What is 5G? Who knows?
In my observation, a most frequently asked question of the last few years, not only in the fields of telecommunications or standardization, has been “What is 5G?” One web search turns up about 73,000 matches for that phrase. Yet a brief literature survey indicates that the number of answers may be of the same order of magnitude as the number of times the question has been asked. This brief article does not attempt to answer the question in depth but simply provides a perspective.
Gs and re-Gs
5G is intended to represent something beyond 4G, which followed 3G and indicates the fourth generation of cellular wireless network technology. Earlier generations of cellular were identified in retrospect as 1G and 2G, but those monikers were not popular at the time. However, the industry focused on the term “3G”, and it became a hit, spawning a successful sequel in 4G.
Many technology industries evolve, but not all with the discrete cadence of the cellular industry. That business is heavily dependent on interoperability, and the various facets of the industry—including components and devices, software and networks, engineering expertise and marketing—are all orchestrated in a worldwide symphony. Cellular operators, which are limited in number, stable over many years, and often strong players in their markets, coordinate closely with a relatively small community of major vendors to steer the technical and market evolution. This evolution is mediated by standardization, particularly through the 3rd Generation Partnership Project (3GPP), a partnership of regional standards-developing organizations that has retained its original name while its focus has turned toward successive generations.
The rollout of new cellular standards is not only tied to industry coordination but also tightly bound by international regulations. National-scale cellular providers operate using radio spectrum that is exclusively licensed for their use by national administrations. Global harmonization and global circulation of mobile devices that operate in such restricted radio bands hinge not only on technical standards but on compatible regulatory environments. The key international requirements are laid out in the Radio Regulations hammered out in a series of World Radiocommunication Conferences (WRCs) of the Radiocommunication Sector (ITU-R) of the United Nations’ International Telecommunication Union (ITU). Much of the content of the Radio Regulations is technologically neutral. However, in the 1990s, the ITU Radio Regulations began to “identify” spectrum for potential use by “International Mobile Telecommunications (IMT),” where IMT is specified by a series of ITU “Recommendations,” which are standards. This “identification” is not a mandatory aspect of the Radio Regulations; identification is “for those administrations wishing to deploy IMT” and is intended to provide guidance for regulators and global equipment manufacturers regarding appropriate radio bands and technologies. The combination has proven very effective in providing guidance to the industry and has been successful beyond any parallel in the history of technology.
As the industry has succeeded, it has, time and again, faced the need for more spectrum in which to operate. Long-term spectrum demand has been channeled into a series of requests for additional spectrum for modernized technology. Roughly once per decade, the cellular industry and ITU have formulated the concept of a new generation of technology that promises greater opportunity and is accompanied by additional spectrum identification. In 2000, significant spectrum was identified for technology and was specified as “IMT-2000” in ITU-R Recommendation M.1457. That recommendation incorporates external standards, such as those of 3GPP, and these are identified through the unique IMT concept of “Global Core Specifications.” Through an IMT-specific activity (currently known as ITU-R Working Party 5D), Rec. M.1457 has been maintained and updated annually or biennially, pointing to evolving 3GPP specifications as well as some others.
Although various technology alternatives were adopted in IMT-2000, the most striking technology thread was multiple access via CDMA. As the decade proceeded, ITU-R undertook the development of a new generation of IMT, known as “IMT-Advanced,” and began intensive discussion on identification of additional IMT spectrum. Meanwhile, alternative technologies rose to prominence, particularly suited to the increasing demands for broadband data services. In the IEEE 802 LAN/MAN Standards Committee, IEEE Std 802.11 introduced OFDM in 1999. This became very successful in the marketplace, particularly beginning with the 802.11g amendment in 2003. IEEE Std 802.16 pioneered the use of OFDMA for broadband wireless access, notably with IEEE Std 802.16e-2005, which was deployed by commercial cellular operators in several countries. That WirelessMAN-OFDMA technology was adopted into IMT-2000 in 2007. In 2006, IEEE 802 authorized a new project with the specific target of meeting the IMT-Advanced requirements. The result, later published as WirelessMAN-Advanced in 802.16m-2011, was one of two technologies (both OFDMA-based) incorporated into IMT-Advanced in ITU-R Rec. M.2012. However, WirelessMAN-Advanced was not deployed in the cellular market, losing out to 3GPP’s LTE.
