Preprocessing of freehand ultrasound synthetic aperture measurements using DNN. - In: IEEE Xplore digital library, ISSN 2473-2001, (2021), S. 1401-1405
Manual ultrasonic inspection is a widely used Nondestructive Testing (NDT) technique due to its simplicity and compatibility with complex structures. However, in contrast to the data acquired using a robotic positioner, manual measurements suffer from perturbations caused by a variable coupling and a varying scanning density. Imaging techniques like the synthetic aperture focusing technique rely on an unperturbed dense measurement from an equidistant measurement grid. Consequently, imaging based on freehand measurements leads to artifacts. This work aims at reducing such artifacts by preprocessing the manual measurements using Deep Neural Networks (DNN). The training of a DNN requires a large set of labeled measurements which is difficult to obtain in NDT. In this work, we present a technique to train the DNN using only synthetic data. We show that the resulting DNN generalizes well on real measurements. We present an improvement in Generalized Contrast to Noise Ratio by a factor of 20 and 3 compared to omitting the preprocessing for synthetic and measurement data, respectively.
Compressed ultrasound computed tomography in NDT. - In: IEEE Xplore digital library, ISSN 2473-2001, (2021), insges. 4 S.
Ultrasound Computed Tomography (UCT) is challenging due to phenomena such as strong refraction, multiple scattering, and mode conversion. In NDT, large speed of sound contrasts lead to strong artifacts if such phenomena are not modeled correctly; however, enhanced models are computationally expensive. In this work, a two-step framework for Compressed UCT based on the integral approach to the solution of the Helmholtz equation is presented. It comprises a physically motivated forward step and an imaging step that solves a suitable inverse problem. Multiple scattering is accounted for through the use of Neumann series. Convergence problems of Neumann series in high contrast settings are addressed via Padé approximants. Compressed sensing is employed to reduce the computational complexity of the reconstruction procedure by reducing data volumes directly at the measurement step, avoiding redundancy in the data and allowing the ability to steer the admissible computational effort at the expense of reconstruction quality. The proposed method is shown to yield high quality reconstructions under heavy subsampling in the frequency and spatial domains.
Every clock counts - 41 GHz wide-range integer-N clock divider. - In: SMACD/ PRIME 2021, (2021), S. 388-391
Make some noise: energy-efficient 38 Gbit/s wide-range fully-configurable linear feedback shift register. - In: SMACD/ PRIME 2021, (2021), S. 384-387
A 4-channel V-band beamformer featuring a switchless PALNA for scalable phased array systems. - In: IEEE Xplore digital library, ISSN 2473-2001, (2021), S. 839-841
This paper presents a 4-channel bidirectional V-band beamformer adopting a switchless PALNA in a SiGe:C 130 nm BiCMOS technology, featuring ft/fmax of 250/340 GHz. Using such technique saves the silicon area occupied by the RF switches avoiding their lossy effect on PAs outputs and LNAs inputs. The designed beamformer contains PAs, LNAs, vector modulators with active balun, passive power dividers/combiners and an integrated SPI interface. On-wafer measurements show that the fabricated beamformer covers the band from 57 GHz to 66 GHz with an average small signal gain of 18 dB and 9 dB all over the channels in both Tx and Rx modes respectively. Furthermore, the beamformer achieves an OP1dB of 10.5 dBm in Tx mode and an IP1dB of -27 dBm in Rx mode. The circuit occupies 11 mm2 and consumes 230 mW and 100 mW per channel in Tx and Rx modes respectively.
