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Fast Timing Acquisition for Low Signal-to-Noise Ratio High Density Optical Recording

Future optical data storage systems are expected to operate at significantly higher densities and lower signal-to-noise ratios (SNRs) than current systems. Partial response maximum likelihood (PRML) and iterative soft decoding methods are potential candidates for detecting data in such low-SNR, high-density channels. At such low SNRs, conventional timing acquisition methods suffer from not only large residual phase errors but also large frequency errors, leading to large timing jitter and high probability that the timing loop will lose lock during the tracking mode. To achieve rapid timing acquisition, an adaptive gains phase-locked loop (PLL) with a variable threshold timing loop detector is proposed and investigated in this study. Moreover, loss of lock rate (LOLR) is suggested as a measure to characterize the quality of the acquisition.