Advanced Antenna Array Engineering for 6G and Beyond Wireless Communications E-Book

Yingjie Jay Guo

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 541

Veröffentlichungsjahr: 2021

Beschreibung

Advanced Antenna Array Engineering for 6G and Beyond Wireless Communications Reviews advances in the design and deployment of antenna arrays for future generations of wireless communication systems, offering new solutions for the telecommunications industry Advanced Antenna Array Engineering for 6G and Beyond Wireless Communications addresses the challenges in designing and deploying antennas and antenna arrays which deliver 6G and beyond performance with high energy efficiency and possess the capability of being immune to interference caused by different systems mounted on the same platforms. This timely and authoritative volume presents innovative solutions for developing integrated communications networks of high-gain, individually-scannable, multi-beam antennas that are reconfigurable and conformable to all platforms, thus enabling the evolving integrated land, air and space communications networks. The text begins with an up-to-date discussion of the engineering issues facing future wireless communications systems, followed by a detailed discussion of different beamforming networks for multi-beam antennas. Subsequent chapters address problems of 4G/5G antenna collocation, discuss differentially-fed antenna arrays, explore conformal transmit arrays for airborne platforms, and present latest results on fixed frequency beam scanning leaky wave antennas as well as various analogue beam synthesizing strategies. Based primarily on the authors' extensive work in the field, including original research never before published, this important new volume: * Reviews multi-beam feed networks, array decoupling and de-scattering methods * Provides a systematic study on differentially fed antenna arrays that are resistant to interference caused by future multifunctional/multi-generation systems * Features previously unpublished material on conformal transmit arrays based on Huygen's metasufaces and reconfigurable leaky wave antennas * Includes novel algorithms for synthesizing and optimizing thinned massive arrays, conformal arrays, frequency invariant arrays, and other future arrays Advanced Antenna Array Engineering for 6G and Beyond Wireless Communications is an invaluable resource for antenna engineers and researchers, as well as graduate and senior undergraduate students in the field.

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IEEE Press Editorial BoardEkram Hossain, Editor in Chief

Jón Atli Benediktsson  

Xiaoou Li  

Jeffrey Reed  

Anjan Bose  

Lian Yong  

Diomidis Spinellis  

David Alan Grier  

Andreas Molisch  

Sarah Spurgeon  

Elya B. Joffe  

Saeid Nahavandi  

Ahmet Murat Tekalp  

Advanced Antenna Array Engineering for 6G and Beyond Wireless Communications

Y. Jay Guo

University of Technology Sydney (UTS), Ultimo, Australia

Richard W. Ziolkowski

University of Technology Sydney (UTS), Ultimo, Australia

Copyright © 2022 by The Institute of Electrical and Electronics Engineers, Inc. All rights reserved.

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Author Biographies

Y. Jay Guo received a Bachelor Degree and a Master Degree from Xidian University in 1982 and 1984, respectively, and a PhD Degree from Xian Jiaotong University in 1987, all in China. His research interest includes antennas, mm‐wave, and THz communications and sensing systems, and beyond 5G mobile communication networks. He has published four books, over 550 research papers including over 280 journal papers, most of which are in IEEE Transactions, and he holds 26 patents.

Prof. Guo is a Fellow of the Australian Academy of Engineering and Technology, a Fellow of IEEE, and a Fellow of IET. He was a member of the College of Experts of Australian Research Council (ARC, 2016–2018). He has won a number of most prestigious Australian Engineering Excellence Awards (2007, 2012) and CSIRO Chairman’s Medal (2007, 2012). He was named one of the most influential engineers in Australia in 2014 and 2015, respectively, and one of the top researchers in Australia in 2020.

Prof. Guo has over 30 years of international academic, industrial, and government research experience. Currently, he is a Distinguished Professor and the Director of Global Big Data Technologies Centre (GBDTC) at the University of Technology Sydney (UTS), Australia. Prior to this appointment in 2014, he served as a Director in the Commonwealth Scientific Industrial Research Organization (CSIRO) for over nine years, leading the research on advanced information and wireless communication technologies. Before joining CSIRO in 2005, he held various senior technology leadership positions in Fujitsu, Siemens, and NEC in the UK.

Richard W. Ziolkowski received the B.Sc. (magna cum laude) degree (Hons.) in physics from Brown University, Providence, RI, USA in 1974; the MS and PhD degrees in physics from the University of Illinois at Urbana‐Champaign, Urbana, IL, USA in 1975 and 1980, respectively; and an Honorary Doctorate degree from the Technical University of Denmark, Kongens Lyngby, Denmark in 2012.

