The LTE standard (4G) meets the needs of most mobile network users. Download speeds of up to several hundred megabits per second make it easy to stream high-resolution video content or download large files within seconds. 5G is available in much of the world but mostly piggybacking on LTE (NSA). Pure 5G standalone (SA) rollout will happen over the next years, yet research into the next generation of mobile communications has already started; 6G is expected to be rolled out by 2030.
But are any needs left unsatisfied by the technically advanced 5G system, which is subject to ongoing development and extension? A pair of authors posed this very question back in September 2018 . What started as a discussion among experts has since gained serious momentum. Political and industrial interest in 6G has triggered a global technological race with billions flowing into research and development.
What needs can 6G meet?
“6G will satisfy the expectations that 5G has created,” was how Dr. Ivan Ndip from the Fraunhofer Institute for Reliability and Microintegration (IZM) pithily described the situation in an interview in spring 2021. Although 5G has yet to reach its full potential, applications are emerging that require 6G for large-scale implementation. Autonomous driving is one example.
At autonomy level 5, which is still a long way off, vehicles will not be as autonomous as the name suggests. After all, vehicles share roads, traffic lights and other infrastructure with countless other road users. For everything to run smoothly, autonomous vehicles must be connected in three ways: with each other, with roadside facilities and with a traffic control centre. Since many situations are safety-critical, such as emergency braking, high transmission speeds and reliable signal transfer are vital.
Vehicles require extremely high data rates to exchange sensor data and download detailed traffic plans. 5G is clearly a big step forward, but with a maximum data rate of 20 gigabits per second and signal latency of a millisecond, it is probably not good enough for true autonomous driving. Completely autonomous vehicles will only be possible with 6G, which is to reduce signal latency by a factor of ten and increase data throughput by a factor of fifty (Table 1).
Autonomous driving is a key cutting-edge application that is pushing 6G research. Other important applications are extended reality (XR) and industrial automation. These sectors hinge on the ultra-low latency promised by 6G for instantaneous decision-making and seamless user experiences.
Focus shifts to machines
In 6G, functions and services for efficient machine-to-machine communications (M2M) will play a vital role.
URLLC and mMTC are two of three key 5G focal points in this area. In addition to autonomous driving, 5G applications include Industry 4.0, smart cities and smart homes. Rather than a single type of M2M communication, many different types are needed. Just look at a connected factory where end-to-end signal transit times in the lower millisecond range need to be combined with minimum latency variation and highest reliability. Smart cities or smart homes have completely different requirements. A smart home needs utility meters, sensors and control elements for everyday items such as waste bins or appliances to remotely provide information or automate processes.
These applications only require sporadic radio communications with small amounts of data. The radio network for a smart city must connect hundreds or even thousands of identical end-point devices, many of them battery powered.
Such applications were inconceivable when mobile communications were first developed but now define the 5G concept. The main focus has shifted from people to devices or machines and the internet of things (IoT).
The 6G vision
Technical development is closely aligned with the demands of different industries. The visions for 6G vary widely and merge to form a fascinating landscape. Bringing this landscape to life will require evolution of existing technologies but also capabilities that are mostly not yet available, but which are within reach on the medium term. The interaction between all these technologies will create the sixth mobile communications generation, but the term fails to describe the true potential of 6G.
Digital twins on the holodeck
Facebook founder Mark Zuckerberg announced the metaverse in autumn 2021 and also changed the company name to Meta. With that he gave once gimmicky VR headsets new market relevance. They are the main tool for implementing Zuckerberg’s vision of extended reality. The company has the means, since VR headset manufacturer Oculus is part of the Meta empire.
Reimagining the original idea behind the VR headset is ambitious and visionary. 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 Zuckerberg’s vision and 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. Ultimately, the long-term goal is 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. Some of these objects have to match up with twins in the real world.
The digital twin is an interactive, virtual representation of a real object or machine that can be manipulated from the metaworld. The ability to operate machines from practically anywhere has potentially far-reaching consequences for the work environment and society at large. One potential impact is the revival of rural areas, since people will no longer need to move to urban areas for work.
When thinking about scenarios like this, you simply cannot ignore 6G. VR headsets do not have the processing power required for the immersive artificial world of the metaverse. And if we want the headset to be compact and look like regular glasses, we need external computing power. If this processing power comes from the cloud, 6G is absolutely necessary.
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 does not have the capacity for this. Networks will also need to allocate computing power intelligently for the various 6G services, and this is where artificial intelligence comes in. In fact, AI will be ubiquitous in 6G networks.
The real internet of things
Although the internet of things is slowly taking shape and industrial and transportation applications have received a boost from 5G, universal connectivity is only possible with 6G. Based on its technical configuration as well as its capacity, 6G should be capable of integrating any number of objects in homes, industries, road transport or infrastructure. This opens up networking opportunities that were never possible before.
Embedded radio sensors can help monitor the condition of bridges and highways, making it easy to see when maintenance is needed. 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 food quality.
