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This paper presents a fast and compressible multiple signal classification algorithm (C-MUSIC) based on the manifold separation technique (MST) for a uniform circular array (UCA), named as MC-MUSIC. Making use of the MST, the steering vector (SV) of the UCA can be converted into a new SV, which has a Vandermonde structure similar to a uniform linear array. Then a noise-like subspace cluster (NLSC) can be generated by applying a new linear relation between the true direction-of-arrival (DOA) and virtual DOA to the new given SV. Finally, the angular field-of-view can be compressed to a small sector by the intersection of the NLSC so that the calculation times of the spatial spectrum can be reduced effectively. Simulations demonstrate the presented method can maintain the high precision of the DOA estimation with low computational complexity. [ABSTRACT FROM AUTHOR]

In array signal processing, Estimating the quantity of signal sources represents a crucial area of investigation. In this paper, a comprehensive introduction and analysis of the estimation methods for determining the number of signal sources are presented, including the background and significance, and the significance of precise estimation of the quantity of signal sources. The influence of factors such as signal-to-noise ratio (SNR), noise background, and number of snapshots on the estimation algorithm is discussed in detail. At the same time, common array models are introduced. Then, different signal source number estimation algorithms are analyzed in detail, and their respective advantages and applicable conditions are pointed out. Finally, the performance of each algorithm in different situations is evaluated by comparing the performance of the algorithms under different SNRs, snapshot numbers, and array elements. The experimental results show that with the increase of the SNR and the number of array elements, the correct estimation probability of the algorithm also increases correspondingly, which provides a reliable experimental basis and performance evaluation for the estimation. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Dalian Polytechnic University is the property of Journal of Dalian Polytechnic University Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

UAV communications have seen a rapid rise in the last few years. The drone class of UAV has particularly become more widespread around the world, and illicit behavior using drones has become a problem. Therefore, localization, tracking, and even taking control of drones have also gained interest. Knowing the frequency of a target signal, its position can be determined (as the angle of arrival with respect to a fixed receiver point) using radio frequency-based localization techniques. One such technique is represented by the subspace-based algorithms that offer highly accurate results. This paper presents the implementation of the MUSIC algorithm on an SDR-based system using a uniform circular antenna array and its experimental evaluation in relevant outdoor environments for drone localization. The results show the capability of the system to indicate the AoA of the target signal. The results are compared with the actual direction computed from the log files of the drone application and validated with a professional direction-finding solution (i.e., Narda SignalShark equipped with the automatic direction-finding antenna). [ABSTRACT FROM AUTHOR]

Aiming at the problem that the coherent signal cannot be estimated when the traditional UCA-RB-MUSIC algorithm is used to detect the partial discharge of the transformer, an improved UCA-RB-MUSIC algorithm is suggested to reconstruct the signals captured by the array so that the number of calls sources is equivalent to the rank of the reconstructed signal matrix. The impact of correlated signals is eradicated. The results of simulation analysis and experimental verification show that when the improved UCA-RB-MUSIC algorithm is used to locate a single and double partial discharge source, the improved positioning error is only half of the mistake before improvement, which enhances the accuracy and resolution of uniform circular array positioning and the accuracy of transformer partial discharge detection.

The channel matrix of the commonly used uniform circular array-based orbital angular momentum (UCA-OAM) system reaches the full-rank state when the degree of freedom (DoF) is limited only by the number of UCA antenna elements. The rank of the channel matrix of the UCA-OAM system is equal to DoF under this condition. However, the practical DoF of the UCA-OAM system is always affected by other transmission factors, such as the transmission distance and the radius of the receiving antenna. Therefore, by exploiting the practical DoF of the UCA-OAM system affected by the transmission distance and the radii of the receiving antenna and transmission antenna, a novel channel capacity model of the UCA-OAM communication system with a deficient-rank channel (DRC) matrix is first proposed. Moreover, the formulas of the channel matrix and channel capacity for the DRC matrix are analytically derived. The results of numerical simulations indicate that when the practical transmission factors including transmission distance and radii of the receiving antenna and transmission antenna are considered, the UCA-OAM communication system with the DRC matrix has less channel capacity than that with the full-rank channel (FRC) matrix. These simulated results provide helpful guidance on the practical application of the UCA-OAM communication system. [ABSTRACT FROM AUTHOR]

In order to solve the problem of direction finding of coherent signals for uniform circular array under the condition of underdetermination, a direction of arrival (DOA) estimation algorithm combining geometric sequence decomposition and sparse reconstruction was proposed.Geometric sequence decomposition was used to split coherent groups and estimate the actual direction vector of each coherent group, while sparse reconstruction was used to estimate DOA for each coherent group.Simulation results demonstrate that when the number of elements of the uniform circular array is M, compared with the existing algorithms, the maximum number of sources that can be estimated by the proposed algorithm is M(M-1).And when the number of sources is large, the success rate and accuracy of direction finding are better.In addition, the proposed algorithm can solve the “angle merger” problem, and has advantages in the direction finding tasks with very few snapshots.

