Number Of Antenna Array Elements Research Articles

Beam-Space MIMO Radar for Joint Communication and Sensing With OTFS Modulation

Motivated by automotive applications, we consider joint radar sensing and data communication for a system operating at millimeter wave (mmWave) frequency bands, where a Base Station (BS) is equipped with a co-located radar receiver and sends data using the Orthogonal Time Frequency Space (OTFS) modulation format. We consider two distinct modes of operation. In <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Discovery</i> mode, a single common data stream is broadcast over a wide angular sector. The radar receiver must detect the presence of not yet acquired targets and perform coarse estimation of their parameters (angle of arrival, range, and velocity). In <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Tracking</i> mode, the BS transmits multiple individual data streams to already acquired users via beamforming, while the radar receiver performs accurate estimation of the aforementioned parameters. Due to hardware complexity and power consumption constraints, we consider a hybrid digital-analog architecture where the number of RF chains and A/D converters is significantly smaller than the number of antenna array elements. In this case, a direct application of the conventional MIMO radar approach is not possible. Consequently, we advocate a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">beam-space approach</i> where the vector observation at the radar receiver is obtained through a RF-domain beamforming matrix operating the dimensionality reduction from antennas to RF chains. Under this setup, we propose a likelihood function-based scheme to perform joint target detection and parameter estimation in Discovery, and high-resolution parameter estimation in Tracking mode, respectively. Our numerical results demonstrate that the proposed approach is able to reliably detect multiple targets while closely approaching the Cramér-Rao Lower Bound (CRLB) of the corresponding parameter estimation problem.

Robust DOA Estimation Using VSS-LMS With Low-Rank Matrix Approximation

Direction-of-arrival (DOA) estimation performance of adaptive filtering-based methods, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e.g.</i> , least mean square (LMS), degrades significantly in adverse conditions ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i.e.,</i> at low signal-to-noise ratio (SNR), small number of antenna array elements and snapshots, and in presence of two closely spaced signal sources). Moreover, these estimation methods require many regulating parameters to efficiently update the step size, which are very difficult to tune manually in practical scenarios. Although the subspace decomposition-based methods, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e.g</i> ., multiple signal classification (MUSIC), provide somewhat better performance in adverse conditions, they are based on the statistical properties of the signal such as spatial covariance matrix (SCM) and its eigenvalue decomposition (EVD), resulting in high computational complexity. In this paper, a robust DOA estimation method is proposed based on a variable step size LMS algorithm with low rank matrix approximation (LRMA), where the received signal de-noising problem is formulated first as a LRMA problem directly using the received signal observations instead of the SCM, and then the variable step size is calculated from the predicted instantaneous error and the estimated powers of reference and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">de-noised</i> signals. The output spatial spectrum is determined by the reciprocal of the antenna array pattern, and the high peaks in the output spatial spectrum give the received signals estimated directions. The proposed method updates the step size efficiently without choosing any regulating parameter, and achieves improved performance even in adverse conditions due to the de-noising feature of LRMA with low computational complexity. Further, we also conduct the convergence and stability analyses of the proposed iterative estimation method with the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">de-noised</i> signal. Numerical results demonstrate that the proposed method outperforms state-of-the-art methods especially those, which yielded based on adaptive filtering.

Detection, Estimation and Radiation Formation Using Smart Antennas for the Spatial Location

The Electromagnetic (EM) waves are impinging on the base station from all the directions, Equally Spaced Uniform Linear Antenna Array (ESULA) are used to process these incoming EM waves to Detect and Estimate the directions of the mobile transmitters. After the process of Detection and Estimation, Electronic Beamforming is used to provide the narrow sharper beam towards the detected user. This Detection, Estimation and Beamforming plays a key role in variety of use cases like Radar, Wireless Communication and Sonar based systems. Smart Antenna Systems are implemented using two strategies namely Direction of Arrival (DoA) and Beamforming (BF). Direction of Arrival is a mechanism of Detecting and Estimating the directions of the mobile transmitters. Beamforming on the other hand is a process of transmission of the EM waves towards the source in a specific direction and providing the Spectral Nulls to other Interfering users. To increase the user capacity and to enhance the user experience Spatial Location based Spatial Division Multiple Access (SDMA) technology is used. To improve the overall performance of the smart antenna systems energy and packet delivery is majorly focused on specific source directions rather than using blind transmission strategy. In this paper performance analysis of algorithms for Direction of Arrival methods as well as the Beamforming methods have been performed. Experimental simulations are conducted and comparison is done with respect to Bias, Resolution and Time complexity for the Direction of Arrival methods. Noise Subspace Method (NSM) DoA algorithm consistently delivered the optimal bias, high resolution detection of the user location in spatial domain and provided lesser time complexity for both the scenarios which uses fewer antenna elements or larger number of antenna array elements at the base station. Similarly for the case of Beamforming methods the Mean Square Error and Beam-directions have been compared.

