5G exhausted the easy spectrum. To reach the terabit-per-second rates targeted for 6G, research has moved into the terahertz (THz) band (0.1–10 THz), which offers tens of gigahertz of contiguous bandwidth — far more than millimetre-wave. The catch is propagation: THz waves suffer huge free-space spreading loss and are absorbed by atmospheric water vapour.
Working principle
Channel capacity scales with bandwidth (Shannon), so the vast THz bandwidth enables extreme data rates over short ranges. To overcome the loss, systems use ultra-massive MIMO with hundreds of antenna elements and highly directional pencil beams. Generating THz signals relies on photonics-based sources (photomixing of two lasers in a UTC photodiode) or electronic frequency multipliers on advanced SiGe/InP processes.
| Parameter | mmWave (5G) | THz (6G) |
|---|---|---|
| Frequency | 24–100 GHz | 0.1–10 THz |
| Bandwidth | Up to ~2 GHz | Tens of GHz |
| Peak rate | ~10 Gb/s | ≥ 100 Gb/s – 1 Tb/s |
| Range | 100s of m | Metres – tens of m |
| Main loss | Blockage | Spreading + molecular absorption |
Key insightTHz absorption peaks (water lines) actually create secure, short-range channels and define usable transmission windows — turning a limitation into a design parameter.
Applications
- Wireless data-centre and backhaul links at fibre-like rates
- Kiosk / proximity terabit downloads and AR/VR tetherless headsets
- Joint communication-and-sensing (THz imaging, spectroscopy)
References & further reading
- Akyildiz et al., “Terahertz band communication: An old problem revisited and research directions,” IEEE Trans. Comms, 2022.
- Rappaport et al., “Wireless Communications and Applications Above 100 GHz,” IEEE Access, 2019.
- ITU-R Vision for IMT-2030 (6G), 2023.