| When messages pass through the channel impaired by insertion, deletion, and substitution errors, due to the unknown positions of random errors in the received data sequence, and these errors are independent of each other, therefore it is difficult to correct these errors. But in some practical systems, such as bit-format media, insertion/deletion channel is frequently used, so encoding and decoding technologies under insertion/deletion channels have attracted people’s great research interest. Low density parity check(LDPC) code, due to its low decoding complexity and good error correction capability, is widely used in the insertion/deletion channels encoding and decoding technologies.This paper mainly focus on the encoding and decoding technologies algorithms under insertion/deletion channels, elaborates the bit-level synchronization and symbol-level synchronization schemes, and on this basis, an improved bit-level synchronization schemes is given. The main work of this paper are summarized as follows:1. The development process and current research of LDPC code and insertion/deletion channels are introduced, and a detailed analysis of the possible type of errors when messages pass through the channels may occur are given, including two decoding algorithm for LDPC codes.2. The MAP detection process of bit-level synchronization is analyzed in detail and the mathematical formula which is used to compute MAP is derived according to the forward backward algorithm. In order to use the correlation between different bits, we present a new symbol-level synchronization coding method, and the superiority of this method is proved by simulation results.3. An improved method of bit-level synchronization is given, this method uses adaptive marker, whose value is determined depending on the neighboring bits of the codeword. The simulation results show that the improved method can indeed improve synchronization performance and reduce the error rate. |
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