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To solve the problem of array detection performance in environments with mesoscale eddies, this study utilizes the Gaussian eddy model to describe the sound speed structure disturbed by eddies. Through numerical simulations, the corresponding sound field is obtained, and the transmission loss influenced by the eddy is analyzed. Furthermore, to investigate the relation between the array gain and spatial correlation in the eddy environments, the differences in vertical correlation at different positions and their effects on the vertical array gain of conventional beamforming (CBF) are studied. When the source is around the eddy center, the conclusions drawn are as follows: (1) The presence of an eddy changes the turning-point depth and the sound field distribution, significantly affecting the direct sound region and the first convergence zone, while having a minor impact on the first shadow zone. (2) In different eddy-induced environments, the first convergence zone maintains a high vertical correlation, but the vertical correlation of the direct sound region is greatly influenced by the eddy. (3) The array gain of CBF is consistent with the vertical correlation. When the correlation between each element of the sound field is great, the array gain increases with the number of array elements. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to numerically demonstrate and comparatively analyze the critically strong and ambiguous impact of the a priori uncertainty of a shallow sea waveguide model in its main physical parameters on the output performance of model-based methods for spatial processing of multimode signals received by a vertical antenna array. The scenario is specified when a relatively weak signal of a remote underwater source is received against the background of intensive interference excited by a subsurface source (like a ship, for example) and ambient sea noise excited by wind waves. The considered array processing methods include matched-signal processing, optimal processing of the signal on the background of interference and noise, and suboptimal processing based on matched-mode array filtering of one of the signal-carrying modes with adaptive selection of its number. Quantitative estimates are obtained from above for the environment uncertainties, or model errors, with respect to the sound velocity in the water column and geoacoustic parameters of the underlying bottom, at which the array gain loss does not exceed a given level. It is shown that such estimates are very different both for different environmental parameters and for processing methods, with the determining role played by the conditions of useful signal reception, namely, the modal composition and intensity levels of the interference and sea noise at the array input. The problem statement and results are considered to be useful to detail the requirements for operational oceanography tools designed to support the effective operation of sonar antenna systems in real sea environments. [ABSTRACT FROM AUTHOR]

In the last decade, Multiple-Input Multiple-Output (MIMO) algorithms have been developed for mobile communication networks in order to increase spectrum efficiency and reduce transmitted power, which are also two of the main Key Performance Indicators of Fifth Generation New Radio (5G NR). Therefore, various MIMO algorithms are being researched for their adaptability to 5G NR specifications. The objective of this study is to examine the array gains achieved with the deployment of multiple transmit antennas and multiple receive antennas in 5G NR Physical Downlink Shared Channel (PDSCH). The study first examines the array gains of Single-Input Multiple-Output (SIMO) and Multiple-Input Single-Output (MISO), then combines the transmitter and the receiver diversities in a MIMO system for 5G PDSCH. The array gains are achieved through precoding and combining vectors obtained by Singular Value Decomposition (SVD) of the channel coefficients matrix. The results show that theoretical array gains can be achieved in end-to-end 5G NR downlink channels. [ABSTRACT FROM AUTHOR]

The recent study [1] addressed how the characteristics of low-frequency acoustic signal propagation in a shallow-water channel under wind wave conditions affect the output performance of a horizontal phased array (PA) is further developed with the aim of comparative analysis of the efficiency of various array signal processing methods. The main focus is quantitative estimates of the additional array gain from optimal processing in comparison to the standard PA method compensated in the direction to the signal source, in dependence on the key parameters: direction and distance to the source, wind speed, and wave dimensions of the array. Numerical simulation is performed for a typical winter hydrological conditions of the Barents Sea, a signal frequency of 250 Hz, and a wide range of distances up to 500 km It is shown that the additional gain from optimizing the array processor can vary widely (from fractions of to a few dB), while the PA efficiency also varies widely and may have a nonmonotonic dependence on distance. [ABSTRACT FROM AUTHOR]

We analyze the influence of statistical effects of the propagation of an acoustic signal excited by a tone source in a shallow-water channel with a rough sea surface on the efficiency of a horizontal phased array. As the array characteristics, we consider the angular function of the array response for a given direction to the source and the coefficient of amplification of the signal-to-noise ratio (array gain). Numerical simulation was conducted in to the winter hydrological conditions of the Barents Sea in a wide range of parameters determining the spatial signal coherence. The results show the main physical effects of the influence of wind waves on the array characteristics and make it possible to quantitatively predict the efficiency of a large horizontal array in realistic shallow-water channels. [ABSTRACT FROM AUTHOR]