Prof. Ziolkowski was the recipient of the 2019 IEEE Electromagnetics Award (IEEE Technical Field Award). He is a Life Fellow of the Institute of Electrical and Electronics Engineers (IEEE Fellow, 1994) and a Fellow of the Optical Society of America (OSA, 2006) and the American Physical Society (APS, 2016). He served as the President of the IEEE Antennas and Propagation Society in 2005. He is also actively involved with the URSI, OSA, and SPIE professional societies. He was the Australian DSTO Fulbright Distinguished Chair in Advanced Science and Technology from 2014 to 2015. He was a 2014 Thomson‐Reuters Highly Cited Researcher.

He is currently a Distinguished Professor in the Global Big Data Technologies Centre in the Faculty of Engineering and Information Technologies (FEIT) at the University of Technology Sydney, Ultimo NSW, Australia. He became a Professor Emeritus at the University of Arizona in 2018, where he was a Litton Industries John M. Leonis Distinguished Professor in the Department of Electrical and Computer Engineering in the College of Engineering and was also a Professor in the College of Optical Sciences. He was the Computational Electronics and Electromagnetics Thrust Area Leader with the Engineering Research Division of the Lawrence Livermore National Laboratory before joining The University of Arizona, Tucson, AZ, USA in 1990. His current research interests include the application of new mathematical and numerical methods to linear and nonlinear problems dealing with the interaction of electromagnetic and acoustic waves with complex linear and nonlinear media, as well as metamaterials, metamaterial‐inspired structures, nanostructures, and other classical and quantum application‐specific configurations.

Acknowledgments

Antennas are a significant, fundamental, and practical research area of electromagnetics. Unfortunately, they have been considered by many academic administrators and government funding agencies simply as being well established, i.e. “old stuff.” However, the wireless communications and sensors community is well aware that antennas are the key enabling technology of all things wireless.

Wireless technologies have become ubiquitous and truly critical in many ways to our everyday lives. These facts have become exceptionally clear now during this 2020 COVID pandemic. Whether you are a homemaker ordering foodstuffs to sustain your family via your cell phone and its network or you are a child learning and doing schoolwork online in your room while your academic parent is lecturing via Zoom from a home office, both being enabled by their computer’s WiFi connection to the family’s MIMO‐based router, or you are a new grandparent seeing the newest member of your family remotely for the first time with FaceTime on your mobile platform or you are an antenna engineer interacting with company colleagues through Microsoft Teams on your handheld device to practice proper social‐distancing protocols or even if you are two authors writing a book on antenna array technologies and are separated by a 19‐hour time difference and a mere 13,000‐km, wireless has meant that we can continue to perform tasks that need to be accomplished and can communicate and interact with family, friends, and colleagues on a regular basis.

Consequently, there have been very real and intense industry pushes and market pulls for various modern antenna systems to empower current fifth‐generation (5G) and future sixth‐generation (6G), and beyond wireless devices, applications, and their associated ecosystems. Scientific and engineering progress in array technologies has particularly benefited from user and stakeholder cravings for higher data rates and lower latencies. Antenna arrays will continue to play a major role in all future wireless generations. Pioneering wireless array research typically stresses advanced features such as steerable beams, multi‐beams, multiband antenna coexistence, antenna reconfiguration, low‐cost feed networks, and conformity to platforms. The various conundrums associated with the evolving land, air, and space networks associated with them will challenge all of us to develop fundamental and applied electromagnetics breakthroughs to solve them.

Under this backdrop, we have had the great privilege of working with a number of very talented PhD students, postdoctoral fellows, visiting scholars, and international collaborators. Our mutual interest and joint research efforts in antennas and antenna arrays for current 5G (fifth‐generation) and future 6G, and beyond wireless ecosystems have deepened our understanding of their fundamentals, as well as their practical considerations necessary to successfully deliver useful systems for commercial applications that actually satisfy most of their generally overambitious, initial performance goals.

