Spectrally Efficient and Robust AGFB-OFDM Design for Q-Band Photonic-Assisted mmWave Communication

Orthogonal frequency division multiplexing (OFDM), a key modulation for 6G, faces scalability challenges in ultra-wideband transmission due to constraints on subcarrier spacing and the maximum size of the inverse fast Fourier transform (IFFT) in 3GPP specifications. To overcome this, we propose an adaptive generalized filter bank OFDM (AGFB-OFDM) scheme that supports ultra-wideband communication while achieving high spectral efficiency, low complexity, and flexible system configuration. Compared with conventional GFB-OFDM, which alleviates CP-OFDM’s out-of-band leakage and bandwidth limitations via IFFT decomposition and subband filtering, AGFB-OFDM further addresses the spectral efficiency loss caused by frequency-domain double sampling. By incorporating a joint adaptive filter modeling mechanism, it ensures accurate alignment between filter response and signal characteristics, significantly improving spectral efficiency. The proposed scheme is experimentally validated in a photonics-assisted millimeter-wave (MMW) communication system comprising a 10 km optical fiber and a 1 m wireless link. The results demonstrate that AGFB-OFDM outperforms conventional CP-OFDM and GFB-OFDM in terms of bit error rate (BER) and spectral efficiency. Furthermore, we propose and evaluate a dynamic subband bandwidth allocation strategy that effectively mitigates frequency-selective fading. This approach significantly enhances system robustness and stability under complex hybrid channel conditions while operating within fixed hardware constraints. To the best of our knowledge, this is the first experimental realization of such an adaptive filter bank modulation in a radio over fiber (RoF) system. This work demonstrates the potential of AGFB-OFDM in enabling robust and spectrally efficient optical-wireless integrated communications.