DSM-Based Ultra-Low-Latency ONU Activation for Uninterrupted TDM-PON Services

Next-generation mobile networks are expected to incorporate ultra-reliable low latency communication (URLLC). However, the activation and ranging process of Time division multiplexing passive optical network (TDM-PON) may provoke conflict to it. In this article, we innovatively use frequency to differentiate joining optical network units (ONUs) and propose a low-latency ONU activation method using delta-sigma modulation (DSM). On the ONU side, the frequency identity, namely electrical tone signal, is converted into binary sequence by DSM, which enables it to be sent directly by optical modules. The registration signal is directly superimposed on the regular upstream (US) burst of the online ONU. Thus, the US traffic does not need to be paused. On the optical line terminal (OLT) side, weak frequency identity information buried in mixed signals can be easily retrieved by coherent detection in the electrical domain with very simple analog devices. Proof of concept experiment results show that the sensitivity of registration signals is -58.3 dBm. When crosstalk ratio = -27dB, the interferometric crosstalk penalty is less than 0.1 dB. After 20 km transmission, the activation requests of different joining ONUs can be detected and distinguished without a quiet window nor degradation on the US traffic.