Gridless parameter estimation in partly calibrated rectangular arrays. - In: IEEE Xplore digital library, ISSN 2473-2001, (2024), S. 8796-8800
Spatial frequency estimation from a mixture of noisy sinusoids finds applications in various fields. The widely used subspace-based methods provide super-resolution parameter estimation at a low computational cost. However, they require an accurate array calibration, which is difficult for large antenna arrays. Sparsity-based methods have been shown to be more robust than subspace-based methods in difficult scenarios, e.g., in the case with a small number of snapshots and/or correlated sources. In this paper, we consider the direction-of-arrival (DOA) estimation in partly calibrated rectangular arrays comprising several calibrated and identical subarrays. We derive a gridless sparse formulation for DOA estimation based on the shift-invariance properties of the array and develop an efficient algorithm in the alternating direction method of multipliers (ADMM) framework. Numerical simulations show the superior error performance of our proposed method compared to subspace-based methods.
https://doi.org/10.1109/ICASSP48485.2024.10446959
Leveraging tensor subspace prior: enhanced sum of nuclear norm minimization for tensor completion. - In: IEEE Xplore digital library, ISSN 2473-2001, (2024), S. 7655-7659
Tensor completion has attracted increasing attention in signal processing, computer vision, and biomedical engineering. By using nuclear norm minimization, a tensor completion problem can be converted into a convex program and enjoys properties gained from matrix completion. The low rank property has been widely used for tensor/matrix completion. However, the prior subspace information can also be utilized, which has been ignored and does not exhibit its full power in the existing formulation. In this paper, we propose a new framework leveraging tensor subspace prior for the sum of nuclear norm (SNN) minimization, which supports a range of tensor decompositions. By using the knowledge of the self-prior (SP)/nonself-prior (NSP) and further designing an efficient algorithm based on the Alternating Direction Method of Multipliers (ADMM), the performance of tensor completion can be enhanced. The superiority of the proposed method is verified by extensive numerical experiments.
https://doi.org/10.1109/ICASSP48485.2024.10447654
Improving the spatial correlation characteristics of antenna arrays using linear operators and wide-band modelling. - In: IEEE Xplore digital library, ISSN 2473-2001, (2024), S. 67-73
The analysis of wireless communication channels at the mmWave, sub-THz and THz bands gives rise to difficulties in the construction of antenna arrays due to the small maximum inter-element spacing constraints at these frequencies. Arrays with uniform spacing greater than half the wavelength for a certain carrier frequency exhibit aliasing side-lobes in the angular domain, prohibiting non-ambiguous estimates of a propagating wave-front’s angle of arrival.In this paper, we present how wide-band modelling of the array response is useful in mitigating this spatial aliasing effect. This approach aims to reduce the grating lobes by exploiting the angle- and frequency-dependent phase-shifts observed in the response of the array to a planar wave-front travelling across it.Furthermore, we propose a method by which the spatial correlation characteristics of an array operating at 33 GHz carrier frequency with an instantaneous bandwidth of 1 GHz can be improved such that the angular-domain side-lobes are reduced by 5-10 dB. This method, applicable to arbitrary antenna array manifolds, makes use of a linear operator that is applied to the base-band samples of the channel transfer function measured in space and frequency domains. By means of synthetically simulated arrays, we show that when operating with a bandwidth of 1 GHz, the use of a derived linear operator applied to the array output results in the spatial correlation characteristics approaching those of the array operating at a bandwidth of 12 GHz. Hence, non-ambiguous angle estimates can be obtained in the field without the use of expensive high-bandwidth RF front-end components.
https://doi.org/10.1109/WSA61681.2024.10511328
Excitation signal design for THz channel sounding and propagation parameter estimation. - In: IEEE Xplore digital library, ISSN 2473-2001, (2024), insges. 5 S.
In this publication, we analyze how the performance of propagation parameter estimation for THz channel sounding can be improved by the power spectrum design of a multicarrier waveform. To this end, we discuss the Fisher information of the propagation parameters and the corresponding deterministic Cramèr-Rao lower bound (CRB) as well as their relation to the carrier powers of the excitation signal. We use these quantities to design waveforms that improve range estimation. In practice, evaluating the Fisher information requires prior knowledge of the propagation scenario which is usually unavailable. Hence, we propose two solutions which we compare numerically to the classical approach of equal power distribution. The evaluation shows that an optimized power distribution can improve the CRB comparable up to a 4 dB gain in signal-to-noise ratio (SNR) if knowledge about the propagation scenario is available and slightly less if the scenario is unknown.
https://doi.org/10.23919/EuCAP60739.2024.10501423
Characterization of typical instantaneous exposure and usage scenarios in the vicinity of 5G massive-MIMO base stations. - In: IEEE Xplore digital library, ISSN 2473-2001, (2024), insges. 5 S.