In this paper, we study the impact of carrier frequency offset (CFO) estimation/compensation on the information rate performance of the zero-forcing (ZF) receiver in the uplink of a multiuser (MU) massive multiple-input–multiple-output (MIMO) system. Analysis of the derived closed-form expression of the per-user information rate reveals that, with the increasing number of BS antennas $M$, an \mathcal{O}(\sqrt{M}) array gain is achievable, which is the same as that achieved in the ideal zero CFO scenario. Moreover, it is observed that, compared with the ideal zero CFO case, the performance degradation in the presence of residual CFO (after CFO compensation) is the same for both ZF and MRC. [ABSTRACT FROM PUBLISHER]

This work analyses the average signal-to-noise ratio (SNR) and ergodic capacity of large-scale relay networks with best relay selection (BRS). First, extreme value theory (EVT) is used to obtain an implicit expression for the asymptotic cumulative distribution function (cdf) of the received SNR when the number of relays is high. Then, via high power approximations, closed-form expressions for the cdf and probability density function (pdf) of the received SNR are achieved, from which closed-form expressions of the average received SNR and ergodic capacity are derived. Insights on the array gain and ergodic capacity behavior of BRS can be observed from the derived results. Simulations show that the derived approximations are tight, even for not-so-large relay networks. [ABSTRACT FROM AUTHOR]

• An ESB-FBMV-ASCBP beamformer was proposed for ultrasound imaging. • The ASCBP utilized an adaptive noise power weight. • The sN-ASCBP used a square neighborhood average to enhance the speckle quality. • The proposed methods showed more improvement in imaging quality than the SCBP. • The proposed methods presented a striking performance in low SNRs. This paper presents an adaptive subarray coherence-based post-filter (ASCBP) applied to the eigenspace-based forward–backward minimum variance (ESB-FBMV) beamformer to simultaneously improve image quality and beamformer robustness. Additionally, the ASCBP can separate close targets. The ASCBP uses an adaptive noise power weight based on the concept of the beamformer's array gain (A G) to suppress the noise adaptively and achieve improved images. Moreover, a square neighborhood average was applied to the ASCBP in order to provide more smoothed square neighborhood ASCBP (SN-ASCBP) values and improve the speckle quality. Through simulations of point phantoms and cyst phantoms and experimental validation, the performance of the proposed methods was compared to that of delay-and-sum (DAS), MV-based beamformers, and subarray coherence-based post-filter (SCBP). The simulated results demonstrated that the ASCBP method improved the full width at half maximum (FWHM) by 57 % and the coherent interference suppression power (CISP) by 52 dB compared to the SCBP post-filter. Considering the experimental results, the SN-ASCBP method presented the best enhancement in terms of generalized contrast to noise ratio (gCNR) and contrast ratio (CR) while the ASCBP showed the best improvement in FWHM among other methods. Furthermore, the proposed methods presented a striking performance in low SNRs. The results of evaluating the different methods under aberration and sound speed error illustrated the better robustness of the proposed methods in comparison with others. [ABSTRACT FROM AUTHOR]

Abstract: It is customary to look over deterministic beamforming techniques as designs that offer a trade-off between mainlobe width and sidelobe level. In this work, we take into consideration that noise reduction and interference rejection are actually more useful metrics for the design of practical systems, and we present a novel analysis as a first step to understand the behavior and limitations of the deterministic beamformers from this system level perspective. The obtained results show that a trade-off between both metrics exists, and they illustrate some misconceptions about the traditionally assumed optimal designs. Finally, a method to approximately calculate the best attainable performance of any deterministic beamformer is presented. [Copyright &y& Elsevier]

This paper investigates orthogonal space-time block-coded (OSTBC) transmission for a multiple-input multiple-output (MIMO) channel with noncoherent amplify-and-forward (AF) relaying in a situation where the source–relay and relay–destination channels undergo Rayleigh fading and Rician fading, respectively. Fading coefficients of the Rician channel are considered to be correlated. Different scenarios are then considered for the Rician channel. We derive exact expressions for the moment-generating function (mgf) and the first and second moments of the instantaneous signal-to-noise ratio (SNR) at the destination to statistically characterize system behavior. We also derive the exact expressions for the probability density function (pdf) and the cumulative distributive function (cdf) to discuss system behavior with the Rician factor. We then analyze system performance by deriving new analytical expressions for the bit error rate (BER), outage probability, amount of fading (AoF), diversity order, and array gain. These performance metrics reveal that strong line-of-sight (LoS) components between a relay–destination link always limit the performance promised by the MIMO scattering environment when both nodes have multiple antennas. [ABSTRACT FROM PUBLISHER]

