Feedforward Phase Estimation for Real-Time PTBC Decoding in High-Speed Optical Access Networks

The surge in data demand fueled by data hungry applications has driven the need for enhanced capacity in sixth-generation (6G) mobile technology. To address this, single-polarization coherent receivers with polarization-time block coding (PTBC) have been proposed. However, the feedback structure of the conventional PTBC decoder may result in phase estimation performance degradation, particularly in high parallelism systems. In this study, we propose a novel PTBC decoder with a feedforward phase estimation suitable for real-time implementation. The approach combines coarse phase estimation, using the phase difference between pilot symbols, and fine phase estimation using blind phase search (BPS), enabling feedforward phase estimation and accurate and rapid phase tracking. We experimentally validate its effectiveness in 16-QAM transmissions, addressing high parallelism and phase estimation challenges. The line data rate of 240 Gbps has been successfully transmitted across a distance of 20 km. The results pave the way for the realization of high-speed single-polarization transmission systems employing PTBC coding techniques.