Time-domain low-complexity clock recovery for non-integer oversampled Nyquist signals with a small roll-off factor

Area of Science:

• Optical Communications
• Signal Processing

Background:

• Short-reach, high-speed inter-datacenter transmission systems require reduced transceiver power consumption and cost.
• Existing clock recovery algorithms (CRAs) struggle with non-integer oversampling factors (OSFs) below two and small roll-off factors (ROFs).
• Current CRAs lack hardware-efficient timing phase error detectors (TPEDs) for these challenging signal conditions.

Purpose of the Study:

• To develop a low-complexity timing phase error detector (TPED) for clock recovery algorithms (CRAs).
• To improve the performance of CRAs for non-integer oversampled Nyquist signals with small roll-off factors (ROFs).
• To enable reduced oversampling factors (OSFs) and component costs in high-speed optical communication systems.

Main Methods:

• Proposed a novel, low-complexity TPED by modifying the time-domain quadratic signal.
• Reselected the synchronization spectral component for improved timing error detection.
• Combined the proposed TPED with a piece-wise parabolic (PWP) interpolator for feedback CRAs.

Main Results:

• The improved CRA significantly enhances performance for non-integer oversampled Nyquist signals with small ROFs.
• Receiver sensitivity penalty remained below 0.5 dB even with OSF reduced to 1.25 and ROF down to 0.001.
• Demonstrated effectiveness for 45 GBaud dual-polarization Nyquist 16QAM signals.

Conclusions:

• The proposed low-complexity TPED effectively addresses limitations of existing CRAs for non-integer OSFs and small ROFs.
• This advancement facilitates reduced OSF and ROF, leading to lower power consumption and cost in short-reach optical systems.
• The developed CRA offers a practical solution for next-generation high-speed data transmission.