Advanced Antenna Systems for 5G Network Deployments

Bridging the Gap Between Theory and Practice

Henrik Asplund, Jonas Karlsson, Fredric Kronestedt, Erik Larsson, David Astely, Peter von Butovitsch, Thomas Chapman, Mattias Frenne, Farshid Ghasemzadeh, Måns Hagström, Billy Hogan, George Jöngren

• Publisher: Academic Press
• Year: 2020
• Print ISBN: 9780128200469
• eBook ISBN: 9780128223864
• Topic: Technology & Engineering
• Subtopic: Electrical Engineering & Telecommunications
• Index: Technology & Engineering

Advanced Antenna Systems for 5G Network Deployments: Bridging the Gap between Theory and Practice provides a comprehensive understanding of the field of advanced antenna systems (AAS) and how they can be deployed in 5G networks. The book gives a thorough understanding of the basic technology components, the state-of-the-art multi-antenna solutions, what support 3GPP has standardized together with the reasoning, AAS performance in real networks, and how AAS can be used to enhance network deployments. - Explains how AAS features impact network performance and how AAS can be effectively used in a 5G network, based on either NR and/or LTE - Shows what AAS configurations and features to use in different network deployment scenarios, focusing on mobile broadband, but also including fixed wireless access - Presents the latest developments in multi-antenna technologies, including Beamforming, MIMO and cell shaping, along with the potential of different technologies in a commercial network context - Provides a deep understanding of the differences between mid-band and mm-Wave solutions

Chapter 1

Introduction

Abstract

This chapter briefly introduces the area of multi-antenna technologies and advanced antenna systems (AAS), how this field of research started, and its early developments. The introduction of multi-antenna technologies to mobile communication systems is also presented and how these, starting from 2G gradually, developed to AAS in 4G and 5G. This chapter also outlines why AAS has become a technology of significant interest during the last few years and why it is now expected to be deployed on large scale in commercial systems. This chapter is concluded with some notes on the contributions from the academic research, which paved the way in the early years for the multi-antenna technologies that are now taken into commercial use.

Keywords

multi-antenna technologies; AAS; massive MIMO; AAS history; mobile communications; academic research

1.1 Multi-antenna Technologies and Advanced Antenna Systems

Multi-antenna technologies can be applied at the transmitter, the receiver, or on both sides of the wireless communication link and explore temporal and spatial properties of the radio channel to enhance performance. It allows sharing of communication resources not only in time and frequency as in conventional wireless communication, but also in the spatial domain. The objective when multi-antennas are applied to mobile communication systems is to improve the network performance in terms of coverage, capacity, and end-user throughput.

An advanced antenna system (AAS) is one solution to implement multi-antenna technologies. In this book, AAS is referred to as an antenna system comprising an AAS radio and associated AAS features, where the latter comprises various multi-antenna techniques and algorithms. An AAS radio is a hardware unit consisting of an antenna array with a large number of radio chains and possibly parts of the baseband functionality. Furthermore, a distinguishing aspect of an AAS is that the radio and the antenna are tightly integrated.

The AAS radio facilitates AAS features such as beamforming and spatial multiplexing. The AAS features can be executed by algorithms in the AAS radio, in the base station baseband unit or both. These concepts will be defined and discussed in detail later in the book, for example, in Chapters 6 and 12.

To distinguish an AAS from a conventional system, the conventional (non-AAS) system consists typically of a passive antenna and remote radio unit comprising a low number of radio chains. Hence the antenna and radio are typically not integrated. There is however no single common and industry-wide definition of AAS, as different industry players have used this term and/or similar terms in different and often overlapping ways. The reason for this lies partially in the fact that the concept of a base station and related terms are intrinsically difficult to define and partially because of differing ideas of what should be encompassed within the AAS definition.

As there are many conventional systems with 2, 4, and 8 radio chains already deployed, the number 8 has commonly been used to define the boundary between AAS and a conventional system, that is, above 8 is typically an AAS. The reason to distinguish AAS from conventional systems is that AAS is associated with a new integrated building practice that has an impact on the whole antenna/radio/baseband architecture and hence also the deployment in mobile networks. However, in this context it should be noted that the building practices of AAS could also be used for 8 or fewer radio chains.

