Beamforming Applications Research Articles

Analysis of Simulated and Measured Indoor Channels for mm-Wave Beamforming Applications

Ray tracing- (RT-) assisted beamforming, where beams are directly steered to dominant paths tracked by ray tracing simulations, is a promising beamforming strategy, since it avoids the time-consuming exhaustive beam searching adopted in conventional beam steering strategies. The performance of RT-assisted beamforming depends directly on how accurate the spatial profiles of the radio environment can be predicted by the RT simulation. In this paper, we investigate how ray tracing-assisted beamforming performs in both poorly furnished and richly furnished indoor environments. Single-user beamforming performance was investigated using both single beam and multiple beams, with two different power allocation schemes applied to multibeamforming. Channel measurements were performed at 28–30 GHz using a vector network analyzer equipped with a biconical antenna as the transmit antenna and a rotated horn antenna as the receive antenna. 3D ray tracing simulations were carried out in the same replicated propagation environments. Based on measurement and ray tracing simulation data, it is shown that RT-assisted beamforming performs well both for single and multibeamforming in these two representative indoor propagation environments.

Adaptive Beamforming Algorithm Based on a Simulated Kalman Filter

Adaptive beamforming is a technique used to steer the radiation pattern towards the desired signal and cancel out any interference signal by finding the appropriate weights for every element in an array antenna, to achieve maximum signal to interference plus noise ratio (SINR). There are many methods to perform adaptive beamforming and one of the method is to use metaheuristic algorithm, to estimate the weights for individual elements in an array. Over the years, various metaheuristic algorithms have been applied to adaptive beamforming. Some of the metaheuristic algorithms have been modified from the original algorithms to improve the algorithms performance in adaptive beamforming application. A new metaheuristic algorithm named Simulated Kalman Filter (SKF), is inspired by the estimation capabilities of Kalman filter, has not been applied to adaptive beamforming application. Therefore, this research presents the first-time application of SKF algorithm to adaptive beamforming. The SKF algorithm, however, often converge prematurely at local optimum due to lack of exploration, preventing it from finding better solution. A modified version of the SKF algorithm, named Opposition-Based SKF (OBSKF), introduced by K. Zakwan, applies Opposition-Based Learning method to improve the exploration capabilities of SKF algorithm. Moreover, a new modified version of the SKF algorithm named SKF with Modified Measurement (SKFMM) is introduced to further improve the exploration capabilities of SKF algorithm by modifying the measurement-update equation. The SKF, OBSKF and SKFMM is applied to an array antenna with 10 elements arranged linearly with 0.5

New perspective on single-radiator multiple-port antennas for adaptive beamforming applications.

One of the most challenging problems in recent antenna engineering fields is to achieve highly reliable beamforming capabilities in an extremely restricted space of small handheld devices. In this paper, we introduce a new perspective on single-radiator multiple-port (SRMP) antenna to alter the traditional approach of multiple-antenna arrays for improving beamforming performances with reduced aperture sizes. The major contribution of this paper is to demonstrate the beamforming capability of the SRMP antenna for use as an extremely miniaturized front-end component in more sophisticated beamforming applications. To examine the beamforming capability, the radiation properties and the array factor of the SRMP antenna are theoretically formulated for electromagnetic characterization and are used as complex weights to form adaptive array patterns. Then, its fundamental performance limits are rigorously explored through enumerative studies by varying the dielectric constant of the substrate, and field tests are conducted using a beamforming hardware to confirm the feasibility. The results demonstrate that the new perspective of the SRMP antenna allows for improved beamforming performances with the ability of maintaining consistently smaller aperture sizes compared to the traditional multiple-antenna arrays.

