Workshop 14

Third International Workshop on Wireless Communications in Terahertz (IWCT)

Tuesday, 3 June 2025, 14:00 – 17:30, room 1.C

Organisers:

• Kenta Umebayashi (Tokyo Univ. Agriculture and Technology, JP)
• Nuutti Tervo (Univ. Oulu, Centre for Wireless Communications – Radio Technologies (CWC-RT) , 6G Flagship, FI)
• Joonas Kokkoniemi (Univ. Oulu, Centre for Wireless Communications – Radio Technologies (CWC-RT) , 6G Flagship, FI)

Motivation and Background

The ambitious goals of future wireless technology in 6G and beyond aim for extreme data rates reaching hundreds of gigabits per second or even terabits per second, necessitating the use of wide signal bandwidths sought from higher frequencies. Over the past years, communication in Terahertz and sub-terahertz bands (0.1–10 THz) have remained an interesting research area to reach the Tbit/s goal. However, recent proposals to develop cellular-like wireless communication systems in these bands have faced criticism. Concerns stem from various factors, including practical business models, deployment challenges, and the difficulties of creating cost-effective and energy-efficient transceiver hardware.
Reaching the Tbit/s goals in practice requires efforts from all research areas spanning from integrated circuit and antenna design up to communication signal processing and system development. This workshop brings together experts from diverse fields to present their latest work and advancements in THz and sub-THz technologies. Through presentations and interactive discussions, participants will explore ways to strengthen collaboration and address the most pressing challenges in THz communications. Cross-disciplinary cooperation offers the potential to overcome technical obstacles and ease design constraints through innovative co-design, paving the way for successful wireless communication at THz and sub-THz frequencies.
The workshop has two goals:

(a) to enhance synergies and cooperation among experts from different research fields, such as RF circuit design, hardware and channel modeling, communications engineering, and digital signal processing for subTHz and THz wireless communications.

(b) enhance the collaboration between EU projects, national projects, and projects in Japan to enable THz wireless communications in future systems.

One of the practical achievements from editions of the workshop is the Global Research Initiative on Wireless Terahertz (GROW-THz) project (Dec. 2024-Mar. 2029) , which brings together organizations from Japan, the EU, and the USA. We wish to see similar collaboration initiatives take place in the future.

Structure

14:00 – 15:30: Session 1: EU-Japan Collaboration in SubTHz and THz Transceivers
Chair:  Joonas Kokkoniemi

• Opening of the workshop: Kenta Umebayashi
• Introduction of session 1 & introducing the keynote: Joonas Kokkoniemi
• Keynote 1 EU-Japan Collaboration: The ThoR success story and its follow-on activities – Prof. Thomas Kürner, (Technische Universität Braunschweig, DE), Tetsuya Kawanishi (Waseda University, JP): 25min + 5min Q/A
  In the years 2018-2022 Horizon 2020 joint EU-Japan project ThoR (“TeraHertz end-to-end wireless systems supporting ultra-high data Rate applications”) focused on demonstrating the application of 300 GHz backhaul and fronthaul links. In this project four partners from Japan and seven partners from the EU covering industry, research institutes and academia have cooperated and managed to successfully set-up a bi-directional 300 GHz link using components from all four participating countries. A net data rate of 2 × 20 Gbps over a distance of 150 m using a total instantaneous bandwidth of 8.64 GHz has been achieved. Furthermore, the demonstrator showed also that the IEEE Std 802.15.3-2023 protocol works correctly for this application. To complement this hardware demonstrator, software simulators, planning methods and antenna measurement techniques have been developed. Both in the EU and Japan the results and components of ThoR have been used in follow-on projects. Many partners are now continuing their successful cooperation within the ASPIRE programme. His talk will give a brief overview on this successful EU-Japan collaboration.
• Technical Talk 1 Wideband PCB characterization and calibration techniques up to 150 GHz – Michael Gadringer, Arash Arsanjani, Ziad Hatab (C. Doppler Laboratory For Technology Guided Electronic Component Design And Characterization, Graz Univ.of Technology, AT): 15min + 5min Q/A
  Printed Circuit Boards (PCBs) are a key component of the electronic industry. As 6G communication systems will also operate at mm-wave frequencies, the traditional interconnects established on a PCB are employed over wider bandwidths and have to take over multiple tasks simultaneously. Comprehensive characterization of the PCBs is required to provide the parameters for state-of-the-art interconnect designs. This talk focuses on conducting wideband PCB measurements up to the mm-wave regime achieved on a probe station. These measurements provide the basis for the parameter extraction in various design processes. The properties of different PCB manufacturing technologies on the measurement process are highlighted in this context.
• Technical Talk 2 Development of High-gain Beam-scanning Antennas in Sub-THz band – Kunio Sakakibara, Yoshiki Sugimoto (Nagoya Institute of Technology, JP): 15min + 5min Q/A
  Long range communication is difficult in terahertz band because the received power decreases in inverse proportion to the square of the operation frequency. However, the gain of the antenna with the same physical aperture increases when the frequency becomes high. Therefore, the development of high-gain antennas is the first challenge in sub-terahertz band. Furthermore, as high-gain antennas narrow the beams, beam-scanning antennas are necessary to cover the required angular area for communication. Thus, high-gain, beam-scanning and low-loss feeding are key technologies in the development of sub-terahertz antennas.Lens antennas are advantageous in terahertz band since it is originally optical technology. The beam-scanning function can be realized by shifting the primary radiator from the focus of the lens. Planar arrays on printed substrate are popular to achieve both low-profile and high-gain antennas. Phased arrays can be composed of antenna elements with RF circuits. AiP (Antenna in Package) technique is a reasonable solution. An antenna is formed in the substrate on which the IC is mounted. The matching design of the connection between the IC and the substrate is necessary such as wire bondi ng or bump connection of flip-chip IC mounting. In the development of sub-terahertz antennas beyond 100GHz band, not only the antenna design techniques but also the material technologies for lens antennas and substrates, metal pattern manufacturing, IC chip mounting techniques are all important. Collaboration of these technologies in various areas are expected to apply the high-frequency techniques to the practical communication and sensing systems in this frequency band.
• Technical Talk 3  300-GHz-Band Phased-Array CMOS Transmitters for Wireless Communication Systems – Kyoya Takano (Tokyo Univ. of Science, JP): 15min + 5min Q/A
  The 300 GHz band is expected to be used in next-generation ultrahigh-speed, high-capacity communications because of its wide bandwidth available for communications. Beamforming and beam steering techniques are needed to increase the equivalent isotropically radiated power (EIRP) in 300 GHz wireless transmitters. Beamforming and beam steering usually use phased-array technology that can be electronically controlled. Antennas used for phased array need to have half-wavelength pitch spacing to prevent the generation of grating lobes, and the corresponding transmitter circuits must also be arranged at half-wavelength intervals. In this talk, I will introduce a two-dimensional (2D) phased-array transmitter proposed by our group in the 300 GHz band with an antenna pitch approximately half the wavelength in the atmosphere. The proposed transmitter consists of a CMOS transmitter integrated circuit chip and an array antenna on a printed circuit board. Only the mixer parts of the CMOS transmitter integrated circuit, which output RF signals, constitute the grid array. The output phase of each RF mixer is controlled by phase shifters in the LO and IF paths located outside the grid array. The pitch of the grid array of CMOS transmitter integrated circuits is expanded to twice the antenna pitch by using interpolated feed antennas for the antenna elements of the array antenna. For demonstration purposes, a 3 ´ 3 2D phased array transmitter is fabricated using a 40 nm CMOS process.

