6G and the reinvention of mobile

US President Donald Trump’s “I want 5G, and even 6G, technology in the US as soon as possible” tweet last February was bound to attract comment. It’s not very often that US Presidents make public calls for mobile communications to evolve faster.

Trump’s tub-thump continued: “6G is far more powerful, faster, and smarter than the current standard.” The use of the word ‘is’ drew the most ire from the technologically-informed Twitterati, because 6G, as a tangible technology, is not.

Commenters questioned whether the President knew what he meant by ‘6G’, when the mobile communications industry has yet to roll out the latest 5G networks and services. Also, very few of its experts had mooted the possibility of a next generation beyond 5G’s anticipated 10-15-year lifespan. This would suggest that a sixth-generation mobile service would not be anywhere close to actualisation before 2030. To pine for 6G in 2019 is plain nuts – isn’t it?

As events unfolded since February 2019, talk of 6G started to look less fanciful. Mention of 6G by a senior technologist had, in fact, already been made earlier that month. While attending a conference, Qualcomm’s SVP of engineering Durga Malladi reportedly commented: “There will be a 6G – probably.” He then, however, qualified this with the suggestion that the companies behind the 5G standard developed it so that it would have the flexibility to support future upgrades and other changes, thereby obviating the necessity for another full generational upshift.

Then, a month after Trump’s tweet, the US Federal Communications Commission (FCC) set a ball rolling with its announcement of a new category of experimental licences for the use of frequencies between the 95GHz and 3THz bands – the highest spectrum ranges, and the ones most likely to be used by a future mobile standard that’s not to be classed as a 5G variant or enhancement.

The decree also makes a total of 21.2GHz of spectrum available for use by unlicensed devices. The FCC selected bands with propagation characteristics that will permit unlicensed devices to use the upper spectrum, while it limited the interference potential to ongoing governmental and scientific operations (such as space research and atmospheric sensing) in the above-95GHz bands. The FCC licences offer ‘innovators’ the chance to run experiments that could last up to 10 years.

Whether or not the 95GHz and 3THz bands are those where a 6G network eventually operates, anyone looking to use these bands enters relatively rarefied spectrum space that differs significantly from the bands used for preceding 3G, 4G and 5G technologies. This is because most 4G communications are on frequencies in the 700MHz and 2.5GHz spectrum bands, while 5G communications operate in the higher 28GHz and 39GHz spectrum bands. Each new generation – 4G over 3G, or 5G over 4G – works at a higher frequency range than the previous contender.

The terahertz range is far above 39GHz and can carry much more data: 6G-gazers anticipate that in order to support the ultra-advanced applications now being associated with 6G – about which more later – access speeds of 1Tbps will be necessary that will deliver near-zero/zero ‘air latency’. (By comparison, 5G hits speeds around 500Mbps, with air latency aimed at 8-12ms, although some proponents reckon between 1-4ms may be feasible.)

The catch is that, generally, transmissions in those high spectrum bands cannot travel far, and cannot travel well through objects; they can, however, carry much more data. So, higher wireless frequencies enable transmission of more information, but not as assuredly as the lower frequencies, because the signals can be more easily obstructed.

This characteristic challenges the would-be architects of a 6G communications concept, but solutions are already forthcoming from some quarters. “New paradigms for transceiver architecture and computing will be needed to achieve 1Tbps,” says Professor Matti Latva-aho, director at the 6G Flagship, a development programme from the University of Oulu, Finland. “There are opportunities for semiconductors, optics and materials in THz applications. Increased complexity will also call for open-source platforms to make the next-generation hardware and software solutions happen.”

Conceptualisation of ways around the 6G conundrum has already encouraged ideas about how a 6G mobile network could come together. A 6G network topology would have to solve its challenges at their most fundamental levels and require a rethink of much of the fundamental technology and infrastructure that previous mobile generations share.