The channel matrix of the commonly used uniform circular array-based orbital angular momentum (UCA-OAM) system reaches the full-rank state when the degree of freedom (DoF) is limited only by the number of UCA antenna elements. The rank of the channel matrix of the UCA-OAM system is equal to DoF under this condition. However, the practical DoF of the UCA-OAM system is always affected by other transmission factors, such as the transmission distance and the radius of the receiving antenna. Therefore, by exploiting the practical DoF of the UCA-OAM system affected by the transmission distance and the radii of the receiving antenna and transmission antenna, a novel channel capacity model of the UCA-OAM communication system with a deficient-rank channel (DRC) matrix is first proposed. Moreover, the formulas of the channel matrix and channel capacity for the DRC matrix are analytically derived. The results of numerical simulations indicate that when the practical transmission factors including transmission distance and radii of the receiving antenna and transmission antenna are considered, the UCA-OAM communication system with the DRC matrix has less channel capacity than that with the full-rank channel (FRC) matrix. These simulated results provide helpful guidance on the practical application of the UCA-OAM communication system.

Copyright of Journal of Chongqing University of Posts & Telecommunications (Natural Science Edition) is the property of Chongqing University of Posts & Telecommunications and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The safety valve is the core component of the pressure-relief protection device for pressure-bearing special equipment. When the safety valve leaks, the medium of the pressure vessel will be lost and wasted, which may cause safety accidents. With the aim to solve the problem of accurately locating the multiple leakage sources of safety valves, a localization method combining a uniform circular array acoustic emission detection and an improved multiple signal classification (MUSIC) algorithm is proposed. First, an improved wavelet threshold function denoising method is introduced to extract acoustic emission signals with high SNR, thereby reducing the rank of the covariance matrix, weakening the noise dispersion caused by eigenvalue reconstruction, avoiding signal and noise cross-confusion, and improving positioning accuracy. By introducing a windowed fast Fourier transform (FFT) frequency division processing link to obtain narrowband signal, the premise of using MUSIC positioning algorithm is established. In addition, a forward/backward spatial smoothing algorithm is introduced in the decoherence link to reduce co-channel interference, reduce the rank loss of the signal covariance matrix, and improve the positioning accuracy of the algorithm. The results show that when the working pressure is 0.70 MPa, 0.75 MPa, and 0.80 MPa, the deviation between the azimuth angle and elevation angle positioning results of each leakage source obtained by the improved MUSIC algorithm and the actual angle does not exceed 2°, and the relative error does not exceed 3.5%. Therefore, the improved MUSIC algorithm can accurately locate multiple leakage sources of the safety valve, and as the working pressure of the safety valve increases, the positioning accuracy of the improved MUSIC algorithm also increases accordingly. [ABSTRACT FROM AUTHOR]

This paper presents the generation of orbital angular momentum (OAM) vortex waves with mode +1 using dielectric resonator antenna (DRA) array. The proposed antenna was designed and fabricated using FR-4 substrate to generate OAM mode +1 at 3.56 GHz (5G new radio band). The proposed antenna consists of 2 × 2 rectangular DRA array, a feeding network, and four cross slots etched on the ground plane. The proposed antenna succeeded in generating OAM waves; this was confirmed by the measured radiation pattern (2D polar form), simulated phase distribution, and intensity distribution. Moreover, mode purity analysis was carried out to verify the generation of OAM mode +1, and the purity obtained was 53.87%. The antenna operates from 3.2 to 3.66 GHz with a maximum gain of 7.3 dBi. Compared with previous designs, this proposed antenna is low-profile and easy to fabricate. In addition, the proposed antenna has a compact structure, wide bandwidth, high gain, and low losses, thus meeting the requirements of 5G NR applications. [ABSTRACT FROM AUTHOR]

