E-band transmitter module based on GaN for 6G mobile communications

By 2030, 6G mobile communications should pave the way for innovative applications such as artificial intelligence, virtual reality and the Internet of Things. This requires significantly higher performance than the current 5G mobile communications standard, combined with new hardware solutions. At the EuMW 2022, Fraunhofer IAF is therefore presenting an energy-efficient GaN-based transmission module for the 6G-relevant frequency ranges above 70 GHz, which was developed together with Fraunhofer HHI. The performance of the module has already been demonstrated at the Fraunhofer HHI.

Self-driving cars, telemedicine, automated factories – promising applications such as these in transport, healthcare and industry depend on information and communication technologies that go beyond the scope of the current fifth generation (5G) mobile communications standard. With data rates of over 1 Tbit/s and latencies of up to 100 µs, 6G mobile communications, which is expected to be introduced in 2030, promises the necessary high-speed networking for the data volumes required in the future.

The Fraunhofer Institute for Applied Solid State Physics IAF and the Fraunhofer Institute for Telecommunications, Heinrich Hertz Institute, HHI have been working on the KONFEKT (“Components for 6G Communications “) project since 2019.

The researchers have developed transmission modules based on the power semiconductor gallium nitride (GaN), with which the frequency ranges around 80 GHz (E-band) and 140 GHz (D-band) can be opened up with this technology for the first time. The innovative E-band transmitter module, which has already been successfully tested by Fraunhofer HHI, will be presented to the specialist audience at the European Microwave Week (EuMW) from September 25 to 30, 2022 in Milan, Italy.

Innovative hardware through broadband compound semiconductors and SLM processes

“Due to the high demands on performance and efficiency, 6G requires new types of hardware,” explains Dr. Michael Mikulla from Fraunhofer IAF, who coordinates the KONFEKT project. “State-of-the-art components are reaching their limits. This applies in particular to the underlying semiconductor technology as well as the construction and antenna technology. To achieve better results in output power, bandwidth and energy efficiency, we employ GaN-based monolithic microwave integrated circuits (MMICs) for our module instead of the currently used silicon circuits. As a wide-bandgap semiconductor, GaN can process higher voltages and at the same time enables significantly lower-loss and more compact components. We are also eliminating surface mount and planar package structures to design a lower-loss beamforming architecture with waveguides and inherent parallel circuitry.”

The Fraunhofer HHI is also heavily involved in the evaluation of 3D-printed waveguides. Several components including power dividers, antennas and antenna feeds were designed, fabricated and characterized using selective laser melting (SLM). This process also enables the rapid and inexpensive manufacture of components that cannot be manufactured using traditional methods, paving the way for the development of 6G technology.

“Through these technical innovations, the Fraunhofer Institutes IAF and HHI Germany and Europe are taking a decisive step towards the mobile communications of the future and at the same time making an important contribution to domestic technological sovereignty,” says Mikulla.

Powerful transmitter modules for future 6G frequency bands successfully demonstrated

The E-band module achieves a linear output power of 1 W in the frequency range from 81 GHz to 86 GHz by coupling the transmission power of four individual modules with extremely low-loss waveguide components. This makes it suitable for broadband point-to-point data connections over long distances, which is a key feature for future 6G architectures.

Various transmission experiments by Fraunhofer HHI have already shown the performance of the jointly developed components: In various outdoor scenarios, signals were transmitted in accordance with the current 5G development specifications (5G-NR Release 16 of the global mobile communications standardization organization 3GPP) at 85 GHz with a bandwidth of 400 MHz .

In a clear line of sight, data was successfully transmitted over a distance of 600 meters in 64-symbol quadrature amplitude modulation (64-QAM), ensuring high bandwidth efficiency of 6 bps/Hz. The Error Vector Magnitude (EVM) of the received signal was -24.43 dB, well below the 3GPP limit of -20.92 dB. With trees and parked vehicles obstructing visibility, 16QAM modulated data could be successfully transmitted over a distance of 150 meters. Even if the line of sight between transmitter and receiver was completely interrupted, four-phase modulated data (Quaternary Phase-Shift Keying, QPSK) could still be sent and successfully received with an efficiency of 2 bit/s/Hz. The high signal-to-noise ratio of over 20 dB in some scenarios is particularly remarkable in the frequency range and is only made possible by the high performance of the components developed.

In a second approach, a transmitter module for the frequency range around 140 GHz was developed, which combines an output power of over 100 mW with an extreme bandwidth of 20 GHz. Tests with this module are pending. Both transmission modules are ideal components for the development and testing of future 6G systems in the terahertz frequency range.

Provided by the Fraunhofer Institute for Applied Solid State Physics IAF