Adaptive Antenna Array Research Articles

Wireless Communications and Applications Above 100 GHz: Opportunities and Challenges for 6G and Beyond

Frequencies from 100 GHz to 3 THz are promising bands for the next generation of wireless communication systems because of the wide swaths of unused and unexplored spectrum. These frequencies also offer the potential for revolutionary applications that will be made possible by new thinking, and advances in devices, circuits, software, signal processing, and systems. This paper describes many of the technical challenges and opportunities for wireless communication and sensing applications above 100 GHz, and presents a number of promising discoveries, novel approaches, and recent results that will aid in the development and implementation of the sixth generation (6G) of wireless networks, and beyond. This paper shows recent regulatory and standard body rulings that are anticipating wireless products and services above 100 GHz and illustrates the viability of wireless cognition, hyper-accurate position location, sensing, and imaging. This paper also presents approaches and results that show how long distance mobile communications will be supported to above 800 GHz since the antenna gains are able to overcome air-induced attenuation, and present methods that reduce the computational complexity and simplify the signal processing used in adaptive antenna arrays, by exploiting the Special Theory of Relativity to create a cone of silence in over-sampled antenna arrays that improve performance for digital phased array antennas. Also, new results that give insights into power efficient beam steering algorithms, and new propagation and partition loss models above 100 GHz are given, and promising imaging, array processing, and position location results are presented. The implementation of spatial consistency at THz frequencies, an important component of channel modeling that considers minute changes and correlations over space, is also discussed. This paper offers the first in-depth look at the vast applications of THz wireless products and applications and provides approaches for how to reduce power and increase performance across several problem domains, giving early evidence that THz techniques are compelling and available for future wireless communications.

ВИКОРИСТАННЯ СХЕМ ШАРП В АЛГОРИТМАХ ОБРОБЛЕННЯ СИГНАЛІВ В АДАПТИВНИХ АНТЕННИХ РЕШІТКА

ВИКОРИСТАННЯ СХЕМ ШАРП В АЛГОРИТМАХ ОБРОБЛЕННЯ СИГНАЛІВ В АДАПТИВНИХ АНТЕННИХ РЕШІТКА

ANTENNAS OF MOBILE TERMINALS IN MODERN MOBILE COMMUNICATION NETWORKS (OVERVIEW)

In connection with the development of technology of mobile terminals (cell phones, smartphones, tablets, computers with wireless modems, etc.) in the standards of UMTS (3G) and LTE (4G) great attention of manufacturers of these devices is concentrating on the modernization and development of antenna systems of mobile stations (terminals). Currently, antenna systems of mobile stations is implementing on base of technology in form of complex configuration microstrip transmission lines, which ensure compliance with the requirements of modern wireless communication standards. Adaptive antenna arrays and MIMO antenna systems are implemented in mobile terminals for road and railway transport, which allow to achieve a sustainable reception of signals from the base stations. As you know, the difficult conditions for the propagation of radio waves in cellular mobile communication systems are associated with their absorption, multiple reflection and scattering. In these cases, the laws that are true for the line of sight conditions (LOS, Line of Sight) no longer work. The properties of antennas integrated into mobile terminals (mobile stations - MS (Mobile Station)) directly depend on the statistical characteristics of the environment and the location of the operating terminal relative to the spatial position of the user. Therefore, when designing MS antennas in UMTS and LTE mobile communication systems in the frequency ranges from 450 to 3700 MHz, it is important to consider all of the above factors.

Wireless data transmission in underwater hydroacoustic environment based on MIMO-OFDM system and application adaptive algorithm at the receiver side

To increase the transmission speed in wireless data transmission systems, it is necessary to change either the bandwidth or the spectral efficiency, or both simultaneously. Systems based on Multi-Input Multi-Output (MIMO) methods can significantly increase spectral efficiency through parallel transmission using several transmitters and receivers. Such systems are particularly attractive for use in underwater acoustic communications systems, which are normally bandwidth-reduced. MIMO system along with OFDM (Orthogonal Frequency-Division Multiplexing) is a popular technology used in wireless networks to provide a high data transfer rate and resistance to multipath and fading of the channel. The implementation of such a system requires being aware of the channel condition at the receiver, and can be provided by means of using channel parameter estimation schemes. The adaptation task on the receiving side, apart from peak of pattern formation in the direction of the signal expected, also includes the interference-source suppression, that is, the issue of implementing spatial filtering of interference from other directions. However, since the signal and noise direction of arrival are unknown, we get a system with adaptive antenna array (AA). In the proposed research, a phase antenna array was used with controlled weighing.

