Physical Layer Service Fairness of 200-Gbps TDM-NOMA Coherent Passive Optical Networks Within Single Timeslot

As coverage increases or network topology becomes more complex, the optical path loss difference between any two access points in tree-like passive optical networks (PON) is uneven, causing service fairness problems at the physical layer. The service fairness of the far-near user access in 200-Gbps coherent PON with various user cases is discussed in this work. A fairness allocation mechanism based on time division multiplexing (TDM) non-orthogonal multiple access (NOMA) in the time-power domain is proposed theoretically to provide fair transmission between the arbitrary two optical network units (ONUs) with the best and the worst performance within single timeslots. Then, a series of subsequent experiments are performed with different path loss and split ratios (SR) to prove the effectiveness and practicality of the proposed NOMA scheme, totally including 12 subcases. Any sub-experiment proves that by optimizing power allocation, the signal-to-interference noise ratio (SINR) or bit-error rate (BER) on the physical layer can be approximated to the same value. The Jain's fairness index at a fixed and flexible hard-decision forward error correction (HD-FEC) standard, and modified fairness index are used to evaluate service fairness in different cases. This TDM-NOMA scheme may address the service fairness issue in next-generation coherent PON with wide coverage.