Research On Capacity Of BICM System Based On LDPC Codes

The main issue of the future wireless communication is poor spectrum resources with the increasing demand of high speed and high quality communication. It is an efficient strategy to improve bandwidth efficiency, by combining regular Low-Density Parity-Check(LDPC) codes of excellent error correction performance and bit-interleaved coded modulation(BICM)systems of high-bandwidth efficiency with high order modulation.At first, this dissertation do a systematic study on the basic principles of the LDPC codes, LDPC codes of classification, rules of check matrix construction method and decoding method of LDPC codes. The advantages and disadvantages of three LDPC codes construction methods are analyzed and compared, focusing on two LDPC decoding method, the classical algorithm and reliability propagation algorithm and its performance is simulated. A improved decoding algorithm based on the traditional decoding algorithm is proposed, simulation results show that it has better performance than traditional algorithms.And then study the Bit-Interleaved Coded Modulation (BICM) system, the basic principles and characteristics. The chapter studied the basic design of the interleaving method, the design of constellation mapping method and the principle of combining demodulation decoding. For a typical constellation of three ways: Gray (Gray) mapping, set partitioning (SP) mapping, mixed (Mixed) mapping, given the Euclidean distance of constellation design criteria. Simulation results show AWGN channel and Raleigh channel, Gray mapping in BICM systems are optimal.Finally focuses on the rule-based LDPC codes and BICM system model used in this paper and the logarithm of likelihood decoding algorithm. First, the analysis of different code length, different column weight, interleaving of the LDPC-BICM system performance. According to the bits'different protection capability in 16 QAM constellation points, we propose to use an inner-interleaved LDPC coding method, it can arrange information bits with a specific way. We design a simulation of 16 QAM modulation, simulation results prove that the new coding scheme is better than random coding schemes.