For instance, although 6G’s advanced ability to handle data loads is typically mentioned in the context of 1Tbps data transfer rates (speeds), content downloads or streaming may not constitute the bulk of its workloads, according to Professor Walid Saad at the Bradley Department of Electrical & Computer Engineering, Virginia Tech. “The development of 6G will not wait for any use case or application. Instead, it will provide wireless capabilities that can let loose the imagination of application developers and service providers,” says Saad, who is lead author of the white paper, ‘A Vision of 6G Wireless Systems’. “Unlike previous wireless system generations, however, which were primarily driven by the need for more data rates – and hence, more spectrum – 6G will be influenced by technological trends being developed in parallel in other fields.”

These trends are more about the control and orchestration of services tied to the highly-distributed infrastructure that will form the ‘Internet of Everything’ (IoE, sometimes defined as the “intelligent connection of people, process, data, things”), and less to do with a boost for traditional voice/data phone apps.

Emergent ‘Internet of Things’ (IoT) services will also require an end-to-end co-design of communication, control and computing functionalities.

To cater for these new service types, some new challenges have to be addressed, the paper expects. These challenges range from characterising the fundamental rate-reliability-latency trade-offs that govern performance, to the exploitation of frequencies beyond sub-6GHz and the transformation of wireless systems into a “self-sustaining, intelligent network fabric” that flexibly provisions and orchestrates communication-computing control-localisation-sensing resources that are tailored to a given IoE scenario.

Some 6G-gazers take the view that to ensure access to 6G quality communications as envisaged, networks would have to move beyond traditional base-station transmission architecture, instead placing more low-power antennas very close to every ‘user’, be it human or thing. That could be achieved by making every connected device – in other words, smartphone or IoT devices – double up as an antenna. This would in turn shift networked communications off traditional base stations, and suggests that more parts of the IoT would be also acquire dual functionality.

“The concept of a network seen as a bunch of interconnected wires fades away, and data and semantic connectivity take a centre stage,” says Roberto Saracco, director of EIT Digital’s Trento Node. “Network intelligence will emerge from swarms of devices,” he adds, describing how 6G would operate as “a true network of devices”, where traditional base stations “wouldn’t be enough anymore”. This would mean that “companies other than the [network] operators could come in and change the network”.

‘The 6G network is likely to be a concept, a virtual one, and not a “real” network you can put a boundary around’

This would represent a disruptive change to the infrastructure owners, IoT equipment vendors and, of course, makers of mobile handsets.

Other core technology advances include ‘backscatter’ communications – connectivity between hyper-low-power devices via RF signals, adds Latva-aho. “A 6G wireless network may shape the radio environment to its liking.”

The month after Trump’s tweet also saw the first 6G Wireless Summit take place in Lapland, Finland. Organised by 6G Flagship, the event gathered academic and mobile industry experts to discuss a range of topics integral to a 6G standard. The summit covered several high-level subjects, from integrated circuit design for terahertz applications to enabling technologies for proposed 6G service. Its outputs have resulted in a white paper, ‘Key Drivers and Research Challenges for 6G Ubiquitous Wireless Intelligence’, published in September 2019.

The event also scoped much review of 5G roll-out, and its likely evolution into the 2020s: for many with an interest in 6G, the concept will be defined by how well 5G meets the expectations placed upon it over the next decade. Where 5G falls short, 6G expectations will begin. “We must already engage in mapping what 6G can become at its boldest,” Latva-aho adds. “The bottom line of 6G is data. The way data is collected, processed, transmitted and consumed within the wireless network – this is what should drive 6G development.”

Interest in 6G, meanwhile, continued apace. In June a flurry of 6G-related announcements were issued by several mobile industry brands. LG Electronics confirmed a partnership with the Korea Advanced Institute of Science and Technology to launch the LGE-KAIST 6G Research Centre. Market rival Samsung, via its Samsung Research subsidiary, established the Next-Generation Communication Research Centre to “investigate 6G potential”.

Around the same time, South Korean telco SK Telecom signed agreements with network hardware vendors Ericsson, Nokia and Samsung to conduct joint R&D projects that will “lead to technical requirements and business models for 6G”. Other vendors that have declared a strategic interest in 6G include Bell Labs and Huawei.

