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      CHAPTER 1

       Introduction

      Mobile networks, which have a 40-year history that parallels the Internet’s, have undergone significant change. The first two generations supported voice and then text, with 3G defining the transition to broadband access, supporting data rates measured in hundreds of kilobits-per-second. Today, the industry is at 4G (supporting data rates typically measured in the few megabits-per-second) and starting the transition to 5G, with the promise of a tenfold increase in data rates.

      But 5G is about much more than increased bandwidth. In the same way 3G defined the transition from voice to broadband, 5G’s promise is primarily about the transition from a single access service (broadband connectivity) to a richer collection of edge services and devices, including support for immersive user interfaces (e.g., AR/VR), mission-critical applications (e.g., public safety, autonomous vehicles), and the Internet-of-Things (IoT). Because these use cases will include everything from home appliances to industrial robots to self-driving cars, 5G won’t just support humans accessing the Internet from their smartphones, but also swarms of autonomous devices working together on their behalf. All of this requires a fundamentally different architecture.

      The requirements for this architecture are ambitious, and can be summarized as having three main objectives.

      • To support Massive Internet-of-Things, potentially including devices with ultra-low energy (10+ years of battery life), ultra-low complexity (10s of bits-per-second), and ultrahigh density (1 million nodes per square kilometer).

      • To support Mission-Critical Control, potentially including ultra-high availability (greater than 10^–5 per ms), ultra-low latency (as low as 1 ms), and extreme mobility (up to 100 km/h).

      • To support Enhanced Mobile Broadband, potentially including extreme capacity (10 Tbps per square kilometer) and extreme data rates (multi-Gbps peak, 100+ Mbps sustained).

      These targets will certainly not be met overnight, but that’s in keeping with each generation of the mobile network being a decade-long endeavor.

       Further Reading

      For an example of the grand vision for 5G from one of the industry leaders, see Making 5G NR a Reality. Qualcomm Whitepaper, December 2016.

      The 5G mobile network, because it is on an evolutionary path and not a point solution, includes standardized specifications, a range of implementation choices, and a long list of aspirational goals. Because this leaves so much room for interpretation, our approach to describing 5G is grounded in two mutually supportive principles. The first is to apply a systems lens, which is to say, we explain the sequence of design decisions that lead to a solution rather than fall back on enumerating the overwhelming number of acronyms as a fait accompli. The second is to aggressively disaggregate the system. Building a disaggregated, virtualized, and software-defined 5G access network is the direction the industry is already headed (for good technical and business reasons), but breaking the 5G network down into its elemental components is also the best way to explain how 5G works. It also helps to illustrate how 5G might evolve in the future to provide even more value.

       Evolutionary Path

      That 5G is on an evolutionary path is the central theme of this book. We call attention to its importance here, and revisit the topic throughout the book.

      We are writing this book for system generalists, with the goal of helping bring a community that understands a broad range of systems issues (but knows little or nothing about the cellular network) up to speed so they can play a role in its evolution. This is a community that understands both feature velocity and best practices in building robust scalable systems, and so has an important role to play in bringing all of 5G’s potential to fruition.

      What this all means is that there is no single, comprehensive definition of 5G, any more than there is for the Internet. It is a complex and evolving system, constrained by a set of standards that purposely give all the stakeholders many degrees of freedom. In the chapters that follow, it should be clear from the context whether we are talking about standards (what everyone must do to interoperate), trends (where the industry seems to be headed), or implementation choices (examples to make the discussion more concrete). By adopting a systems perspective throughout, our intent is to describe 5G in a way that helps the reader navigate this rich and rapidly evolving system.

1.1 STANDARDIZATION LANDSCAPE

      As of 3G, the generational designation corresponds to a standard defined by the 3rd Generation Partnership Project (3GPP). Even though its name has “3G” in it, the 3GPP continues to define the standards for 4G and 5G, each of which corresponds to a sequence of releases of the standard. Release 15 is considered the demarcation point between 4G and 5G, with Release 17 scheduled for 2021. Complicating the terminology, 4G was on a multi-release evolutionary path referred to as Long Term Evolution (LTE). 5G is on a similar evolutionary path, with several expected releases over its lifetime.

      While 5G is an ambitious advance beyond 4G, it is also the case that understanding 4G is the first step to understanding 5G, as several aspects of the

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