Application of Adaptive Digital Beamforming to Osaka University Phased Array Weather Radar

The X-band phased array weather radar (PAWR) at Osaka University has a rapid scanning rate and is capable of high-density observations in elevation; it produces approximately 100 plan position indicator radar images with a 60-km range, at different elevation angles, in less than 30 s. The PAWR uses a fan-shaped beam with a narrow beamwidth (1.2°) in azimuth and a wider beamwidth (from 5° to 10°) in elevation. With digital beamforming (DBF), the elevation beamwidth can be reduced to 1.2°, using 128 antenna elements arranged in tandem. Although the fan-shaped beam is useful for rapid scanning, the received signals tend to be affected by ground clutter. In this paper, we investigate the clutter suppression capability of common DBF methods: Fourier, Capon, and minimum mean-square error (MMSE) beamforming. Furthermore, to improve performance when the PAWR data contain errors—such as lacking data caused by mechanical problems—a correction method is proposed. The effect of clutter suppression using MMSE is shown to be greatly improved if used together with the proposed correction method. The resulting method is shown to sufficiently suppress clutter in all elevation angles above a few degrees, even in the presence of strong clutter; its clutter reduction performance is compared and found to be superior to the ones of the analyzed conventional DBF methods.

Influence of blade skew on axial fan component noise

Microphone arrays can be used to detect sound sources on rotating machinery. For this study, experiments with three different axial fans, featuring backward-skewed, unskewed, and forward-skewed blades, were conducted in a standardized fan test chamber. The measured data are processed using the virtual rotating array method. Subsequent application of beamforming and deconvolution in the frequency domain allows the localization and quantification of separate sources, as appear at different regions on the blades. Evaluating broadband spectra of the leading and trailing edges of the blades, phenomena governing the acoustic characteristics of the fans at different operating points are identified. This enables a detailed discussion of the influence of the blade design on the radiated noise.

Blind Synchronization in Wireless Acoustic Sensor Networks

The challenge of blindly resynchronizing the data acquisition processes in a wireless acoustic sensor network (WASN) is addressed in this paper. The sampling rate offset (SRO) is precisely modeled as a time scaling. The applicability of a wideband correlation processor for estimating the SRO, even in a reverberant and multiple source environment, is presented. An explicit expression for the ambiguity function, which in our case involves time scaling of the received signals, is derived by applying truncated band-limited interpolation. We then propose the recursive band-limited interpolation (RBI) algorithm for recursive SRO estimation. A complete resynchronization scheme utilizing the RBI algorithm, in parallel with the SRO compensation module, is presented. The resulting resynchronization method operates in the time domain in a sequential manner and is, thus, capable of tracking a potentially time-varying SRO. We compared the performance of the proposed RBI algorithm to other available methods in a simulation study. The importance of resynchronization in a beamforming application is demonstrated by both a simulation study and experiments with a real WASN. Finally, we present an experimental study evaluating the expected SRO level between typical data acquisition devices.

Airy pattern approximation of a phased microphone array response to a rotating point source.

Deconvolution of phased microphone array source maps is a commonly applied technique in order to improve the dynamic range and resolution of beamforming. Most deconvolution algorithms require a point spread function (PSF). In this work, it is shown that the conventional definition of the PSF, based on steering vectors, is changed when the source is rotating. The effect of rotation results in an increase in the resolution and aperture of the array. The concept of virtual array positions created by source rotation is used to derive an approximation of the PSF based on an Airy pattern. The Airy pattern approximation is suitable for use in deconvolution of rotating source maps as it is more accurate and computationally less expensive than the conventional PSF definition. The proposed Airy pattern approximation was tested with both CLEAN and DAMAS deconvolution algorithms. On the same hardware, it was significantly faster when compared to the conventional definition. The limitations of the Airy pattern approximation are shown in a synthesized broadband test case with a high dynamic range. However, in most practical beamforming applications, the proposed Airy pattern approximated PSF for deconvolution is a suitable option considering its accuracy and speed.

A Planar Dual-Polarized Microstrip 1-D-Beamforming Antenna Array for the 24-GHz Band

A planar linearly dual-polarized mm-wave antenna array is designed, fabricated, and investigated in detail. The requirements are two orthogonal polarizations with good purity and suitability of the array column for 1-D beamforming applications. Since single-layer fabrication without using vertical interconnection accesses is another important requirement, the chosen radiating elements are square microstrip patches, fed at two orthogonal edges. The array feeding is designed in series microstrip line fashion, providing a highly compact structure. In that way, 1-D beamforming agility is gained, when multiple array columns are arranged side by side and the individual columns are fed with appropriate phases. The sidelobe level of the array columns is decreased by implementing an amplitude taper within the series array, following the Dolph–Chebychev distribution. A fast scattering parameter calculation procedure is presented to achieve an efficient simulation and design process. The simulated and measured antenna properties are very stable over a bandwidth of 500 MHz around the center frequency proving that such a challenging dual-polarized design can be successfully implemented at millimeter-wave (mm-wave) frequencies with just one metallization layer on a grounded substrate. The design parameters and the design procedure are demonstrated in a step by step manner to give sufficient insight into the process together with the possibility of reusing the antenna array itself, as well as the underlying concepts.

