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Passive radar has drawn a lot of attention due to its applications across military and civilian sectors. Under this working paradigm, the utilization of antenna arrays is instrumental, as it increases the signal quality and enables precise target positioning. These promising features rely, however, on the precise calibration of the antenna array, as the different hardware components introduce impairments that compromise the beamforming capabilities of the system. We propose a technique that employs a low-power external beacon signal to produce precise information about the target location, avoiding the angular ambiguities present in other solutions in the literature. The experimental results demonstrate the method's ability to effectively correct the amplitude and phase inconsistencies while compensating for frequency drifts, enabling beamforming capabilities and direction-of-arrival estimation. Among the tested beacon waveforms, the pseudo-random noise-based signals proved the most robust, especially in low-power scenarios. Additionally, the method was validated in a passive radar setup, where it successfully detected a vessel using opportunistic signals. These findings highlight the method's potential to enhance passive radar performance while maintaining a low probability of detection, a key aspect in military applications, as well as its applicability to civilian purposes, such as infrastructure monitoring, environmental observation, and traffic management. [ABSTRACT FROM AUTHOR]

This paper introduces a novel framework for evaluating vehicle-to-vehicle (V2V) communication systems, employing beamforming and null steering techniques. Addressing challenges such as electromagnetic interference from other vehicles within the network as well as diverse road conditions, the framework defines the simulation environment for V2V networks across different traffic scenarios to assess system reliability. The analytical components of the proposed framework are structured as follows: a comprehensive framework is developed, serving as the basis for implementing a simulator that leverages advanced spatial signal processing algorithms to evaluate V2V networks across specific scenarios, accounting for the effects of positional errors. The framework integrates multiple blocks, including road modeling, system modeling, and performance evaluation, providing adaptability for different algorithms or configurations. Positional inaccuracies are examined, highlighting their effects on system performance, particularly in scenarios where null steering accuracy is imperfect, thus underscoring the need for enhanced interference management strategies. [ABSTRACT FROM AUTHOR]

Beamforming represents a pivotal technology in massive multiple-input multiple-output (MIMO) systems, as it facilitates the regulation of transmission and reception operations. Beamforming techniques' categorization is based either on their hardware architecture or implementation strategy. This paper proposes an orthogonal beamforming technology founded on a specific implementation method that utilizes predetermined orthogonal beams to serve users. The suggested approach incorporates numerous orthogonal beams relying on a substantial number of antennas at the base station. The primary objective of this approach is to enhance the performance of massive MIMO systems by augmenting spectral efficiency and accommodating more users. The proposed beamforming approach is well suited for millimeter frequency bands. The purpose of this paper is to explore the suggested orthogonal beamforming technology. The concept of this approach is described at first and then followed by an evaluation of its efficacy for a single user through the allocation of orthogonal beams. The suggested approach is also examined in the context of multiuser systems, and the results are compared with the adaptive ZF beamforming technique. Furthermore, the paper presents solutions to the issues that may arise in multiuser systems, for example, ensuring that each orthogonal beam is assigned to only one user. The simulations conducted in this study demonstrate that the suggested approach outperforms the ZF technique in terms of both the spectral efficiency and the number of serviced users. Specifically, the suggested approach can enhance SE by approximately 40.6% over the ZF technique, and it can support up to double the number of users when compared to the ZF approach. [ABSTRACT FROM AUTHOR]

Metasurfaces have garnered significant attention in recent years for their ability to manipulate electromagnetic (EM) wave propagation, owing to their high design flexibility, low profiles, and ease of fabrication. This study proposes the use of polarization-dependent anisotropic metasurfaces to manipulate the phase of orthogonal linearly polarized EM waves, enabling polarization multiplexing with distinct functionalities based on incident polarizations. Additionally, the proposed metasurfaces enable the generation of single pencil beams, multiple pencil beams, circularly and elliptically shaped radiation beams, offering versatile polarization manipulation capabilities. The radiation theory of planar array antennas was employed to predict the far-field patterns of the metasurfaces, demonstrating satisfactory agreement with simulated results and affirming the feasibility of the proposed method. The ability of focusing the incoming EM wave into a focal point or multi focal points and generating vortex beam carrying orbital angular momentum (OAM) under the incidence of orthogonal linearly polarized waves are also demonstrated by the proposed anisotropic metasurfaces. This proposed metasurfaces pave the way for the development of multifunctional metadevices capable of advanced EM regulation through polarization and phase modulations in free space, with potential applications in wireless communication, imaging, and radar systems. [ABSTRACT FROM AUTHOR]

