Coding And Modulation-Research On The Key Technology In Mobile Communication System

Channel coding and modulation are key technologies for efficient information transmission over wireless channel. Channel coding can offer error-correcting ability through redundancy and modulation changes the signal to the shape which is adapted to channel transmission. There are great improvements on channel coding and modulation in recent years especially Turbo code and LDPC codes have exhibited excellent performance. But in the view of information theory, there are still long road to approach the goal especially in multi-user and broadband conditions. This thesis first focuses on the decoding of LDPC codes and the application in MIMO and CR system of LDPC codes. Then OvCDM is investigated since it is a great break in coding and modulation theory. The coding is done on signal directly and without the limitation of finity field. The coding rate can exceed 1. The Turbo idea which can also been applied to OvCDM. A novel decoding method for Turbo-OvCDM is proposed in this thesis.The contents and major contributions of this thesis are as the following:1. Explain the principles of LDPC codes. Two novel decoding methods are proposed based on BP and WBF decoding methods respectively. The new methods both can acquire better tradeoff between performance and complexity. The new UMP-BP mothod has nearly the same performance as BP method for random constructed LDPC codes at high SNR. And the new WBF mothod defeats all the other WBF methods for FG LDPC codes. LDPC codes are also been applied to MIMO system. The excellent performance of LDPC codes is proved in real MIMO wireless channel.2. The CR model based on OFDM is explained. Then LDPC codes together with constellation rotation are applied to the CR system. The signaling message is transmited with jinformation message imultaneously. The relationship between constellation rotation and set partitioning in coded modulation is analyzed. 3. The relationship between OvCDM and common multiplexing and multiaddress tenologies is exlained theoretically. Turbo-OvCDM is applied in AWGN and Rayleigh fading channel. The identity analysis of OvCDM and the performance of Turbo-OvCDM are presented. Novel decoding method for Turbo-OvCDM is proposed for better performance.