Proposed Beamforming Technique Research Articles

Windowed Radon Transform and Tensor Rank-1 Decomposition for Adaptive Beamforming in Ultrafast Ultrasound.

Ultrafast ultrasound has recently emerged as an alternative to traditional focused ultrasound. By virtue of the low number of insonifications it requires, ultrafast ultrasound enables the imaging of the human body at potentially very high frame rates. However, unaccounted for speed-of-sound variations in the insonified medium often result in phase aberrations in the reconstructed images. The diagnosis capability of ultrafast ultrasound is thus ultimately impeded. Therefore, there is a strong need for adaptive beamforming methods that are resilient to speed-of-sound aberrations. Several of such techniques have been proposed recently but they often lack parallelizability or the ability to directly correct both transmit and receive phase aberrations. In this article, we introduce an adaptive beamforming method designed to address these shortcomings. To do so, we compute the windowed Radon transform of several complex radio-frequency images reconstructed using delay-and-sum. Then, we apply to the obtained local sinograms weighted tensor rank-1 decompositions and their results are eventually used to reconstruct a corrected image. We demonstrate using simulated and in-vitro data that our method is able to successfully recover aberration-free images and that it outperforms both coherent compounding and the recently introduced SVD beamformer. Finally, we validate the proposed beamforming technique on in-vivo data, resulting in a significant improvement of image quality compared to the two reference methods.

Preliminary Investigation of Magnetic Resonance Imaging Guided Beamforming in Flexible Type Ultrasonic Array Transducers

A flexible-shaped ultrasonic array probe that can be used in a high magnetic field environment in an MRI gantry has been developed. Given that this probe can be fixed according to the shape of the skull’s surface, it is particularly applicable for imaging in the brain. To perform ultrasonic beamforming using a bent probe, it is necessary to measure the bent shape. Therefore, in this research, the curvature of the probe was estimated using MRI. A phantom with ellipse surface close to the shape of a skull was created using a 3D printer. The probe was arranged along the phantom surface to perform MRI and ultrasonic beamforming. The ultrasonic array transducer had 192 elements made from 1-3 composite piezoelectric materials with an element spacing of 0.3 mm. Eight MR position markers were attached to the probe in parallel in two rows of four each, with the array transducer in between. The delay time of each element in dynamic focusing for reception was calculated from its position estimated by the curvature of the probe. To evaluate the feasibility of this method, a B-mode image of 0.98 mm-diameter-thread targets placed in water was generated. The beam width at half maximum of the echo peak in the lateral direction from the thread target set up near the transmission focal point was calculated based on the B-mode image. It was found that the beam width of 1.32 mm in the proposed method, which was close to the thread diameter, whereas that was 4.38 mm in the conventional method that did not consider the bending of the probe. Consequently, the proposed beamforming technique is feasible for ultrasonic imaging through an arbitrary curved surface. Practical applications with a head phantom mimicking skull and cerebral tissue are expected.

Alternating Beamforming With Intelligent Reflecting Surface Element Allocation

Intelligent reflecting surface (IRS) has become a promising technology to aid next generation wireless communication systems. In this paper, we develop an alternating beamforming technique with a novel concept of IRS element allocation for multiple-input multiple-output systems when a base station supports multiple single antenna users aided with a single IRS. Specifically, we allocate each IRS element separately to each user, thus, in the beamforming stage allowing the IRS element only consider a single user at a time. In result to this separation, the complexity is vastly decreased. The proposed beamforming technique tries to maximize the minimum rate of all users with minimal complexity. In the numerical results, we show that the proposed technique is comparable to the convex optimization-based benchmark with sufficiently less complexity.

An Adaptive Bidirectional Multibeam High-Altitude Platforms Aeronautical Telecommunication Network Using Dual Concentric Conical Arrays

