Research On Rateless Encoding Technology Of QC-LDPC And DVB-S2 Standard LDPC Codes Based On Kite Codes Over AWGN Channel In Awgn Channel

Channel coding technology has been rapidly developed since Shannon expatiated on the reliable communication methods over noisy channels in 1948. So far, low-density paritycheck(LDPC) codes are recognized as “good codes” which are most close to the Shannon limit for its excellent performance in practical engineering applications, and have attracted extensive attention of researchers both at home and abroad. Due to the different characteristics of the parity check matrix and encoding algorithm, there appeared many different codes derived from LDPC codes, for example, the quasi cyclic low density parity check(QC-LDPC) codes and the LDPC codes in the DVB-S2 standard studied in this thesis, of which the parity check matrices are different and coding methods are also different.LDPC codes and other traditional error correcting codes have a fixed rate, but the fountain codes have broken the shackles and achieved a way of rateless encoding by a steady flow of encoding symbols transmitted from the transmitter. The rateless characteristic of fountain codes can enhance the effectiveness of information transmission by adaptively adjusting the coding rate according to the channel state without channel state information at the transmitter. Kite code is a kind of fountain codes of excellent performance, and is also applicable to more general channel.The purpose of this research is to combine the fountain codes with high effectiveness and LDPC codes with high reliability to play their respective advantages, and improves the reliability and effectiveness of information transmission. The traditional QC-LDPC codes and the LDPC codes in DVB-S2 standard have a variable coding rate, but not rateless. The algorithm proposed in this thesis, can achieve the rateless encoding and decoding like fountain code.The conventional Belief Propagation(BP) iterative decoding algorithm is not applicable to the LDPC codes encoded in a rateless way, so in this thesis, an enhanced BP algorithm is proposed for decoding the rateless LDPC codes. Simulation and implementation of two rateless LDPC codes are achieved over AWGN channel, and the BER performance is good. Finally, the simulation results show that this kind of rateless encoding and decoding algorithm is right and practical.The main contribution of this thesis is that the deficiencies of random and semi random encoding Kite codes is discussed, and then the rateless encoding and decoding algorithms of QC-LDPC codes and the DVB-S2 standard LDPC codes are proposed based on Kite codes. The parity check matrix of QC-LDPC codes and DVB-S2 standard LDPC codes have a characteristic of cycle row or cycle column, so in practical situations, the storage requirements of rateless encoder is acceptable, and the proposed rateless coding algorithm of this two codes has practical significance.