A Novel Pilot-Aided Timing Recovery Algorithm With High Tolerance to Impairments for OQAM-Based Digital Multi-Band Systems

Timing recovery (TR) plays an important role in the digital signal processing (DSP) of coherent receivers. In TR, timing error (TE) is extracted by the timing recovery algorithm (TRA) and fed back to adjust the clock sampling phase. However, widely-used Gardner and Godard TRAs are sensitive to spectral roll-off factor and differential group delay (DGD), and more importantly, are inapplicable to the offset quadrature amplitude modulation (OQAM) system. In this paper, we propose a novel pilot-aided TRA for the OQAM-based digital multi-band (OQAM-DMB) system, which is robust to different impairments including rotation of state of polarization (RSOP), DGD, spectral roll-off, residual chromatic dispersion (rCD), residual carrier frequency offset (RFO), and laser linewidth. 1.12-Tbit/s simulations and 320-Gbit/s experiments show that OQAM-DMB based on the proposed algorithm works properly for all spectral roll-off factors and exhibits excellent tolerance against DGD, RSOP, rCD, RFO, and laser linewidth, and outperforms QAM-DMB using conventional TRAs. The digital phase-lock loop can be locked for the clock frequency offset within ±80 ppm and all initial sampling phase offsets. Although investigated in OQAM-DMB, the proposed algorithm is also applicable to conventional QAM-DMB.