In the direction-of-arrival (DOA) estimation methods for uniform circular arrays (UCAs) with directional sensors, the high computational complexity arises when achieving the estimation accuracy by leveraging all the sensors in the element space. We present a low-complexity sectorized DOA estimation scheme for directional UCAs. It models the radiation pattern within half-power bandwidth in a closed mathematical expression and thereby constructs reconfigurable sectorized steering vectors of an arbitrary angular sector by using the Hadamard cyclic vector with the Vandermonde structure. The DOA estimation over the azimuth plane throughout the element space is transformed to DOA estimates within multiple individual angular sectors. The new scheme comprises three stages, i.e., submatrix extraction, sectorized weighted beamforming and sector DOA estimation. The feasibility and effectiveness of the proposed scheme are validated by numerical simulations. The simulation results demonstrate that, compared to the previous sector-free DOA estimation methods based on the entire azimuth plane, our scheme has a low hardware and computational complexity under an acceptable estimation error. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Data Acquisition & Processing / Shu Ju Cai Ji Yu Chu Li is the property of Editorial Department of Journal of Nanjing University of Aeronautics & Astronautics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A reconfigurable ultra-wideband multimode terahertz OAM antenna array based on graphene and vanadium dioxide (VO 2) is presented in this paper. The uniform circular array (UCA) composed of circularly polarized (CP) antennas, which include a ring radiation patch, a parasitic patch, a perovskite substrate and an irregular VO 2 ground plane. The radiation patch is covered with a layer of graphene, by changing the chemical potential of graphene, the working bandwidth and axial ratio bandwidth of the antenna can be changed. By changing the phase state of VO 2 (metal state / insulation state) to control the working state of the antenna. The impedance bandwidth (IBW) of the CP antenna proposed is 115.09% (1.73–6.42 THz), the axial ratio bandwidth (ARBW) is 43.97% (2.36–3.69 THz). Using the CP antenna unit can simplify the complex feed network, and only feeding the equal amplitude and equal phase excitation can realize the vortex wave. Changing the number and rotation angle of the antenna unit can realize multimode vortex waves with the l = 0, ±1, ±2, ±3, the purity is approximately 1, respectively. The proposed UCA has excellent application prospect in the 6G communication. [ABSTRACT FROM AUTHOR]

In order to solve the problem of direction finding of coherent signals for uniform circular array under the condition of underdetermination, a direction of arrival (DOA) estimation algorithm combining geometric sequence decomposition and sparse reconstruction was proposed. Geometric sequence decomposition was used to split coherent groups and estimate the actual direction vector of each coherent group, while sparse reconstruction was used to estimate DOA for each coherent group. Simulation results demonstrate that when the number of elements of the uniform circular array is M, compared with the existing algorithms, the maximum number of sources that can be estimated by the proposed algorithm is M(M--1). And when the number of sources is large, the success rate and accuracy of direction finding are better. In addition, the proposed algorithm can solve the "angle merger" problem, and has advantages in the direction finding tasks with very few snapshots. [ABSTRACT FROM AUTHOR]

Copyright of Telecommunication Engineering is the property of Telecommunication Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract In order to improve the quality of the received signal and system spectral efficiency, accurate beamforming using a given antenna array is essential for multiple-input multiple-output (MIMO) systems. To obtain desired MIMO transmission performance, construction of codebooks which are composed of matching beamforming vectors to the array structure is important. To effectively cover different types of mobile traffic, the base station for 5G new radio employs antenna arrays in various sizes and shapes. Nevertheless, the codebooks adopted by the 3GPP standard so far are based on the uniform linear array and the uniform planar array, necessitating design techniques for a wider class of antenna arrays. In this paper, we propose codebook construction methods for the uniform circular array with parameters to flexibly set the initial phase and step size based on the channel characteristics of the user equipment (UE). When tested over the 3GPP spatial channel model, the proposed codebooks show a substantial amount of gain over the conventional codebooks in all UE locations within the cell.

Vortex electromagnetic wave carries the Orbital Angular Momentum (OAM), and thus has a spiral wavefront structure, which contains the azimuthal information of the target in the echo signal when performing radar imaging compared with planar waves. Hence, this kind of electromagnetic wave shows great potential for various applications in the field of radar detection and imaging, and it is expected to become the development direction of new-system radars. This paper describes in detail the research progress in vortex radar imaging technology in recent years. First, the characteristics of the vortex electromagnetic wave and the principles of imaging using a uniform circular array are introduced. Then the paper reviews the developmental history and research status of vortex radar imaging technology, according to three research directions: vortex radar imaging model, vortex radar gaze imaging algorithm, and vortex radar motion imaging. Finally, the prospects for the development of vortex radar imaging have been presented, along with the key scientific issues and trends for the future developments of vortex radar imaging.

