Linear Array Beamforming Research Articles

Sparsity-Based Adaptive Beamforming for Non-Uniform Linear Arrays in Multipath Environment

Sparsity-Based Adaptive Beamforming for Non-Uniform Linear Arrays in Multipath Environment

Joint design of antenna selection and transmit linear array beamformer for integrated radar and communications

The design of integrated radar-communication (IRC) systems is seen as a promising solution to alleviate the congestion of spectrum resource in recent years. Additionally, with the deployment of large-scaled arrays in base stations, sparse array design via antenna selection has become prominent to reduce system overheads and alleviate mutual coupling effect. In this paper, we propose a joint design of antenna selection and transmit beamformer for IRC systems to realize the dual operations of radar and communications. Specifically, we propose a joint model that achieves a trade-off between minimizing the total number of antennas for IRC and suppressing the peak sidelobe level (PSL) of overall transmit beampattern with well-controlled mainlobe ripples. Unlike the existing schemes that focus on individual beamformer design with varying sparse array configurations, we impose a group sparsity on the beamforming matrix and jointly optimize multiple beamformers to obtain a common sparse array for the constellation of all communication symbols. To solve the resulting non-convex problem, we employ the alternating direction method of multipliers to split the original problem into parallel subproblems which are then solved iteratively. Simulation results illustrate the superiority of the proposed method over the conventional approaches in obtaining a lower PSL using fewer antennas with dual functions.

Eigenbeam-space transformation based steerable differential beamforming for linear arrays

Since linear differential arrays with small apertures can obtain high directivity and frequency-independent spatial response, much attention has been paid to the design of differential beamformers steered to the endfire direction. Although some works focus on the design of steerable differential beamformers with linear arrays, the synthesis of steerable frequency-invariant beampatterns by linear arrays still needs to be investigated. In this paper, an eigenbeam-space transformation based steerable differential beamforming is proposed for linear arrays. The major contributions are as follows. (1) For the beamformer steered away from the endfire direction, an interference suppression constraint might be imposed to ensure a valid beampattern in the situation where the interference from the endfire direction is very strong, which is not considered in the state-of-the-art approaches of the literature. (2) The synthesis of steerable differential beamformers is formulated as an optimization problem in the eigenbeam-space domain and the optimization problem is solved in a closed form. By experimentally determining the best pair of integers mt and N′, the proposed hybrid least-squares-error solution obtained in the eigenbeam-space domain has shown some advantages over the null constrained method and the weighted least-squares method implemented in the element-space domain.

Impact Localization Using Nonequidistant T-Shaped Sensor Clusters

In this article, a nonequidistant T-shaped sensor cluster used for localizing the impact on structures is presented. The normal T-shaped sensor cluster configuration, in which all the sensors are equidistantly set, can effectively remove blind areas because it is a combination of two impact-localization techniques: equidistant linear sensor array beamforming and an L-shaped sensor cluster method. The normal T-shaped sensor cluster can reduce the number of sensors while guaranteeing acceptable accuracy. However, equidistant linear sensor array beamforming suffers from the “spatial aliasing” effect, which results in a localization accuracy that is not sufficiently high. Thus, further optimizing the normal T-shaped sensor cluster to increase its accuracy is necessary. As confirmed in various reports, the nonequidistant linear sensor array can reduce the effects of “spatial aliasing,” which is a typically encountered phenomenon in the equidistant linear sensor array. In contrast to the normal T-shaped sensor cluster, the proposed nonequidistant T-shaped sensor cluster uses the nonequidistant linear sensor array beamforming method for impact localization in the regions near vertical directions. Thus, the impact localization accuracy is improved with the same number of sensors.

Efficient Cell-Specific Beamforming for Large Antenna Arrays

We propose an efficient method for designing broad beams with spatially flat array factor and efficient power utilization for cell-specific coverage in communication systems equipped with large antenna arrays. To ensure full power efficiency, the method is restricted to phase-only weight manipulations. Our framework is based on the discovered connection between dual-polarized beamforming and polyphase Golay sequences. Exploiting this connection, we propose several methods for array expansion from smaller to larger sizes, while preserving the radiation pattern. In addition, to fill the gaps in the feasible array sizes, we introduce the concept of ϵ-complementarity that relaxes the requirement on zero side lobes of the sum aperiodic autocorrelation function of a sequence pair. Furthermore, we develop a modified Great Deluge algorithm (MGDA) that finds ϵ-complementary pairs of arbitrary length, and hence enables broad beamforming for arbitrarily-sized uniform linear arrays. We also discuss the extension of this approach to two-dimensional uniform rectangular arrays. Our numerical results demonstrate the superiority of the proposed approach with respect to existing beam-broadening methods.

