Joint time delay and frequency offset estimation scheme for multiple ONUs' activation in point-to-multipoint coherent...

Area of Science:

• Optical Networking
• Telecommunications Engineering
• Signal Processing

Background:

• Coherent passive optical networks (PONs) utilizing digital subcarrier multiplexing (DSCM) are key for next-generation access networks.
• Time and frequency division multiple access (TFDMA) enhances flexibility and efficiency in PONs.
• Efficient optical network unit (ONU) activation is critical for upstream synchronization without impacting latency.

Purpose of the Study:

• To propose a novel ONU activation method for TFDMA coherent PONs.
• To enable joint estimation of time delay and frequency offset during ONU activation.
• To ensure ONU activation does not introduce significant delay or degradation to upstream data transmission.

Main Methods:

• A registration signal combining Zadoff-Chu and Gold sequences is transmitted with data, eliminating the need for a quiet window.
• Time delay and frequency offset are estimated at the receiver by calculating correlation values of the registration signal.
• Successive interference cancellation is employed to support simultaneous registration of multiple ONUs.

Main Results:

• The proposed scheme achieves a time delay estimation accuracy of 1 ns and frequency offset estimation accuracy of 1 MHz.
• Experimental validation in a 6x10 GHz subcarrier coherent PON system confirms the method's effectiveness.
• The activation scheme introduces no additional delay for upstream signal transmission with an SNR penalty below 0.2 dB.

Conclusions:

• The novel ONU activation method is effective for TFDMA coherent PONs.
• The scheme meets stringent latency requirements for next-generation access networks.
• Accurate and efficient ONU activation is achievable without compromising upstream data transmission quality.