1.2 Brief History of multi-antenna Technologies and Advanced Antenna System

1.2.1 Before Mobile Communication Systems

The use of antenna arrays to direct radio signals is not new and is not restricted to the field of telecommunications. The technique was used by Guglielmo Marconi in 1901 to increase the gain of the Atlantic transmissions of Morse codes [1]. Marconi used four 61 m high tower antennas arranged in a circular array in Poldhu, England, to transmit the Morse signal for the letter “S,” a distance of 3425 km to Signal Hill, St. John, Newfoundland, Canada. Another early attempt to use multi-antenna techniques was made by Karl Ferdinand Braun who demonstrated the gains achievable by phased array antennas in 1905. Marconi and Braun received the Nobel Prize in physics 1909 for “recognition of their contributions to the development of wireless telegraphy” [2].

Antenna diversity techniques to overcome fading were developed in the 1940s [3]. The use of antenna array-based beamforming was also developed to steer the power in a certain direction as to improve coverage of the transmitted or received signals. Radar systems were developed that make intrinsic use of phased arrays for direction finding. Radio astronomy also makes use of antenna arrays. For this purpose, the antenna arrays are very large scale; in some cases, the elements of the array are tens of thousands of kilometers apart in order to be able to directionally detect very long-wavelength signals from outer space.

The concept of steering signals based on arrays of transmitters or sensors is not restricted to the electromagnetic domain; arrays are also deployed in sonar systems for directional processing. In fact, the two ears on a human or an animal, spaced apart, utilize the time difference of the reception of an audio signal to determine the direction of the sound source. Such binaural information can also be used to separate sound from background noise.

1.2.2 Introduction of multi-antenna Technologies to Telecom

In mobile communication, fixed, directional sector antennas were used already in the first analog mobile communication networks, AMPS, TACS, and NMT, in the early 1980s. These antennas were implemented as columns of antenna elements and were designed to maximize the area coverage. Such antennas with fixed coverage area have been, and are still being, used in all cellular mobile communication systems. They are, by far, the most common antenna type in use.

The telecom industry has acknowledged the potential of multi-antenna systems for a long time and signs of multi-antenna interest for mobile communication can be traced at least back to the early 1990s. Antenna systems allowing for dynamic, steerable beamforming were conceptualized at the same time as the advent of digital cellular systems with GSM and D-AMPS. At that time, requirements on capacity and coverage were still modest and network equipment was relatively expensive and thus a prohibitive factor for large-scale adoption. It is, however, in more recent years with the introduction of 4G (LTE) a decade ago that the use of multi-antenna techniques exploiting antennas arrays became ubiquitous both for transmission and receive purposes. The number of phase adjustable antennas in the array on the base station side was, however, for long kept at a modest level of 2, 4, or 8 in commercial networks. With the advent of AAS and spurred by coming introduction of 5G, antenna arrays with substantially more elements and radio chains have received significant industry interest and are now seen as a powerful and commercially viable tool for evolving the telecommunications environment. Such AAS are thus already playing a key role in both 4G and 5G.

1.2.2.1 2G—Early attempts

In GSM, there was no standard support for multi-antenna technologies. Trials were made by some network vendors, for example, Ericsson [4–6] and Nortel, and mobile network operators (MNOs) and academia to evaluate the technology potential [7]. The Buzzword at that time was adaptive antennas, to emphasize that the antenna gain pattern could be modified based on traffic conditions. The installations were however physically large and expensive. The initial focus of GSM multi-antennas was on improving capacity at 900 MHz but as the 1800 MHz band became available, the need for multi-antenna solutions as the capacity booster was reduced. Deploying additional 1800 MHz carriers was a much more cost-efficient and practical solution compared to increasing the number of antennas. The performance potential versus the size and cost for multi-antenna solutions at that time did not provide enough incentive to drive the industry toward large-scale multi-antenna deployments.

1.2.2.2 3G—Introduced but not widely used

In 3G, support for multi-antenna features in the standard was initially very limited. The focus for the first release of 3G was mainly on voice and packet data at modest rates (384 kbps). In order to increase throughput, 2×2 downlink multiple-input multiple-output (MIMO) was introduced in a later release. The observed gains in field were however limited, as the vast majority of mobile terminals already present in the 3G networks, did not have MIMO capability. The new multi-antenna features even had an initial negative impact on those legacy terminals, and hence there was great reluctance among the network operators to enable MIMO functionality.