This research aims to design hybrid analog and digital beamforming to improve the signal‐to‐noise ratio (SNR) and spectral efficiency (SE) of communication links. Considering the complexity and cost associated with fully connected multiple‐input multiple‐output (MIMO) communication models, a partially connected system model is adopted for the downlink millimeter‐wave (mmWave) communication model. The analog beamforming utilizes the adaptive search (AdaLS) algorithm to minimize interference and enhance user power, whereas digital beamforming is optimized using the proposed Chaotic Chebyshev Aquila Optimization (CCAO) algorithm. The CCAO algorithm integrates chaotic Chebyshev–based solution mapping with the conventional Aquila Optimization Algorithm to enhance exploration capability. The system model is illustrated, and the problem is formulated to maximize the signal‐to‐interference‐plus‐noise ratio (SINR) through the selection of the required signal at the receiver. The digital beamformer is designed using Lagrange's multiplier, and the analog beamformer is optimized using AdaLS. The proposed CCAO algorithm is detailed, incorporating chaotic dynamics to explore the solution space effectively. The research evaluates the performance of the proposed method against conventional approaches, showcasing improved normalized beam gain and SINR. [ABSTRACT FROM AUTHOR]

The acoustic analysis of a moving object, such as in pass-by or fly-over tests, is a very important and demanding issue. These types of analyses make it possible to characterize the machine in quite realistic conditions, but the typical difficulties related to source localization and characterization are usually exacerbated by the need to take into consideration and to compensate for the object movement. In this paper, a technique based on acoustic beamforming is proposed, which is applicable to all those cases where the object under investigation is moving. In the proposed technique, the object's movement is not regarded as a problem but as a resource, enabling a virtual increase in the number of microphone acquisitions. For a stationary acoustic emission from a moving object, each time segment of the acquired signal is treated as if it is coming from a microphone (virtual) positioned differently relative to the object's reference system. This paper describes the technique and presents examples of results obtained from both simulated and real signals. Performance analysis is conducted and discussed in detail. [ABSTRACT FROM AUTHOR]

This paper investigates the optimization of cylindrical metasurface meta-covers designed to enable beamforming capabilities in single linear antennas. This study focuses on the development and application of advanced optimization tools to tailor the electromagnetic response of these metasurfaces, enabling precise control over the radiation patterns of the antenna. In particular, we develop a genetic algorithm-based optimization tool, which achieves precise manipulation of the main beam direction and null placement in the radiation pattern. The results further expand the applications of metasurface-based meta-covers in enhancing the functionality of dipole antennas in various communication and sensing systems. [ABSTRACT FROM AUTHOR]

In the rapidly advancing field of edge computing, improving the end-to-end transmission rate is crucial to accommodating the needs of latency-sensitive applications. To address this, this article introduces Reconfigurable Intelligent Surfaces (RIS) to examine the challenge of maximizing the minimum attainable rate among users in a cell-free massive MIMO system from an edge computing perspective. In this article, a framework is proposed to improve the end-to-end user transmission rate by alternately optimizing the precoding matrix of Access Points (APs) and the phase shift matrix of the RIS. For the optimization of the APs' precoding matrix, this framework utilizes a Second Order Cone Programming (SOCP) method. In order to optimize the continuous phase shifts at the RIS, this framework uses a Semidefinite Relaxation (SDR) technique. For the optimization of the discrete phase shifts at the RIS, a projection-based method is proposed in this framework. By integrating these two forms of beamforming, the proposed framework significantly improves the end-to-end transmission rate, meeting the critical requirements of latency-sensitive applications in edge computing scenarios. [ABSTRACT FROM AUTHOR]