Abstract In this paper, we present a low complexity sparse beamspace direction-of-arrival (DOA) estimation method for uniform circular array (UCA). In the proposed method, we firstly use the beamspace transformation (BT) to transform the signal model of UCA in element-space domain to that of virtual uniform linear array (ULA) in beamspace domain. Subsequently, by applying the vectoring operator on the virtual ULA-like array signal model, a novel dimension-reduction sparse beamspace signal model is derived based on Khatri-Rao (KR) product, the observation data of which is represented by the single measurement vectors (SMVs) via vectorization of sparse covariance matrix. And then, the DOA estimation is formulated as a convex optimization problem by following the concept of a sparse-signal-representation (SSR) of the SMVs. Finally, simulations are carried out to validate the effectiveness of the proposed method. The results show that without knowledge of the number of signals, the proposed method not only has higher DOA resolution than the subspace-based methods in low signal-to-noise ratio (SNR), but also has far lower computational complexity than other sparse-like DOA estimation methods.

Mixed source localization plays an important role in passive radars. Aiming at the problem of low accuracy via phase difference method under a uniform circular array, this paper proposes a matrix differencing method for mixed far-field and near-field source localization. First, a two-dimensional MUltiple SIgnal Classification (MUSIC) method was utilized to estimate the azimuth and elevation angles of far-field sources. Thereafter, the covariance matrix difference method was exploited to extract the difference matrix of near-field sources. The azimuth and elevation angles of the far-field sources were estimated using the Estimation of Signal Parameters via Rotational Invariance Techniques-like (ESPRIT-like) method. Furthermore, the distance of the near-field sources was obtained by the one-dimensional MUSIC method. Finally, simulations were performed to verify the performance of the proposed algorithm. The proposed algorithm could effectively identify the mixed source when the two-dimensional Direction-Of-Arrival (DOA) of the far-field and near-field sources were the same. Moreover, the proposed algorithm could improve the accuracy of the mixed source parameter estimation. Results show that when the signal-to-noise ratio was set to 20 dB, the 2-D DOA estimation error of the near-field source was approximately 0.01°, and the distance error of the near-field source was approximately 0.1 m.

The effects of random array deformations on Direction-of-Arrival (DOA) estimation with root-Multiple Signal Classification for uniform circular arrays (UCA root-MUSIC) are characterized by a conformally mapped generalized Polynomial Chaos (gPC) algorithm. The studied random deformations of the array are elliptical and are described by different Beta distributions. To successfully capture the erratic deviations in DOA estimates that occur at larger deformations, specifically at the edges of the distributions, a novel conformal map is introduced, based on the hyperbolic tangent function. The application of this new map is compared to regular gPC and Monte Carlo sampling as a reference. A significant increase in convergence rate is observed. The numerical experiments show that the UCA root-MUSIC algorithm is robust to the considered array deformations, since the resulting errors on the DOA estimates are limited to only 2 to 3 degrees in most cases. [ABSTRACT FROM AUTHOR]

The inspection of wellbore casings has been extensively investigated owing to the increasing concern for safety in oil and gas production. However, efficient techniques for inspecting asymmetry defects have not been achieved. In this study, we developed a uniform circular array (UCA) to address the problem of borehole pulsed eddy current (PEC) techniques for asymmetry defect inspection in downhole casings. Based on the borehole PEC system model, the UCA developed with multiple independent probes was designed to achieve asymmetry defect inspection, and the three-dimensional magnetic field data of borehole depths, circumferential azimuths, and sampling times could be obtained. Furthermore, a multichannel data acquisition circuit, which guarantees downhole operation at 150 °C, was developed for the synthesized UCA. Using azimuth dimension information from the synthesized UCA at a certain borehole depth, we obtained an inspection approach for the width and penetration depth of asymmetry defects in the circumferential and radial directions, respectively. Simulations and field experiments were conducted, and the results demonstrate the effectiveness of the proposed method in inspecting asymmetry defects. [ABSTRACT FROM AUTHOR]

To improve the computation and real-time performances of the multiple signal classification (MUSIC) algorithm in 3D space, a fast sound source localization method based on the bat algorithm (BA) and the 3D-MUSIC, called BA-based 3D-MUSIC algorithm (3D-BMUSIC), is presented in this paper. 3D-BMUSIC greatly reduces the computation load by replacing the regular grid search with the BA. First, the near-field spherical wave model is established to obtain the spectral function of the 3D-MUSIC. Then, the spectral function is defined as the fitness function, which calculates the fitness value corresponding to each bat position. Finally, the global optimal bat position with the largest fitness value, as sound source localization, is obtained by successive iteration and sorting. The simulation and experiment show that 3D-BMUSIC accurately estimates the DOA and distance of near-field sources, and the root-mean-square error (RMSE) of 3D-BMUSIC is less than that of 3D-MUSIC. In addition, 3D-BMUSIC effectively reduces the computation time by approximately 96–98%. With shorter computation time and higher efficiency, 3D-BMUSIC promotes hardware implementation and is more suitable for high-precision localization of near-field sound sources. [ABSTRACT FROM AUTHOR]