“The human experience of 6G of instant communication and augmented reality, which should remove the normal barriers of distance between people, will certainly differ from today’s experience,” explains Satish Dhanasekaran, president of the Communications Solutions group at Keysight Technologies. For applications where humans are not the endpoint, such as industrial automation, autonomous systems and massive networks of sensors, precise timing will emerge as the key attribute of 6G networks, he adds. “The ITU calls this ‘Time Engineered Communications’. This is not about just achieving lower latencies [in the range] delivered by 5G but is concerned with the precise time of an event, such as data delivery.”

Meanwhile, EIT Digital’s Saracco foresees 6G as “a platform driven by services and service interaction, supported by a flat network and decentralised control”. He says: “The 6G network is likely to be a concept, a virtual one, and not a ‘real’ network you can put a boundary around. [When it arrives] 6G will consist of devices that dynamically connect with each other, networks of different types which connect one another. For a few services there might be an orchestration – but not necessarily provided by a network operator.” Otherwise, services are more likely to be managed at the edges.

“The bottom line of 6G is data,” insists 6G Flagship director Latva-aho. “The way in which data is collected, processed, transmitted and consumed within the wireless network, should drive 6G development.”

Saad, however, believes that the communications requirements of emergent IoT/IoE-type use-cases – such as virtual-reality applications, autonomous vehicles, brain-computer interfaces and haptics – are likely to be exclusively supported by 6G infrastructure and technologies. This is because such deployments require much higher data rates, higher reliability, and lower latency figures, than the initial version of 5G can provide. “6G will most likely still be supporting extant 4G/5G services, although it may rely on existing 5G technologies to do so,” Saad says. “In other words, 4G/5G infrastructure and techniques will still be embedded and co-located with 6G.”

“The adoption of new network capabilities and services must be supported by compelling business models,” Dhanasekaran adds. “6G technologies should amplify some network services that emerge in the 5G era, [thus] creating value for vertical industries. They will also drive many new network services. These could be structured and priced according to the type of service and its value to the target user.” Put another way, 6G will be financed by projected revenues from business and industrial subscribers, rather than individual subscribers, as today’s revenue model mostly is.

“Operators will need new pricing models tailored towards machine-type/IoT services,” explains Saad. “For such services, users are no longer individuals or business users, but owners of fleets of autonomous vehicles, robots, or drones, whose communication services needs are radically different from a typical individual subscriber. Moreover, 6G will provide services beyond communications, such as localisation, imaging, or sensing services. With these, new economic models are needed to tariff and possibly bundle such services, dependent on demand.”

New economic models will bring new technological challenges for the communications engineers who’ll be tasked with bringing 6G to life. “Communications engineers and scientists will have to push the boundaries of different technologies,” says Dhanasekaran. The disciplines he includes on his list range from materials and device science to ultra-low-power circuits, to data reduction techniques, novel network topologies, biological systems and new communication protocols. “Arguably, the biggest challenge will be how the structured development is managed so that the resulting networks are flexible, adaptable and can support the deployment of applications,” he adds, “and result in the seamless co-existence of heterogenous networks.”

Another tele-engineering challenge that 6G brings forward, says Saad, is how to continuously maintain reliable, high-speed, low-latency communication links for massive systems. “To address 6G challenges, it is imperative to develop new skills that go beyond the rigid communication theory fundamentals. This requires us to develop new fundamental science [ie, more than RF technology] for ultra-reliable low-latency communications at scale – expanding on the lessons learned from 5G in this area – by drawing upon interdisciplinary fields across engineering and economics, for instance.”

However, an understanding of the fundamental physics of radio channels remains critical, says 6G Flagship’s Latva-aho. “The real challenge everywhere is that communications fundamentals and RF engineering, which would be needed to develop THz communications expertise, is not popular among youngsters,” he says. “We will soon face a lack of RF experts, which may slow down 6G development.”

Saad adds: “[With 6G] we have to explore fields such as artificial intelligence and machine learning, economics, psychophysics, optimisation theory, and even neuroscience. Tomorrow’s communications engineering/technologists, therefore, must be truly interdisciplinary individuals.”