Multiuser steered signed quadrature spatial modulation for millimeter‐wave massive multiple‐input multiple‐output with hybrid beamforming

AbstractIn this article, signed quadrature spatial modulation (SQSM) scheme is intrinsically amalgamated with both fully digital geometric mean decomposition (GMD)‐based precoding technique and analog beamforming (ABF) for transmission over millimeter‐wave (mmWave) channel. Explicitly, the proposed scheme combines SQSM and GMD‐based hybrid beamforming (HBF) in downlink multiuser scenario, where the Frobenius norm‐based user selection algorithm is considered. This proposed scheme is denoted as multiuser steered SQSM (MUS‐SQSM). The ABF is used to mitigate the severity of the propagation loss in mmWave band by using power amplifiers and phase shifters. The performance of the proposed scheme in terms of both the bit error rate and the average mutual information is assessed in comparison to the conventional SQSM scheme performance. Simulation results show that significant improvements are realized by both the user selection algorithm and the application of ABF technique as the number of antenna array elements increases. It is also demonstrated that MUS‐SQSM scheme is robust against the channel estimation errors. Furthermore, the proposed MUS‐SQSM scheme with HBF benefits from the multiplexing gain of SQSM, the diversity gain of serving multiple users, and from the beamforming gain. All these gains increase the energy efficiency of the proposed model; thus, the proposed scheme can be considered in 5G wireless systems deployment.

A High Performance Terahertz Photoconductive Antenna Array Detector With High Synthesis Efficiency

A 2 × 2 terahertz photoconductive antenna (PCA) array detector with high efficiency synthesis characteristic that improves the signal-to-noise ratio (SNR) of the detected signals has been reported in this paper. By processing the substrate material through a special micromachining process, the current signal generated by the adjacent antenna elements as opposed to that generated by the antenna gap is eliminated. Experiments show that the amplitude of the current signal output by the PCA array detector is consistent with the amplitude of the synchronous superposition of the current signals output by antenna elements, and the synthesis efficiency of the device achieves 93.7%. At the same time, the antenna array detector has low current noise, and its highest SNR is 62 dB under the excitation of different light energy, which is related to the number of antenna array elements.

Adaptive Array Antenna in Ground Station Control System for Massive LEO CubeSat Constellation Tracking

Since Low Earth Orbit has become a popular orbit to place satellites, CubeSat constellation tracking is challenging. The higher capacity and capability of a new Ground Station tracking system are in demand and this motivates researchers to come out with a solution to mitigate the traditional Ground Station degradation performance. This paper discusses the implementation of the Least Mean Square algorithm to the Adaptive Array Antenna for the Ground Station tracking system application. The simulation results show the main beam pattern’s capability to perform instantaneous tracking and steering towards the targeted CubeSat while suppressing the side lobes towards the other interfering CubeSats when massive CubeSats constellations take place. Planar and circular array antennas are analyzed by setting the optimum weighting factors to be adapted. Three scenarios of CubeSats constellations are simulated. The Adaptive Array Antenna’s performance for each scenario is analyzed based on the beam width characteristics and the Signal-to-Interference Ratio of the beam pattern. The number of CubeSats tracked by the Adaptive Array Antenna and the system’s capability to perform fast tracking as the number of antenna array elements is also discussed in this paper. Finally, solutions to mitigate the Least Mean Square algorithm’s limitation to perform fast tracking when massive interferer CubeSats are nearby are proposed.

Design and development of planar antenna array for mimo application

Multi-Input Multi-Output (MIMO) is the need for recent communication system for the enhancement of channel capacity. While the number of antenna array elements increased, the spacing between the array elements and size of the antenna reduced. Hence high coupling between the elements occur, and thus the channel capacity reduced. There were several existing methods employs, however there were some limitations like reduced gain, dielectric constant, and bandwidth. So as to overcome this and to increase the performance characteristics such as bandwidth, gain of MIMO antennas and to lessen the dielectric constant of substrate material this proposed scheme is introduced. Using these considerations and requirements, an array of two-element MIMO system will be designed and developed with a less dielectric material ( $$ \varvec{\varepsilon}_{{\varvec{r }}} < 4 $$ ). So in this Taconic RF-35 (dielectric constant is 3.5), Two T-Shaped antennas are employed for 2.45 GHz (ISM band) with multiple modes of operation to achieve the improved bandwidth of about − 10 db. Simulation is done by HFSS 13.0.