Random Beamforming in Millimeter-Wave NOMA Networks

This paper investigates the coexistence between two key enabling technologies for the fifth generation (5G) mobile networks, non-orthogonal multiple access (NOMA) and millimeter-wave (mmWave) communications. Particularly, the application of random beamforming to the addressed mmWave-NOMA scenario is considered in this paper, in order to avoid the requirement that the base station knows all the users' channel state information. Stochastic geometry is used to characterize the performance of the proposed mmWave-NOMA transmission scheme, by using the key features of mmWave systems, e.g., mmWave transmission is highly directional and potential blockages will thin the user distribution. Two random beamforming approaches which can further reduce the system overhead are also proposed to the addressed mmWave-NOMA communication scenario, where their performance is studied by developing analytical results about sum rates and outage probabilities. Simulation results are also provided to demonstrate the performance of the proposed mmWave-NOMA transmission schemes and verify the accuracy of the developed analytical results.

Strategies to predict radiated sound fields from foldable, Miura-ori-based transducers for acoustic beamfolding.

To bypass challenges of digital signal processing for acoustic beamforming applications, it is desirable to investigate repeatable mechanical approaches that accurately reposition transducers for real-time, simple guiding of acoustic energy. One promising approach is to create arrays configured on origami-inspired tessellated architectures. The low dimensionality, easy implementation, compactness, and use of straightforward folding to guide acoustic energies suggest that tessellated arrays may bypass limitations of conventional digital signal processing for beamforming. On the other hand, the challenge of developing such reconfigurable arrays lies in determining tessellation design and folding extent that direct sound as required. This research assesses the utility of the computationally efficient, approximate solutions to Rayleigh's integral to predict radiated sound fields from tessellated arrays based on Miura-ori fold patterns. Despite altering assumptions upon which the integral is derived, it is found that the salient beam-steering properties and amplitudes are accurately reconstructed by the analytical approach, when compared to boundary element model results. Within the far field angular space accommodated by the formulation assumptions, the analytical approach provides a powerful, time-efficient, and intuitive means to identify tessellated topologies and folding extents that empower desired wave-guiding functionalities, giving fuel to the concept of acoustic beamfolding.

Design of transmission-type coding metasurface and its application of beam forming

Transmission-type coding metasurface capable of shaping the transmitted field patterns is introduced in this letter. The metamaterial bits are the basic elements of coding metasurface and are designed as cascaded structures composed of patterned metallic sheets and dielectric substrates. Metasurfaces function as shaping the transmitted field patterns are constructed by assembling those metamaterial bits with different sequences. Experimental studies are carried out at the microwave regime showing required split beam patterns shaped by a fabricated coding metasurface. The measured field characteristics are well agreed with the simulated results. Our work adds another method to design the coding metasurface and exhibits its potential of engineering transmitted electromagnetic field.

Random Beamforming in Millimeter-Wave NOMA Networks

This paper investigates the coexistence between two key enabling technologies for the fifth generation (5G) mobile networks, non-orthogonal multiple access (NOMA) and millimeter-wave (mmWave) communications. Particularly, the application of random beamforming to the addressed mmWave-NOMA scenario is considered in this paper, in order to avoid the requirement that the base station knows all the users' channel state information. Stochastic geometry is used to characterize the performance of the proposed mmWave-NOMA transmission scheme, by using the key features of mmWave systems, e.g., mmWave transmission is highly directional and potential blockages will thin the user distribution. Two random beamforming approaches which can further reduce the system overhead are also proposed to the addressed mmWave-NOMA communication scenario, where their performance is studied by developing analytical results about sum rates and outage probabilities. Simulation results are also provided to demonstrate the performance of the proposed mmWave-NOMA transmission schemes and verify the accuracy of the developed analytical results.

