Sequence-domain enhanced NOMA scheme for hollow-core fiber and W-band seamless integrated transmission

This paper proposes a sequence-domain enhanced non-orthogonal multiple access (NOMA) scheme for hollow-core fiber (HCF) and W-Band seamless integrated transmission. In contrast to traditional power-domain NOMA that processes symbols on a symbol-by-symbol basis, the proposed scheme aggregates multiple consecutive quadrature phase shift keying (QPSK) symbols into high-dimensional sequences and maximizes the minimum Euclidean distance among the selected sequences through a subset selection process based on an annealing algorithm. This scheme combines sequence-level modulation with successive interference cancellation (SIC), effectively suppressing error propagation under low signal-to-noise ratio conditions while preserving the spectral efficiency of power-domain NOMA. Experiments in a photonics-assisted W-Band fiber-terahertz integrated system with 60 km HCF show that the optimal power division ratio (PDR) is 4 and the peak-to-peak voltage (Vpp) is 350 mV. At the same net rate, the proposed sequence-domain enhanced NOMA scheme achieves a 0.59 dB bit error rate (BER) gain over traditional NOMA at the 20% soft-decision forward error correction (SD-FEC) threshold. Selecting 16 sequence points has a BER performance improvement of 0.53 dB compared to selecting 32 sequence points. Moreover, under identical conditions, HCF outperforms standard single-mode fiber (SSMF) due to its lower nonlinearity and attenuation. The proposed scheme effectively enhances multi-user access reliability and adapts to channel conditions, providing a feasible technical path for future long-distance, high-capacity integrated transmission.