The Study Of LDPC Codes And Its Application To 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.Orthogonal Frequency Division Multiplexing (OFDM) is a technology which disperses a high-rate data stream to several orthogonal sub-carriers for transmission. Therefore, it reduces the symbol-rate of sub-carriers and lengthens the symbol duration greatly, making it effective on overcoming the multipath fading effect and narrow-band interference. OFDM technology also makes high spectrum efficiency, which is an effective data transmission way.Both LDPC codes and OFDM technology are studied in this paper. The working and the results obtained are summarized as follow:1. The definition of LDPC codes and its coding/decoding ideas are systematically summarized, a general algorithm of changing any parity-check matrix to lower triangular form, which is suitable for quick encoding, is given out, along with a girth checking algorithm. Absolutely random LDPC codes construction is improved, a new half random construction of LDPC codes with linear time coding and no 4-cycles is brought out. The simulation result supports that improved half random construction can give out LDPC code with better performance and linear time coding than absolutely random construction at high coding efficiency.2. The principle of OFDM and its DSP implementation are introduced in detail.