Pilot-Tone Assisted Successive Interference Cancellation for Uplink Power- and Frequency-Division Multiplexing Passive Optical Network

Frequency division multiplexing (FDM) passive optical network (PON) is considered as a competitive solution for 5G-advanced and 6G mobile fronthaul (MFH) to support multiple radio units (RUs) with shared trunk fiber and distributed unit (DU). However, it is likely to cause uplink signal overlapping by laser wavelength drift, and guard bands should be reserved between FDM channels, which limits the spectral efficiency (SE). In this work, we propose to aggregate multiple uplink FDM channels using power division multiplexing and jointly adopt successive interference cancellation (SIC) at the receiver to improve the uplink SE. We first theoretically derive the SE of such power- and frequency-division multiplexing (PFDM) PON with both guard band and SIC together, and reveal that PFDM PON can achieve higher SE than the pure FDM PON with guard band only. Focusing on the case of two overlapped uplink signals, we propose a pilot-tone assisted SIC to improve the estimation accuracy of frequency offset and phase noise in heavily overlapped uplink signals. In the proof-of-concept experiments, compared to the orthogonal case without considering the guard band, 0.29 bit/s/Hz SE penalty due to the residual interference after SIC is observed when two uplink signals are completely overlapped. The results showed that, in the presence of laser drift, PFDM PON becomes more spectrally-efficient than FDM PON when the relative wavelength drift exceeds 20% of the signal bandwidth.