Our presentation of antenna and antenna arrays for current 5G and evolving 6G, and beyond systems in this book is organized into eight logical chapters that reflect our thoughts and the findings generated in those endeavors. Consequently, we are deeply indebted to our colleagues for their dedication and great contributions to the state of the art which are highlighted in these chapters. In particular, we would like to acknowledge specific inputs to them as follows:

Chapter 2: Ji‐Wei Lian, Visiting Student, University of Technology Sydney (UTS), Australia

Chapter 3: Prof. Ming‐Chun Tang, Chongqing University, China

Chapter 4: Dr. Can Ding, Lecturer, UTS, Australia and Dr. Hai‐Han Sun, postdoctoral researcher, Nanyang Technology University (NTU), Singapore

Chapter 5: Dr. He Zhu, postdoctoral researcher, UTS, Australia

Chapter 6: Dr. Pei‐Yuan Qin, Senior Lecturer, and Ph.D student Li‐Zhao Song, UTS, Australia

Chapter 7: Dr. Stanley (Shulin) Chen, postdoctoral researcher, UTS, Australia; Dr. Debabrata K. Karmokar, Lecturer, University of South Australia, Australia; Prof. José Luis Gómez Tornero, Technical University of Cartagena, Spain; and Ji‐Wei Lian, visiting student at UTS, Australia; Prof. Zheng Li, Beijing Jiaotong University, China.

Chapter 8: Prof. Yanhui Liu, Research Principal, UTS, Australia, and Ming Li, PhD student, UTS, Australia.

We thank them all for their invaluable time and efforts and wish them even greater successes in their future endeavors and careers.

We would also like to express our gratitude to University of Technology Sydney (UTS) for their whole‐hearted support to our antennas research team.

Finally, we happily acknowledge our wives, Clare Guo and Lea Ziolkowski, and thank our lucky stars for their endless understanding, support and patience, particularly when we disappear for uncountable hours on cosmic efforts such as this :-)

1A Perspective of Antennas for 5G and 6G

The roll‐out of the fifth generation (5G) of wireless and mobile communications systems has commenced, and the technology race on the sixth‐generation (6G) mobile and wireless communications systems has started in earnest [1, 2]. 5G promises significantly increased capacity, massive connections, low latency, and compelling new applications. For example, device‐to‐device (D2D) and vehicle‐to‐vehicle (V2V) communication systems will help facilitate the realization of autonomous transport. The rapid access to and exchange of “Big Data” will increasingly impact real‐time economic and political decisions. Similarly, highly integrated, accessible “infotainment” systems will continue to alter our social relationships and communities. Wireless power transfer will replace cumbersome, weighty, short‐life batteries enabling widespread health, agriculture, and building monitoring sensor networks with much less waste impact on the environment. 6G networks aim to achieve a number of new features such as full global coverage, much greater data rates and mobility, and higher energy and cost efficiency. These will usher in new services based on virtual reality/augmented reality and artificial intelligence [3].

At the core of wireless devices, systems, networks, and ecosystems are their antennas and antenna arrays. Antennas enable the transmission and reception of electromagnetic energy. Antenna arrays enhance our abilities to direct and localize the desired energy and information transfer. To achieve the many stunning and amazing 5G and 6G promises, significant advances in antenna and antenna array technologies must be accomplished.

1.1 5G Requirements of Antenna Arrays

One of the most important features of 5G is the employment of massive antenna arrays, with the size of the array currently varying from 64 to 128 and 256 elements. Such a large number of antenna elements in an array provide an unprecedented variety of possibilities. These include a means to increase the network capacity; the distance and data rates of individual links between the base station and mobile users; and the reduction of interference between different users and cells.

1.1.1 Array Characteristics

Generally speaking, there are three ways to exploit the benefits of antenna arrays in 5G wireless communication systems [4, 5], namely diversity, spatial multiplexing, and beamforming. These concepts are explained as follows.

a) Diversity and Diversity Combining

It is a fact that mobile wireless communication channels typically suffer from both temporal fading and frequency fading. As a consequence, the quality of the channel varies with time and across different frequencies. Thus, the specific characteristics of the two propagation channels observed between any two pairs of transmitting and receiving antennas are usually different due to the variation in the scattering along the corresponding propagation paths. The peaks and troughs of the strength of the received signal at one antenna would be different from those at another antenna in a rich scattering environment. If the correlation between those two signals is low, one can combine them through so‐called diversity combining to obtain a greater signal‐to‐interference‐and‐noise ratio (SINR). The latter is also known as diversity gain. A simple viewpoint is that diversity combining techniques aim to improve the quality of the individual links between the base stations and the user terminals by increasing the SINR.

