Studies On LDPC And Its Application In OFDM Systems

The needs of wireless communication service grow rapidly at modern society, it hopes that the wireless communication can provide high transmission qualities and huge transmission capacities at the same time. Therefore, it has brought forward higher request to the development of communication technology. LDPC codes and OFDM technology are two key technologies of the future broadband wireless communication to raise the communication quality and the data rate. This thesis mainly studies the structure of LDPC codes, then researches the scheme of effective LDPC-OFDM systems applied to future broadband wireless communication combining of OFDM systems.The main problem of LDPC implementation is the high complication of its coding. Therefore, the aim of LDPC research in this thesis is to make the coding complication lower through the improvement of coding scheme and the structure of parity-check matrix. Firstly, the improvement of coding scheme is studied, the main thought is how to change the parity-check matrix to an approximate lower triangle matrix using greedy algorithm, then coding directly from the parity-check matrix, thus, the coding complication can be lowered to linear to the code length. Then, detailed analysis of the structure of parity-check matrix is presented. the emphasis is on QC-LDPC and PS-LDPC, which are constructed from cyclic-shift of identity matrix. The parity-check matrix of QC-LDPC or PS-LDPC can be coded from shift registers, which has simple coding structure, and is easy to implement.Finally, this thesis studies the initialization of decoding which suitable to multi-order modulation based on OFDM systems, then optimizes the initialization algorithm aiming at multi-path environment. The simulation results show that LDPC coded OFDM systems has good performance under multi-path environment, and applies a reference to the future broadband wireless communication systems using LDPC-OFDM technology.