6G - a vision of tomorrow’s wireless communications

Even though 5G networks are expected to undergo further growth and development for years to come, technology strategists are already offering up visions that look far beyond 5G. If their 6G scenarios become reality, we can expect a wonderland of communications in the 2030s. Rohde & Schwarz has been a leading supplier of test and measurement equipment since the start of the digital wireless communications era. Now the technology company is supporting the industry as a close partner to help make the vision of the sixth generation of wireless communications a reality.

Is it just about faster speeds?

Since the introduction of the LTE standard, most mobile users have found that their needs were satisfied. With download rates of up to several hundred megabits per second, it is no problem to stream high-resolution video content or download large files within seconds. Already available countrywide in many places, 5G is multiplying the available speed, but it has practically no other real benefits for individual users. Ideas for the next stage of evolution have already existed for some time, however. But has the technically advanced 5G system – which is subject to ongoing development and extension – left any requirements uncovered that could possibly motivate this further evolution?

This question was floated by a pair of authors in September 2018*). Since then, the topic has gained a remarkable level of momentum on its own. While it began as a topic of discussion for experts, 6G has since developed into a sort of "policy elephant" for technology and industry that is receiving nourishment in the form of research and development grants in the billions worldwide. Based on examination of the potential of current technologies as well as upcoming technologies that are either currently under development or visible on the horizon, a vision has crystallized that is leaving behind everything that was previously possible by far.

*) Klaus David, Hendrik Berndt: 6G vision and requirements: Is there any need for beyond 5G? IEEE Vehicular Technology Magazine, Vol. 13, Issue 3, Sept. 2018

From person to person

Everything started very conventionally over three decades ago. Following the first analog generation (1G) reaching back to the 1950s, the first generation of digital wireless communications emerged in the early 1990s. The European Global System for Mobile Communications (GSM) 2G standard developed into a major export product, as did the GSM system simulator from Rohde & Schwarz. This system is still regarded as a pioneer of wireless communications.

The first generation of digital wireless communications was designed purely as a voice telephone system. Even simple data services like sending text messages had to be patched on later. The rapid growth of the internet quickly gave rise to the desire to also have mobile access to the internet. Data applications were thus a key element in the requirement specification for the next generation known as 3G, which was launched in 2001. However, it quickly became obvious that the 3G system did not have the necessary capacity to support the rapid growth in data traffic. The name of the next standard (4G) made it clear that designers did not intend to repeat the same mistake. Long Term Evolution (LTE) was built to meet future requirements for an extended period of time through ongoing updates. The very first networks based on this standard went live in 2010 and still form the backbone of the wireless communications system.

All of the standards up to 4G were targeted at human-centric communications. The primary focus was on fast acquisition of information (the downlink), and HD video streaming was seen as the killer application. 4G was entirely sufficient in this context. The stimuli for further development have come from a totally different direction.

Small talk among machines

In the meantime, various industries had begun developing scenarios that required very high-performance wireless communications infrastructure with features that LTE could not support. For example, Industry 4.0 is based on extremely reliable radio links with end-to-end signal transit times in the lower millisecond range. Machines that are built to synchronously perform a common task at full speed need data infrastructure that can keep up with their pace of operations. While this is not a problem with ordinary cable connections, it is a challenge when using radio. However, radio is mandatory in order to ensure the flexibility that characterizes Industry 4.0.

The transport sector is providing an entirely new application field for wireless communications. Even in the still distant level 5, autonomous driving will not be nearly as autonomous as the term might suggest. Ultimately, vehicles must share the roads, traffic lights and other infrastructure with countless other road users – producing interactions that require a high level of orchestration. This means that vehicles must be connected to one another as well as to equipment deployed along the roads and to a traffic control center. Since there are many possible safety-critical situations such as emergency braking, fast and dependable signal transfer is a top priority.

In contrast, the requirements associated with smart city and smart home wireless applications are quite different. Devices such as utility meters and waste containers are being equipped with sensors and control elements that can be remotely queried or activated, for example. The goal is to eliminate the need to manually access the devices and allow actions to be triggered based on the acquired data. Only sporadic radiocommunications is required and the quantity of data is very small. A typical scenario might involve thousands of similar user devices that are battery-powered. A radio system like LTE that is designed for high performance is clearly overdimensioned when it comes to such low performance applications. Moreover, some special requirements like reduced current consumption are not satisfied.

It was applications of this kind that influenced the design of 5G. The main focus has shifted from people to devices and machines, i.e. the internet of things (IoT).

Is there something missing?

5G is already well-developed in many countries. However, the focus – even in the standardization by the responsible organization 3GPP – was initially on the application group enhanced Mobile Broadband (eMBB). The expected boom in factory, transport and IoT connectivity has not yet materialized. However, applications are already appearing where 5G would not be sufficient even if all of its technical options were exploited in a consistent manner. Different development stages are also planned for 5G. Starting with Release 18 of the standard specification (the final version is expected in 2024), the term 5G-Advanced will be used. Despite the lack of any formal agreement, the industry has already basically decided to attribute certain performance features to a new network generation known as 6G. The target for the introduction of 6G has been set – more or less out of habit – for the year 2030.