On-grid Adaptive Compressive Sensing Framework for Underdetermined DOA Estimation by Employing Singular Value Decomposition

In the field of Array Signal Processing, the problem of Direction of Arrival (DOA) estimation has attracted colossal attention of researchers in the past few years. The problem refers to estimating the angle of arrival of the incoming signals at the receiver end, from the knowledge of the received signal itself. Generally, an array of antenna/sensors is employed at the receiver for this purpose. In over-determined DOA estimation, the number of signal sources, whose direction needs to be estimated are usually lesser than half the number of antenna array elements, whereas the challenge is to estimate the DOAs in under-determined case, where the signal source number is quiet larger than the number of antenna array elements. This paper tackles such a problem by the application of multiple level nested array. Instead of subspace-based techniques for the estimation, sparse signal representation for Compressive Sensing (CS) framework is used, which eliminates the requirement of prior information about the source number and also the tedious task of computing the inverse of the covariance matrices. In this paper, we propose an adaptive approach for Least Absolute Shrinkage and Selection Operator (LASSO) with reduced number of computations by singular value decomposing of the received signal vector. The outcomes of this paper showcase that the presented algorithm achieves high degree of freedom (DOF), good resolution, minimum root mean square error and less computational complexity with increased speed of estimation.

Capacity of Multiconnectivity mmWave Systems With Dynamic Blockage and Directional Antennas

The challenges of millimeter-wave (mmWave) radio propagation in dense crowded environments require dynamic re-associations between the available access points (APs) to reduce the chances of losing the line-of-sight path. However, the antenna beamsearching functionality in the mmWave systems may introduce significant delays in the course of AP re-association. In this paper, we analyze user performance in dense urban mmWave deployments that are susceptible to blockage by the dynamically moving crowd. Our approach relies on the ergodic capacity as the key parameter of interest. We conduct a detailed evaluation with respect to the impact of various system parameters on the ergodic capacity, such as AP density and height, blocker density and speed, number of antenna array elements, array switching time, degree of multiconnectivity, and employed connectivity strategies. Particularly, we demonstrate that dual connectivity delivers the desired performance out of all possible degrees of multiconnectivity, and there is an optimal density of mmWave APs that maximizes the capacity of cell-edge users. We also show that the use of low complexity “reactive” multiconnectivity design, where the beamtracking is only performed when the currently active connection is lost, together with the utilization of iterative beamsearching algorithms, does not significantly deteriorate the ergodic capacity.

RADIO SOURCE DIRECTION FINDING IN WIDE FREQUENCY BAND USING CIRCULAR ANTENNA ARRAY

For the VHF broadband direction finder, coherent and incoherent direction finding algorithms for switched and non-switched connection of the antenna array (AR) to receiving device in single-signal and multi-signal direction finding modes are developed and investigated.Their synthesis is based on the methods of space-time theory of radio systems. Numerical calculation of the direction finding characteristics of the algorithms for different number of antenna array elements determines the operating range upper limiting frequency, in which this configuration provides single-value estimates of the azimuth and elevation angle. Statistical simulation modeling shows that for an odd number of antennas, the antenna array amplitudephase response is unique in a wider frequency band than for an even number of antennas. Due to this MUSIC based property applied in the space of antenna array elements, direction finding algorithm is developed for wide frequency band with several signals overlapping in frequency, with switched and non-switched AR connection to a radio receiver. It is shown that the use of ESPRIT and MUSIC methods in free-space diagram does not allow for direction finding in a wide frequency band with the antenna array fixed configuration. The results of the field studies of the developed algorithms are presented for the single-signal and multi-signal modes of operation, software and hardware implemented in the VHF radio direction finder. A comparative analysis of the developed algorithms with the known APs with fixed configuration is performed. It is shown that with the same AR configuration, it is the direction finding algorithm that determines the frequency range in which the direction finding is unique.

