  We proposed and experimentally demonstrated a new hybrid code structure based
on the overlapping of two light sources to produce the effect of multi-voltage
amplitudes. And we also proposed an efficient polarity reversal threshold (RRT)
algorithm for multilevel based OCC system. Then taking the issue of SPO into
account, a novel adaptive sampling method (ASM) is proposed, which can
effectively alleviate the problem of SPO and further enhance the performance of
multilevel OCC. It is demonstrated that a data rate of 8.4 Kbit/s can be
achieved by applying the proposed two algorithms.