An efficient aeronautical telecommunication network (ATN) is proposed in this article based on adaptive multibeam antenna arrays and high-altitude platforms (HAPs). First, the network structure is demonstrated, and its geometry is analyzed based on a geocentric coordinate system that converts the global positioning system (GPS) and altitude data of aircrafts and HAPs into direction-of-arrival (DOA) information which is required for subsequent beamforming operation. The antenna array is then formed by designing a low-profile dual concentric conical array (DCCA) with uniform elements distribution and is used at the aircraft and HAP to achieve bidirectional beamforming. The antenna array elements are fed by an adaptive-exponent sine profile function to reduce the sidelobe levels while the low-profile dual conical array structure reduces the secondary major lobe and backlobe levels. The proposed beamforming technique is also capable of providing multibeam towards several aircrafts at the same time for effective resource sharing and management. The radiation performance of the array is demonstrated, analyzed, and compared with the concentric circular array where it is found that the secondary major lobe has been reduced by 13 dB with sidelobe level down to -40 dB relative to the mainlobe level. In addition, the bit energy-to-noise power spectral density and probability of bit error of the proposed aeronautical network has been investigated at different operating frequencies including 3.5 GHz and millimeter wave (mm-wave) frequencies of 28 and 39 GHz. The simulation results have shown that a channel capacity of about 3 Gbps can be achieved for BPSK and QPSK signals using bidirectional beamforming for a channel bandwidth of 400 MHz at 28 and 39 GHz mm-wave frequencies while it is about 773 Mbps at 3.5 GHz for 100 MHz bandwidth that can be provided over a line-of-sight distance of 896 km between an aircraft and HAP.

Instantaneous, Zero-Feedback Fading Mitigation With Simple Backscatter Radio Tags

This work offers a novel, backscatter radio-based, blind beamforming technique that assists the reception of signals in multipath conditions. The technique is based on simple, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">assistive</i> backscattering tags, implemented without any means of signal amplification. These tags can <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">blindly</i> (i.e., without feedback) modify the phase of the associated wireless channels, leading to constructive addition of the multipath components (i.e., alignment). Such alignment events offer distributed beamforming gain. Analysis is performed and an expression for the probability of alignment is offered, along with an expression for the achievable gain, corroborated by simulations and experimental results. It is shown that increased number of assistive tags offers higher beamforming gain, at the expense of increased delay. The effectiveness of the proposed beamforming technique is highlighted with experiments and measurements on the radio frequency identification (RFID) Gen2 standard. Commercial RFIDs that initially could not be interrogated due to insufficient impinged power, were successfully interrogated hundreds of times/minute with the assistance of the beamforming tags. It was experimentally shown that the proposed beamforming tags can offer power gains in the range of 0.4 – 3.7 dB. While the technique was tested on commercial RFIDs, it is not limited to a specific communication standard.

Cross power spectral density based beamforming for underwater acoustic communications

In underwater acoustic (UWA) communications, beamforming is often used to improve the detection performance of a receiver. For beamforming, there have been methods presented in time domain, e.g. fractional delay (FD) method, and in frequency domain, e.g. time-frequency-time with cross spectral density matrix (TFT-CSDM) method. The former brings accurate direction of arrival (DOA) estimation but with high complexity and is vulnerable to noise; while the latter brings less accuracy but with lower complexity. In this paper, we propose and investigate a time-frequency-time with cross power spectral density (TFT-CPSD) beamforming method for a vertical linear array (VLA) of hydrophones. The proposed method is compared with the FD and the TFT-CSDM methods in a receiver designed for guard-free orthogonal frequency-division multiplexing (OFDM) with superimposed data and pilot signals. The comparison is based on data obtained in sea trials at distances 30–50 km in the northwest Pacific Ocean. The results demonstrate that the proposed TFT-CPSD method possesses higher accuracy than the TFT-CSDM method, and lower complexity than the FD method. Besides, the OFDM receiver with the TFT-CPSD beamforming outperforms a receiver with the TFT-CSDM beamforming and the FD beamforming at signal to noise ratio (SNR) −14 to 14 dB. The proposed beamforming technique possesses the merits of energy conservative and energy leakage reduction, which can also be applied to single-carrier transmission.

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.

Cooperative Beamforming for Cognitive-Radio-Based Broadcasting Systems in Presence of Asynchronous Interference

To address the asynchronous interference issue in a generalized scenario with multiple primary and multiple secondary receivers, in this paper, we propose an innovative cooperative beamforming technique. The cooperative beamforming design is formulated as an optimization problem that maximizes the weighted sum transmission rate of secondary destinations while maintaining the asynchronous interference at the primary receivers below their target thresholds. In particular, we obtain the optimum beamforming directions and allocate power values among such beamforming directions. In light of the intractability of the power allocation problem, an approximation is used to convert the nonconvex and nonlinear optimization problem into a convex and linear one. Due to the multiple interference constraints corresponding to multiple primary receivers, the power allocation scheme is still complex. Therefore, we also propose a low-complexity power allocation algorithm. The proposed beamforming technique is extended for the case when cooperating CR nodes (CCRNs) have statistical channel knowledge of the primary receivers by developing an upper bound on the probability of introducing asynchronous interference at a given primary receiver beyond a given threshold value. We also propose two CCRN selection strategies for cooperative beamforming.