Despite several efforts from terminal and network vendors, downlink MIMO functionality in 3G did not take-off in practice. Another basic multi-antenna feature, four-way receive (RX) diversity was shown to have excellent gains in uplink for HSUPA operation, allowing doubling of uplink capacity and enhanced uplink coverage. But similar to the fate of downlink MIMO in 3G, that feature also had limited uptake mainly due to the need for costly site visits to upgrade from older 2 RX antennas to new antennas that could support four-way RX.

In contrast, the multicarrier feature that was first introduced in the 3G standard just after MIMO was introduced became successful as it supported increase of peak rates, improved spectral efficiency, and gave capacity gains. Multicarrier had the advantage that it gave gains with new terminals but also worked seamlessly in networks with large populations of legacy terminals as there were no backward compatibility issues and it was relatively easy to deploy.

A lesson learned from 3G was thus that MIMO functionality needs to be supported from the first release in the next generation, to avoid the issues with legacy terminals in the network.

In China, a TDD-based 3G system, time division synchronous code division multiple access (TD-SCDMA), was introduced that included beamforming functionality from start. TD-SCDMA was included in the 3GPP standard as one of the 3G solutions. It was commercially used in China, but, largely because of the late introduction, the spread outside China was limited.

1.2.2.3 4G—Intrinsic, initially limited but gradually evolving

Already the first release of LTE supported basic MIMO techniques; for example, downlink spatial multiplexing with up to four layers to the mobile terminal as well as support for multi-user MIMO (MU-MIMO), see Section 8.2 for an in-depth survey of LTE history and evolution. The spatial domain was further explored in the following LTE releases with more advanced features being added to the standard. For TDD, reciprocity-based AAS solutions were possible already from start since reference signals in the uplink were defined, however, the main purpose of those were not reciprocity based operation.

The first step toward AAS support in standardization came in LTE release 10, as spatial multiplexing of up to eight layers was introduced. The feature was never completed, since the associated radio requirements were not introduced. However, this was the beginning of an expansion of support for MIMO-related functionality over time by the introduction of new enhanced MIMO functionality in every coming 3GPP release.

During Release 11, the industry realized that advanced, integrated base stations with large numbers of phase and amplitude adjustable antennas were on the horizon and that the existing framework for radio performance requirements and evaluations, which was based on the classic single antenna base station architecture, was insufficient. Therefore, 3GPP began studying solutions for AAS radio requirement specification. This led to a process over several years during which the over-the-air (OTA) AAS radio specification was developed. Simultaneously, a new channel model suitable for AAS was developed and features were specified for AAS to enhance MU-MIMO and terminal measurements for base stations with up 32 antennas. Another addition was the introduction of feedback-based two-dimensional beam steering (horizontal and vertical), also a feature enabled by AAS.

1.2.2.4 5G—Intrinsic and advanced

Just as LTE supported MIMO from the first release to alleviate legacy terminal issues, advanced beamforming functionality, and support for AAS base stations have been included as an integral part of the first 5G release, see Chapter 9, on 5G NR specifications. Support for reciprocity-based operation for TDD and UE measurements of up to 32 base station antennas was introduced. The need for solutions...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Authors
• Preface
• Acknowledgments
• Abbreviations
• Chapter 1. Introduction
• Chapter 2. Network Deployment and Evolution
• Chapter 3. Antennas and Wave Propagation
• Chapter 4. Antenna Arrays and Classical Beamforming
• Chapter 5. OFDM-Based MIMO Systems
• Chapter 6. Multi-antenna Technologies
• Chapter 7. Concepts and Solutions for High-Band Millimeter Wave
• Chapter 8. 3GPP Physical Layer Solutions for LTE and the Evolution Toward NR
• Chapter 9. 3GPP Physical Layer Solutions for NR
• Chapter 10. End-to-End Features
• Chapter 11. Radio Performance Requirements and Regulation
• Chapter 12. Architecture and Implementation Aspects
• Chapter 13. Performance of Multi-antenna Features and Configurations
• Chapter 14. Advanced Antenna System in Network Deployments
• Chapter 15. Summary and Outlook
• Appendix 1. Mathematical Notation and Concepts
• Index