In this paper, we study the two-dimensional direction of arrival (2D-DOA) estimation problem in a switching uniform circular array (SUCA), which means performing 2D-DOA estimation with a reduction in the number of radio frequency (RF) chains. We propose a covariance matrix completion algorithm for 2D-DOA estimation in a SUCA. The proposed algorithm estimates the complete covariance matrix of a fully sampled UCA (FUCA) from the sample covariance matrix of the SUCA through a neural network. Afterwards, the MUSIC algorithm is performed for 2D-DOA estimation with the completed covariance matrix. We conduct Monte Carlo simulations to evaluate the performance of the proposed algorithm in various scenarios; the performance of 2D-DOA estimation in the SUCA gradually approaches that in the FUCA as the SNR or the number of snapshots increases, which means that the advantages of a FUCA can be preserved with fewer RF chains. In addition, the proposed algorithm is able to implement underdetermined 2D-DOA estimation. [ABSTRACT FROM AUTHOR]

This paper addresses the two-dimensional (2D) direction-of-arrival (DOA) estimation issue for signals with known waveforms but unknown amplitudes using uniform circular array (UCA). Unlike maximum likelihood (ML) methods such as decoupled maximum likelihood (DEML), parallel decomposition (PADEC) and so forth, which estimate DOA by spectrum peak search, we propose an efficient interferometer-based method with known waveforms. The proposed method first estimates spatial signature matrix based on ML method whose each column contains 2D DOA information corresponding to a source. Then, an interferometer procedure is performed to obtain 2D DOA estimate of each source from a closed-form solution separately and in parallel. Several simulation results show that the proposed method can achieve a significantly improvement in performance that coincides with the ML method as well as Cramér-Rao Bound (CRB), especially under some poor conditions, such as low SNR, fewer sensors or small snapshots. In addition, the performance will not degrade as the number of sources increases if the source signals are uncorrelated with each other. Meanwhile, it reduces a great amount of computational complexity without loss of too much accuracy. Thus, the proposed method is quite suitable for 2D DOA estimation with known waveforms in practice. [ABSTRACT FROM AUTHOR]

The uniform circular array (UCA) has been considered to be an effective way to generate orbital angular momentum (OAM) waves. However, by using UCA to transmit multiplexing OAM signals, the peak-to-average power ratio (PAPR) is unavoidable, which brings the low efficiency to the power amplification. In this letter, the interferometry code is introduced to reduce the PAPR in the antenna element of OAM multiplexing transmission at the transmitter. Specifically, the system architecture of OAM by UCA is proposed with the interferometry code spread for PAPR reduction. The simulations and experiments confirm the validity and efficiency of the proposed scheme. [ABSTRACT FROM AUTHOR]

This paper presents the generation of orbital angular momentum (OAM) vortex waves with mode +1 using dielectric resonator antenna (DRA) array. The proposed antenna was designed and fabricated using FR-4 substrate to generate OAM mode +1 at 3.56 GHz (5G new radio band). The proposed antenna consists of 2 × 2 rectangular DRA array, a feeding network, and four cross slots etched on the ground plane. The proposed antenna succeeded in generating OAM waves; this was confirmed by the measured radiation pattern (2D polar form), simulated phase distribution, and intensity distribution. Moreover, mode purity analysis was carried out to verify the generation of OAM mode +1, and the purity obtained was 53.87%. The antenna operates from 3.2 to 3.66 GHz with a maximum gain of 7.3 dBi. Compared with previous designs, this proposed antenna is low-profile and easy to fabricate. In addition, the proposed antenna has a compact structure, wide bandwidth, high gain, and low losses, thus meeting the requirements of 5G NR applications.

In this paper, we propose a uniform circular array antenna with a simple feeding structure operating in the 5.2 GHz band for orbital angular momentum (OAM) mode multiplexing. The proposed antenna can generate simultaneously two types of OAM modes (l=±2) using eight radiating patches and a feed circuit consisting of one hybrid coupler and two concentric series-parallel feedlines. Because the two feedlines are designed concentrically with different radii, they do not intersect each other in the same plane, thus having the advantage of being spatially efficient. The successful creation of the two OAM modes was confirmed through the measured radiation pattern and helical phase distribution. The dual-mode OAM transmission test shows that the proposed antenna can be successfully employed for OAM mode multiplexing by obtaining >12.4 dB of isolation between the two OAM mode channels. [ABSTRACT FROM AUTHOR]