Energy-efficient autonomous resource selection for power-saving users in NR V2X. - In: IEEE Xplore digital library, ISSN 2473-2001, (2021), S. 972-978
Energy efficiency has recently drawn significant attention in diverse applications, such as vehicle-to-everything (V2X) communications. This paper investigates a joint energy efficiency and sum-rate maximization problem in autonomous resource selection in the 5G new radio (NR) vehicular communication while catering for reliability and latency requirements. An autonomous resource allocation problem is formulated as a ratio of sum-rate to energy consumption, where the objective is to maximize the total energy efficiency of power-saving users subject to the reliability and latency requirements. The energy efficiency problem is a mixed-integer programming optimization problem that is computationally complex when the number of users increases. Therefore, a heuristic algorithm, density of traffic-based resource allocation (DeTRA), is proposed to solve the problem. The traffic density per traffic type is considered a metric to split the radio resources and trigger an appropriate resource selection strategy. The simulation results show that the proposed algorithm outperforms the existing schemes in terms of energy efficiency.
Verification of dual-polarized ultra-wideband channel sounder for THz applications. - In: IEEE Xplore digital library, ISSN 2473-2001, (2021), insges. 5 S.
The lower THz bands are foreseen as candidates to achieve the data-rates demanded in the sixth generation (6G) of wireless communications. Hence, multiple measurements for characterization of propagation at these frequencies in different scenarios are being conducted all around the world. This also impulses activities on standardization of measurement equipment and methodologies to define common practices and make measurements from different actors comparable. Therefore, in the present paper we investigate the accuracy of a dual-polarized ultra-wideband channel sounder in the time, angular, and polarization domains by means of a verification methodology based on interferometry.
Enable software-defined radios for real-time MIMO channel sounding. - In: To measure is to know, (2021), insges. 5 S.
This paper describes a field-programmable gate array (FPGA)-based implementation of a switched multiple input multiple output (MIMO) channel sounder realization by use of software-defined radio (SDR) hardware (NI USRP-2954, X310 series with UBX 160 daughterboard). Essential basic functionalities are the synchronous switching of the antenna elements at both link ends and an integrated automatic gain control (AGC) at the receiver. To meet the high timing requirements in the switched MIMO setup, an FPGA-based AGC is introduced. The detector of the AGC is based on a sample-by-sample calculation of the average and maximum of the I/Q samples within a sliding window. The used SDR hardware allows a minimum AGC update interval of approx. 14 [my]s and a timing accuracy of the antenna switching of 5 ns. Our setup demonstrates the applicability of state-of-the-art SDRs as a sounding system for continuous acquisition of the time-variant, directional mobile radio channel.
Characterization of urban radio channels and base station antenna correlation in the 3.75 GHz band. - In: 2021 IEEE 93rd Vehicular Technology Conference (VTC2021-Spring), (2021), insges. 5 S.
Single side mMIMO channel measurements over 100 MHz bandwidth at 3.75 GHz were performed in two German cities. In dense urban as well as urban/suburban environments, a total track length of about 20 km has been measured. Multipath parameters by means of the high-resolution parameter estimator RIMAX are estimated and subsequently used to derive the statistics of large scale parameters and to allow a comparison to the statistics from standard channel model (3GPP, WINNER). While most of the parameters match quite well, for the angular spread at the base station (BS) partly larger deviations are observed. The correlation properties between the 32 dual polarized antenna patches of the BS antenna are investigated with respect to the antenna patch separation as well as to the distance between the BS and user equipment (UE).
Statistics of vehicular detectability for cooperative passive coherent location at urban crossroad. - In: Radar on the move, (2021), insges. 6 S.
The statistical study of target detectability is crucial in radar system design. In this regard, signal-to-noise ratio (SNR) of the received signal at the radars receiver is a key parameter and therefore every influence on SNR should be taken into account. One of the main influences is the fluctuation of the target scattering/reflectivity to the incident electromagnetic wave. Consequently, the target fluctuation models and their accuracy become important. For monostatic radar system, various models can be found in the literature. In contrast, this paper studies a case of vehicular sensing scenario with multistatic configuration for an urban crossroad and proposes a modelling method of the target fluctuation by taking into account the target information, such as size, shape and composed materials, and the wave information, such as polarizations and aspect angles. Furthermore, the derived target fluctuation models are then applied directly to the formulation of the probability of detection for multistatic radar system. These probabilities of detection are also compared to that of monostatic radar system.