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Pérez, Eduardo; Kirchhof, Jan; Krieg, Fabian; Römer, Florian;
Subsampling approaches for compressed sensing with ultrasound arrays in non-destructive testing. - In: Sensors. - Basel : MDPI, ISSN 1424-8220, Volume 20 (2020), issue 23, 6734, Seite 1-23

Full Matrix Capture is a multi-channel data acquisition method which enables flexible, high resolution imaging using ultrasound arrays. However, the measurement time and data volume are increased considerably. Both of these costs can be circumvented via compressed sensing, which exploits prior knowledge of the underlying model and its sparsity to reduce the amount of data needed to produce a high resolution image. In order to design compression matrices that are physically realizable without sophisticated hardware constraints, structured subsampling patterns are designed and evaluated in this work. The design is based on the analysis of the Cramér–Rao Bound of a single scatterer in a homogeneous, isotropic medium. A numerical comparison of the point spread functions obtained with different compression matrices and the Fast Iterative Shrinkage/Thresholding Algorithm shows that the best performance is achieved when each transmit event can use a different subset of receiving elements and each receiving element uses a different section of the echo signal spectrum. Such a design has the advantage of outperforming other structured patterns to the extent that suboptimal selection matrices provide a good performance and can be efficiently computed with greedy approaches.



https://doi.org/10.3390/s20236734
Reum, Thomas; Töpfer, Hannes;
A bicomplex finite element method for wave propagation in homogeneous media. - In: Compel : international journal of computation & mathematics in electrical & electronic engineering.. - Bradford : Emerald, ISSN 2054-5606, Bd. 39 (2020), 5, S. 1031-1039

Purpose The purpose of this paper is to present the advantageous applicability of the bicomplex analysis in the context of the Finite Element Method (FEM). This method can be applied for wave propagation problems in various environments. Design/methodology/approach In this paper, the bicomplex number system is introduced and accordingly the differential equation for time-harmonic Maxwells equations in homogeneous media is derived in detail. Besides that, numerical simulations of wave propagation are performed and compared to the traditional approach based on classical FEM related to the Helmholtz equation. The appropriate error norm is investigated for different discretizations. Findings The results show that the use of bicomplex analysis in FEM leads to the higher accuracy of the electromagnetic field determination compared to the traditional Helmholtz approach. By using the bicomplex-valued formulation, the complex-valued electric and magnetic fields can be found directly and no additional FEM calculations are necessary to get the whole field. Originality/value The direct bicomplex formulation overcomes the use of the second order derivatives, which leads to the higher accuracy. In general, accurate calculations of the wave propagation in FEM is still an open problem and the approach described in this paper is a contribution to this class of problems.



https://doi.org/10.1108/COMPEL-01-2020-0010
Häfner, Stephan; Dürr, André; Waldschmidt, Christian; Thomä, Reiner;
Mitigation of leakage in FMCW radars by background subtraction and whitening. - In: IEEE microwave and wireless components letters : a publication of the IEEE Microwave Theory and Techniques Society.. - New York, NY : IEEE, Bd. 30 (2020), 11, S. 1105-1107

Leakage in frequency-modulated continuous-wave (FMCW) radar with a homodyne receiver induces strong signal components in the lower frequency parts of the radar observations. There, the dynamic range of the observations has been reduced, such that close and weak targets are hard to detect. In this letter, a signal processing method is proposed to mitigate the leakage. First, background subtraction is applied to cancel the leakage. As the cancellation is imperfect, a noisy signal portion remains: the leakage noise. A statistical model is developed to describe the leakage noise as a colored noise process. This model is parameterized from measurements and used to whiten the observations. As a result, the dynamic range is improved, and the close targets become better detectable.



https://doi.org/10.1109/LMWC.2020.3023850
Hassan, Nina; Käske, Martin; Schneider, Christian; Sommerkorn, Gerd; Thomä, Reiner; Matolak, David;
Measurement-based determination of parameters for non-stationary TDL models with reduced number of taps. - In: IET microwaves, antennas and propagation. - London : IET, ISSN 1751-8733, Bd. 14 (2020), 14, S. 1719-1732

This study proposes a new strategy of extracting parameters for tapped delay line (TDL) channel models from vehicle to infrastructure channel measurements. The proposed approach is based on an already existing method to derive parameters for a non-stationary model using first-order Markov chains. It will be shown that with the proposed method, the number of taps necessary to regenerate the delay spread of a channel can be significantly reduced. An approach will be discussed to evaluate the performance of the model. The feasibility of the method will be confirmed using channel sounding measurements.



https://doi.org/10.1049/iet-map.2019.0945
Gentile, Camillo; Molisch, Andreas F.; Chuang, Jack; Michelson, David G.; Bodi, Anuraag; Bhardwaj, Anmol; Ozdemir, Ozgur; Khawaja, Wahab Ali Gulzar; Guvenc, Ismail; Cheng, Zihang; Rottenberg, Fran¸cois; Choi, Thomas; Müller, Robert; Han, Niu; Dupleich, Diego;
Methodology for benchmarking radio-frequency channel sounders through a system model. - In: IEEE transactions on wireless communications. - New York, NY : IEEE, Bd. 19 (2020), 10, S. 6504-6519

