation in the CUDA NPP library is relatively naive, and performance scales expensively with increasing structuring element size. The objective of this work is to produce a freely available GPU capability for morphological operations so that fast GPU processing can be readily available to those in the morphological image processing community. Open-source extensions to CUDA (hereafter referred to as LTU-CUDA) have been produced for erosion and dilation using a number of structuring elements for both 8 bit and 32 bit images. Support for 32 bit image data is a specific objective of the work in order to facilitate fast processing of image data from 3D range sensors with high depth precision. Furthermore, the implementation specifically allows scalability of image size and structuring element size for processing of large image sets. Images up to 4096 by 4096 pixels with 32 bit precision were tested. This scalability has been achieved by forgoing the use of shared memory in CUDA multiprocessors. The vHGW algorithm for erosion and dilation independent of structuring element size has been implemented for horizontal, vertical, and 45 degree line structuring elements with significant performance improvements over NPP. However, memory handling limitations hinder performance in the vertical line case providing results not independent of structuring element size and posing an interesting challenge for further optimisation. This performance limitation is mitigated for larger structuring elements using an optimised transpose function, which is not default in NPP, and applying the horizontal structuring element. LTU-CUDA is an ongoing project and the code is freely available at https://github.com/VictorD/LTU-CUDA.
  •  
50.
  • Tsakmalis, A., et al. (författare)
  • Constrained Bayesian Active Learning of Interference Channels in Cognitive Radio Networks
  • 2018
  • Ingår i: IEEE Journal on Selected Topics in Signal Processing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1932-4553 .- 1941-0484. ; 12:1, s. 6-19
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper, a sequential probing method for interference constraint learning is proposed to allow a centralized cognitive radio network (CRN) accessing the frequency band of a primary user (PU) in an underlay cognitive scenario with a designed PU protection specification. The main idea is that the CRN probes the PU, and subsequently, eavesdrops the reverse PU link to acquire the binary ACK/NACK packet. This feedback indicates whether the probing-induced interference is harmful or not and can be used to learn the PU interference constraint. The cognitive part of this sequential probing process is the selection of the power levels of the secondary users that aims to learn the PU interference constraint with a minimum number of probing attempts while setting a limit on the number of harmful probing-induced interference events or equivalently of NACK packet observations over a time window. This constrained design problem is studied within the active learning (AL) framework and an optimal solution is derived and implemented with a sophisticated, accurate, and fast Bayesian learning method, the expectation propagation. The performance of this solution is also demonstrated through numerical simulations and compared with modified versions of AL techniques we developed in earlier work.
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