From an antenna point of view, diversity can be obtained by exploiting either the distance between adjacent antennas, i.e., their positions, or different polarizations at the receiver and the transmitter. However, a fundamental requirement is that the mutual coupling between these diversity antennas must be low. Most modern base station antennas employ polarization diversity, i.e., each antenna element is dual‐polarized typically with two pairs of slanted dipole “arms” in the ±45° directions. In 5G millimeter‐wave (mm‐wave) systems, for example, a popular antenna configuration is to have beamforming antenna arrays with ±45° polarizations, respectively.

b) Spatial Multiplexing

Multiplexing is the process of combining multiple digital or analog signals into a data stream for their transmission over a common medium, thus sharing a scarce resource. Spatial multiplexing aims to establish separate data streams in parallel using the same time/frequency resources. Thus, the space dimension is reused, i.e., multiplexed.

The simplest spatial multiplexing scheme is to employ sectorized antennas, a conventional technique for frequency reuse. More advanced spatial multiplexing schemes employ spatial–temporal (or frequency) coding by virtue of multiple input and multiple output (MIMO) antennas. A MIMO system requires the use of multiple antennas at least at the base stations. MIMO is implemented with two basic schemes as described below.

The first spatial multiplexing scheme is known as single user MIMO (SU‐MIMO). By virtue of multiple antennas at both the base station and the user terminals, SU‐MIMO first splits the data stream transmitted toward a specific user into multiple data streams. It then recombines them together at the user terminal to improve the information throughput and system capacity. One major challenge to SU‐MIMO is the need for the tightly packed multiple antennas in the terminals to be decoupled.

The second spatial multiplexing scheme is known as multiuser MIMO (MU‐MIMO). MU‐MIMO aims to maximize the overall data throughput between all of the users and their associated base station. While it employs an antenna array at the base station, only one or a few antenna elements are present at each user terminal. Since user terminals are typically well dispersed within a radio cell and their individual channels are likely to be uncorrelated, the benefits of MU‐MIMO are easier to achieve.

Both SU‐MIMO and MU‐MIMO protocols are intended for implementation in most 5G systems.

c) Beamforming

Spatial filtering can be regarded as a simple version of MU‐MIMO. Beamforming achieves this spatial filtering by coherently combining the fields radiated by the array elements to direct their radiated energy into particular directions. These multiple beams are created at the base station to communicate with different users simultaneously.

Beamforming offers two benefits to a communication system. The first is capacity. If there is no overlap of the beams, simultaneous communications can take place in the same frequency band and at the same time without causing much interference. The second is the gain of the antenna array. Higher gain translates into information exchange over greater distances or higher data rates due to increased SINR values. Unlike 3G and 4G antenna arrays that provide coverage with fixed beam patterns and directivity, 5G arrays must support on‐demand beam coverage according to real‐time application scenarios and user distributions. Moreover, they must be able to support beam management in order to deliver precise coverage in target areas while significantly suppressing interference in other areas.

For beamforming to be effective, large antenna arrays are necessary to generate narrow beams and produce scattering from mobile users with small angular spreads. The latter is to ensure that the majority of the signals transmitted and received from a mobile platform is covered by a narrow base station antenna beam. These requirements, in conjunction with wide bandwidths, support the use of millimeter wave (mm‐wave) communications for 5G. In particular, mm‐waves propagate in a pseudo‐light fashion so the scattering of the signals to and from a mobile platform is highly localized. Furthermore, since their wavelengths are small, an electrically large mm‐wave array can be fit easily into a physically small space.

1.1.2 Frequency Bands

Another major challenge associated with 5G antenna arrays is the simultaneous support of all allotted frequency bands [6]. As the number of bands being considered to meet current and future 5G needs increases, significant antenna array innovations are required to support all of them. Moreover, existing 4G bands must be supported as well [7].

Owing to the stringent requirements placed on the radiation patterns produced by cellular systems and on the levels of their impedance matching to sources to maximize their realized gains, the mobile communication industry has so far adopted an approach of using different antennas to support different frequency bands. However, because of the limited space at base station antenna sites and in mobile platforms, the coexistence of these different antennas has posed serious challenges already. It is extremely difficult to maintain low coupling levels between antennas operating over the same band and even harder to suppress the scattering interactions between antennas that operate over different bands. The latter can cause significant distortions to the radiation patterns. It is with this background that the decoupling and de‐scattering issues will be addressed in Chapters 2 and 3, respectively.