Method for estimating the radiated sound power of moving sound sources with linear array beamforming

Due to the existence of the Doppler effect, a frequency shift and band expansion occur in the measured signal that belongs to the moving sound source. To estimate the radiated sound power of the moving sound sources, this study proposes a method that is based on linear array beamforming. By applying this method, the influence of the Doppler effect on the received signal for each sensor is eliminated by interpolating the de-dopplerisation. The estimated result is obtained according to the conversion relation between the linear array beamforming output and the radiated sound power of the source. The sound power estimation error for the different motion states can be studied by considering the sound source frequency, amplitude, test distance, and other influencing factors by performing a simulation. The sound power estimation experiment of the double-moving sound sources verifies the effectiveness of the proposed method. Overall, the proposed methodology provides a simple and effective way to measure the radiated power of the moving sound sources.

A novel T-shaped sensor cluster for acoustic source localization

This study proposes a new sensor cluster configuration for localizing an acoustic source in a plate using uniform linear array beamforming and T-shaped sensor clusters. This technique requires neither the properties of the plate material nor a dense array of sensors to find the direction of arrival of the acoustic source. It functions by placing four sensors in a cluster in the shape of the letter “‘T” over a small region of the plate. Uniform linear array beamforming-based source localization is carried out by the constructive interference of different sensor signals. However, this approach has the disadvantage of a very low resolution when the direction of arrival approaches certain values. The L-shaped sensor clusters use the information from the time difference of arrival between the sensors to estimate the direction of arrival, which has a high resolution in all directions except for the direction that is very close to vertical to the cluster. In this study, we numerically and experimentally demonstrate that the proposed T-shaped sensor cluster can accurately localize the acoustic source with no blind area. We also detail its superior performance compared to both uniform linear array beamforming and L-shaped clusters. In the experimental investigation, the maximum deviation of impact source localization was reduced significantly, from 54° to 4° for an aluminum plate, and from 42° to 3° for a composite plate. Furthermore, this novel combined sensor array layout requires only a few sensors, which can significantly reduce the cost of structural health monitoring practice.

Modular Hybrid Beamforming for mmWave Fixed Wireless Access

Fixed wireless access has been spreading recently as a complement to wired or fiber solutions, and its implementation on millimeter waves has attracted attention for its potentially high data rates, achievable also in densely populated areas. New hardware and software solutions are needed to overcome various technical issues at those frequencies. We propose a novel modular hybrid beamforming (MHB) architecture, whereby, in receive mode, each module comprises a set of antennas connected to fixed analog beamformers, in turn connected by configurable switches to a smaller set of radio frequency chains. The outputs of all modules are then jointly processed by a digital beamformer. In particular, an MHB performing discrete Fourier transform beamforming for uniform linear arrays is studied. We address the problems of a) switch configuration, b) power allocation and digital beamformer design, and c) channel estimation. For both a) and b) we target the maximization of the total weighted spectral efficiency (WSE) under power and per-user average spectral efficiency (SE) constraints, and we propose greedy efficient solutions. For c) we propose a multistage scheme. We assess the MHB performance in terms of WSE, estimation accuracy, estimation overhead, and computational complexity, and compare them with existing solutions in literature.

Multi-dimension to one-dimension transformation approach for multi-dimensional antenna array pattern synthesis

ABSTRACTA new multi-dimension to one-dimension transformation (MTOT) approach is presented to synthesize multi-dimensional antenna array pattern. In the new approach the multi-dimensional antenna array pattern synthesis issue is mathematically transformed into a one-dimensional (1D) pattern synthesis issue by taking advantage of the general characteristics of the pattern function, which makes all existing linear array pattern synthesis and beamforming methods applicable to addressing relevant multi-dimensional array pattern synthesis issues. The new method provides a general way for multi-dimensional array pattern synthesis. Simulations of the new approach are conducted to show its effectiveness. The simulation results show that the new method can well accomplish the pattern synthesis mission for different multi-dimensional array configurations.