Accurate estimation of DOA and MAI mitigation in the presence of channel impairments at low SNR

Environmental effects may cause antenna array element positions to become disturbed, introducing array shape uncertainties. The presence of these uncertainties causes a rapid degradation in the detection, resolution and estimation performance of array processing algorithms. In this paper, the performance of the Multiple Signal Classification - Direction of Arrival (DOA) algorithm for estimating the direction of the incident angles of all the received signals impinging on the antenna array elements is analysed at low Signal to Noise Ratio (SNR). The investigation is achieved under different scenarios such as changing the number of antenna array elements at different values of SNR. The root mean square error of the estimated angles is computed and compared with the true angles of the desired user. The simulation results assure that in the presence of the reference signal, the DOA algorithm can identify the direction of the desired user with high accuracy and high resolution. Moreover, the Affine Projection Algorithm (APA) is implemented to enhance the accuracy of the estimated direction in order to generate a main beam towards the desired user and null towards interfering users.

Packet Level Performance Assessment of mmWave Backhauling Technology for 3GPP NR Systems

Recently standardized millimeter-wave (mmWave) band 3GPP New Radio systems are expected to bring extraordinary rates to the air interface efficiently providing commercial-grade enhanced mobile broadband services in hotspot areas. One of the challenges of such systems is efficient offloading of the data from access points (AP) to the network infrastructure. This task is of special importance for APs installed in remote areas with no transport network available. In this paper, we assess the packet level performance of mmWave technology for cost-efficient backhauling of remote 3GPP NR APs connectivity “islands”. Using a queuing system with arrival processes of the same priority competing for transmission resources, we assess the aggregated and per-AP packet loss probability as a function environmental conditions, mmWave system specifics, and generated traffic volume. We show that the autocorrelation in aggregated traffic provides a significant impact on service characteristics of mmWave backhaul and needs to be compensated by increasing either emitted power or the number of antenna array elements. The effect of autocorrelation in the per-AP traffic and background traffic from other APs also negatively affects the per-AP packet loss probability. However, the effect is of different magnitude and heavily depends on the load fraction of per-AP traffic in the aggregated traffic stream. The developed model can be used to parameterize mmWave backhaul links as a function of the propagation environment, system design, and traffic conditions.

Accurate estimation of DOA and MAI mitigation in the presence of channel impairments at low SNR

Environmental effects may cause antenna array element positions to become disturbed, introducing array shape uncertainties. The presence of these uncertainties causes a rapid degradation in the detection, resolution and estimation performance of array processing algorithms. In this paper, the performance of the Multiple Signal Classification - Direction of Arrival (DOA) algorithm for estimating the direction of the incident angles of all the received signals impinging on the antenna array elements is analysed at low Signal to Noise Ratio (SNR). The investigation is achieved under different scenarios such as changing the number of antenna array elements at different values of SNR. The root mean square error of the estimated angles is computed and compared with the true angles of the desired user. The simulation results assure that in the presence of the reference signal, the DOA algorithm can identify the direction of the desired user with high accuracy and high resolution. Moreover, the Affine Projection Algorithm (APA) is implemented to enhance the accuracy of the estimated direction in order to generate a main beam towards the desired user and null towards interfering users.

DoA estimation of highly correlated stochastic sources using neural model

ABSTRACTMultiLayer perceptron (MLP)-based neural model for an efficient 1D DoA estimation of highly correlated stochastic EM sources is proposed. Model extracts this information from a spatial correlation matrix obtained by sampling stochastic signals by a receiving antenna array. Algorithm for optimal selection of correlation matrix elements from the upper triangle of the matrix is suggested to reduce the number of antenna array elements needed to obtain an accurate neural model with relatively simple architecture. This approach is verified by determining the azimuth position of two sources with the mutual correlation in the range [0.8–0.95] using antenna arrays with different number of elements.

Minimal Polynomial Method for Estimating Parameters of Signals Received by an Antenna Array

The effectiveness of the projection minimal polynomial method for solving the problem of determining the number of sources of signals acting on an antenna array (AA) with an arbitrary configuration and their angular directions has been studied. The method proposes estimating the degree of the minimal polynomial of the correlation matrix (CM) of the input process in the AA on the basis of a statistically validated root-mean-square criterion. Special attention is paid to the case of the ultrashort sample of the input process when the number of samples is considerably smaller than the number of AA elements, which is important for multielement AAs. It is shown that the proposed method is more effective in this case than methods based on the AIC (Akaike’s Information Criterion) or minimum description length (MDL) criterion.

