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Efficient Uplink Configuration for 6G Fronthaul in Photonic Terahertz Communications via Optical Carrier Sharing Scheme
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- Citation
- IEEE Transactions on Terahertz Science and Technology, Early Access
- ISSN
- 2156-342X
- Publisher
- IEEE
- Language
- English
- Type
- Journal Article
- Abstract
- In this paper, we present an uplink architecture for photonic terahertz (THz) fronthaul based on optical carrier sharing in a 300-GHz optical-heterodyne system. In the considered active remote antenna unit (RAU), a local laser is already required as the optical local oscillator (LO) for THz generation by photomixing. We exploit this mandatory LO in a dual role: one portion is used for downlink photomixing with a uni-travelingcarrier photodiode (UTC-PD), while the remaining portion serves as the optical carrier for uplink data modulation. This removes the need for a dedicated uplink light source and its associated control overhead at the RAU without increasing the number of active components in the uplink branch. To assess bidirectional robustness over a single-fiber link, we develop a closed-form Rayleigh-backscattering (RB) return-power model and derive optical signal-to-interference ratio (SIR) expressions for both the intensity-modulation/direct-detection (IM/DD) uplink and the UTC-PD-based downlink, revealing asymmetric uplink/downlink impairment behavior and the resulting bidirectional operating trade-off. We experimentally validate simultaneous bidirectional transmission using downlink orthogonal frequency-division multiplexing (OFDM) and uplink discrete Fourier transform (DFT)-spread OFDM over a 1-m 300-GHz wireless link and up to 20-km single-mode fiber. Within the stable operating region identified by the RB/SIR analysis, no significant coexistence penalty is observed in either direction. Reliable 20-Gb/s transmission over 20-km SMF is demonstrated in both directions. We further quantify dispersion-induced power fading and its impact on achievable baud rates. Finally, an end-to-end wireless link-budget analysis indicates that the current reach is primarily limited by the THz receiver front-end sensitivity and free-space path loss, rather than by the optical fronthaul itself, suggesting scalability as THz front-end technology improves.
- Keyword
- 6G, bidirectional transmission, fronthaul, optical heterodyning, radio-over-fiber, Rayleigh backscattering, Terahertz communications
- KSP Keywords
- Active components, Bidirectional transmission, Data modulation, Dispersion-induced power fading, Dual role, End to End(E2E), Fiber link, Fourier transform(FT), Intensity-modulation/direct-detection(IM/DD), Light sources, Local Oscillator