Following the seminal work by Zheng and Tse on the diversity and multiplexing tradeoff (DMT) of multiple-input multiple-output (MIMO) channels, in this paper, we introduce the array gain to investigate the fundamental relation between transmission rate and reliability in MIMO systems. The array gain gives information on the power offset that results from exploiting channel state information at the transmitter or as a consequence of the channel model. Hence, the diversity, multiplexing, and array gain (DMA) analysis is able to cope with the limitations of the original DMT and provide an operational meaning in the sense that the DMA gains of a particular system can be directly translated into a parameterized characterization of its associated outage probability performance. In this paper, we derive the best DMA gains achievable by any scheme employing isotropic signaling in uncorrelated Rayleigh, semicorrelated Rayleigh, and uncorrelated Rician block-fading MIMO channels. We use these results to analyze the effect of important channel parameters on the outage performance at different points of the DMT curve. [ABSTRACT FROM PUBLISHER]

For receive-side maximal-ratio combining (MRC) and maximum-average-SNR beamforming (BF), the wireless-channel fading correlation impacts the symbol-detection performance—decreasing correlation improves/degrades MRC/BF performance—whereas the numerical complexity of these methods is fixed—high/low for MRCIBF. Matching signal processing complexity to the actual correlation conditions and, thus, to the achievable performance is possible with a superset of MRC and BF known as maximal-ratio eigencombining (MREC). For imperfectly known and correlated fading gains, new closed-form expressions are derived for the probability density function of the MREC-output SNR, as well as for the outage probability (OP) and the average error probability. These new expressions permit seamless evaluation for any correlation value of MREC, MRC, and BF performance measures, such as the amount of fading, the deep-fade probability, diversity and array gains, and the OP. Our results confirm that, in realistic scenarios, adaptive MREC can achieve MRC-like performance for EF-like complexity. [ABSTRACT FROM AUTHOR]

• A non-intrusive monitoring technique is developed for detecting an acoustic source in pipes with a noisy turbulent background excitation. • The technique is based on vibratory measurements on the outer surface of the pipe and a beamforming treatment. • Vibroacoustic models are proposed to predict numerically the vibrations induced by the source and the turbulent boundary layer. • The array gains obtained with two beamforming treatments are studied using the virtual experiments. • Significant array gains are observed with the MaxSNR treatment and are analysed in regards of the vibroacoustic characteristics of the pipe. This study concerns a monitoring technique based on vibration measurements for identifying the presence of an acoustic source in a fluid-filled pipe conveying turbulent flow. In such situation, the source-induced vibrations can be smeared with the flow-induced vibrations, which hinders the source detection. To increase the signal-to-noise ratio (SNR), beamforming techniques can be applied to the vibrations measured by an array of accelerometers mounted on the pipe. However, the current problem is more complex and challenging than most typical beamforming applications due to strong fluid–structure coupling and to the presence of resonant modes and internal flow excitations. Numerical vibroacoustic methods are presented to predict the vibratory response of a pipe excited by a monopole source and/or a turbulent boundary layer (TBL). The cross-spectral matrices of the computed radial accelerations induced by the monopole source to be detected and by the TBL are used for assessing the performance of two vibroacoustic beamforming techniques. The array gains using both, the conventional and the MaxSNR beamforming approaches are estimated. Results indicate superior performance of the MaxSNR, which leads to significantly higher array gain. [ABSTRACT FROM AUTHOR]

• A vibroacoustic leak detection system for sodium heated steam generator is studied. • An array of accelerometers fixed on the external shell is used for detection. • Two types of beamforming treatments are studied to increase the Signal to Noise ratio. • A water experiment confirms the efficiency of the MaxSNR treatment. A technique based on vibration measurements has been developed to detect water leaking into sodium in view to improving the monitoring of steam generators. Leak-induced vibrations can be masked by background noise. This problem can be overcome by employing a beamforming technique to increase the signal-to-noise ratio (SNR). In order to study the feasibility and efficiency of this technique for the present configuration, experimental investigations were performed on a mock-up composed of a straight cylindrical pipe coupled to a hydraulic circuit by two flanges. A sound emitter introduced in the pipe simulates the source to be detected while the background noise vibrations are controlled by flow speed. Beamforming is applied to the signals measured by an array of accelerometers mounted externally on the pipe. Two different types of beamforming are considered: the conventional (Bartlett) type and an advanced type based on SNR maximization (MaxSNR). After analysing the vibroacoustic behaviour of the mock-up, the article focuses on the efficiency of the two beamforming treatments for narrow and broad bands. [ABSTRACT FROM AUTHOR]

This paper investigates the symbol error rate (SER) performance of the multiple-input multiple-output (MIMO) multi-channel beamforming (MB) in the general double-scattering channel. We derive an asymptotic expansion on the marginal eigenvalue distribution of the MIMO channel matrix, and apply the result to get an approximate expression on the average SER at high signal-to-noise ratio (SNR). Two parameters pertaining to the SER, i.e., the diversity gain and the array gain, are analyzed. Our results show that it suffices for the double-scattering channel to have only limited scatterers, if the same diversity gain as the Rayleigh channel is desired; however, once the number of scatterers is below a certain level, the array gain in the double-scattering channel will vary with the SNR logarithmically. [ABSTRACT FROM AUTHOR]