1.1.3 Component Integration and Antennas‐in‐Package (AiP)

Clearly, the number of antenna ports and radios for 5G systems will grow dramatically with the increasing numbers of massive antenna arrays and operating bands. This growth implies that the number of cables that connect the radios to the antennas would increase accordingly. This increase necessarily leads to increased fabrication complexities, losses in the cables and connectors, and difficulties in the control of passive intermodulation (PIM) and testing. To mitigate these problems, one needs to change antenna system design methodologies to introduce much higher levels of integration. To this end, there has been a high expectation that 5G antennas, the mm‐wave band antennas in particular, will become highly integrated systems.

Integrated antenna and radio systems eliminate the need for multiple cables between the radios and antennas, thus increasing their reliability by reducing part counts and handling, and simplifying their testing and installation. As a result, there has been an increasing need for effective antenna‐in‐package (AiP) solutions. In addition to managing the radiation performance of the antenna elements and arrays, one must consider several issues for AiP designs. These include, for instance, the materials; process selection and control; power and heat management; and new testing techniques. As an example, Figure 1.1 shows a 64‐element AiP system at 28 GHz. It has four flip‐chip‐mounted transceiver ICs that support its dual‐polarized operation [8]. For clarity, the heat sink below the ball‐grid‐array (BGA) interface is not shown.

Figure 1.1 An illustration of a 64‐element antenna‐in‐package (AiP) assembly breakout.

Source: From [8] / with permission of IEEE.

One particular new challenge associated with highly integrated 5G antenna arrays is obtaining accurate antenna beam patterns. Depending on their actual implementation, methods for testing active antennas vary. Current examples include the following [4]:

a) Sample Testing

This approach involves the fabrication of a number of fixed analog beamforming circuits that provide the requisite amplitude and phase excitations to the antenna array to produce the desired beams including narrow beams for user traffic and broad beams for user management. Each circuit produces one specific beam. This allows one to sample each of the desired beam types and steering directions. For practical reasons, it is difficult to perform a comprehensive test of all of the possible beams generated by a large array. Therefore, only those beams of greatest interest are likely to be tested.

b) Element‐by‐Element Testing

The far‐field vectorial pattern of each element, i.e., the amplitude and phase distribution in the far‐field of the array, can be measured with respect to a common reference. Any beamforming pattern can then be synthesized numerically by adding all the element patterns with the corresponding appropriate complex weights. This approach is the most flexible method since all possible patterns can be tested. Nevertheless, one can argue realistically that the synthesized beam patterns may differ from the real ones to a certain extent because all of the actual interactions are not explicitly included.

c) Employ Beam Testers

Beam testers are effectively flexible beamforming networks. By connecting a beam tester to an antenna array, one can test a variety of the beams defined by the beam tester using a traditional method for antenna pattern testing. The 3rd Generation Partnership Project (3GPP), which unites seven telecommunications standard development organizations (ARIB, ATIS, CCSA, ETSI, TSDSI, TTA, and TTC), has defined three Over‐the‐Air (OTA) test methods for MIMO antennas: the direct far‐field (DFF) method using a far‐field chamber, the indirect far‐field (IFF) method using a compact range, and the near‐field to far‐field transform (NFTF) method using a near‐field chamber. All three OTA approaches are conventional methods familiar to antenna engineers.

It must be recognized that when active electronics are added to a radiating aperture to form a MIMO antenna, the antenna ports are now embedded in the system. As a result, it becomes much more difficult to measure the true gain and antenna efficiency. Because a massive MIMO antenna has a large number of antenna elements and its radiating aperture can be excited in many ways to create different beams, both narrow and broad, it is truly difficult to fully test and validate beam performance in terms of conventional figures of merit, e.g., pattern characteristics, beam shapes, beam steering, side lobe levels, and null locations. Testing is further complicated because measurements for both the transmit case and the receive case must be performed to understand the operating characteristics of both RF chains.

To facilitate the manufacturing and adoption of large antenna arrays in 5G and beyond systems, the wireless industry is pushing to increase the level of integration of the system frontend modules (FEM). Figure 1.2 shows the AiP roadmap of the TMY Technology (TMYTEK) company for their 5G mm‐wave products [9]. Each enclosure block represents one particular level of component integration. The industry trend is to integrate the antenna arrays with all of the radio frequency (RF) and intermediate frequency (IF) modules into one package. Characterization of all of the beams produced by such modules is undoubtedly a new challenge for antenna designers.

