Research On Construction Of Structurized LDPC Codes With Big Girth In Deep Space Communication

In the 21 st century, deep space communication is facing more and more serious challenges with the continuous extension of deep space exploration, thus it's necessary to adopt channel coding technology with high gain to guarantee the reliability of information transmission. As a kind of high-gain channel coding technology, low-density parity-check(LDPC) codes have been widely concerned for their outstanding performance near Shannon limit and have broad application prospects in the field of deep space communication. Therefore, it's a worthy issue to design the LDPC codes which is suitable for deep space communication. The main works accomplished in this thesis are as follows:This thesis introduces the characteristic of deep space communication and the development of channel coding technology at first. And then, several common construction methods and encoding/decoding algorithms are analyzed in detail after the basic theory of LDPC codes is summaried. At last, according to the main factors affecting the performance of LDPC codes under the background of deep space communication, two novel approaches to construct QC-LDPC codes with big girth are proposed as following:1. Taking aim at the character of limited power resources and low SNR in deep space communication, a method to construct QC-LDPC codes with big girth based on Fibonacci sequence is proposed in this thesis. According to the features of Fibonacci sequence, the shift coefficients of exponent matrix are determined briefly by Fibonacci number through a mathematical expression, which could save required memory ulteriorly to deal with the feature of resource constraint in deep space communication. The QC-LDPC codes with girth-eight constructed by the above method improve the link gain in deep space channel and have good performance at low SNR. Simulation results indicate that our proposed codes reveal good error correction capability in deep space's Additive White Gaussian Noise channel, which provides a viable option for data's reliable transmission in future deep-space communication.2. In order to reduce the encoding complexity on the base of ensuring error correction performance in deep space communications, an approach to construct QC-LDPC codes with big girth and fast encoding characteristic is proposed in this thesis. The Chinese remainder theorem is adopted to construct the parity check matrix of QC-LDPC codes, together with the Independent Row-Column Mapping Sequence algorithm and dual diagonal structure for fast encoding. Theory analysis and simulation results show that our proposed codes could use the parity check matrix to encode directly as the existence of dual diagonal structure, and the girth is eight, so it's more suitable for practical deep space applications.