Unlocking the THz Frontier: How 6G Will Harness Terahertz Waves for Ultra‑Fast Wireless

Chapter 1 Introduction

Terahertz (THz) waves occupy the spectral region between microwaves and optical waves, with frequencies from 0.1 THz to 10 THz and wavelengths from 3 mm to 30 µm. The broad, continuous bandwidth can support Tbit/s data rates, making the THz band a focal point for next‑generation wireless (6G) research, with commercial deployment expected around 2030. THz waves also show great promise for imaging, spectroscopy, and sensing.

Understanding this frequency range requires interdisciplinary research that bridges RF electronics, high‑frequency semiconductor technology, and photonic approaches. This white paper concentrates on 6G communications, summarizing THz fundamentals and application characteristics.

Chapter 2 Towards the Next Wireless Standard – 6G

2.1 From 5G to 6G – Vision and Key Technologies

National 5G networks have enabled new services such as enhanced mobile broadband (eMBB), ultra‑reliable low‑latency communication (URLLC), and massive machine‑type communication (mMTC). While 5G will evolve through 3GPP Release 18, academia and industry have already begun researching the foundations of 6G, targeting commercial rollout around 2030.

The ITU‑R 5D working group started drafting the IMT‑2030 vision in 2021, defining the framework and goals for future IMT (to be called “6G”). The first set of 3GPP specifications is expected in 2023/2024, with performance requirements defined, and standardization work beginning in 2026/2027.

Potential 6G use cases include holographic communication, extended reality (XR), and digital twins, all demanding extremely high data rates and ultra‑low latency. The vision is a seamless cyber‑physical fusion where devices, humans, and the digital world interconnect, requiring sensors and actuators to transmit and process data at very high rates securely.

Table 1 defines 6G KPI targets, which are 10‑100× more stringent than 5G, introducing new metrics such as latency jitter for time‑sensitive industrial control.

New 6G standards will be human‑centric and sustainable, addressing energy consumption and operational expenditures (OPEX) while providing affordable, scalable services to remote areas.

2.2 6G Research Areas

Figure 1 outlines the identified 6G research domains, including disruptive technologies that could exceed the Shannon limit.

Ultra‑high‑speed channel coding – Existing codes (Turbo, LDPC, Polar) must be enhanced to meet the extreme throughput, reliability, and low‑power requirements of 6G.

New waveforms and multiple access – While OFDM remains a strong candidate, alternative waveforms (e.g., OTFS) and non‑orthogonal multiple access (NOMA) are under investigation to accommodate diverse spectrum, device, and system constraints.

Massive MIMO – Higher frequencies and shorter wavelengths demand denser antenna arrays to compensate for increased path loss.

New network topologies – Cell‑free networks, aerial platforms (HAPS), and non‑terrestrial networks (NTN) aim to provide low‑loss, short‑range links with redundancy, extending coverage to remote, maritime, and space environments.

Terahertz communication and sensing – THz bands (100 GHz – 3 THz) offer multi‑GHz bandwidth for ultra‑high‑speed links and high‑resolution sensing, including joint communication‑sensing (JCS) concepts that integrate radar‑like capabilities.

Photonics and visible light communication (VLC) – Photonic technologies provide high‑bandwidth, low‑cost alternatives to RF, with LiFi enabling indoor high‑speed links using LED modulation.

Reconfigurable intelligent surfaces (RIS) and metamaterials – RIS can steer and focus wireless energy, effectively creating programmable propagation environments that may extend beyond the Shannon limit.

Distributed computing and AI – 6G will rely on distributed processing, neuromorphic computing, and AI‑driven network control to meet stringent performance and energy targets.

Chapter 3 THz Wave Properties and Applications

3.1 New 6G Spectrum: Millimeter‑Wave and Terahertz

5G uses up to 400 MHz carrier bandwidth in the millimeter‑wave range. 6G aims to exploit the sub‑THz and THz bands (above 100 GHz) to achieve multi‑GHz continuous bandwidth, dramatically increasing channel capacity according to the Shannon‑Hartley theorem.

