Partial Transmit Subcarrier Technology Based on m-Sequence for Simplified PAPR Reduction in 400G TFDM Coherent PON

Coherent passive optical networks (CPONs) are emerging as a promising solution for future 200G and even 400G optical access network. Recently, time-frequency division multiplexing (TFDM) PON has been proposed as a solution to the flexibility challenge in CPON, providing more flexible bandwidth allocation for downstream access. Implementing TFDM PON through digital subcarrier multiplexing is a simple and efficient approach, but it increases the peak-to-average power ratio (PAPR) of the transmitted signal, thereby reducing the overall power budget due to the peak power constraints of digital-to-analog converters (DACs), and this issue worsens as the number of subcarriers increases. In our previous work, we proposed the Partial Transmit Subcarrier (PTSC) technique, which reduces PAPR in TFDM PON systems through subcarrier phase rotation. In this work, we propose an m-sequence-based PTSC (m-PTSC) scheme that optimizes phase factor selection to reduce computational complexity. For 4- and 8-subcarrier systems, the proposed method reduces the number of phase factors by 93.75% and 99.90%, respectively. Experimental validation in a 400-Gbps TFDM PON system shows that m-PTSC reduces PAPR by 2.9 dB and improves the power budget by 0.95 dB in the 4-subcarrier system, while in the 8-subcarrier system, m-PTSC achieves a 5.5-dB PAPR reduction and a 2.14-dB power budget improvement, all with only 0.6% protection overhead and pilot.