Performance evaluation of GPON and XG-PON coexistence using CO-OFDM in fiber access networks

This research investigates the coexistence of Gigabit Passive Optical Networks (GPON) and Next-Generation Passive Optical Network (XG-PON) for access networks. Advanced modulation Coherent Optical Orthogonal Frequency Division Multiplexing (CO-OFDM) with 4 Quadrature Amplitude Modulation (4-QAM) is used for the XG-PON downstream to get a 10 Gbps data rate, and Non-Return to Zero (NRZ) modulation format is used for the upstream to get 2.5 Gbps. In contrast, for the GPON system, the NRZ modulation format is used to achieve 2.5 Gbps and 1.25 Gbps for both downstream and upstream, respectively. The network employs a 1:32 split ratio, accommodating 31 GPON users and one XG-PON user over a 20 km distance. To evaluate GPON performance, eye diagrams, Q-factor vs. distance, and received power vs. Log Bit Error Rate (BER) metrics were examined in both downstream and upstream. For XG-PON, constellation diagrams, optical signal-to-noise ratio (OSNR) vs. log BER, error vector magnitude (EVM) vs. power receiver, and power transmission vs. log BER were used to measure system performance for CO-OFDM downstream. Eye diagrams, Q-factor, and received power vs. Log BER estimation were employed for upstream analysis. Results demonstrate that the proposed system achieves robust performance and effective coexistence between GPON and XG-PON, ensuring high-quality service delivery across both technologies.