ITU-R approached the new technology by broadening the concept of IMT to include IMT-2000 and IMT-Advanced (which would both continue to evolve) as well as additional varieties of IMT to be developed in the future. The 2012 WRC identified additional spectrum for IMT, replacing “IMT-2000” with the more general term “IMT” so as not to connect specific spectrum to specific versions. Just before the 2015 WRC, the ITU Radiocommunication Assembly nonetheless added IMT-2020 to the lexicon as the next evolution under the IMT umbrella.
What is 4G?
Before we all began asking what 5G is, this same question arose regarding 4G.
OFDMA was the striking common technology thread in IMT-Advanced and denoted a major demarcation of a new generation. It was, and remains, technically appropriate to identify the OFDMA technology as the mark of 4G. Still, as noted, OFDMA had found its way into evolutions of IMT-2000, and opinions varied as to how closely the meaning of 4G should be tied to IMT-Advanced.
Even ITU struggled with the distinction between 4G and IMT-Advanced. During the development of the work, ITU-R Working Party 5D had explicitly decided not to use the term “4G.” However, in a 2010 press release announcing IMT-Advanced, ITU-R said that “LTE-Advanced” and “WirelessMAN-Advanced” were “accorded the official designation of IMT-Advanced, qualifying them as true 4G technologies” . This stance conflicted with commercial identification of LTE and WirelessMAN (and even some updated CDMA-based) technologies as 4G. Indeed, even in 2018, many LTE implementations lacking the suite of LTE-Advanced features are recognized by industry and the public as 4G. ITU soon quietly backed off its stance that IMT-Advanced was the mark of true 4G. Currently, ITU states that “The term ‘4G’ remains undefined… ITU cannot hold a position on whether or not a given technology is labelled with that term for marketing purposes” .
The perspective of this article is that the Gs are not standardized terms or certification marks, and neither the ITU nor any other entity establishes their requirements. Most IMT-2000 technologies can be characterized as 3G or higher, and the IMT-Advanced technologies can be characterized as 4G or higher. However, the terminology is loosely used, even within the cellular industry, and no entity determines the official definition. ITU recognition provides a sound credential for a G claim, but technologies not in any way represented in ITU may nevertheless be fairly identified with a G.
ITU-R began planning for IMT-2020 in 2012, and a set of Recommendations and Reports were prepared by Working Party 5D, including the vision, framework, and objectives document (Rec. ITU-R M.2083) that was referenced by WRC 2015. This activity resulted in some new signals about 5G trends. In particular, as a follow-up to WRC 2015, an agenda item (1.13) was added to WRC 2019 to consider identification of spectrum for IMT in a number of higher-frequency bands ranging from around 24 to 86 GHz, signaling that IMT-2020 is partially related to millimeter-wave radio. Further, Rec. ITU-R M.2083 indicated a much wider range of applications as compared to prior versions of IMT. In particular, IMT-2020 will be specified to address three “usage scenarios”:
- enhanced mobile broadband (eMBB), extending the services provided by IMT-Advanced;
- ultra-reliable and low-latency communications (URLLC), addressing applications such as industrial manufacturing, remote surgery, and controlled automobiles;
- massive machine type communications (mMTC), considering a very large number of low-cost, low-energy devices typically transmitting a relatively low volume of non-delay-sensitive data.
These decisions indicated an intention to drastically expand the scope of IMT and, therefore, the breadth of applications to be supported within IMT-identified spectrum. This could be broadly understood to represent the notion that the cellular communications industry, including the operators and vendors, would expand their business beyond a focus on supporting handheld devices.
ITU-R has completed follow-up documentation specifying the IMT-2020 development process, schedule, technical requirements, and evaluation criteria, setting a proposal deadline of June 2019 and planning to complete the IMT-2020 Recommendation by October 2020. 3GPP has already provided information regarding its intended submission.
