A wireless connection to the 6G network

Faster, more flexible, and with more range: For more than twenty years, Ingmar Kallfass, director of the Institute for Robust Power Semiconductor Systems at the University of Stuttgart, has been researching and developing technologies for faster communication channels and global connectivity. In his work, he combines semiconductor technologies with wireless communication systems. His goal: higher data rates for mobile communications and the internet. He plans to use a terahertz point-to-point link  to accelerate the rollout of the 6G network. In the interview, Kallfass explains how this can be achieved wirelessly and why semiconductors are crucial.

At the Institute of Robust Power Semiconductor Systems (ILH), we focus on systems for power electronics and high-frequency electronics. In both cases, we leverage the advantages of modern semiconductors to enhance the performance of communication systems. We want to make mobile networks and the internet even faster and more reliable –and to do that, we’re bringing semiconductors and communications together.

Semiconductors have a crucial property without which modern technology would not function: their electrical conductivity can be altered by their material composition and controlled at extremely high speeds using control signals. Semiconductor devices can be integrated into microchips. These microchips are found not only in computer processors, mobile communications, and internet communications, but also in electric drives and renewable energy systems. They are at the heart of all modern technologies.

A custom-designed version of such microchips is also used in a terahertz radio link that we developed. We're talking about very high radio frequencies here, and those require particularly fast microchips. We want to use these radio links to make our communications even faster and more reliable – even over long distances. And we want to use this technology to drive the development of the next generation of mobile communications – 6G.

Radio links make it possible to transmit and receive data over the air between two defined fixed points. Such fixed wireless connections are relatively easy and flexible to set up. That is why they are primarily used in areas where large amounts of data are generated and where network expansion has not yet progressed very far.

Here on the University of Stuttgart campus, we operate a point-to-point connection spanning about 100 meters from one roof to another. What makes our radio link unique is its frequency range: we use a radio frequency of 300 gigahertz (GHz). That is about four to five times more than is typical for conventional radio links. That’s exactly what makes the difference. The higher the frequency, the higher the achievable data rates. This means you can transfer much more data in the same amount of time. With our fixed wireless link, we can already achieve data rates of 200 gigabits per second (Gbit/s) – that’s about ten times faster than conventional radio links. In the lab, we have even managed to achieve speeds of over 200 Gbit/s.

The main advantage of our radio link is that it remains stable even in adverse weather conditions. It is extremely robust and has already successfully withstood rain, fog, and snow in real-world testing, as well as significant fluctuations in temperature and humidity. This sets it apart from other forms of wireless communication, such as laser technologies. High humidity or raindrops interfere with such optical connections, while we continue to transmit reliably. 

That's right; 200 Gbit/s isn't unusual via fiber optics. However, fiber optics have one major drawback: installing them is labor-intensive and very costly. We want to create a cost-effective and more practical solution that complements the expansion of the fiber-optic network. We are convinced that the rollout of the 6G network can be achieved much more quickly in the near future using our wireless technology in the backhaul network.

In a mobile communications network, our devices connect to a base station. These, in turn, transmit the data via the backhaul network to the main network, which connects all base stations to one another. Base stations are usually connected to each other via fiber optics. In Germany, with LTE and 5G, base stations could not be planned and connected quickly enough. This resulted in areas with no mobile communications service. A wireless connection would be much easier, more flexible, and, above all, more affordable.

Wireless technology allows us to bridge gaps in the fiber-optic network. We’re talking about the “last mile” here: We can easily connect households in rural areas to the network via radio links at high data rates. Our radio link also offers a real solution for emergency calls in hard-to-reach areas. We demonstrated that this is possible in 2024 with the first 6G mountain-to-valley connection in the Alps.

In order to achieve these high rates of data, we need to develop more powerful microchips. We are working together with the Fraunhofer Institute for Applied Solid State Physics in Freiburg, which manufactures our designs. In his doctoral thesis here at the ILH, my colleague Simon Haußmann is researching how to integrate these specialized microchips into the wireless system and connect them to the cellular network and the internet. Simply put, these chips convert and amplify signals from low-frequency ranges – where our cell phones and Wi-Fi operate – into the terahertz range. We test our chips directly in live operation using real internet traffic.

The other major challenge we're working on is developing more powerful modems. You can think of modems as fast computers that convert internet data into signals. While standard modems are compatible with our system, they limit the data rate – they’re essentially too slow. That’s why we’ve been running several modems in parallel so far. That is not very practical and quite costly. To achieve high data rates in the future, we are developing and testing more powerful modems in collaboration with the Karlsruhe Institute of Technology (KIT).

We don’t just want to cover “the last mile”; we want to go beyond that and create real added value in modern communication. Data traffic is growing exponentially, and our network will soon be unable to handle it. My vision is to take our technology from the lab scale to the internet, thereby helping to enable faster, more stable, and more flexible communication even in the most remote corners of the world – and that is what continues to motivate me and my team forward. 

About Ingmar Kallfass
Prof. Ingmar Kallfass studied electrical engineering at the University of Stuttgart and returned to his alma mater in 2013 after holding research positions at University College Dublin, the University of Ulm, the Fraunhofer Institute for Applied Solid State Physics (IAF) in Freiburg, and the Karlsruhe Institute of Technology (KIT). Since then, he has directed the Institute for Robust Power Semiconductor Systems (ILH) at the University of Stuttgart.
Kallfass's research focuses on the development of systems for power and high-frequency electronics, as well as wireless communication systems with high data rates for broadband Internet applications. In his research, he works closely with the Fraunhofer IAF and KIT. As a project manager, he conducts research at the ATLAS Collaborative Research Center (CRC 1667) in Stuttgart on satellite communications with extremely high data rates in very low Earth orbit (VLEO). He is also involved in supporting and training the next generation of researchers at the Research Training Group “Intelligent Methods for Test and Reliability.”