Of course, a 10-year cycle has been the rule for generations since 2G and it seems an obvious choice to continue. The previous generations also differed in technical terms, for example different channel access methods (ways of using the radio channel). The channel access method as well as the type of data coding and usable transmission bandwidth have a major influence on the system performance. As a supplier of test and measurement equipment, Rohde & Schwarz has supported and shaped this technology right from the start.

Since 5G, technical advances have been driven by the fantasies of various industries. Future scenarios are emerging from different directions and commingling to produce a fascinating overall panorama. Bringing this panorama to life will require technologies that are not yet available at all for the most part, but which are within reach on the medium term. The interaction between all of these technologies will be known as the "sixth wireless generation". However, this austere term comes far from describing the entire vision that is targeted.

Digital twins on the holodeck

Facebook founder Marc Zuckerberg presented his vision of the future of the enterprise last autumn. The master plan calls for the long-term conversion of the current social media platform into a "metaverse". From virtual reality (VR) and augmented reality (AR) to extended reality (XR): merging the real world and the virtual world to form an artificial world. Embodied as digital personalities or avatars that are projected holographically in the extended reality space, users will be able to switch seamlessly between chat rooms, game worlds and shopping malls – while never leaving the synthetic environment. While all of the details of how this will work have not yet been clarified, it is clear that VR glasses will play a major role.

Of course, this isn't entirely new. VR glasses have been commercially available for years and are already being used, mainly for industrial applications. Specialists use the glasses, for example, to project a 3D model of a part to be mounted into the real image – together with information on how to handle the part. The person wearing the glasses can even interact manually with the holographic projection as if it were real. This includes touching and manipulating the projection. Making such a system available in the millions and affordable for everyone is one of the guiding scenarios for 6G.

Extended reality – the combination of real and virtual worlds – encompasses a number of other substantial visions if taken to its logical conclusion. The long-term goal is to achieve total immersion into a new world that is experienced as if it were real. This includes elements such as three-dimensional optical resolution capable of fully stimulating human eyesight, an appropriate acoustic environment, instantaneous reaction by all synthetic objects (tactile internet) and finally, a credible representation of all of these things.

What is significant, however, is that some of these objects correspond to counterparts from the real world. These "digital twins" are in fact interactive virtual representations of real-world objects and machines that can be manipulated from the metaworld. The ability to operate them at any arbitrary distance from the machine has potentially far-reaching consequences for the organization of work. Potential societal knock-on effects could include a revival of rural areas if the need to be present in urban centers is decreased.

What does all of this have to do with 6G? The computing power needed to individually facilitate this immersive artificial world for each user will outstrip the capabilities of VR glasses by far – especially if the glasses need to be as graceful and unobtrusive as normal glasses. External computing power will be required, which might involve nothing more than a smartphone in the user's pocket. In cases where this is not enough power, the task can be delegated to a nearby computer or transferred on the go to a cloud server (edge, fog, cloud computing).

This is where 6G gets involved. Transferring extremely large quantities of data to the glasses with video resolutions of at least 8K in stereo requires transport capacities of several hundred gigabits per second along with signal transit times of a tenth of a millisecond to enable natural reactions in real time. 5G is not designed for such performance. Intelligent provision of computing power for the various 6G services on the basis of artificial intelligence will be another task for the network. In fact, AI will be ubiquitous in the 6G network.

6G technical KPIs

Given the challenging applications that 6G will address, all of the important radio network performance parameters must be enhanced in lockstep. The following key performance indicators (KPI) are under discussion for 6G, corresponding 5G figures are shown for comparison:

Pioneering the vertical domain

Providing coverage over large areas is a common theme in the world of wireless communications. In 6G, however, white spots on the map should not be an issue any more. On the contrary: High-performance wireless communications to support immersive experience will be targeted across all of the earth's surface – including the countryside and outside of residential areas – but also in the third dimension. This vision even incorporates the underwater world. Wherever humans and machines can exist, they should be accessible via fast wireless communications. This requires not only new technologies such as optical signal transmission underwater where radio waves are absorbed, but also extensive above-ground infrastructure. For example, this might include fleets of satellites as well as flying platforms such as airships and drones.

The real internet of things

The internet of things has been around conceptually for a good while already. Now it is also gradually taking shape in the real world too. Especially in industry and in transport, its growth should be accelerated by 5G. Smart home and smart city applications will also make their own contributions. However, even then it would still be too early to speak of all-encompassing connectivity. That is part of the 6G vision. Based on its technical configuration as well as its capacity, 6G should be capable of integrating an arbitrary number of devices in every imaginable category. Everything we wish to have contact with or which plays a role in our lives – encompassing private, commercial as well as public contexts – is a potential candidate for connectivity. Take, for example, bridges and highways. How is their current condition? When do they need to be repaired and where? Embedded radio sensors could provide the relevant information. The RFID tags commonly used in retail sales and logistics can only be read from a short distance. Equipped with special sensors and a larger range, however, they could be used to monitor the quality of foodstuffs and send relevant reports, for example.