Robust Adaptive Beamforming for Uniform Linear Arrays With Sensor Gain and Phase Uncertainties

A robust adaptive beamforming method is proposed in this paper for uniform linear arrays with respect to sensor gain and phase uncertainties. The sensor gain and phase parameters are obtained by solving a series of linear equations that describe the specific structure of the array covariance matrix for a uniform linear array. Partly calibrated parameter constraints are required due to the rank defect of the coefficient matrix. The necessary condition to enable the partly calibrated sensors to estimate all the unknown gain and phase parameters is also deduced. Sensor noise power, and hence, interference-plus-noise covariance matrix (INCM) can then be calculated with the sensor gain and phase information. The robust adaptive beamformer is finally formed using the reconstructed INCM. In comparison with other reconstruction-based beamformers, the proposed method achieves satisfactory performance when sensor gain and phase uncertainties dominate the steering vector mismatch. The effectiveness of the proposed method is also confirmed by experimental results.

An efficient traffic monitoring and control system using aerial platforms and vertical arrays

In this paper, a reliable traffic monitoring system is proposed based on aerial platform (AP) wireless sensor network with a new adaptive vertical linear array beamforming technique. This proposed beamforming technique improves the system performance compared with recent techniques using the same number of antenna elements which makes aerial platforms more feasible to establish wireless sensor network for traffic monitoring application. Four coverage scenarios of the proposed AP traffic monitoring system are examined at coverage diameters of 16 and 60 km and two bit rates of 38.4 and 250 kb/s. The simulation results depicts better performance of the proposed antenna technique in all the four examined coverage scenarios. At the worst case (60 km coverage diameter, 2400 MHz frequency and bit rate of 250 kb/s), the probability of bit-energy to noise-spectral-density (\(E_{b}/N_{o})\) to be less than 4 dB is zero for the proposed technique while it was 0.14 in the case of optimized concentric circular array technique and 0.76 for the conventional spot-beam antenna. Also, at the coverage diameter of 16 km and bit rate of 38.4 kb/s at 868 MHz, the results show that the probability of \(E_{b}/N_{o} < 34\) dB of the proposed technique is zero while it was 0.15 in the case of optimized concentric circular array and 0.72 for the conventional spot-beam antenna.

Characterization of Kerfless Linear Arrays Based on PZT Thick Film.

Multielement transducers enabling novel cost-effective fabrication of imaging arrays for medical applications have been presented earlier. Due to the favorable low lateral coupling of the screen-printed PZT, the elements can be defined by the top electrode pattern only, leading to a kerfless design with low crosstalk between the elements. The thick-film-based linear arrays have proved to be compatible with a commercial ultrasonic scanner and to support linear array beamforming as well as phased array beamforming. The main objective of the presented work is to investigate the performance of the devices at the transducer level by extensive measurements of the test structures. The arrays have been characterized by several different measurement techniques. First, electrical impedance measurements on several elements in air and liquid have been conducted in order to support material parameter identification using the Krimholtz-Leedom-Matthaei model. It has been found that electromechanical coupling is at the level of 35%. The arrays have also been characterized by a pulse-echo system. The measured sensitivity is around -60 dB, and the fractional bandwidth is close to 60%, while the center frequency is about 12 MHz over the whole array. Finally, laser interferometry measurements have been conducted indicating very good displacement level as well as pressure. The in-depth characterization of the array structure has given insight into the performance parameters for the array based on PZT thick film, and the obtained information will be used to optimize the key parameters for the next generation of cost-effective arrays based on piezoelectric thick film.

Optimisation of excitation tolerances for robust beamforming in linear arrays

A method for robust amplitude beamforming in linear antenna arrays is presented. The admissible tolerances on the array excitations, described as real-valued intervals, are maximised regardless their nominal values, while guaranteeing that the bounds of the radiated power patterns fit a-priori defined mask constraints. A set of representative numerical results, concerned with different mask constraints as well as comparisons with state-of-the-art approaches, is reported and discussed to assess the effectiveness of the proposed approach.

Double zero minimum variance distortionless response beamformer

Adaptive beamformers (ABFs) place deep beampattern notches near interferers to suppress the interferers' power in the ABF output. The common sample matrix inversion (SMI) Minimum Variance Distortionless Response (MVDR) ABF computes the beamformer weights by substituting the sample covariance matrix (SCM) for the unknown ensemble covariance matrix in the MVDR expression. Errors in the SCM estimate of interferer direction due to limited sample support or interferer motion degrade the ABFs ability to suppress the interferer. This presentation exploits array polynomial properties to design a robust ABF. The array polynomial for a uniform linear array beamformer is the z-transform of the array weights. The array polynomial zeros on the unit circle correspond to the beampattern nulls. The proposed double zero (DZ) MVDR ABF solves for the MVDR weights using the SCM for a half-aperture subarray, then convolves the half-aperture weights with themselves to obtain the full aperture ABF weights. The resulting array polynomial for the DZ MVDR ABF has second-order zeros, producing broader and deeper notches in the interferer direction. The DZ MVDR ABF outperforms the SMI MVDR and covariance matrix tapered ABFs in simulations with stationary and moving interferers. [Work supported by ONR 321US.]