In order to improve the quality of the received signal and system spectral efficiency, accurate beamforming using a given antenna array is essential for multiple-input multiple-output (MIMO) systems. To obtain desired MIMO transmission performance, construction of codebooks which are composed of matching beamforming vectors to the array structure is important. To effectively cover different types of mobile traffic, the base station for 5G new radio employs antenna arrays in various sizes and shapes. Nevertheless, the codebooks adopted by the 3GPP standard so far are based on the uniform linear array and the uniform planar array, necessitating design techniques for a wider class of antenna arrays. In this paper, we propose codebook construction methods for the uniform circular array with parameters to flexibly set the initial phase and step size based on the channel characteristics of the user equipment (UE). When tested over the 3GPP spatial channel model, the proposed codebooks show a substantial amount of gain over the conventional codebooks in all UE locations within the cell. [ABSTRACT FROM AUTHOR]

Copyright of Systems Engineering & Electronics is the property of Journal of Systems Engineering & Electronics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Radar coincidence imaging (RCI), used in conjunction with a uniform circular array (UCA), is presented in this paper. When performing two-dimensional (2-D) imaging for a target, using RCI in conjunction with a uniform linear array (ULA), in three-dimensional (3-D) coordinates, the symmetry phenomenon occurs in certain situation. To overcome this problem, using RCI with a UCA is proposed. First, the symmetry phenomenon of RCI with a ULA and the causes are introduced. Then, the RCI method with a UCA is presented, the signal model is given based on the UCA, and the imaging method is introduced. Finally, the general relationship between the resolution of RCI with a UCA and the independent characteristic of the reference radiation field is analyzed. In view of this, RCI with a UCA has better adaptability to 2-D imaging in 3-D coordinates. Simulation results validate the theoretical analysis and the imaging method.

Physical layer security is a cross research hotspot of information security and wireless communications. Recently, orbital angular momentum (OAM) technology has attracted widespread attention due to its potential of improving capacity and spectrum efficiency. However, there are few researches on system security based on OAM technology. In this work, we studied the security of the proposed OAM wiretap system by applying physical layer security theory to OAM communications. Firstly, we proposed a uniform circular array-based multi-mode OAM system and derived the secrecy capacity. Secondly, the phase profiles, channel capacity and received power of OAM beams are analyzed in terms of various system parameters in oblique scenarios at 30GHz. Thirdly, we discussed the security of the proposed OAM wiretap system. The results show that the system using vortex waves is superior to conventional communication systems using planar electromagnetic waves in terms of system security due to the inherent divergence and spiral phase structure of OAM beams. Moreover, we found that the distortion of OAM beams during transmission and the center shift at receiving end will occur and that system is more stable for high-mode OAM propagation in oblique scenarios. This work can provide an effective guidance for the research and application of OAM communications.

In order to improve the direction-of-arrival (DOA) estimation performance of quasi-stationary signals (QSS) using a uniform circular array (UCA), this paper addresses novel method in the context of sparse representation framework. Based on the Khatri-Rao transform, UCA can achieve a higher number of degrees of freedom to resolve more signals than the number of sensors. Then, by exploiting the two-dimensional (2-D) joint grid of UCA, the estimations of elevation and azimuth angles can be obtained from the sparse representation perspective. Finally, an expectation-maximization iteration method is developed to estimate DOAs of QSS from a Bayesian perspective. Since SBL makes full use of the sparse structure of QSS, thus the proposed algorithm possesses higher angular resolution and better DOA estimation precision compared with existing methods. Numerical simulation demonstrate the validity of the proposed method.

In this paper, the authors propose an effective classification and localization algorithm of mixed far-field and near-field sources using a uniform circular array under the unknown mutual coupling. In practice, the assumption of an ideal receiving sensor array is rarely satisfied. The effects of unknown mutual coupling would degrade the performance of most high resolution algorithms. Firstly, according to rank reduction type method, the direction of arrival of far-field sources is estimated directly without mutual coupling elimination. Then, these estimates are adopted to reconstruct the mutual coupling matrix. Finally, both direction and range parameters of near-field sources are obtained through MUSIC search after mutual coupling effects and far-field components elimination. The proposed algorithm only requires the second order cumulant and any three dimensional spectrum search is circumvented. Some simulation results would prove that the proposed algorithm can reduce more than eighty percent estimating error of mixed sources localization compared to those algorithms without mutual coupling compensation.

