Sparse arrays offer evident advantages over their uniform linear counterparts, including larger aperture and higher angular resolution. Despite their benefits, typical sparse arrays, such as nested and coprime arrays, exhibit increased complexity, and mutual coupling effects between array elements can not be neglected. In contrast, the sparse uniform linear array (SULA) features uniform inter-element spacing, where the distance between elements exceeds half a wavelength, resulting in a larger aperture and reduced mutual-coupling effects. However, estimating the direction of arrival (DOA) with the SULA may lead to inevitable angle ambiguity. Recently, FMCW radar has gained significant attention due to its capability of high-precision ranging under conditions of high signal-to-noise ratios. This study leveraged the high-precision ranging characteristics of FMCW radar to achieve unambiguous DOA estimation by utilizing absolute distance values from targets to each SULA element. Simulation experiments validated the effectiveness of the proposed algorithm.

Mastering real-time and accurate downhole information is crucial for ensuring drilling safety, improving drilling efficiency, and maximizing economic benefits. In recent years, logging while drilling (LWD) technologies, represented by mud pulse telemetry (MPT), achieved significant success. However, they still face challenges such as a large amount of downhole information conflicting with low information transmission rates, severe channel distortion, strong noise interference, and weak surface receiving signals. Therefore, this review collects and updates the papers, patents, and conference articles in the relevant field over the past ten years. Starting from the basic structure of communication systems, the downhole signal coding and modulation technologies of the MPT system are discussed. The attenuation reflection brought by the mud channel and various noise interferences in the system are described. The surface noise cancellation, channel equalization, synchronization, and decoding are studied in detail. By analyzing the theoretical principles, development breakthroughs, and relevant challenges that can improve the development of LWD technologies, this review aims to assist researchers in the field in obtaining the latest references and strategies.

The essence of frequency-modulated continuous wave (FMCW) radar-ranging is to estimate the frequency of the beat signal, and the frequency’s accuracy determines the range’s accuracy. This paper introduces a coherent spectral model based on the correlation between the phase and frequency of the FMCW radar beat signal. A coherent chirp z-transform (CZT) algorithm is proposed by applying the coherent spectral model to the CZT algorithm. The simulation results proved that the ranging accuracy of the coherent CZT algorithm is better than other algorithms. Generally, there are two Cramer-Rao bounds (CRB) in range estimation. The first CRB assumes that the phase is unknown, and the second CRB assumes that the phase is known. Most existing ranging algorithms can only reach the first CRB, while the coherent CZT algorithm can reach the second CRB. The efficiency of the coherent CZT algorithm has been confirmed in three radar-ranging experiments with targets of various sizes and shapes. The experimental results also showed that the coherent CZT algorithm has a higher accuracy than 50 μm, and its root mean squared error (RMSE) is significantly lower than other algorithms.

A direction-finding algorithm by the time-modulated array (TMA) is proposed for binary phase shift keying (BPSK) signals. In the proposed scheme, only two antenna elements and a single RF channel are required, and the switch period has no relation with the symbol period of the BPSK signal. Numeric simulations are provided to examine the performance of the proposed scheme, and a two-element TMA test platform is constructed to verify its effectiveness.

Non-intrusive load monitoring is an attractive approach to obtain the energy consumption information without monitoring every device in a building. The main difficulty in the problem is to disaggregate the total power into the power used by specific devices. To solve the problem, this paper proposes an event-based scheme, in which the events corresponding to the appliance on or off are detected and then the events corresponding to the operation of a single device are matched. Finally, the events belonging to a single device are clustered so that the total power is disaggregated into the single device. The experiments are tested on the REDD dataset and the results are compared with the available algorithm, which verifies the validity of the algorithm.

In this study, an interference detection and mitigation method is proposed for frequency-modulated continuous-wave radar systems based on time-domain signal reconstruction. The interference detection method uses the difference in one-dimensional fast Fourier transform (1D-FFT) results between targets and interferences. In the 1D-FFT results, the target appears as a peak at the same frequency point for all chirps within one frame, whereas the interference appears as the absence of target peaks within the first or last few chirps within one frame or as a shift in the target peak position in different chirps. Then, the interference mitigation method reconstructs the interference signal in the time domain by the estimated parameter from the 1D-FFT results, so the interference signal can be removed from the time domain without affecting the target signal. The simulation results show that the proposed interference mitigation algorithm can reduce the amplitude of interference by about 25 dB. The experimental results show that the amplitude of interference is reduced by 20–25 dB, proving the effectiveness of the simulation results.