The IoT boost will also change how connected radio sensors are powered, which presents a huge challenge for their large-scale deployment. The sheer quantity of these sensors as well as the degree of miniaturization makes it unfeasible to exchange the power cells. Since many applications are conceived for long-term deployment over many years, the sensors must be able to provide their own power. Zero energy devices and energy harvesting are two buzzwords here. Today’s RFID sensors work with electromagnetic energy harvested directly from a nearby reader or scanner. But 6G sensors will have to make do without this convenience and obtain power from suitable local sources such as heat, light or motion. As with many other 6G topics, research in this area is still in its infancy.
A network of radio networks
6G will be not only an inexhaustible basis for the internet of things, but also a new kind of internet. With 6G, fixed, mobile terrestrial and non-terrestrial networks will integrate seamlessly into a constantly changing heterogeneous network landscape (organic network). Commercial, private and public subnetworks of all sizes will coexist, ranging from the macrocells that exist today and provide coverage over an entire square kilometre – to attocells and zeptocells with coverage for a single room or vehicle. Openness, virtualization and disaggregation are required to tailor network
functionality to the customer application and to spark innovation of new services The disaggregated network’s function blocks must provide multivendor support in compliance with the standard. Rohde & Schwarz is an active member of the O-RAN alliance, which is already laying the foundations for this.
The race is underway
Initial discussions of 6G only began a few years ago, but since then a lot has happened in industry, research institutes and the political world.
Research initiatives have been set up around the world, financial support has been granted and alliances have been forged. Politicians understand that competitiveness – and the economic prosperity of their countries – may rest on equal participation in the 6G system while avoiding dependency. In the spring of 2021, Japan and the USA agreed to invest 4.5 billion dollars in 6G research. South Korea has an ambitious plan to invest some 195 million dollars over the next four years and will be ready for preliminary field tests by 2026.
Europe has launched its flagship 6G project, Hexa-X, with organizations from nine different countries. Rohde & Schwarz is actively working with relevant research organizations worldwide. Separately, the German Federal Ministry of Education and Research is providing 700 million euros in funding until 2025.
In the short term, 250 million euros will go to four national research hubs where Rohde & Schwarz is involved as a partner or project coordinator.
And then there is China. Of course, China has no intention of giving up its strong 5G position simply because the next generation of technology has arrived. China’s Ministry of Science and Technology is working with other ministries and government agencies to coordinate national resources and get 6G ready for deployment as quickly as possible.
► Rohde & Schwarz has been a close partner to industry as well as a leading supplier of T&M equipment since the very beginning of the digital mobile communications era. The company’s products and expertise are already in use today in various 6G research and development projects, and the company is committed to also provide the measuring equipment needed for 6G large scale rollout.
6G RESEARCH AREAS
There is a need for further research and development in the following areas:
FREQUENCIES: 5G is using the millimetre wave range (> 20 GHz) for individual communications for the first time. FR2 (7.125-24 GHz) is the most promising frequency for mass 6G rollout. But 6G will also use higher frequencies: up to 100 GHz and higher for sensing and 90-170 GHz for backhaul. Even the terahertz range (300 GHz to 3 THz) is being explored.
ANTENNAS: at such high frequencies which correspond to short wavelengths, the antennas have dimensions in the millimetre range. Base stations will combine up to 60 000 of these antennas into arrays to supply simultaneous coverage for hundreds of mobile devices via individual directional beams. Reconfigurable intelligent surfaces (RIS) are being developed today. They could be deployed
on building walls, for example, to improve the performance of wireless communications in terms of coverage and efficiency.
ARTIFICIAL INTELLIGENCE (AI): AI will be a major hallmark of 6G. It bears the potential to dynamically adjust the network to cope with varying environment and customer demand. AI will be used in technical components as well as in network planning and monitoring. The ultimate goal is to achieve a zero-touch (self-optimizing) network in terms of cost, energy, spectral and operational efficiency.
VIRTUALIZATION: all of the main network components should be defined and addressable via standardized abstract functions. This ensures that products from different manufacturers can be combined while leaving room for specific technical configurations.
SELF-POWERED SENSORS: quantity wise, myriads of miniature sensors will form the largest share of the internet of things. They will need to operate maintenance-free for prolonged periods of time while obtaining power through energy harvesting.
INTEGRATED RADIO, SENSOR AND COMPUTER NETWORK: 6G will be much more than just a radio network. Integrated location and sensing functions will allow the position of network users to be pinpointed down to the centimeter while checking his vital functions. The network’s processing power will also be massively distributed and harnessed either close to the network user or in remote data centres depending on requirements (edge, fog and cloud computing).
DATA INTEGRITY: 6G networks will form the backbone of business and industry – even more than 5G. Countless business processes and services will be based on these networks. Data security is therefore critical. Users must be correctly authenticated with absolute reliability. Every connection will require encryption. Block chain technology is being considered as a way to avoid dependence on central instances in order to ensure data integrity.
ENERGY EFFICIENCY: energy demands inevitably also rise when data communications grow exponentially. The energy consumed per bit transmitted needs to fall in order to keep energy efficiency in check.
 David, K., Berndt, H.: 6G vision and requirements: Is there any need for beyond 5G? IEEE Vehicular Technology Magazine, Vol. 13, Issue 3, Sept. 2018.