In this paper, we present a low complexity sparse beamspace direction-of-arrival (DOA) estimation method for uniform circular array (UCA). In the proposed method, we firstly use the beamspace transformation (BT) to transform the signal model of UCA in element-space domain to that of virtual uniform linear array (ULA) in beamspace domain. Subsequently, by applying the vectoring operator on the virtual ULA-like array signal model, a novel dimension-reduction sparse beamspace signal model is derived based on Khatri-Rao (KR) product, the observation data of which is represented by the single measurement vectors (SMVs) via vectorization of sparse covariance matrix. And then, the DOA estimation is formulated as a convex optimization problem by following the concept of a sparse-signal-representation (SSR) of the SMVs. Finally, simulations are carried out to validate the effectiveness of the proposed method. The results show that without knowledge of the number of signals, the proposed method not only has higher DOA resolution than the subspace-based methods in low signal-to-noise ratio (SNR), but also has far lower computational complexity than other sparse-like DOA estimation methods. [ABSTRACT FROM AUTHOR]

The orbital angular momentum (OAM) based communication is a promising technology in the wireless communication system for its improving spectrum efficiency. However, for the OAM demultiplexing, it requires a very large aperture size in the receiving end due to the OAM beam divergence and the amplitude null in the beam center, which restricts the full development of OAM based communication. In this paper, we propose a novel partial arc sampling receiving (PASR) scheme based on the augmented dynamic mode decomposition (ADMD) to solve this issue. We explore the use of the phase delay coordinates in the conventional DMD to sort the arbitrary OAM modes with arc sampling receiving. Simulation results demonstrate the accuracy and robustness of the proposed approach in sorting both integral and fractional OAM modes with the PASR scheme. Our work offers a practical approach for demultiplexing OAM beams in radio communication systems with fewer receiving devices, especially for the long-distance transmission case. [ABSTRACT FROM AUTHOR]

We consider the design of a uniform circular array (UCA) system under array misalignment over line-of-sight (LoS) channels. UCAs have been considered as useful array structures since their LoS channels can be diagonalized without the channel state information at the transmitter (Tx). However, such a characteristic holds only when transceiver arrays are perfectly aligned. To overcome this difficulty, we propose an optimal design method and transceiver architectures for UCA systems under array misalignment that achieve channel capacity without knowledge of misalignment angles. To this end, we first verify that the singular values of the misaligned UCA system are independent of tilting and center-shift and small relative array rotation, but fluctuate with the Radii Product to Distance Ratio (RPDR). Using the result, we present an optimal design method for UCA systems that performs an one-dimensional search for the RPDR to maximize channel capacity, and we show that a simple zero-forcing (ZF) receiver can achieve the maximum channel capacity because of the channel characteristic at the optimal design criteria. Additionally, we propose a low-complexity precoding scheme for UCA systems in which the optimal design criteria cannot be fulfilled. The simulation results demonstrate the validity of the proposed design method and transceiver architectures. [ABSTRACT FROM AUTHOR]

Copyright of Journal of National University of Defense Technology / Guofang Keji Daxue Xuebao is the property of NUDT Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The vortex electromagnetic (EM) wave carrying orbital angular momentum (OAM) has been introduced in radar imaging to take full advantage of its special phase front. It has been demonstrated that the azimuthal and range resolution are decided by the number of OAM mode and frequency bandwidth respectively. In this paper, theelevation resolution of the vortex wave transmitted by a uniform circular array is derived for the first time through the calculation of correlation function of two closely adjacent points. Since large number of OAM modes should be applied to achieve high-resolution image, which is difficult to realize in practice, the sparse Bayesian learning (SBL) is introduced to reconstruct the targets for 2-D EM vortex imaging. Simulation results show that the targets located at different elevation angle can be reconstructed correctly and higher resolution can be achieved based on the SBL reconstruction algorithm.

This paper addresses the two-dimensional (2D) direction-of-arrival (DOA) estimation issue for signals with known waveforms but unknown amplitudes using uniform circular array (UCA). Unlike maximum likelihood (ML) methods such as decoupled maximum likelihood (DEML), parallel decomposition (PADEC) and so forth, which estimate DOA by spectrum peak search, we propose an efficient interferometer-based method with known waveforms. The proposed method first estimates spatial signature matrix based on ML method whose each column contains 2D DOA information corresponding to a source. Then, an interferometer procedure is performed to obtain 2D DOA estimate of each source from a closed-form solution separately and in parallel. Several simulation results show that the proposed method can achieve a significantly improvement in performance that coincides with the ML method as well as Cramér-Rao Bound (CRB), especially under some poor conditions, such as low SNR, fewer sensors or small snapshots. In addition, the performance will not degrade as the number of sources increases if the source signals are uncorrelated with each other. Meanwhile, it reduces a great amount of computational complexity without loss of too much accuracy. Thus, the proposed method is quite suitable for 2D DOA estimation with known waveforms in practice.

