Dual-pilot phase recovery with pair-wise maximum-ratio combining for coherent PONs

Area of Science:

• Optical Communications
• Digital Signal Processing

Background:

• Non-orthogonal multiple access (NOMA) combined with digital subcarrier multiplexing (DSCM) offers dense and flexible coherent passive optical networks (PONs).
• NOMA signal superposition introduces biases in pilot-aided carrier-phase recovery (CPR), and bandwidth limitations affect edge subcarriers.

Purpose of the Study:

• To propose a unified digital signal processing (DSP) framework to address NOMA-induced phase bias and transceiver limitations in coherent PONs.
• To improve the robustness and performance of carrier-phase recovery and signal detection in NOMA-DSCM systems.

Main Methods:

• A unified DSP framework incorporating dual-pilot CPR with pair-wise maximum-ratio combining (MRC) across adjacent subcarrier pairs.
• Inserting pilots into both NOMA signals to create a composite pilot reference, suppressing interference-induced phase bias.
• Utilizing a reliability estimate for weighting subcarrier branches in MRC to achieve diversity gain.

Main Results:

• The dual-pilot CPR demonstrated more robust phase recovery compared to conventional methods under NOMA interference.
• The proposed framework achieved up to 2.29 dB Signal-to-Interference-plus-Noise Ratio (SINR) gain at low optical power.
• Average Bit Error Rate (BER) was reduced by 75.89% for ONU 1 and 30.33% for ONU 2.

Conclusions:

• The proposed unified DSP framework effectively mitigates NOMA-induced phase bias and transceiver penalties in coherent PONs.
• Dual-pilot CPR and MRC significantly enhance phase recovery robustness and overall system performance.
• The framework offers substantial SINR gain and BER reduction, enabling more reliable data transmission in high-density optical networks.