SOLUTION OF THE PROBLEM OF COMPUTATIONAL STABILITY AND CONSISTENCY OF SAMPLE ESTIMATES OF THE CORRELATION MATRIX OF OBSERVATIONS BY THE METHOD OF DYNAMIC REGULARIZATION

The problem of forming sample estimates of the correlation matrix of observations that satisfy the criterion "computational stability – consistency" is considered. The variants in which the direct and inverse asymptotic forms of the correlation matrix of observations are approximated by various types of estimates formed from a sample of a fixed volume are investigated. The consistency of computationally stable estimates of the correlation matrix for their static regularization was analyzed. The contradiction inherent in the problem of regularization of the estimates with a fixed parameter is revealed. The dynamic regularization method as an alternative approach is proposed, which is based on the uniqueness theorem for solving the inverse problem with perturbed initial data. An optimal mean-square approximation algorithm has been developed for dynamic regularization of sample estimates of the correlation matrix of observations, using the law of monotonic decrease in the regularizing parameter with increasing sample size. An optimal dynamic regularization function was obtained for sample estimates of the correlation matrix under conditions of a priori uncertainty with respect to their spectral composition. The preference of this approach to the regularization of sample estimates of the correlation matrix under conditions of a priori uncertainty is proved, which allows to exclude the domain of computational instability from solving the inverse problem and obtain its solution in real time without involving prediction data and additional computational cost for finding the optimal value of the regularization parameter. The application of the dynamic regularization method is shown for solving the problem of detecting a signal at the output of an adaptive antenna array in a nondeterministic clutter and jamming environment. The results of a computational experiment that confirm the main conclusions are presented.

Optical Adaptive Antenna Array for Multiuser Mobile Optical Communication

In this paper, an optical adaptive antenna array system for multi-user optical mobile communication is studied. A coherent signal source is embedded in a spherical optical phased cell array with an external spherical lens system. The system can predict the signal power of the receiving end according to the channel transfer matrix and perform power compensation when transmitting the signal. Correspondingly, a pure phase lossless desired light field recovery algorithm is proposed and used for space division multiple access and free power allocation of antenna array systems. A small-scale optical adaptive antenna array experimental system is built and tested with good performance and consistent with the expected results.

Организация локальной навигационной системы с использованием адаптивных малоэлементных антенных решеток

The operation principles of local navigation system with the use of adaptive low-element antenna array are considered in this paper. The system will allow determining the coordinates of the vessel with high accuracy. For the eliminating the ambiguity of phase measurements of distances, the necessity of the formation of microwave signals with a small frequency shift was justified. The method of microwave signal forming is discussed. It is shown that the use of adaptive low-element antenna arrays improves system performance without a significant increase in the cost of the system. Adaptive antenna arrays minimize the effect of multipath propagation, which inevitably occurs while microwave propagation over the water surface.

Analysis of the efficiency of space­time access in the mobile communication systems based on an antenna array

We performed analysis of effectiveness of various methods and criteria of space-time processing of the signals by an adaptive antenna array with a view to identifying the algorithm suitable for using in arrangement of space-time access to mobile communication systems. It was shown that all methods are based on the assessment of an integrated vector of weight coefficients, included in the reception tract of every antenna element and controlled by certain algorithms. It was shown that recursive procedures that make it possible to correct the vector of weight coefficients in the dynamic situation, including non-stationary signal-interference situation, are more constructive for using in problems of space-time access. This is especially important for communications with mobile subscriber stations and allows reducing the time for processing calling signals due to the rapid convergence of recursive procedures. A comparative analysis of Widrow-Hoff and Kalman-Bucy algorithms was conducted. It was shown that the Kalman-Bucy procedure, in addition to optimality, in complicated signal-interference situation is characterized by maximally short time of convergence to the sustainable state. The convergence of the procedure is ensured on the time interval, allocated for the action of calling signals of subscriber stations in a mobile network. We proposed the model for studying the influence of initial conditions on the effectiveness of space-time access by the parameter of the convergence rate of the algorithm for adaptive space-time signal processing in an antenna array. It is possible to approximate the vector value to the optimal due to configuration of the integrated vector of weight coefficient based on the use of the information about directions of arrival of calling signals of subscriber stations in a mobile network. The results of the calculations of the indicator of the signal/(interference + noise) ratio on the convergence pitch for different algorithms of an adaptive antenna array were obtained. It was shown that it was possible to improve essentially the transitive characteristics of the algorithms for a linear four-element adaptive antenna array due to the successful initial choice of the value of the integrated vector of weight coefficients. This made it possible to increase the value of the signal/ (interference + noise) ratio at the outlet of an antenna up to 4 dB

Methods beamforming adaptive digital array and their study using a computer model

The article describes the computer model of an adaptive digital antenna array. We considered in detail its features and specifications. The results of experimental research methods beamforming digital adaptive antenna array using a computer model. We studied four methods of providing independent beams forming the directivity pattern, calibration of the receiving channels, interference suppression and measurement navigation parameters.