Recently, a single source location problem has attracted special attention in many previous works. A method was lately proposed to estimate three-dimensional (3-D) parameters (i.e. range, azimuth angle, elevation angle) for single source using a geometry restriction-free Uniform Circular Array (UCA), whereas it required a strong presupposition. In this letter, considering the problem of estimating 3-D parameters of a single near-field source, we expand the signal model to a generalised one based on the previous work. This expansion is more available to common situations including near-field condition. In addition, in contrast to the previous work, the proposed method is shown to be more accurate and computationally efficient. Numerical simulations are provided to verify the performance of the proposed method. [ABSTRACT FROM AUTHOR]

Signal estimation at the antenna is a major challenge of the antenna array structure because the received signals have different directions. Therefore, in this paper, a Genetic Algorithm (GA) is applied to the uniform circular array for the optimization of array structure in regard to its geometry. On the optimized array structure, four different algorithms (Estimation of Signal Parameter via Rotational Invariance Technique – ESPRIT, First Order Forward Prediction - FOFP, Beamscan, and Multiple Signal Classification - MUSIC) have been implemented in order to estimate the signal direction accurately with quick estimation time. The accuracy has been calculated with Root Mean Square Error (RMSE) indices. From the experimental analysis, it has been found that the performance of the ESPRIT algorithm is better than the others in terms of accuracy and estimation time. [ABSTRACT FROM AUTHOR]

Copyright of Telecommunication Engineering is the property of Telecommunication Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this paper, we employ the geometry of uniform circular array to achieve classification and localization of mixed near-field and far-field sources. Considering that the eigendecomposition of the covariance matrix requires high computational cost, we develop the propagator method to obtain the noise subspace and reduce complexity. Firstly, since the direction parameters of far-field sources at centrosymmetry sensors hold a conjugate structure while the covariance matrix of near-field sources holds a Hermitian structure, we exploit the covariance differencing approach to extract the pure near-field sources from mixed sources. Then, we improve the ESPRIT-like method and one-dimensional MUSIC method to determine the 2-D direction-of-arrival (DOA) and range of near-field sources, respectively. Finally, by calculating the noise power of mixed sources, we utilize the oblique projection approach to extract the pure far-field sources and exploit the 2-D MUSIC method to determine the 2-D DOA of far-field sources. Simulations demonstrate that the proposed algorithm can avoid the pseudo-peaks in the 2-D DOA spatial spectrum of far-field sources and provide the satisfactory performance of mixed source localization. [ABSTRACT FROM AUTHOR]

Copyright of Telecommunication Engineering is the property of Telecommunication Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The theory of multiplexing electromagnetic signals by means of twisted photons generated by a uniform circular array (UCA) is developed in the case when the receiving antenna represents an array of elements located on a circular arc. The radiating elements are characterized by certain current distributions and are not points, in general. The polarization of created electromagnetic waves is fully taken into account. The notion of discrete twisted photons of the order N is introduced and orthogonality of these modes modulo N is established. Both paraxial and planar discrete twisted photons are considered. The explicit expressions for the signals received are obtained. It is shown that, in the simplest scenario, a K times decrease of the circular arc where the receiving array antenna is placed results in a K times decrease of the number of independent information channels. In the more sophisticated approach, one can restore all N ≫ 1 independent information channels in receiving the signal by an array antenna with N elements located on a circular arc with the central angle 2 π / K. However, this problem becomes rapidly ill-conditioned as one increases K. The method mitigating this issue is described. The estimates for the corresponding condition numbers are found. The scenario with beam steering, where the radiation produced by the UCA is concentrated near the receiving circular arc array antenna, is also investigated. The orthogonality of the information channels is proved in this case and the corresponding transformation matrix and its condition number are found. • Multiplexing signals with twisted photons by circular arc phased arrays is elaborated. • Explicit expressions for the signals received by antennas are obtained. • Asymptotics of singular values of the Vandermonde matrix is found. • Multiplexing by OAM combined with beam steering is investigated. [ABSTRACT FROM AUTHOR]

In recent years, orbital angular momentum (OAM) waves have been applied to improve the performance of radar target detection and imaging. However, the phase singularity of conventional OAM beams and the doughnut-shaped intensity distribution will degrade the performance of target detection. To solve the divergence problem in OAM multiplexing systems, the generation method of OAM beams propagating along a transverse plane is proposed using a uniform circular array, which is validated by full-wave simulation. Compared with conventional OAM beams, simulation results indicate that the generated beams with different OAM modes all propagate along the transverse plane while maintaining the regular wavefront shapes. This work can provide the development of new radar paradigm with technical support.