Figure 1.2 Three levels of AiP implementation by TMYTECH.

Source: From [9] / with permission of TMY Technology Inc.

1.2 6G and Its Antenna Requirements

5G mobile and wireless systems are ground‐based. Consequently, they have coverage requirements similar to earlier generations of terrestrial networks. In contrast, space‐communication networks provide vast coverage for people and vehicles at sea and in the air, as well as in remote and rural areas. They are complementary to terrestrial networks. Clearly, future information networks must seamlessly integrate space networks with terrestrial networks to achieve significant advances beyond 5G. This integrated wireless ecosystem may become one of the most ambitious targets of 6G systems [10]. It is currently envisaged that 6G wireless systems will support truly global wireless communications, anywhere and anytime. An integrated space and terrestrial network (ISTN) is expected to be at the core of beyond 5G communication systems. As a consequence, the development of the technologies to achieve a high‐capacity, yet low‐cost, ISTN is of significant importance to all of the emerging 6G wireless communication systems.

Currently, there are a number of commercial and government spaceborne and airborne platforms that support various applications in communications and sensing. These include geostationary Earth orbit (GEO), medium Earth orbit (MEO), and low Earth orbit (LEO) satellites. As their names indicate, they operate at different altitudes relative to the Earth’s center. Various airborne platforms also operate at different altitudes such as high‐altitude platforms (HAPs), airplanes, and unmanned aerial vehicles (UAVs, otherwise known as drones). It is anticipated that any eventual 6G and beyond mobile wireless communication networks will thus consist of three network layers, namely the space network layer, the airborne network layer, and the terrestrial network layer. An illustration of a potential ISTN architecture is shown in Figure 1.3. Figure 1.3 clearly suggests that there will be a huge number of dynamic nodes constituting the mobile airborne networks, in addition to the dynamic nodes of the ground and space (satellite) networks [10].

Figure 1.3 An illustration of a potential ISTN architecture for 6G and beyond.

Source: From [10] / with permission of IEEE.

Airborne networks have a number of unique characteristics. First, most of their nodes would have multiple links to achieve network reliability, high capacity, and low latency. Second, most of them will be mobile. Therefore, both their network links and topologies will vary with time, some faster than others. Third, the distances between any two adjacent nodes will vary significantly, from hundreds of meters to tens of kilometers. Fourth, the power supplied to any node would be limited. Consequently, as in the case for terrestrial networks, the energy efficiency of each node not only impacts the operation costs, but also the commercial viability of the entire network. Fifth, it is highly desirable for antennas on most airborne platforms to be conformal in order to meet their aerodynamic requirements and to maintain their mechanical integrity.

All of the noted, desirable ISTN features pose a number of significant and interesting challenges for future 6G antennas and antenna arrays. The antennas, for example, must be compact, conformal, and high‐gain. They must be reliable, lightweight, and low‐cost. The corresponding arrays must provide individually steerable multiple beams; dynamic reconfiguration of their patterns, polarizations, and frequencies to cope with the movement of the platforms; and overall high energy efficiency. The biggest challenge among all of them is arguably the reduction of the overall energy consumption. One promising solution is to employ analog steerable multi‐beam antennas. Hybrid beamforming is another. Since beamforming and beam scanning can be done by antenna reconfiguration through electronic switching or tuning, the energy required is negligible in comparison to employing a full digital beamforming approach.

1.3 From Digital to Hybrid Multiple Beamforming

There are several ways to form multiple beams from an array. Major schemes can be categorized into digital, analog, and crossover strategies. We begin by describing digital beamforming and a major crossover of much recent excitement, hybrid beamforming.

1.3.1 Digital Beamforming

Given an antenna array, digital beamforming is the ultimate way to achieve optimal performance. It is the most flexible approach to generating individually steerable and high‐quality multiple beams. With a single antenna array of large enough size and the same set of RF circuits, one can effectively create as many beams as desired by applying different complex weights (amplitude and phase) to each element of the array in the digital domain. More advanced digital beamforming schemes employ algorithms such as eigen‐beamforming to obtain the maximum SINR values [11]. Fully digital beamforming with massive antenna arrays serves as a powerful technology to meet some of the most challenging desired features of future wireless communication networks including capacity, latency, data rates, and security.

A high‐level digital beamformer for reception is shown in Figure 1.4