Researchers at CEA-Leti Explore 6G Technology Roadmap in mm-Wave Bands

As countries around the world begin rolling out 5G wireless networks, CEA-Leti, a technology research institute, is looking ahead to 6G technologies that will surpass the data-transfer capability of 5G. The wireless communication in mm-Wave bands, ranging from 20 to 300 GHz, is expected to be a key enabling technology for 6G wireless systems. This is because of the huge available bandwidth that can accommodate ultra-high data-rate communications. Within that range of mmWave bands, CEA-Leti's research is investigating D-band, a new spectrum at 140 GHz that may play a major role in 6G wireless communication.

In a paper written for the 6G Wireless Summit, which was scheduled to take place in March but got cancelled because of the coronavirus pandemic, CEA-Leti, and Siradel, a French engineering firm, said researchers are considering several beyond-5G applications. These include high-capacity backhaul, enhanced hot-spot kiosks, and short-range device-to-device communication. These applications have data-transfer speed requirements, typically greater than 100 Gbps per cell or per link, which exceeds the capability of 5G and are not affected by the main constraints imposed by the sub-THz frequencies.

Scenarios envisaged for wireless connectivity in sub-THz bands associated KPIs

The paper, titled "Technology Roadmap for Beyond 5G Wireless Connectivity in D-band", provides an overview of the potential applications and the challenges to realizing them, and presents scenarios for applications in the new spectrum. It also discusses the trade-offs between scenario requirements and current silicon-technology limits to building a 6G roadmap.

Jean-Baptiste Doré, a CEA-Leti scientist and one of the authors of the paper, commented that challenges to using D-band wireless communication include free-space wave-propagation losses that increase with the square of the frequency and have to be compensated for using high-gain antennas. This entails severe constraints on antenna directivity and alignment.

The constraints include physical barriers to sub-THz wave propagation, which can be blocked or strongly attenuated by walls, trees, or even windows. Even in a clear propagation path, high-gain antennas are required. To address this challenge, CEA-Leti is designing technologies that are beyond the state of the art with high directivity and an electronically steerable antenna.

Ray-tracing tool from SIRADEL predicts the propagation of in-street back-haul for sub-THz wireless performance assessment. The tool benefits from detailed 3D representations to get a realistic prediction of the blockages and losses due to trees and street or indoor furniture. 

Subterahertz hardware integrated circuit technologies. ASK: amplitude-shift keying; PSK: phase-shift keying; QAM: quadrature amplitude modulation; QPSK: quadrature phase-shift keying; InP: indium phosphide; mHEMTs: metamorphic high electron mobility transistors; GaAs: gallium arsenide; OOK: on-off keying.

Because CMOS technologies cannot produce devices that deliver the maximum transistor frequency needed for sub-THz applications, CEA-Leti is investigating optimized RF circuit designs with innovative architectures for these applications, and new materials and devices to address D-band frequencies and beyond.

Two recent papers were accepted for presentation at IMS2020 and RFIC2020 concerning low-noise amplifiers and programmable high-order frequency multipliers for channel bonding, respectively.

Doré further stated that for device-to-device communication, they have demonstrated that it is possible to reach multi-Gbps throughput using spatial multiplexing and a simple RF architecture. The main outcome is that with the proposed mixed-signal, analog & digital, the required power delivered by transistors is limited to microwatts (10-6 Watts) which makes CMOS technologies possible.

The design of key enabler technologies for 6G has already started. This work includes the investigation of new materials and devices for the sub-THz band, enhanced RF CMOS architectures and antenna systems as well as high-performance digital processing. CEA-Leti teams also are investigating heterogeneous integrations on system-on-chip and/or system-in-package.