A recurring discussion is whether it is useful to specify a typical exposure in addition to the theoretical maximum exposure for massive-MIMO systems, but currently no reliable method exists. Therefore, typical 5G use cases are investigated, grouped according to their throughput, and three typical data rates are derived. To evaluate the reproducibility of data rates and corresponding exposures, three measurement runs have been performed at four measurement points (MP) with different cell utilization by other users, while a 5G UE generated the typical data rates in the vicinity of the MP. Furthermore, temporal variations have been considered by evaluating three different averaging times. The results demonstrate that the exposure values are reproducible within typical measurement uncertainty across different averaging times and even across different measurement runs. Therefore, this method is considered to be capable of providing reproducible measurements of the typical exposure in addition to the maximum possible exposure.
https://doi.org/10.23919/EuCAP60739.2024.10501436
Characterization of propagation from measurements at sub-THz for ISAC applications in an emulated dynamic industrial scenario. - In: IEEE Xplore digital library, ISSN 2473-2001, (2024), insges. 5 S.
The large blocks of free instantaneous bandwidth at (sub-)THz and the utilization of high gain radio interfaces makes the (sub-)THz suitable for sensing applications. In this paper we present the analysis of novel dual-polarized double directional measurements at 190 GHz in an industrial setting with integrated sensing and communication applications in view. The set-up consists of a bi-static configuration emulating two access points with beam-steering capabilities in a machine room. One access point serves a machine with a wireless link, while the other access point senses the environment to detect moving objects. The objective is to detect possible obstructions that could interrupt the communication link or cause accidents on the production line. The results have shown that the system aspects as narrow beams and large bandwidths allow the early identification of objects in the environment from the measured channel impulse response.
https://doi.org/10.23919/EuCAP60739.2024.10501207
Hybrid antenna measurement and post-processing for 5G small cell exposure assessment with site-specific mounting conditions. - In: IEEE Xplore digital library, ISSN 2473-2001, (2024), insges. 5 S.
Ongoing mobile radio small cell deployment requires detailed analysis of the electromagnetic exposure which is dependent on the installation environment. To facilitate site-specific small cell exposure analysis, a hybrid exposure assessment approach is utilized which combines antenna nearfield measurement and post-processing. An equivalent current antenna model is investigated under virtually varying installation conditions, considering three real applications of small cell installation. The equivalent current antenna model's results are in good agreement with reference measurements and geometry-based simulations. Antenna pattern deviations vary between 0.9 dB and 2.9 dB, depending on the installation environment selected. This highlights the advantages of using the hybrid exposure assessment approach which adequately captures and reflects changes in the installation surroundings. Additionally, it yields comparable results to established methods and provides extensive flexibility for virtual exposure estimations by taking into account varying installation environments.
https://doi.org/10.23919/EuCAP60739.2024.10501705
Ray tracing and measurement-based characterization of inter/intra-machine THz wireless channels. - In: IEEE Xplore digital library, ISSN 2473-2001, (2024), insges. 5 S.
We characterize the wireless propagation channels at 300 GHz in an industrial environment through measurements and ray tracing simulations. Two different scenarios are considered representing wireless connections between an access point and an industrial machine (inter-machine scenario), and between two components inside the same machine (intra-machine scenario) are considered. For both scenarios, we compute the channel response in terms of power angle delay profile and compare the results obtained through measurements and simulations, which show a good match.
https://doi.org/10.23919/EuCAP60739.2024.10501627
Reproducibility studies of instantaneous and 6-minute average exposure measurements around 5G massive-MIMO base stations. - In: IEEE Xplore digital library, ISSN 2473-2001, (2024), insges. 5 S.
Measurements of RF exposure to mobile radio base stations are important for risk communication. We measured instantaneous exposure with a focus on 5G with an exposimeter on an identical route on three afternoons to study the reproducibility. Due to different walking speeds, the relationship between time and place was not identical for the measurements, so time is not suitable as a reference for comparison. When the distance walked was used as reference, accuracy problems of the exposimeter's internal GPS system occurred, resulting in a mismatch between the actual location and the GPS location. This problem was successfully corrected by using the gradient descent with momentum method. The three measurements show a variation in maximum measured exposure of up to 5.4 dB for a selected section of the route, which is reduced to 2.8 dB when averaged over 6-minute intervals, which is acceptable given typical measurement uncertainties of ±3 dB.
https://doi.org/10.23919/EuCAP60739.2024.10501516
Grid-free harmonic retrieval and model order selection using convolutional neural networks. - In: IEEE Xplore digital library, ISSN 2473-2001, (2024), insges. 5 S.
Harmonic retrieval techniques are the foundation of radio channel sounding, estimation and modeling. This paper introduces a Deep Learning approach for joint delay- and Doppler estimation from frequency and time samples of a radio channel transfer function. Our work estimates the two-dimensional parameters from a signal containing an unknown number of paths. Compared to existing deep learning-based methods, the signal parameters are not estimated via classification but in a quasi-grid-free manner. This alleviates the bias, spectral leakage, and ghost targets that grid-based approaches produce. The proposed architecture also reliably estimates the number of paths in the measurement. Hence, it jointly solves the model order selection and parameter estimation task. Additionally, we propose a multi-channel windowing of the data to increase the estimator's robustness. We also compare the performance to other harmonic retrieval methods and integrate it into an existing maximum likelihood estimator for efficient initialization of a gradient-based iteration.
https://doi.org/10.23919/EuCAP60739.2024.10501588