The Research Of LDPC Codes And The Application In OFDM System

LDPC codes and OFDM technology are two key technologies of the future broadband wireless communication to raise the communication quality and the data rate. And applying the LDPC codes into the LDPC-COFDM system will have promising application.First, this topic studies the basic principle of the LDPC codes, for irregular LDPC codes in IEEE802.16e standard, Elaborate the special construction method of their parity check matrix and fast encoding algorithm, then focus on several LDPC codes decoding algorithms which are commonly used. In the decoding algorithms, in order to reduce the performance loss of UMP BP-Based decoding algorithm compared to LLR-BP decoding algorithm, an improved UMP BP-Based decoding algorithm is proposed. When the check nodes process the message, the Normalized BP-Based decoding algorithm and Offset BP-Based decoding algorithm are integrated effectively by setting a correction factor and an offset factor reasonably. When the variable nodes process the message, Oscillation Compensation algorithm based on LLR-BP decoding algorithm is introduced. Simulation results show that based on the irregular LDPC codes in IEEE802.16e standard and under the condition of the same bit error rate within a certain range, the improved UMP BP-Based decoding algorithm improves the decoding performance greatly compared with the UMP BP-Based, Normalized BP-Based and Offset BP-Based of these three decoding algorithms, quite efficiently approaches to the LLR-BP decoding algorithm which has excellent performance.While this topic studies the OFDM techniques, the irregular LDPC codes in IEEE802.16e standard are applied into OFDM systems, and we propose LDPC-COFDM system scheme, improved UMP BP-Based decoding algorithm is adopted too. For different coding rules, different code length and different bit rates, different modulation, different decoding iterations of these factors, we simulate and analyse the LDPC-COFDM systems, it has been proved that applying irregular LDPC codes in IEEE802.16e standard and improved UMP BP-Based decoding algorithm into the OFDM system will obtain excellent performance.