Особенность использования планарных антенных решеток с центральной симметрией в схеме компенсатора помех

Matters concerned with analyzing the performance of an interference canceler equipped with a specially configured antenna array (AA) are discussed. As is known, the performance of an adaptive system depends directly on the characteristics and arrangement of antenna array elements. It is shown that the use of planar centrally symmetric AAs in the interference canceler scheme entails an essential drawback pertinent to operation of the adaptive system as a whole. Namely, there are some cases of interference arrival directions (jamming environment) in which the canceler fails to suppress the active interference. With such environment, the jams are statistically independent, act from different directions, and their number is by one fewer than the number of AA elements. This is due to the fact that for the considered jamming environment cases the rank of the jammer subspace is less than the number of acting jammers. As a result, an attempt to set up the array pattern zeroes in the directions of all jams is not met with success. The problem of searching jamming environments for which the above-mentioned drawback takes place is analyzed. The special jam action directions for which the interference canceler shows poor performance are calculated taking a four-element planar AA as an example. The obtained theoretical results are confirmed by simulating the interference canceler operation. The constructed interference canceler model does not contain the destabilizing factors available in real hardware, a circumstance that opens the possibility to estimate the effect of jamming environment as the only influencing factor. The simulation results make it possible to estimate the canceler performance in unfavorable jamming environment. For the considered case, the suppression ratio has been reduced up to 2.7 dB with the interference-to-noise ratio equal to 60 dB at the canceler input, as a result of which the acting jams pass to the canceler output almost without having been suppressed at all. The interference canceler performance both in favorable and unfavorable environments is clearly shown by an antenna pattern. To overcome the considered drawback, it is recommended to alter the AA geometry and use a redundant number of antenna elements and other receiving system anti-jam algorithms.

Spatiotemporal-MIMO Channel Estimator and Beamformer for 5G

With requirements of spiraling data rates and limited spectrum availability, there is an increased interest in mm-wave beamformer-based communications for 5G. For upcoming cellular networks, the critical point is to exploit the increased number of employable antennas at both Tx and Rx to: 1) combat increased path loss; 2) tackle higher interference due to higher user density; and 3) handle multipath effects in frequency selective channels. Toward this, a multi-beam spatiotemporal superresolution beamforming framework is proposed in this paper as a promising candidate to design beampatterns that mitigate/suppress co-channel interference and deliver massive gain in the desired directions. Initially, channel and signal models suitable for the mm-wave MIMO system are presented using the manifold vectors of both Tx and Rx antenna arrays. Based on these models, a novel subspace-based channel estimator is employed, which estimates delays, directions, velocities, and fading coefficients of the desired signal paths. This information is then exploited by the proposed spatiotemporal beamformer to provide a massive array gain that combats path loss without increasing the number of antenna array elements and to be tolerant to the near-far problem in a high interference environment. The performance of the proposed channel estimator and beamformer is examined using computer simulation studies.

Performance Analysis of Adaptive Beamforming Algorithms for Smart Antennas

In this paper, adaptive beamforming techniques for smart antennas based upon Least Mean Squares (LMS), Sample Matrix Inversion (SMI), Recursive Least Squares (RLS) and Conjugate Gradient Method (CGM) are discussed and analyzed. The beamforming performance is studied by varying the element spacing and the number of antenna array elements for each algorithm. These four algorithms are compared for their rate of convergence, beamforming and null steering performance (beamwidth, null depths and maximum side lobe level).

Simulation and Evaluation of a Simple Adaptive Antenna Array for a WCDMA Mobile Communication

This paper presents a uniform Linear Array model of a simple adaptive antenna array based on signal-to-interference and noise ratio (SINR) maximization. The SINR using the adaptive antenna array was investigated for a conventional narrowband beam former by varying the number of antenna array elements and number of interfering signals or users. The results obtained were compared with that of omni-directional antenna. The graph obtained from the results showed significant improvement in SINR as the number of antenna elements increases in the presence of large interferers for odd numbered array.

Evaluation of the Interference and Noise Suppression Capability of Uniform Linear Array Adaptive Beamforming Antenna

This paper evaluates the interference and noise suppression capability of uniform linear array adaptive beamforming antenna, at base stations of WCDMA mobile communication system. The signal-to-interference and noise ratio (SINR) was the performance index used for the evaluation and analysis. SINR was investigated for a conventional narrow band beam former by varying the number of antenna array elements, the inter-element spacing and number of interfering signals or users. The results were compared with that of omni-directional antenna. The graph obtained showed significant improvement in SINR as the number of antenna elements increases in the presence of large interferers for odd numbered array. the most common of all the array geometries employed in cellular and personal communication systems (PCS) (2), and it is the simplest to be used in investigating SINR improvement. In this paper, we provide a detailed presentation of SINR improvement ability of a ULA. In particular, we consider the effect of varying the number of antenna elements, number of interfering users and the inter-element spacing on the SINR improvement with the exclusion of mutual coupling. The performance of omni-directional antenna and adaptive antenna array were compared based on SINR maximization.