Mixed microwave-digital and multi-rate approach for wideband beamforming applications using 2-D IIR beam filters and nested uniform linear arrays

The presented work explores novel methods for synthesizing approximately frequency independent array factors at lower hardware complexity for wideband beamforming applications. The proposed approach employs 2-D infinite impulse response (IIR) digital beam filters together with nested uniform linear arrays (ULAs). The array is designed to have multiple levels of nesting. Each level of nesting consists of a ULA covering a temporal subband of the incident wideband signal. The use of nested arrays provides the required aperture size using a smaller number of elements compared to using a single ULA to capture the entire wideband signal. The use of different levels of nesting allows the operation of the digital processor for each sub-band at different clock rates. This is a hierarchical approach that saves both digital VLSI hardware and power consumption. The 2-D IIR digital beam filters that process each subband signal from each of the nested subarray achieves wideband beamforming. Simulations illustrate approximately frequency independent passbands as required in wideband beamforming.

Fully automatic gain control beamformer for smart antenna array system

Purpose The aim of this investigation is to make the Bessel beamformer fully automatic when it is combined with Root MUSIC (MUltiple SIgnal Classification) and is based on the array processing in the application of beamforming and Direction of Arrival (DOA) algorithm for source position. The concept is analyzed for modified Bessel beamformer with Root MUSIC to form a non-blind array processing technique which is then used to focus a beam towards a desired user and place nulls towards interferers for capacity improvement. Design/methodology/approach The idea is manipulated for modified Bessel beamformer with Root MUSIC relies on MATLAB software with the goal to obtain high efficiency in terms of signal recovery, directive gain by minimizing MSE and place nulls towards interferers. Findings The finding of the analysis is presented in adaptive environment and provided in the tables. The paper shows that the presented method leads to superior results and can be used as a better alternative in many practical applications to avoid operator involvement. Research limitations/implications The adaptive processes described in the paper are still limited to simulation due to non availability of real system for testing. Practical implications The paper can be extended to a next level by implementing the proposed algorithms in the real time environment using FPGA technology. Originality/value This is our original work that can offer scientific contribution to signal processing community and may provide better results as an automatic beamformer.

Subarray compressive beamforming for midfrequency active sonar on a cylindrical array

Subarray compressive beamforming is adapted to a cylindrical array for midfrequency active sonar detection of low-Doppler targets in reverberant environments. Low Doppler targets are difficult to detect due to spreading caused by side-lobes and the width of the main lobe. Compressive beamforming and, in particular, subarray compressive beamforming will be shown to drastically mitigate Doppler spreading and interference from static objects. A straightforward application of compressive beamforming to simulated data results in nearly perfect suppression of spread due to sidelobes and good isolation of low Doppler targets from the zero Doppler ridge. Artificially subdividing the array allows for multiple fully resolved sparse estimates of the incident sound field. The set of estimates from the set of subarrays may be combined to form a single sparse estimate, often fully suppressing zero Doppler clutter. Performance of both compressive beamforming and subarray compressive beamforming will be demonstrated using simulated data having realistic Doppler spreading due to multipath and environmental sources of Doppler spreading. Performance will be compared to conventional beamforming methods on the cylindrical array. In addition to practical applications, some theoretical challenges with adaptation to the cylindrical array will be discussed. [Work supported by a NAVSEA Phase I SBIR award.]

Fast and Accurate Rank Selection Methods for Multistage Wiener Filter

Reduced-rank adaptive processing (RRAP) has received considerable attention in recent years. One of the key problems with this technique is how to determine an appropriate dimension for the reduced-rank subspace. In this paper we study in detail four types of rank selection methods for the widely used RRAP approach-multistage Wiener filter (MWF). All of these methods have a computational complexity of order O(1), compared with other existing methods with an order of O(i) or even O(i 2 ) at the ith stage of the MWF. The main idea underlying these methods is to find a recursive algorithm to calculate the stopping criterion. The first two algorithms, based on the generalized discrepancy principle (GDP) and error estimation (EE) respectively, are fast versions of existing approaches. The last two algorithms, based on fast Ritz values estimation (RVE) and new information (NI) respectively, are new and proposed in this paper. In addition to requiring less computation, simulation results show that the proposed algorithms have a higher accuracy in adaptive beamforming applications for both narrowband and broadband signals.