The last example simultaneously involves multiple areas of current research. If a small movable object is monitored to be able to take it out of circulation when necessary, its exact position must be known. Many other applications also require information about the location of the communications partner since 6G services will generally be provided on a local basis. For technical reasons, 6G will use highly focused directional radio beams in order to target the radio energy towards specific remote stations. A 6G network will thus include a radio network as well as a sensor network that is capable of determining the position of radio users with centimeter accuracy in 3D space. The techniques to be used for this purpose are still under investigation, but radar technology in the access points is one possibility.

Another problem related to mass deployment of radio sensors involves how to supply them with energy. The sheer quantity of these devices as well as the degree of miniaturization makes it unfeasible to exchange the power cells. However, since many applications are conceived for long-term deployment over many years in some cases, the sensors must be able to provide their own power. Zero energy device and energy harvesting are relevant buzzwords here. Modern RFID sensors are designed to function in this manner, but they are directly supplied with electromagnetic energy by a nearby reader device. 6G sensors will have to make do without this convenience and obtain power from suitable local sources such as heat, light or motion. Like many other 6G topics, research in this area is still in the early stages. Nevertheless, T&M equipment from Rohde & Schwarz is already helping us understand the energy consumption patterns of devices, making low-power design possible.

6G will be not only an inexhaustible basis for the internet of things, but also a new kind of internet. Just as we like to call the conventional internet a network of (computer) networks, it will be possible to describe 6G as a network of radio networks. The monolithic structure of today's wireless networks will give way to a constantly changing heterogeneous network landscape ("organic network"). Commercial, private and public subnetworks of all sizes will be interconnected in this manner, ranging from the macro cells that exist today and provide coverage over an entire square kilometer – to "atto" and "zepto cells" with coverage for a single room or automobile.

To allow the process of docking a network to the overall structure to be automated, it is desired to virtualize as many network functions as possible. This involves describing the functions in a purely abstract manner – an approach that was first attempted to some extent in 5G. The network's function blocks must provide multivendor support for this abstract language and interpret it in compliance with the standard. Rohde & Schwarz is involved in the O-RAN Alliance, which is promoting standardization and interoperability in this area. The worldwide standardization of 6G technology, as already with previous generations, is very important.

Where everything is ultra

As they sketch out their 6G scenarios, technology visionaries refuse to accept any bounds on their imagination. The sky is the limit. While 5G made do with only three application groups (eMBB, mMTC and URLLC), the 6G vision involves more groups – and even combinations of groups. As they go about naming their creations, the experts enjoy using superlatives. A simple rule is that all performance characteristics are prefixed with ultra. As the nomenclature continues to evolve and standardization remains well in the future, technical articles can be found featuring terms like further enhanced ultra mobile broadband (feUMBB), ultra high sensing low latency communications (uHSLLC), ultra high density data services (uHDD), ultra high energy efficiency (uHEE), ultra high reliability & sensing (uHRS), ultra high reliability & user experience (uHRUx), ultra low latency reliability & security (uLLRS) and so on.

One obvious question is whether the science fiction world we have described here is truly as close to being realized as its architects would like to suggest. Much depends on whether researchers can reach their goals within the specified timeframe so that series products can be manufactured. Considering the worldwide interest in this key technology that is expected over the coming decades as well as the significant funding that is available – not to mention the size of the market or the relevant political dimension – there appears to be plenty of commitment and enthusiasm for 6G.

The race has started

Since initial discussion of 6G began only a few years ago, the wheels have been set into motion in industry, research institutes and the political world. Research initiatives have been founded worldwide while financial aid has been granted and alliances forged. Politicians have understood that the ability to compete – not to mention the economic prosperity of entire countries – can potentially rest on equal participation in the 6G system. Avoiding a state of dependency is thus a key consideration. For example, Japan and the United States have agreed at the highest level to jointly invest USD 4.5 billion into 6G research.

Europe has launched a 6G flagship project known as Hexa-X. Organizations from nine different countries are participating in this project. Separately, the German Federal Ministry of Education and Research is providing funding in the amount of EUR 700 million through 2025. Of this, 250 million will soon go to four national research hubs that have already submitted their requests for funding for programs in which Rohde & Schwarz also participates. South Korea is pursuing an ambitious plan that will involve initial field trials in the year 2026. The country is planning to invest about USD 195 million until then. What about China? Of course, China is not planning to give up the strong position it achieved with 5G because another generation of technology has arrived. China's Ministry of Science and Technology is working with other ministries and government agencies to coordinate the national resources needed to get 6G ready for deployment as quickly as possible.

Since the very start of the digital wireless communications era, Rohde & Schwarz has served as a close partner to industry as well as a leading supplier of T&M equipment. The company's products and expertise are already in use today in various 6G research projects. The measuring equipment needed for 6G is being made available on a step by step basis.