Presents corrections to the paper, (Corrections to "Windowed Two-Dimensional Fourier Transform Concentration and Its Application to ISAR Imaging").

In this letter, the focus is on vibration related to Rammstein concerts, which took place in July 2023 at the Silesian Stadium, Poland. First, the concert-induced signals underwent preliminary study in the time domain (waveforms) and the time–frequency domain (spectrograms). Next, the investigation was improved by filtering, allowing for better ambient noise band interpretation. The signal quality enhancement was confirmed by frequency and time–frequency metrics. Finally, after the filtering, Lissajous curves (2-D motion) were produced, clearly indicating the significant improvement of the signal filtering.

This article presents a robust technique for inverse synthetic aperture radar (ISAR) image enhancement using bivariate multitaper spectrum estimation with simultaneous concentration. The proposed method aims to average multiple focused ISAR images obtained using orthonormal windows. As a result, an image with an improved concentration and reduced noise is obtained. Compared to state-of-the-art methods, the presented approach efficiently suppresses stationary and non-stationary noise in ISAR images, leading to contrast and entropy enhancement. Extensive simulations are shown to illustrate the superiority of the proposed technique quantitatively, confirming its utility in practical systems. Ultimately, the real-life high-resolution ISAR image processing result is shown, demonstrating the method’s performance in active frequency-modulated continuous wave (FMCW) radars.

Presents corrections to the paper, (Corrections to “Multitaper ISAR Noise Suppression”).

This work presents the results from field tests of a recently proposed Random-Padded Orthogonal Time Frequency Space Modulated (RP-OTFSM) waveform designed for integrated short-range sensing and telecommunication (ISAC) systems. The system consists of two nodes. The first is a software-defined radio (SDR)-based transmitter working at a carrier frequency of 5.8 GHz with 20 MHz bandwidth, which sends 4-QAM modulated data in the delay-Doppler domain of OTFS. The second is a digital SDR-based receiver with two antennas, one for reference and another for surveillance, built from two parts: a digital data decoder for communication purposes and a passive radar workstation for sensing applications. The main aim of the sensing radar module is to estimate the range and velocity of vehicles moving in the surrounding urban environment. The paper briefly summarizes the generation, transmission, and decoding of the RP-OTFSM waveform. It is shown that both tasks of the system are successfully completed in the receiver: 1) after channel estimation and correction, digital data are recovered, and 2) cars driven nearby are correctly detected. Using experimental results, the benefits and limitations of using the OTFSM waveform in ISAC systems are presented.

This paper presents a novel approach to inverse synthetic radar (ISAR) image enhancement using time-frequency (TF) vertical synchrosqueezing (VSS). The authors proposed adding the signal extraction block to the ISAR image processing path. Since the vertical synchrosqueezing technique does not change the signal amplitude-phase dependencies but only performs its decomposition and denoising, the proposed method is noninvasive. It was shown that denoising the signal by the VSS in the TF domain reduces the side lobe level of the ISAR image and enables its denoising. For imaging purposes, the authors derived four novel TF signal parameter estimators in the TF domain that are practically investigated in a radar application. The proposed technique was extensively tested through simulation studies and on data obtained from measurements using high-resolution wideband frequency modulated continuous wave (FMCW) radar. The usefulness of the proposed technique is shown using simulated and real-life results.

This paper addresses two substantial issues connected with using synthetic aperture radar (SAR) imaging to improve the robustness of airborne navigation systems for Global Positioning System (GPS) signal jamming. The first is related to the problem of automatic trajectory correction estimation based on image registration. The authors propose a method dedicated to SAR systems called cumulative minimum square distance matching (CMSDM). It allows for real-time trajectory error estimation of the inertial navigation system (INS) and, as a result, enables correction estimation when the global navigation satellite system (GNSS) signal is unavailable or jammed. The intense simulation study and real-life data processing show the essential improvement and acceleration of processing compared to the state-of-the-art technique. For the correct operation of the navigation system based on the CMSDM algorithm, precise knowledge of the altitude of the airborne platform is necessary. With a jammed GNSS signal, this may not be achievable with traditional methods. Thus, the second issue discussed in this article is the estimation of the airborne platform’s altitude with the use of SAR images. Also, in this case, the experiment has shown that the proposed solution works correctly and can be a precious source of navigational data.

This paper presents a novel non-parametric technique for two-dimensional spectrum readability enhancement. The approach is based on relocating a windowed bivariate Fourier transform with regard to its frequency estimates computed using a moving analyzing window. To this aim, four spatial instantaneous frequency estimators are proposed. A strongly concentrated spectrum with improved component separability is obtained with the proposed technique. The method was intensively tested using simulated and real-life signals. As an example of the method application, inverse synthetic aperture radar (ISAR) images were created and then focused, significantly improving the contrast and entropy. However, the presented technique can be applied to other bivariate signal analyses whenever the windowed two-dimensional Fourier transform (W2D-FT) is applied.

This article presents the pioneering results of successful target detection using a fully operational and cooperative 5G cellular network as a source of illumination in a passive radar system. The electromagnetic wave generated by the real-life base station allowed for remote sensing of a moving car in bistatic geometry, which shows the feasibility of passive radar in which new generation radio networks serve as an illuminator of opportunity. This article describes passive radar principles, the theoretical fundamentals of the 5G signal structure, and the proposed processing for 5G network-based passive radar. Also, the 5G passive radar demonstrator is described, and the trial results show the possibilities and limitations of using new radio standards in the context of passive radars.

In this letter, a novel angular jerk estimator (AJE) in the time-frequency (TF) domain is proposed. For this purpose, the properties of the short-time Fourier transform (STFT) are taken into consideration, which allows for computation of the instantaneous angular jerk for each time and frequency(t,ω)coordinate. Additionally, apart from the introduced AJE, two novel forms of the instantaneous chirp rate (CR) and the instantaneous frequency (IF) estimators are provided, which is an improvement on the capabilities of these tools when compared to approaches existing in the literature. The proposed estimators are presented in analytic form, tested from the perspective of their precision, and compared to the Cramer-Rao Lower Bound (CRLB) as well as validated under numerical experiments.