Efficient transmission schemes for correcting insertions/deletions in DPPM

Differential pulse-position modulation (DPPM) shows significant power and bandwidth efficiency in wireless optical communications and does not need symbol synchronization, but suffers from serious insertion/deletion errors if the low-complexity symbol-by-symbol detection is used. In this paper, the DPPM transmission scheme combining the watermark with the low-density parity-check (LDPC) code is proposed. Specifically, the equivalent source and channel models are developed to disclose the insertion/deletion characteristics. Then, trellis graphs are built based on the watermark and the equivalent source and channel models. On the trellis, Viterbi algorithm can be executed to convert the insertions/deletions to small number of substitutions, which can be finally recovered using LDPC codes. Simulation results reveal that the scheme performs well with the insertions and deletions introduced by low complexity symbol-by-symbol detection. The proposed method lays the feasibility of the practical applications of DPPM considering the complexity and significant performance.