• Wireless communication in millimeter wave (mmWave) bands, which range from 20 GHz to 300 GHz, is expected to be a key enabling technology for 6G wireless systems, because the huge available bandwidth 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 for 6G wireless communication.

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

• The paper, titled "Technology Roadmap for Beyond 5G Wireless Connectivity in D-band"¹, provided an overview of those potential applications and the challenges to realizing them, and presented scenarios for applications in the new spectrum. It also discussed the trade-offs between scenario requirements, and current silicon-technology limits to building a 6G roadmap.  
  

Severe constraints on antenna directivity and alignment                                                                                                                                                                                                                                                    

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. That entails severe constraints on antenna directivity and alignment," said Jean-Baptiste Doré, a CEA-Leti scientist and one of the authors of the paper. 

• 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 state of the art with high directivity and an electronically steerable antenna
  

• 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.
  

For device-to-device communication, we have demonstrated that is possible to reach multi-Gbps throughput using spatial multiplexing and a simple RF architecture," Doré said. "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.