The IMT-2020 requirements spell out an ambitious and challenging program for the cellular industry that certainly will demand many technical advances. If the current generation is 4G, then IMT-2020 invokes a new view of 5G or beyond. However, unlike 3G and 4G, which could be understood as embodying specific technologies, IMT-2020 is positioned as an application-expanding effort involving optimization of technologies in a variety of environments.
What else is 5G?
The vision of enhanced mobile broadband and an expanded set of wireless applications has stimulated not only the cellular industry but others as well. Some of the ambitions are individual and others are standardization based.
Within the IEEE, many activities relevant to 5G have arisen. IEEE has organized a coordination of those efforts as the “IEEE 5G” Initiative . Many technical activities and fields of interest are represented there. The website identifies 5G as “next generation networking,” which is clearly much broader than IMT-2020. The initiative compiles the “IEEE 5G and Beyond Standards Database” and supports an “IEEE 5G Roadmap” activity as well.
5G cannot be contained within ITU or any specific control group. Any endeavor that relates to a “generation” must represent some level of coordination of technologies and timeframes. A credible 5G will represent an integrated network specification set that could support a large operator deployment, be stable for the long haul, will support multiple applications and access technologies, and will evolve .
Outside the IEEE, other visions of 5G have been articulated. For example, CableLabs  has envisioned 5G wireless from the cable telecommunications industry perspective and sees IEEE and Wi-Fi technology standards as part of “the essential core of 5G.”
The Final G?
Technology industries typically evolve based on technical innovations that are driven from the bottom up, by new discoveries and newly practical implementations. The concept of a decade-long coordinated effort to plan and push out a new technology generation worldwide is an exceptional case. 3G and 4G cellular, and perhaps 5G cellular as well, are ideal examples of the exception. However, while 3G and 4G were focused on specific deployment scenarios—communicating to human beings via handheld devices—5G is anticipating a much broader role. With this broadened focus, it is difficult to envision 5G as a coherent set of products and services. As a result, it is easy to imagine that the variety of differentiated scenarios will fracture the market into a set of differentiated industries with separate players, business models, and cost structures. As a result, the upgrade timescales of those industries may vary as well. It may be difficult to coordinate those disparate industries with the kind of singular focus required to integrate global technology innovations into a decade-long mass action. As a result, 5G may be the last of a royal lineage.
- ITU, “ITU paves way for next-generation 4G mobile technologies,” 2010. [Online]. Available: http://www.itu.int/net/pressoffice/press_releases/2010/40.aspx#.Wom3jSM-LVs
- ITU-R, “ITU-R-FAQ on International Mobile Telecommunications (IMT),” 2014. [Online]. Available: https://www.itu.int/en/ITU-R/Documents/ITU-R-FAQ-IMT.pdf
- IEEE, “IEEE 5G.” [Online]. Available: https://5g.ieee.org
- R. Marks, “IEEE 802 5G Propositions,” 2016. [Online]. Available: https://mentor.ieee.org/802-ec/dcn/16/ec-16-0064-01-5GSG.pdf
- CableLabs, “Cable: 5G Wireless Enabler,” 2017. [Online]. Available: https://www.cablelabs.com/insights/cable-5g-wireless-enabler
Roger B. Marks (IEEE Fellow) received his Ph.D. degree in applied physics from Yale University and is engaged with EthAirNet Associates. Marks has participated in IEEE 802 since 1998, serving during that time on the IEEE 802 Executive Committee and as Chair of the IEEE 802.16 Working Group. He was instrumental in efforts leading to the incorporation of IEEE Std 802.16 into the ITU-R’s “3G” IMT-2000 standard and its “4G” IMT-Advanced standard. Marks participates in the IEEE 802.11 Working Group, serving as Vice Chair of the Advanced Access Network Interface Standing Committee. He is also active in the IEEE 802 Working Group, serving as Technical Editor of IEEE Std 802c-2017 and the P802.1CQ project as well as participating in the IEEE 802 “Network Enhancement for the Next Decade” Industry Connections Activity (Nendica). Marks is a member of the IEEE Registration Authority Committee. (e-mail: email@example.com)