Development of a comprehensive channel propagation model for high-fidelity design and deployment of wireless communication networks necessitates an exhaustive measurement campaign in a variety of operating environments and with different configuration settings. As the campaign is time-consuming and expensive, the effort is typically shared by multiple organizations, inevitably with their own channel-sounder architectures and processing methods. Without proper benchmarking, it cannot be discerned whether observed differences in the measurements are actually due to the varying environments or to discrepancies between the channel sounders themselves. The simplest approach for benchmarking is to transport participant channel sounders to a common environment, collect data, and compare results. Because this is rarely feasible, this paper proposes an alternative methodology - which is both practical and reliable - based on a mathematical system model to represent the channel sounder. The model parameters correspond to the hardware features specific to each system, characterized through precision, in situ calibration to ensure accurate representation; to ensure fair comparison, the model is applied to a ground-truth channel response that is identical for all systems. Five worldwide organizations participated in the cross-validation of their systems through the proposed methodology. Channel sounder descriptions, calibration procedures, and processing methods are provided for each organization as well as results and comparisons for 20 ground-truth channel responses.



https://doi.org/10.1109/TWC.2020.3003617
Da Rosa Zanatta, Mateus; Costa, João Paulo Carvalho Lustosa da; Antreich, Felix; Haardt, Martin; Elger, Gordon; Lopes De Mendon¸ca, Fábio Lúcio; De Sousa, Rafael Timóteo;
Tensor-based framework with model order selection and high accuracy factor decomposition for time-delay estimation in dynamic multipath scenarios. - In: IEEE access : practical research, open solutions.. - New York, NY : IEEE, ISSN 2169-3536, Bd. 8 (2020), S. 174931-174942

Global Navigation Satellite Systems (GNSS) are crucial for applications that demand very accurate positioning. Tensor-based time-delay estimation methods, such as CPD-GEVD, DoA/KRF, and SECSI, combined with the GPS3 L1C signal, are capable of, significantly, mitigating the positioning degradation caused by multipath components. However, even though these schemes require an estimated model order, they assume that the number of multipath components is constant. In GNSS applications, the number of multipath components is time-varying in dynamic scenarios. Thus, in this paper, we propose a tensor-based framework with model order selection and high accuracy factor decomposition for time-delay estimation in dynamic multipath scenarios. Our proposed approach exploits the estimates of the model order for each slice by grouping the data tensor slices into sub-tensors to provide high accuracy factor decomposition. We further enhance the proposed approach by incorporating the tensor-based Multiple Denoising (MuDe).



https://doi.org/10.1109/ACCESS.2020.3024597
Häfner, Stephan; Thomä, Reiner;
Compensation of motion-induced phase errors and enhancement of Doppler unambiguity in TDM-MIMO systems by model-based estimation. - In: IEEE sensors letters : ISLECD.. - New York, NY : IEEE, ISSN 2475-1472, Volume 4 (2020), issue 10, 7003504, 4 Seiten

Utilization of multiple input multiple output (MIMO) systems in radar and channel sounding has gained increased attention in recent years. Quite often, time-division multiplexing (TDM) is employed to realize orthogonal waveforms at the transmitter. Apart from its advantages, TDM has two severe drawbacks. First, motion-induced phase variations become indistinguishable from phase migration due to the signal's arrival direction. This is termed angle-Doppler coupling, which causes ambiguities in angle, and Doppler estimation. Second, the unambiguously resolvable Doppler, i.e., the Doppler bandwidth, is reduced. In this letter, a model-based estimation approach will be proposed, which compensates for angle-Doppler coupling, and restores the Doppler bandwidth. A data model for the MIMO observations is derived, which is exploited by a maximum likelihood estimator to infer angle, delay, and Doppler from the observations. The performance of the proposed approach will be testified by simulations.



https://doi.org/10.1109/LSENS.2020.3020700
E-Asim, Fazal-; Almeida, André L. F.; Haardt, Martin; Cavalcante, Charles C.; Nossek, Josef A.;
Rank-one detector for Kronecker-structured constant modulus constellations. - In: IEEE signal processing letters : a publication of the IEEE Signal Processing Society.. - New York, NY : IEEE, ISSN 1558-2361, Bd. 27 (2020), S. 1420-1424

To achieve a reliable communication with short data blocks, we propose a novel decoding strategy for Kronecker-structured constant modulus signals that provides low bit error ratios (BERs) especially in the low energy per bit to noise power spectral density ratio (E_b/N_o). The encoder exploits the fact that any M-PSK constellation can be factorized as Kronecker products of lower or equal order PSK constellation sets. A construction of two types of schemes is first derived. For such Kronecker-structured schemes, a conceptually simple decoding algorithm is proposed, referred to as Kronecker-RoD (rank-one detector). The decoder is based on a rank-one approximation of the "tensorized" received data block, has a built-in noise rejection capability and a smaller implementation complexity than state-of-the-art detectors. Compared with convolutional codes with hard and soft Viterbi decoding, Kronecker-RoD outperforms the latter in BER performance at same spectral efficiency.



https://doi.org/10.1109/LSP.2020.3010133
Semper, Sebastian; Döbereiner, Michael; Pawar, Sankalp; Landmann, Markus; Del Galdo, Giovanni;
eadf: representation of far-field antenna responses in Python. - In: SoftwareX. - Amsterdam [u.a.] : Elsevier, ISSN 2352-7110, Bd. 12 (2020), 100583, S. 1-6

https://doi.org/10.1016/j.softx.2020.100583
Mostafa, Mohamed H.; Chamaani, Somayyeh; Sachs, Jürgen;
Singular spectrum analysis-based algorithm for vitality monitoring using M-sequence UWB sensor. - In: IEEE sensors journal. - New York, NY : IEEE, ISSN 1558-1748, Bd. 20 (2020), 9, S. 4787-4802

https://doi.org/10.1109/JSEN.2019.2962721