Power-Division Non-Orthogonal Multiple Access (NOMA) in Flexible Optical Access With Synchronized Downlink/Asynchronous Uplink

The data traffic in optical access networks increases dramatically, driven by wired and wireless services. Limited by the available bandwidth with low-cost optical and electrical devices, modulations and multiple access schemes with higher spectral efficiency are desirable. The current time-division multiplexing and wavelength-division multiplexing cannot fulfill the requirement due to the low spectral efficiency and high cost. The multistack flexible optical access network shows its benefit by low cost, reduced fiber deployment, increased flexibility, and ultra-high network extension capability. With varying path losses to different users, the network performance is significantly limited by users with high path losses generated by more couplers or long fibers. These users cannot have good service qualities using the existing multiple access schemes. We propose to use the power-division non-orthogonal multiple access with synchronized downlink and asynchronous uplink. The performance and reliability are significantly improved for high path loss users, by optimizing all users as a group and adjusting the power ratio adaptively. In the uplink, the asynchronous transmission enables low latency and simple DSP in optical network units. The simulation shows a significantly better performance. And the proposed scheme is experimentally demonstrated by our testbed with 2.5-dB increased power margin in synchronized downlink and one-order-of-magnitude BER floor reduction in asynchronous uplink.