3D-OMP and 3D-FOMP algorithms for DOA estimation

Adaptive antennas and antenna array processing have vital effects on enhancing the performance of wireless communication networks. One of the most significant applications of adaptive antenna systems is the Direction of Arrival (DOA) detection. Several schemes have been proposed in the literature for DOA estimation in two-dimensional space. Among them, Orthogonal Matching Pursuit (OMP) algorithm provides several advantages in comparison to other schemes. The OMP algorithm reduces complexity and improves resolution of detection. Furthermore, in this algorithm, the number of signal emitters is not required to be known. In this paper, we extend the OMP algorithm and propose Three Dimensional OMP (3D-OMP) scheme for DOA estimation in three dimensional space. We provide a redundant dictionary for 3D-OMP scheme by employing azimuth and elevation angles. Simulation results show the high performance of the 3D-OMP algorithm when the signal to noise ratio is higher than −10dB. Moreover, the 3D-OMP algorithm has a high efficiency in detecting multiple signal sources, simultaneously. Then, we evaluate the accuracy of the estimated directions by the 3D-OMP algorithm via comparing the variance of estimation error with the Cramer-Rao bound. Nevertheless, DOA estimation by the 3D-OMP algorithm has a substantial challenge where it cannot distinguish between two adjacent signal sources. To resolve this challenge, we propose Three Dimensional Focused Orthogonal Matching Pursuit (3D-FOMP) algorithm. The 3D-FOMP algorithm is an improved version of the 3D-OMP algorithm. It can detect two adjacent signal sources when the beam former has a single peak corresponding to a direction between right directions. In addition, we show the 3D-OMP and 3D-FOMP algorithms have lower complexities in comparison to the 3D-MUSIC and 3D-ESPRIT schemes when Root Mean Square Error (RMSE)>0.3o. This accuracy is persuasive for most applications. Moreover, simulation results show the capability of the 3D-FOMP algorithm to detect adjacent signal sources and it outperforms the 3D-OMP, 3D-MUSIC and 3D-ESPRIT algorithms for all values of signal to noise ratio.

Broadband Frost Adaptive Array Antenna with a Farrow Delay Filter

In a broadband adaptive array antenna with a space-time filter, a delay filter is required before digital beamforming when the Frost algorithm is used to obtain the weight vector. In this paper, we propose a Farrow structure instead of a direct form FIR structure to implement the time delay filter since it can satisfy the demand for real-time update and is very suited for the FPGA platform. Furthermore, a new off-line algorithm to calculate the Farrow filter coefficient is presented if the filter coefficient is symmetric. Finally, simulations are presented to illustrate that the design methodology for the Farrow filter is correct. The simulations also prove that the Frost broadband adaptive antenna effectively mitigates the interferences with a Farrow filter.

Impact of Element Pattern Symmetry on the Effective Degrees of Freedom in Dual-Polarized GNSS Adaptive Antenna Arrays

The effect of element pattern symmetry on the performance of dual-polarized global navigation satellite system adaptive antenna arrays is investigated. To this end, using analytical expressions for the far-fields of circular microstrip antennas, the steady-state beamforming performance of a two-element dual-polarized array with three degrees of freedom (DOFs) is studied through many Monte Carlo simulations. It is shown that in the presence of randomly polarized interferers, regardless of the element pattern symmetry, the dual-polarized array can use all its DOF effectively to suppress up to three interferers and is as effective as a four-element right-handed circularly polarized (RHCP) array. It is, however, shown that if the interferers are RHCP, the dual-polarized array can use its DOF effectively only when the element patterns are asymmetric (unequal in E- and H-planes) and is ineffective in suppressing more than one interferer when the element patterns are symmetric (equal in E- and H-planes). This limitation is important in practice if the interferers are known to be RHCP and the array ground plane is small, since the patterns of microstrip antennas with small ground planes can become nearly symmetric. This finding is verified with a fabricated prototype of a two-element dual-polarized array with a small ground plane.