Distributed Beamforming and Autonomous Participation Decision making in Cooperative CR Systems in Presence of Asynchronous Interference

We propose a distributed beamforming for cooperative cognitive radio (CR) networks, that reduces the required feedback overhead in terms of sharing the channel state information (CSI) between the cooperating CR relays. Assuming the reciprocity of the channels of each cooperating CR node toward the CR receiver, as well as toward the primary receiver, the proposed beamforming technique only requires sharing the location information of the CR relays among the cooperating CR relays, rather than the global CSI. Reducing the required feedback overhead provides enhanced scalability of the cooperative CR network with lower deployment cost. In this paper, we also propose two autonomous decision making strategies that can help each CR user to independently decide whether to participate in the cooperative transmission or not. This participation decision is tackled from a game theoretic approach, by quantifying the reward and cost functions of each CR relay. The first proposed strategy, named regret testing-based strategy, is proved to asymptotically achieve an approximate Nash equilibrium state of the system. However, it has higher complexity and slower convergence time. So we also propose a suboptimal decision making strategy, named learning-based strategy, that has lower complexity and faster convergence time.

Worst-case-based robust beamforming for wireless cooperative networks

Abstract It is known that distributed beamforming techniques can improve the performance of relay networks by using channel state information (CSI). In practical applications, there exist unavoidably estimation errors of the CSI, which results in outage of quality of service (QoS) or overconsumption of transmit power. In this paper, we propose two worst-case-based distributed beamforming techniques that are robust to the channel estimation errors. In the worst-case-based approaches, the worst case in a set that includes the actual case is optimized. Therefore, the performance of the actual case can be guaranteed. In our first approach, the maximal total relay transmit power in the set is minimized subject to the QoS constraint. This distributed beamforming problem can be approximately solved using second-order cone programming (SOCP). In our second method, the worst QoS in the set is maximized subject to the constraints of individual relay transmit powers. It is shown that the resultant problem can be approximately formulated as a quasi-convex problem and can be solved by using a bisection search method. Simulation results show that the proposed beamforming techniques are robust to the CSI errors and there is no outage of QoS or power in the proposed methods.

Stereophonic hands-free communication system based on microphone array fixed beamforming: real-time implementation and evaluation

Abstract In this article, the authors propose an optimally designed fixed beamformer (BF) for stereophonic acoustic echo cancelation (SAEC) in real hands-free communication applications. Several contributions related to the combination of beamforming and echo cancelation have appeared in the literature so far, but, up to the authors’ knowledge, the idea of using optimal fixed BFs in a real-time SAEC system both for echo reduction and stereophonic audio rendering is first addressed in this contribution. The employment of such designed BFs allows positively addressing both issues, as the several simulated and real tests seem to confirm. In particular, the stereo-recording quality attainable through the proposed approach has been preliminarily evaluated by means of subjective listening tests. Moreover, the overall system robustness against microphone array imperfections and noise presence has been experimentally evaluated. This allowed the authors to implement a real hands-free communication system in which the usage of the proposed beamforming technique has proven its superiority with respect to the usual two-microphone one in terms of echo reduction, and guaranteeing a comparable spatial image. Moreover, the proposed framework requires a low computational cost increment with regard to the baseline approach, since only few extra filtering operations with short filters need to be executed. Nevertheless, according to the performed simulations, the BF-based SAEC configuration seems to not require the signal decorrelation module, resulting in an overall computational saving.

A Distributed Amplify-and-Forward Beamforming Technique in Wireless Sensor Networks

We consider <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i> far-field terminals with one source and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i> -1 interferences that transmit to a wireless sensor network (WSN) with <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i> uniformly distributed relaying nodes. Each relaying node receives a signal mixture from the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i> transmitters in the first phase, multiplies it with a properly selected beamforming weight and retransmits the resultant signal to a single receiving terminal in the second phase. The decentralized nature of the WSN dictates every node to compute its beamforming weight based only on its limited locally available information and without the knowledge of the locations and the channels of any other node in the network. Unfortunately, the optimal beamforming weights that maximize the signal-to-interference-plus-noise ratio (SINR) at the receiver cannot be computed locally. To circumvent this problem, we derive accurate local approximates of the SINR-optimal beamforming weights. Our proposed beamforming technique uses the so-obtained locally computable weights and, hence, can be implemented in a distributed fashion. The performance of the proposed distributed beamformer is analyzed both when the directions of the interferences are perfectly known and when they are imperfectly estimated. The advantages of the proposed distributed beamformer in comparison with a conventional distributed beamformer are analytically proved and are further verified by various simulation results.