Investigations on Adaptive Beamforming for Linear and Planar Smart Antenna Arrays using Sample Matrix Inversion Algorithm

In this paper sample matrix inversion (SMI) algorithm is used to generate beam for a smart antenna. The capability of adaptive beam generation by SMI algorithm is investigated for linear and planar arrays. The accuracies of main beam toward user and null toward interferer, beam width and side lobe level with respect to the variation of block length are reported. General Terms Smart antenna, SMI algorithm

Generalised loading algorithm for adaptive beamforming in ULAs

A new method for adaptive beamforming in uniform linear arrays (ULAs) is introduced. The proposed method is based on generalised loading of the covariance matrix of the data vector received by the array. The covariance matrix is loaded with a Hermitian matrix which is chosen to shape the directional response of the array. Simulation results show that the proposed approach offers better handling of mismatches between presumed and actual array steering vectors. It produces output signal-to-interference-plus-noise ratio values higher than some well-known approaches in the literature with much less complexity.

Particle velocity gradient based acoustic mode beamforming for short linear vector sensor arrays.

In this paper, a subtractive beamforming algorithm for short linear arrays of two-dimensional particle velocity sensors is described. The proposed method extracts the highly directional acoustic modes from the spatial gradients of the particle velocity field measured at closely spaced sensors along the array. The number of sensors in the array limits the highest order of modes that can be extracted. Theoretical analysis and numerical simulations indicate that the acoustic mode beamformer achieves directivity comparable to the maximum directivity that can be obtained with differential microphone arrays of equivalent aperture. When compared to conventional delay-and-sum beamformers for pressure sensor arrays, the proposed method achieves comparable directivity with 70%-85% shorter apertures. Moreover, the proposed method has additional capabilities such as high front-back (port-starboard) discrimination, frequency and steer direction independent response, and robustness to correlated ambient noise. Small inter-sensor spacing that results in very compact apertures makes the proposed beamformer suitable for space constrained applications such as hearing aids and short towed arrays for autonomous underwater platforms.

Pulse Splitting for Harmonic Beamforming in Time-Modulated Linear Arrays

A novel strategy for harmonic beamforming in time-modulated linear arrays is proposed. The pulse splitting technique is exploited to simultaneously generate two harmonic patterns, one at the central frequency and another at a preselected harmonic of arbitrary order, while controlling the maximum level of the remaining sideband radiations. An optimization strategy based on the particle swarm optimizer is developed in order to determine the optimal parameters describing the pulse sequence used to modulate the excitation weights of the array elements. Representative numerical results are reported and discussed to point out potentialities and limitations of the proposed approach.

Beamforming design for linear loudspeaker array with different feeding distribution

In the recent years, loudspeaker array has been widely considered and used in household appliance products. For the flat-panel TV, how to use the ultra-thin loudspeaker array to generate a directional beam is becoming the current research focus. In this paper, the beamforming effects of linear loudspeaker array with different feeding distributions are compared. The simulation configures 7 loudspeakers in a line with a gap of 14cm. Its directional diagrams under 1KHz are examined with 5 types of feeding distributions, which include the uniform, binomial, triangular, inverted triangular and Dolph-Chebyshev distributions. The simulation shows that the linear loudspeaker array beamforming is significantly impacted by the feeding distributions and Dolph-Chebyshev distribution has the ideal performance in beamforming. which is because it makes a good compromise between the main lobe width and the side lobe height.

Adaptive Beamforming for Uniform Linear Arrays With Unknown Mutual Coupling

This letter proposes a new adaptive beamforming algorithm for uniform linear arrays (ULAs) with unknown mutual coupling. It is based on the fact that the mutual coupling matrix (MCM) of a ULA can be approximated as a banded symmetric Toeplitz matrix as the mutual coupling between two sensor elements is inversely related to their separation, and hence it is negligible when they are separated by a few wavelengths. Taking advantage of this specific structure of the MCM, a new approach to calibrate the signal steering vector is proposed. By incorporating this improved steering vector estimate with a diagonally loaded robust beamformer, a new adaptive beamformer for ULA with unknown mutual coupling is obtained. Simulation results show that the proposed steering vector estimate considerably improves the robustness of the beamformer in the presence of unknown mutual coupling. Moreover, with appropriate diagonal loading, it is found that the proposed beamformer can achieve nearly optimal performance at all signal-to-noise ratio (SNR) levels.