Estimating Angle of Arrival (AOA) for Wideband Signal by Sensor Delay Line (SDL) and Tapped Delay Line (TDL) Processors

Angle of arrival (AOA) estimation for wideband signal becomes more necessary for modern communication systems like Global System for Mobile (GSM), satellite, military applications and spread spectrum (frequency hopping and direct sequence). Most of the researchers are focusing on how to cancel the effects of signal bandwidth on AOA estimation performance by using a transversal filter (tap delay line) (TDL). Most of the researchers were using two elements array antenna to study these effects. In this research, a general case of proposed (M) array elements is used. A transversal filter (TDL) in phase adaptive array antenna system is used to calculate the optimum number of taps required to compensate these effect. The proposed system uses a phase adaptive array antenna in conjunction with LMS algorithm to work an angle of arrival (AOA) estimator for wideband signals rather than interference canceller. An alternative solution to compensate for the effect of signal bandwidth is proposed by using sensor delay line (SDL) instead of fixed delay unit since it has variable time sampling in the time domain and not fixed time delay, depending on the angle of arrival of received signals. The proposed system has the ability to estimate two parameters for received signals simultaneously (the output Signal to Noise Ratio (SNR) and AOA), unlike others systems which estimate AOA only. The comparison of the simulation results with Multiple Signal Classification (MUSIC) technique showed that the proposed system gives good results for estimating AOA and the output SNR for wideband signals. (SDL) processor shows better performance result than (TDL) processor. MUSIC technique with both (SDL) and (TDL) processors shows unacceptable results for estimating (AOA) for the wideband signal. 

Повышение эффективности подавления помех за счет коррекции частотных характеристик приемных каналов в навигационной аппаратуре потребителей

Space-time signal processing in adaptive electronic systems, including navigation, remains the subject of intensive research, as it allows to improve the efficiency of receiving useful signals under the influence of natural or intentional interference. The bibliography on this subject is very extensive and includes a large number of articles of scientific and applied nature, dissertations, monographs, patent materials. Much of this work has references to monographs by R. Monzingo and B. Widrow, which set out the basic principles, criteria and algorithms of spatial-temporal signal processing. To date, the development of space-time signal processing is largely constrained by the imperfection of the element base. The use of modern navigation equipment consumers high-speed signal processors that implement advanced methods and algorithms of digital signal processing, provides the ability of digital methods to form the desired beam pattern of the antenna system and to adjust the frequency characteristics of the reception channels, to implement complex algorithms for optimal processing of useful signals, operative to control the main operation modes of equipment. One of the most important applications of space-time signal processing is noise suppression, and its effectiveness depends on the degree of inter-channel correlation of these signals received by antenna elements of the adaptive antenna array. To maximize the coefficient of interference suppression required the adoption of measures on alignment of frequency and phase characteristics of the receiving circuits, and high precision computation of weighting coefficients. The article considers the questions of spatial filtering of the interference when adaptive interference compensator adjusted frequency characteristics of the receiving channels, and means of satellite navigation. Gradient algorithm of spatial compensation of noise, and also influence of adaptive correction of frequency characteristics of receiving channels on quality of suppression of noise is presented. The formation of a directional diagram of a multi-element adaptive antenna array with spatial noise suppression is demonstrated by modeling in the Matlab environment.

Improved Design of an Adaptive Massive MIMO Spherical Antenna Array

Massive capacity and connectivity are the main boundaries towards standing the Internet of Everything (IoE) basis and defining modern wireless generation requirements. These needs cannot be achieved by already deployed phased array antenna in terms of distributed and oriented geometry, dimensions and design. We propose in the present paper an innovating massive multiple input multiple output (MIMO) spherical array network aiming to draw a new three-dimensional configuration to enhance the beam steering, improve bandwidth, total capacity and the scan flexibility. Resolved issues in concordance with 5G requirements are adaptive massive MIMO by using millimeter-wave antenna arrays, small cell design and definition of recommended operational frequency considering the International Telecommunication Union (ITU) norms and directives. The new geometric forms of spherical smart antenna could easily scan all 3D space, ensure higher capacity and reach tens of Giga bit per second (Gbps) value besides eradicating energy wastage aspect of Beam Division Multiple Access (BDMA) in base stations. Mathematical design is detailed and performed simulation results are presented using MATLAB software Tool.

Performance of Tri-Band Multi-Polarized Array Antenna for 5G Mobile Base Station Adopting Polarization and Directivity Control

In this paper, the performance of tri-band multi-polarized adaptive array antenna for 5G mobile base station is introduced adopting the polarization and directivity control. First, the design of multi-band circularly polarized antenna element at 28/38/48 GHz is presented. The measured results show that the designed antenna element has a reflection coefficient of less than −20 dB in the assigned frequency bands of 28/38/48 GHz with a realized antenna gain of 7.82 dB, 8.39 dB, and 7.73 dB, respectively. Based on the designed antenna element, a 32-element are distributed in an octagonal prism configuration is presented as possible candidates for the future 5G mmWave cellular networks. The antenna array performance is studied in terms of gain, radiation efficiency, return loss, and axial ratio for different scenarios, in addition, the metrics of total scan pattern and coverage efficiency are investigated. To optimize the antenna parameters and synthesizing multi-beam patterns, a modified version of hybrid gravitational search algorithm and particle swarm optimization algorithm is introduced. This enhancement has improved the global search ability and accelerates the convergence capability. The proposed array antenna achieved good S11 < −20 dB with high isolation between the array elements. Besides, an acceptable realized gain of 16.85 dB on average with a radiation efficiency of more than 82 % is obtained in the entire operation bands.