Coffee break

 16:00 – 17:30: Session 2: SubTHz/THz topics in EU projects
Chair: Nuutti Tervo

• Introduction of session 2 & introducing the keynote: Nuutti Tervo
• Keynote 2 mmW/THz Phased-Array Transceiver Design for 6G Era – Kenichi Okada , (Institute of Science Tokyo, JP): 25min + 5min Q/A
  In this presentation, theoretical background of millimeter-wave/THz communication will be introduced as well as design challenges of Sub-THz transceiver by CMOS. Sub-THz transceivers realized by 65nm CMOS technology will be introduced, including 300GHz-band 4-element phased-array transmitter by CMOS, D-band 640Gbps MIMO transceiver, and mmW Massive MIMO receiver.
• Technical Talk 4 6GTandem -Sub-THz innovation: enablers or obstacles for standardization – Liesbet Van der Perre, (KU Leuven, BE): 15min + 5min Q/A
  Immersive entertainment experiences and XR-enhanced professional education are only two examples of applications that could benefit from the great communication and positioning potential offered by the high-bandwidths available at mmwave and Sub-THz frequencies. This motivation has been clear and technological progress has been great for several decades. Yet, obstacles have been encountered on the road to reliable connectivity, standards and commercial success. The 6GTandem project adopts a novel perspective towards the deployment and operation of sub-THz systems: An infrastructure of dense distributed radio units exploiting RF over polymer microwave fiber (PMF) connections, is proposed. Dual-frequency protocols further support strong sub-THz links. This innovation opens perspectives to literally circumvent obstacles in space and frequency, and eventually unleash the potential of the sub-THz bands.
• Technical Talk 5 THz and Sub-THz research in 6GFlagship and related EU projects – Joonas Kokkoniemi, (Univ. of Oulu, FI): 15min + 5min Q/A
  The THz research has been declining with the beginning of 6G standardization. The primary reason is that the THz has proven to be hard to implement on access networks. However, there are plenty of applications where millimeter wave (mmWave, 30—300 GHz) and THz (>300 GHz) can offer great benefits. Such examples are fixed wireless links like backhauls, applications where accurate sensing is required, and satellite communications. On top of these, it is likely that the later revisions of 6G and beyond will explore higher frequencies for access networks. The potential of high frequencies in these applications have kept THz relevant. There are very large numbers of research activities globally regarding THz communications. This talk will give an overview of the THz activities in 6G Flagship and EU funded projects.
• Technical Talk 6 Energy efficiency aspects from PA models to AR/VR applications in Hexa-X-II and 6G SHINE projects – Abdur Rahman Mohamed Ismail (IMEC): 15min + 5min Q/A
  Energy efficiency is a key challenge in 6G systems, especially for power-intensive components like power amplifiers (PAs) and high-throughput applications such as AR/VR. Based on state-of-the-art sub-THz PA designs, we propose power and non-linearity models across different technologies to support link budget analysis and system performance evaluation. Virtual reality (VR) demands high data rates to support high-quality video transmission. In the 6G sub- network, the sub-THz is a potential candidate for the VR application. At those frequencies, the small wavelength of THz signals enables the realization of the integration of a larger number of antennas compared with mm-wave or low band frequency. How to optimize the power consumption for the access point (AP) and head-mounted displays (HMDs) in the sub-THz band has not yet been studied in the literature. We present a simulation framework for evaluating the power consumption of sub-THz multi-user MIMO VR systems, incorporating PA-aware power modeling. An optimization problem is formulated to minimize the average power consumption of the AP and/or HMDs while meeting throughput and BER requirements. We explore trade-offs between complexity and power for various VR configurations, including video resolutions, compression schemes, and antenna setups. Additionally, we assess computation offloading from HMDs to APs as a strategy to reduce energy usage in battery-constrained devices.
• Closing: Kenta Umebayashi