SINR Balancing Technique for Downlink Beamforming in Cognitive Radio Networks

We propose a novel signal to interference and noise (SINR) balancing technique for a downlink cognitive radio network (CRN) wherein multiple cognitive users (also referred to as secondary users (SUs)) coexist and share the licensed spectrum with the primary users (PUs) using the underlay approach. The proposed beamforming technique maximizes the worst SU SINR while ensuring that the interference leakage to PUs is below specific thresholds. Due to the additional interference constraints imposed by PUs, the principle of uplink-downlink duality used in the conventional downlink beamformer design cannot be directly applied anymore. To circumvent this problem, using an algebraic manipulation on the interference constraints, we propose a novel SINR balancing technique for CRNs based on uplink-downlink iterative design techniques. Simulation results illustrate the convergence and the optimality of the proposed beamformer design.

Fast Beamforming for Mobile Satellite Receiver Phased Arrays: Theory and Experiment

The purpose of this paper is to present a robust and fast beamforming algorithm for the low-cost mobile phased array antennas. The proposed beamforming algorithm uses a sequentially perturbation gradient estimation method to update the control voltages of the phase shifters, with the objective of maximizing the received power by the array. This algorithm does not require either the knowledge of phase shifter characteristics or signal direction-of-arrival. Moreover, in this paper, the algorithm parameters are derived for the stationary and mobile platform configurations. For the stationary array, it is shown how the proper selection of the beamforming parameters limits the noise effects and increases the array output power. For the mobile array, a condition for the fast convergence is derived and the advantage of using nonuniform step size to update the control voltages is illustrated. When phase shifters suffer from the imbalanced insertion loss the proposed beamforming technique perturbs the phase-conjugate condition to increase the total received power. This algorithm has been implemented with the low-cost microwave components and applied to a Ku-band phased array antenna with 34 sub-arrays. The experimental results verify the broadband performance, and the fast convergence of the algorithm for different platform maneuvers.

Smart cell sectorization for third generation CDMA systems

AbstractSmart antennas are a powerful means to provide the increased bandwidth efficiency needed to deliver advanced third generation (3G) interactive multimedia services anywhere and anytime. In this paper we focus on the development of smart antennas located at the base stations of a code division multiple access (CDMA) cellular system. First, we review the main characteristics of antenna array systems and highlight some issues related to the inclusion of smart antennas in a 3G CDMA system. A classification of the proposed beamforming techniques and a discussion on the advantages and drawbacks of smart antennas are provided. Then, we introduce an original smart antenna technique based on rotation and resizing of the available sectors much simpler than common smart antennas based on beamforming techniques addressing a specific user. We discuss on the impact of the proposed technique in the base station architecture. Finally, we provide simulation results in order to show the effectiveness of the proposed approach and to relate transmission performance to system parameters. It turns out that the smart sectorization technique provides significant capacity improvements under statistically uniform user distribution (up to about 80 per cent for data traffic). Copyright © 2002 John Wiley &amp; Sons, Ltd.

Efficient transmit beamforming in pulse-echo ultrasonic imaging

A high performance ultrasound imaging system requires accurate control of the amplitude of the array elements, as well as of the time delays between them, both in the transmit and receive modes. In transmission, conventional array aperture windowing implies a different driving voltage for each element of the array, an expensive solution for systems with a large number of channels. In this paper, we present a simple, versatile, and inexpensive beamforming method that operates the aperture windowing in the transmit mode, simply controlling the lengths of the electric pulses driving the array elements. Computer simulations and experimental measurements are presented for different types of arrays. They confirm that the proposed beamforming technique improves the contrast resolution of the imaging system, reducing the off-axis intensity of the radiated field pattern. Moreover, the axial resolution is slightly enhanced, because the overall length of the transmitted ultrasonic pulse is reduced.