Двумерные адаптивные антенные решетки в арифметике комплексных и действительных чисел

Двумерные адаптивные антенные решетки в арифметике комплексных и действительных чисел

Імпульсна характеристика адаптивної антени мережевих супутникових систем для оцінки кореляційної матриці перешкоди

Мета: На основі просторової фільтрації запропонувати метод прямого обчислення зворотної кореляційної матриці перешкоди при невідомих параметрах вхідного впливу для управління діаграмою спрямованості адаптивної антенної решітки, використовуючи імпульсну характеристику просторового фільтра. Методи: підхід базується на теорії випадкових процесів і адаптивної обробки сигналів. Результати: запропонований метод прямого обчислення зворотної кореляційної матриці показав можливість проводити такі обчислення без апріорних знань про направлення приходу перешкоди, про кореляційної функції перешкоди, а також про спектральні характеристики перешкоди. Метод дозволяє зменшити час обчислення зворотної кореляційної матриці і виключити похибки, які викликаються конструктивними розбіжностями радіоканалів адаптивної антенної решітки, що в свою чергу знижує помилку вимірювання напрямку на джерело перешкод. Обговорення: метод пропонується для забезпечення доступності та цілісності (підвищення завадостійкості) навігаційних даних мережевих супутникових систем.

FOMP algorithm for Direction of Arrival estimation

Adaptive antennas and antenna array processing are much significant issues for improving the performance of wireless communication systems. One of the most important applications of adaptive antenna systems is the Direction of Arrival (DOA) estimation. Recently, compressive sensing algorithms, including convex relaxation methods and greedy algorithms, have been recognized as a type of novel DOA estimation methods. The Orthogonal Matching Pursuit (OMP) is an example of compressive sensing methods. Using the OMP method for DOA estimation has many advantages in comparison to other algorithms. In spite of these advantages, the DOA estimation by OMP algorithm has a substantial challenge. The OMP algorithm cannot distinguish between two adjacent signal sources. In the DOA estimation by OMP algorithm, when there are two adjacent sources, the mutual coherent condition of the compressive sensing methods is violated. The situation gets worse when there are two sources from two adjacent DOAs. In this situation, the beam former has a single peak. In this paper, we propose the Focused Orthogonal Matching Pursuit (FOMP) algorithm for estimation of DOA. The FOMP algorithm is an improved version of the OMP algorithm. It can detect two signal sources exactly when they are very close and beam former has a single peak corresponding to a direction between right directions. Simulation results demonstrate the advantages of the proposed scheme. It can be observed the FOMP algorithm could detect very close signal sources with a negligible error.

Hybrid Amplitude Control Antenna Array System for Energy Efficient W-CDMA Network with Adaptive Coverage and Capacity

This paper introduces a novel technique and mathematical formulation of two dimensional elastic footprint variations and adaptive sector configuration variations by using a hybrid adaptive amplitude control antenna array system. The antenna array system can control the elevation beam-widths from 6.84° to 13° and the azimuth beam-widths from 33° to 93° for obtaining the adaptive capacity and coverage. The work illustrates the application of the antenna array system in the energy efficient W-CDMA network. The antenna array half-power beam width variation is achieved by using the antenna array amplitude control and co-located multiple antenna array switching. The Node-Bs can adaptively switch to three, four, five, six and non uniform sector configurations with the antenna array beam width control and adaptive neighbor relations. Sector configurations will vary according to the pre-defined specific traffic loading percentages out of Node-B’s total channel capacity to reduce the energy consumption of the entire network. The paper introduces an adaptive footprint overlaps shifting technique, where the sector with less traffic load will expand its footprint towards the sector with higher traffic load and the sector with higher traffic load will shrink its footprint by maintaining a fixed footprint overlaps to improve the coverage and the capacity of the network. The footprints overlap shifting is applicable only for the active sector antennas facing each other. The results confirm that the proposed antenna array system outperforms the automatic tilt optimization and can control coverage, capacity and improve the energy efficiency of the W-CDMA network.