Speech enhancement extracts the voice we want to listen to from the background noise and is essential for speech applications, such as automatic speech recognition, to work effectively in noisy environments. This article introduces a novel beamforming technique that tracks the speaker’s movement and keeps extracting the target speaker’s voice, even when the speaker is moving while talking. Beamforming requires spatial information of the target source and interfering signals such as the direction of arrival. We discuss our previously proposed method to estimate time-varying spatial information by incorporating powerful artificial intelligence technology. This method enables high-performance beamforming even when the target speaker is moving. [ABSTRACT FROM AUTHOR]

This paper addresses achieving the high time-bandwidth product necessary for low signal-to-noise ratio (SNR) target detection and localization in complex multipath environments. Time bandwidth product is often limited by dynamic environments and platform maneuvers. This paper introduces data-driven wideband focusing methods for passive sonar that optimize parameterized unitary matrices to align signal subspaces across the frequency band without relying on wave propagation models which are subject to mismatch in complex multipath environments. The methods minimize the log-determinant of the wideband covariance, a measure indicative of matrix rank, ensuring the coherence of wideband data and preserving SNR. We propose two approaches: a fully adaptive method with parameters scaling directly with the number of frequency bins, and a partially adaptive method that shares parameters across frequencies to improve robustness to noise. Simulations are conducted in a shallow-water waveguide scenario to demonstrate the flexibility of data-driven focusing over traditional model-based approaches. Results from the SWellEx-96 S59 event validate our methods, showing improvement in tonal target detection and localization in the presence of strong wideband interference. [ABSTRACT FROM AUTHOR]

In adaptive beamforming, the array signal processing adjusts its sensor delays and weights based on the incoming data. In conventional beamforming, these parameters are instead given from a predefined model. Adaptive beamformers can improve measurement precision by dynamically rejecting spatial interference. While an established theory is available on the behavior of adaptive beamformers in textbook scenarios, their expected performance on realistic pulse-echo imaging scenes is still mostly uncharted. Imaging performance can be evaluated by individual pixel precision and aggregated metrics such as resolution and contrast. The achievable gain is strongly related to the sparsity of the scene and the availability of data to appropriately estimate the spatial covariance matrix. In pulse-echo measurements, the nonstationary interference poses a special problem for adaptive beamforming, which is a current research question of academic and industrial interest. The current work establishes a performance bound for adaptive beamforming in simulated realistic pulse-echo scenarios. This is derived and numerically implemented as the clairvoyant minimum variance distortionless response beamformer. The proposed framework allows for an a priori assessment of the applicability of adaptive beamforming, for a given scenario. The performance of the implemented algorithms can be directly compared with the theoretical limit in a simulated environment. [ABSTRACT FROM AUTHOR]

Beamforming technology using loudspeaker arrays is widely used in sound applications, but current sparse array design methods focus on optimizing a single beam for a single target direction, limiting their applicability to multi-channel sound systems. This paper presents a design method for sparse loudspeaker line arrays to generate wideband frequency-invariant beams in multiple target directions. A model based on tapped delay lines is developed and a two-stage design approach is proposed. In the first stage, a compressive sensing framework combined with an extended fast iterative shrinkage-thresholding algorithm is employed to determine the optimal locations of active drivers. In the second stage, the excitations of the active drivers are calculated using the least squares method. Numerical simulations show a 32.3% reduction in the number of drivers compared to that of traditional uniform linear loudspeaker arrays while maintaining frequency-invariant properties. The proposed algorithm exhibits considerable computational efficiency, rendering it highly suitable for addressing large-scale optimization problems and substantially reducing the design time. This design method is applicable to sound projection scenarios and can be extended to other multi-channel beamforming systems to achieve reliable beam performance and reduce system costs. [ABSTRACT FROM AUTHOR]

