CEA-Leti Explores mmWave Bands for 6G

Article By : Nitin Dahad

Research explores optimized RF circuits to address D-band frequencies for beyond-5G and 6G...

France-based technology research institute CEA-Leti has demonstrated a 140GHz 100 Gbps transmission using a simple mixed signal RF architecture as it explores a technology roadmap to address ‘beyond-5G’ applications and 6G in the D-band spectrum. D-band covers frequencies from 110GHz to 170GHz.

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 spectrum at 140 GHz that may play a major role for 6G wireless communication.

In a paper entitled “Technology Roadmap for Beyond 5G Wireless Connectivity in D-band”, which was to be presented at the cancelled 6G Wireless Summit in March, CEA-Leti and Siradel, a French engineering firm, said their researchers are considering several beyond-5G applications. These include high-capacity backhaul, enhanced hot-spot kiosks and short-range device-to-device communication. The data-transfer speed requirements for these applications, 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 provided an overview of those potential applications and the challenges to realizing them. It also presented scenarios for applications in the new spectrum. Included in the discussion were the trade-offs between scenario requirements, and current silicon-technology limits to building a 6G roadmap.


6G Being Discussed?

Asked about the silicon constraints in an interview with EE Times, Jean-Baptiste Doré, a CEA-Leti scientist and one of the authors of the paper, told us, “With CMOS, we can still design chip sets for the low part of the D-band, but today we are at the boundary of what CMOS can deliver at these frequencies.” 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.

Transmitarray Antenna_Credit @CEA
Antenna driver IC mounted on the back of the focal source of a D band transmit-array (Image: CEA-Leti)

He added, “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.”

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.

The design of these key technologies to enable 6G has already started. This 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. Dore said, “At Leti, we are working on the technology roadmap for the integrated RF chipset and antenna design. We started thinking about new technologies for sub-THz bands that can integrate with CMOS and have already started on the antenna and chip set design.” It is investigating heterogeneous integrations on system-on-chip and/or system-in-package.

Channel bonding architecture utilized in CEA-Leti’s recent demo of the 100Gbps transmission in the D-band (Image: CEA-Leti)

“For device-to-device communication, we have demonstrated that it 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 and digital, the required power delivered by transistors is limited to microwatts (10^-6 Watts) which makes CMOS technologies possible.”

CEA-Leti said there are already field trials ongoing for 140GHz communications, as a race is on to find an integrated module that can address the high performance and low-cost requirement. Doré said, “We already have some partners and are looking for additional funders to develop the technology.” We asked who the partners were but Doré declined to disclose them. However, one of them is an established semiconductor player, he added.

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