Investigation On Trellis-based Synchronization-error Correction Codes

Synchronization errors, including insertions and deletions in symbol level, occur in many communication and recording systems, such as Differential Pulse-Position Modulation(DPPM) and Bit Patterned Magnetic(BPM) recording. Researchers have proposed a variety of coding schemes to tackle with this problem. One of these schemes is using convolutional codes based on the modified trellis diagram, which can correct insertion, deletion, and substitution errors simultaneously. For insertion/deletion errors in DPPM, high effective decoding schemes based on trellis diagram of convolutional codes are designed in this thesis.For these special error patterns in DPPM, an iterative method with detection and decoding to correct synchronization errors is proposed. Based on the soft decision detection method and the Viterbi decoding method of convolutional codes, the presented scheme performs iteration between the soft decision detector and the pruned trellis diagram based Viterbi decoder, according to the fact that the chip lengths corresponding to different bit sequences entered DPPM modulator are not equal. Simulation results show that the proposed scheme can achieve lower frame error rate and provides a significant performance gain compared to the system without iteration.Furthermore, to improve the performance of the convolutional coding scheme in DPPM, a coding scheme using Reed-Solomon(RS) codes concatenated with convolutional codes is proposed for DPPM system. The inner decoder, which is the convolutional decoder, can correct synchronization errors, whereas the outer decoder, i.e. the RS decoder, can correct bursts of substitution errors caused by the channel and imperfect synchronization of the inner decoder. Simulation results show that, this scheme can correct the insertion, deletion and substitution errors in DPPM system.In summary, this thesis proposes an iterative detection and decoding method to correct synchronization errors in DPPM. Furthermore, a concatenated coding scheme with RS codes and convolutional codes is used in DPPM system.