Artificial noise (AN)-aided techniques have been considered to be promising and practical candidates for enhancing physical layer security. However, there has been a lack of analysis regarding the AN effect on the eavesdropper (EV) from the perspective of the signal-to-interference plus noise ratio (SINR) regarding the existence of the EV's channel state information (CSI) at the legitimate transmitter. In this paper, we analyze the performance of AN-aided secure transmission from the SINR perspective when a legitimate transmitter has and does not have the EV's CSI. Based on the analyzed EV's SINRs for the above two cases, the secrecy gap, which is the difference between the two secrecy capacities, is defined and analyzed. Based on the derived secrecy gap, we have analyzed the asymptotic performances of the secrecy capacity and gap when the number of antennas of the legitimate transmitter and the number of antennas of the EV have large values. Through asymptotic analysis, it is demonstrated that the AN-aided secure transmission under the practical environment (i.e., the case that the EV's CSI is not available at the legitimate transmitter) can nearly achieve an ideal performance (i.e., the performance when the EV's CSI is available at the legitimate transmitter) in a massive antenna system. [ABSTRACT FROM AUTHOR]

Metasurface-based imaging is attractive due to its low hardware costs and system complexity. However, most of the current metasurface-based imaging systems require stochastic wavefront modulation, complex computational post-processing, and are restricted to 2D imaging. To overcome these limitations, we propose a scanning virtual aperture imaging system. The system first uses a focused beam to achieve near-field focal plane scanning, meanwhile forming a virtual aperture. Secondly, an adapted range migration algorithm (RMA) with a pre-processing step is applied to the virtual aperture to achieve a 3D high-resolution reconstruction. The pre-processing step fully exploits the feature of near-field beamforming that only a time delay is added on the received signal, which introduces ignorable additional calculation time. We build a compact prototype system working at a frequency from 38 to 40 GHz. Both the simulations and the experiments demonstrate that the proposed system can achieve high-quality imaging without complex implementations. Our method can be widely used for single-transceiver coherent systems to significantly improve the imaging depth of field (DOF). [ABSTRACT FROM AUTHOR]

The frequency diverse array (FDA) is an architecture capable of beamforming in both range and angle, improving upon the traditional phased array (PA) which can only achieve beamforming in angle. The FDA employing directional modulation (DM) for secure directional communications (SDC) can reduce bit error rates (BERs) in both range and angle, again improving upon the traditional PA which can only reduce BER in angle. In this paper, we document the challenges involved in the design and implementation of a two-element linear FDA employing fast-time binary phase-shift keying (BPSK) modulations. We also show that the experimentally collected field data match well with the results of simulations based on our analytical model. [ABSTRACT FROM AUTHOR]

Reconfigurable Intelligent Surface (RIS) panels have garnered significant attention with the emergence of next-generation network technologies. This paper proposes a novel data-driven approach that leverages Light Detecting and Ranging (LiDAR) sensors to enhance user localization and beamforming in RIS-assisted networks. Integrating LiDAR sensors into the network will be instrumental, offering high-speed and precise 3D mapping capabilities, even in low light or adverse weather conditions. LiDAR data facilitate user localization, enabling the determination of optimal RIS coefficients. Our approach extends a Graph Neural Network (GNN) by integrating LiDAR-captured user locations as inputs. This extension enables the GNN to effectively learn the mapping from received pilots to optimal beamformers and reflection coefficients to maximize the RIS-assisted sumrate among multiple users. The permutation-equivariant and -invariant properties of the GNN proved advantageous in efficiently handling the LiDAR data. Our simulation results demonstrated significant improvements in sum rates compared with conventional methods. Specifically, including locations improved on excluding locations by up to 25% and outperformed the Linear Minimum Mean Squared Error (LMMSE) channel estimation by up to 85% with varying downlink power and 98% with varying pilot lengths, and showed a remarkable 190% increase with varying downlink power compared with scenarios excluding the RIS. [ABSTRACT FROM AUTHOR]

The Third Generation Partnership Project (3GPP) in Release 16 introduced New Radio in unlicensed spectrum (NR-U) to further enhance the capacity of licensed spectrum. The user equipment’s (UE) power consumption is an important metric identified by researchers in long-term evolution (LTE) and NR, and now in NR-U. In long-term evolution (LTE) and NR, 3GPP has introduced discontinuous reception (DRX) to save the UE’s power consumption and it can also be used in NR-U. In the DRX procedure, UE sleeps when there is no data packet to serve and wakes up at regular periodic intervals to check if there are any data packets in the downlink. The UE can sleep longer and skip most channel monitoring occasions, which helps to save the power of the UE. In this article, we analyze the power consumption of the UE in the DRX mechanism over NR-U networks. We model the DRX using semi-Markov-based modeling to analyze the power consumption of the UE, and the average delay experienced by the UE in the NR-U DRX mechanism. Analytical analysis indicates that power consumption increases with increasing DRX-ON duration and decreases with increasing sleep duration. The power consumption reduces at the cost of delay, i.e., delay increases with an increase in sleep duration. [ABSTRACT FROM AUTHOR]

