Research And Simulation Of OFDM Based On LDPC

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 apply LDPC code into the OFDM system, in which LDPC code is the channel code, then design a LDPC coded OFDM system. Realize the encoding and decoding of LDPC codes in the system. Then research the performance of the LDPC coded OFDM system.Low-density parity-check (LDPC) codes are a class of linear block codes which can be represented by sparse parity-check matrix or Tanner garphs. LDPC codes come to be one of the best coding technologies because of their iterative decoding algorithm with low complexity and approaching Shannon limity capacity performance. They are taking more and more researchers' attention and recognition in recent years. The struct of parity-check matrix dose not only decide the encode of the LDPC codes, but also play an important role on the decode of the LDPC codes. First, this thesis studies the fundamental of the parity-check matrix of the LDPC codes which includes the definition and structure of the LDPC, the constructed mathods of the LDPC and the encode and decode methods of the LDPC. The emphasis of these studies is the constucted of the LDPC. Then, the thesis presents a class of improved LDPC constructed based on Gallager's form. The new method keeps the basic form of the Gallager's form and removes cycles of length of 4 which can affect the performance of the iterative decode method. The result of the simulation indicates that the performance of the new code is highly improved.Finally, based on the OFDM system, this thesis applies the LDPC codes to the multi-order modulation system. The simulation results show that LDPC coded OFDM system has good performance, and applies a reference to the future broadband wireless communication systems using LDPC-OFDM technology.