Research On Reliability Mechanism Of Data Transmission In CMMB System

CMMB, which is the shortened form of China Mobile Multimedia Broadcast, is a research production by our own country. It has a broad range of applications in the field of mobile multimedia broadcast services. At present, the 3G is granted in China and the CMMB has provided commercial services during the Beijing Olympic Games. All of these facilitate CMMB's development courses. Synchronously, providing more reliable services to meet the need of clients, becomes the breakthrough difficulty for the CMMB. There are two parts of data transmission mechanism in CMMB system. One is the transmission mechanism on the link layer. The other is the technique on the physical layer. So this thesis does a deep research on the reliability mechanism of data transmission on the link layer and physical layer of CMMB system.This thesis first introduces the transmission method and the techniques of CMMB, including network structure, data transmission scheme and encapsulation method on the link layer, STiMi techniques on the physical layer, including LDPC theory and application. Then after analyzing the shortage of original scheme, this thesis put forward a new XPE-FEC mechanism for the link layer. This mechanism designs XPE-FEC frame and improves XPE encapsulation and CRC coding for XPE data. Simulation results show that the new scheme out-performs the old scheme in terms of reliability metrics.Besides, this thesis does research and improvement on the techniques of the physical layer. After analyzing the peculiar structure of CMMB-LDPC, the thesis designs new encoding and decoding sheme for the flexibility. Then by the Matlab simulator, the thesis analyzes the performance of LDPC code, under different simulated scenes from aspects as: code length, code rate, iterative number. Based on this, this thesis analyzes the original BP decoding algorithm of LDPC and then improves on the BP decoding algorithm. The simulation results show that the new algorithm can reduce the complexity of the harware realization at the premiss of ensuring the decoding performance.