Radio Frequency Beamforming Based on a Complex Domain Frontend

The state-of-the-art phased array-based digital beamforming systems suffer from disadvantages of high power consumption, high cost, and system complexity due to the massive use of transmitter/receiver (T/R) modules and high-speed digital and digital–analog mixed devices. In this paper, we point out that by proposing a new concept “complex domain” radio frequency (RF) frontend, the relatively slowly changed waveform delay information required to accomplish adaptive beamforming can be separated from wideband RF signals, based on which a self-contained beamforming system can be implemented with a low-speed baseband. By introducing vector RF multipliers in the proposed frontend, the amplitude and phase of RF signals can be simultaneously controlled by the real and imaginary parts of complex numbers, such that beamforming algorithms derived in complex domain can be directly applied without any form of transformation. By doing so, the massive use of conventional T/R modules and high-speed baseband devices can be avoided. Theoretical analysis and experimental demonstration based on commercial components have validated the proposed approach. Our method is able to significantly simplify the realization and decrease the cost of wideband digital beamforming systems, and can be widely used in low cost, power efficient beamforming applications.

Elman Recurrent Neural Network Application in Adaptive Beamforming of Smart Antenna System

In this paper an artificial Elman Recurrent Neural Network (ERNN) is used for smart antenna adaptive beamforming. Neural network is used to calculate the optimum weights of uniform linear array antenna that steer the radiation pattern of the antenna by directing multiple narrow beams toward the desired users and make nulling in the direction of unwanted users. Two different supervised training algorithms are used to train the ERNN , they are Levenberg Marquardt (LM) algorithm and Resilient Backpropagation (Rprop) algorithm. Uniform linear array is used with five element and the spacing between element equal to half wavelength .The results of ERNN training using LM and Rprop showed that the performance of Neural Network (NN) trained by LM training algorithm is better than Rprop training algorithm ,since it consider the fastest backpropagation training algorithm but it requires more memory than other algorithms.

L-Band Digital Array Radar Demonstrator for Next Generation Multichannel SAR Systems

Successful state-of-the-art space synthetic aperture radar (SAR) systems-based in active electronic steerable antenna (AESA) have reached a high degree of operation flexibility and achieved performance. Nevertheless, the possibility to provide wide-swath images with high resolution is still a challenge requiring the application of new concepts and system architectures. Multiple channel-based SAR systems have become the perfect trend to follow in next generation SAR programs, as they will allow to overcome the resolution/coverage tradeoff by enabling the application of digital beamforming (DBF) or multiple input multiple output (MIMO) techniques. This paper presents a multichannel reconfigurable SAR system prototype concept being developed as demonstrator for next generation SAR operation and applications, enabling the use of DBF on receive or MIMO-SAR. System architecture and key subsystems are described, with emphasis in reconfigurable capabilities and internal calibration. Example performance results for practical application of presented architecture are also provided.

Small aperture microphone arrays

Superdirectional microphone arrays are arrays that are typically smaller than the acoustic wavelength and attain directional gains that exceed those of a classical delay-sum beamformer. Early superdirectional microphones utilized a combination of a velocity microphone along with a pressure microphone. Later, a single sensor superdirectional microphone was discovered that utilized the combination of pressure and pressure-difference (which is proportional to the acoustic particle velocity) through appropriate porting of the incident acoustic field to both sides of the microphone diaphragm. In the early 1980s, with the advent of multichannel FFT analyzers, there was a renewed interest in using superdirectional microphone arrays to estimate the acoustic intensity and to calculate the acoustic power flow from sources. The estimation of the vector acoustic intensity led to many transducer designs that utilized up to 6 pressure microphones and commensurate signal processing. In this talk we will show some of the early acoustic intensity probes that were designed to estimate the acoustic intensity. These small arrays have been utilized in many other beamforming applications. We will show one where a superdirectional beamformer is also capable of source direction finding by utilizing some simple adaptive beamformer implementations.