Combining SEFDM Technique With IBFD Communication System in an ROF Link for Achieving Ultra-High Spectral Efficiency

Oriented to the requirements of future high-frequency wireless communication systems, this paper proposes a method of combining spectrally efficient frequency-division multiplexing (SEFDM) technique with the in-band full-duplex (IBFD) communication system and applying it to microwave photonic transmission links to achieve ultra-high spectral efficiency. The microwave photonic link not only realizes the transmission of SEFDM signals received by the IBFD system but also realizes the analog self-interference cancellation (SIC) function. The digital SIC and SEFDM demodulation functions are seamlessly integrated following the analog SIC. Utilizing a cross-iterative algorithm, the adverse effects of the signal of interest (SOI) on the digital SIC of the received signal are mitigated, leading to a substantial improvement in both the SIC depth and demodulation performance of the SEFDM signal compared to the conventional least squares (LS) algorithm. An experiment has been conducted. The SOI and self-interference (SI) have symbol rates of 300 Msym/s and 600 Msym/s, respectively, and share a center frequency of 2 GHz and a bandwidth compression factor of 0.8. When the SI to SOI power ratio is 10.3 dB, the analog SIC depth is around 18.3 dB. The conventional LS algorithm achieves a digital SIC depth of 12.6 dB but the error vector magnitude (EVM) is 13.2%. In contrast, our proposed iterative method improves the SIC depth to 15.1 dB and reduces the EVM to 4.1%. The feasibility of the system is also verified by incorporating a 25.2-km fiber.