Intelligent reflecting surfaces (IRS) are valuable tools for enhancing the intelligence of the propagation environment. They have the ability to direct EM Waves to a specific user through beamforming. A significant number of passive elements are integrated into metasurfaces, allowing for their incorporation onto various surfaces such as walls and buildings. In certain situations, metasurfaces may need to be installed on surfaces that are not flat, such as surfaces with curves or surfaces with two sides. Line of sight and non line of sight rays are radiated toward IRS and both components must be considered in channel modeling. In this work, a unit cell with three polarization modes, consisting of absorption, reflection, and a 1-bit phase shift, is designed and investigated. The unit cell in the nonplanar metasurface is composed of two vertical surfaces. A mathematical model is used to analyze two vertically-faced metasurfaces. The results include S parameter values and full structure radiation pattern in simulation and measurement. It is demonstrated that both absorption reflection mode and phase shift mode are achieved within a specific frequency band. The simulations demonstrate that an appropriate absorption level, reaching − 10 dB, is achieved in absorption mode. In reflection mode, a 180-degree phase shift is achieved within the same frequency band. Reports on the radiation pattern of two vertically faced structures indicate that there is no quantized beam when there is a one-bit phase shift. Channel modeling and signal to noise ratio of the designed metasurface in wireless network is represented in comparison with planar metasurface with the same cell number. [ABSTRACT FROM AUTHOR]

The inherent openness of wireless communication environments makes signals prone to eavesdropping. Therefore, to enhance the security performance, this study explores several support systems involving flying reconfigurable intelligent surfaces (RIS). These systems integrate unmanned aerial vehicles operating at high altitudes and possessing high mobility with low-cost RISs that offer high efficiency. Additionally, to maximize secrecy performance, both successive convex approximation and minimization-maximization optimization with penalty-based algorithms are introduced to optimize base station and RIS beamforming. The simulation validates that the performance of the proposed algorithm can surpass those of existing methods in terms of secrecy rate. [ABSTRACT FROM AUTHOR]

Non-orthogonal multiple access (NOMA) is a technology that leverages user channel gains, offers higher spectral efficiency, improves user fairness, better cell-edge throughput, increased reliability, and low latency, making it a potential technology for the next generation of cellular networks. The application of NOMA in the power domain (NOMA-PD) with multiple-input multiple-output (MIMO) and other emerging technologies allows to achieve the demand for higher data rates in next-generation networks. This survey aims to funnel down NOMA MIMO resource allocation issues and different optimization problems that exist in the literature to enhance the data rate. We examine the most recent NOMA-MIMO clustering, power allocation, and joint allocation schemes and analyze various parameters used in optimization methods to design 5G systems. We finally identify a promising research problem based on the signal-to-interference-plus-noise ratio (SINR) parameter in the context of NOMA-PD with MIMO configuration. [ABSTRACT FROM AUTHOR]

Beamforming is essential for improving transmission in wireless sensor networks (WSNs), particularly in cognitive radio networks (CRNs) with several secondary users (SU) equipped with transmitting antennas. Optimizing beamforming while minimizing interference with primary users (PU) is of great interest. This study proposes an improved particle swarm optimization (PSO) algorithm to enhance beamforming performance. This approach aims to maximize the power of the beam directed to the SU receiver while controlling interference in the PU protection region. The results show that this algorithm constantly improves beam focus and signalto-noise ratio to effectively optimize beamforming. Firstly, beam focusing becomes narrower as the number of antenna elements increases, generating optimal transmission conditions. Secondly, the algorithm achieves a considerable improvement in signal-to-noise ratio as the number of antenna elements increases. Furthermore, optimization performance improves as the number of antenna elements increases, as shown by the best fitness values. The simulations also illustrate the performance of the proposed method. [ABSTRACT FROM AUTHOR]

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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.)