Figure 2 shows the allocation of 5G and prospective 6G spectrum, highlighting FR1 (≤ 71 GHz), FR2 (71 GHz – 71 GHz), and the D, G, H/J bands (110 GHz – 330 GHz) under consideration for 6G.

3.2 THz Applications

Spectroscopy and imaging – THz spectroscopy can identify chemicals, pharmaceuticals, and explosives via unique spectral fingerprints, while THz imaging penetrates non‑metallic, non‑polar materials without ionizing radiation.

Communication – Exponential data traffic growth drives the need for Tbit/s links; THz offers the required bandwidth.

Sensing and positioning – Joint communication‑sensing enables high‑resolution radar‑like environmental mapping and centimeter‑level localization for industrial control, robotics, and VR.

Chapter 4 THz Generation: Electronic and Photonic Techniques

4.1 From Electronics to Photonics

Over the past two decades, THz research has bridged the gap between microwave electronics and photonics, attracting attention for sensing, imaging, and data communication.

4.2 Closing the “THz Gap”

Generating continuous, directional THz radiation remains challenging due to high losses and carrier velocity limits in electronic devices, and the lack of suitable low‑bandgap materials for photonic devices.

4.3 THz Radiation Sources

Three main approaches:

Electronic sources – Frequency multipliers, resonant tunneling diodes (RTD), and MMICs provide compact, room‑temperature operation but limited efficiency at THz frequencies.

Photonic sources – Quantum cascade lasers (QCL) and nonlinear optical processes can generate THz photons, often requiring cryogenic cooling.

Hybrid electro‑optical methods – Photomixing in UTC‑PD or PIN photodiodes converts two near‑infrared lasers into THz radiation, offering wide tunability.

4.4 Photomixing and Optical Down‑Conversion

Two continuous‑wave lasers (ν₁, ν₂) are combined in a fast photodiode; the beat frequency ν_THz = |ν₁ – ν₂| generates THz radiation. This method provides broad tunability and can be integrated with existing fiber‑optic infrastructure.

Chapter 5 Millimeter‑Wave and THz Semiconductor Technologies

Advancing to frequencies above 100 GHz demands semiconductor technologies with high electron mobility, saturation velocity, breakdown field, and thermal conductivity.

Key material families:

III‑V compounds (GaAs, InP, GaN) – Offer high electron mobility and large bandgaps; GaN on SiC or Si provides high power and thermal performance.

SiGe HBTs and BiCMOS – Combine high‑speed analog performance with CMOS digital integration.

Figure 24 compares material parameters; Figure 25 summarizes state‑of‑the‑art mmWave power amplifiers up to 500 GHz.

Chapter 6 Channel Measurements Above 100 GHz

Accurate channel models are essential for 6G system design. Measurements were performed at 158 GHz, 300 GHz, and up to 325 GHz in outdoor street‑canyon (UMi) and indoor atrium scenarios using time‑domain channel sounding with wideband (2 GHz) chirp sequences.

Key findings:

Path‑loss follows the free‑space model when directional antennas with fixed effective aperture are used, mitigating the frequency‑dependent loss.

Outdoor measurements (10 m – 170 m) show clear line‑of‑sight (LOS) components and multipath clusters, with similar total received power at 158 GHz and 300 GHz.

Indoor atrium measurements reveal richer multipath, increasing total received power despite higher frequency.

Figures 27‑33 illustrate system block diagrams, CIRs, and angle‑resolved power maps.

Chapter 7 Conclusion

Terahertz technology is a potential cornerstone of 6G, promising Tbit/s throughput, ultra‑low latency, and new use cases in communication, spectroscopy, imaging, and sensing. Commercialization will require continued advances in semiconductor devices, photonic integration, and robust channel models. The upcoming WRC 23 will shape the spectrum allocation agenda for future 6G deployments.

Chapter 8 References

[1] “5G Evolution and 6G,” NTT DOCOMO, White Paper, Jan 2022. [2] “Key drivers and research challenges for 6G ubiquitous wireless intelligence,” University of Oulu, 2019. … (remaining references omitted for brevity)