Research And Improvement For Physical Layer Technology Of CMMB

With the coming of 3G Time, Mobile TV is becoming compelling. In this context, Chinese SARFT made national standard CMMB (China Mobile Multimedia Broadcasting) with independent intellectual property rights. CMMB's physical layer channel standard is STiMi, researched by our nation. Fully considering the characteristics of the mobile multimedia broadcasting services, STiMi adopts the advanced forward error coding (LDPC code) technology and the OFDM modulation technology, result in the advantages such as high anti-interference ability, high-mobility supporting and low power consumption. The main work in this paper is that the platform of the physical layer of CMMB is set-upped and the decoding algorithm of LDPC is inprvoved.In this paper, on the base of introducing the channel standards of STiMi in detail, the key technology of the physical layer transmission of CMMB, such as RS, LDPC, Bit-Interweave and OFDM , are researched and realized by using Matlab language. Furthermore, the data process of the physical layer is simulated, and the transmission performance is analyzed. At the same time, this paper analyzed the transmission performance of the environments of in/out door and different speed by simulation.STiMi adopts the advanced technology to realize the high-speed transmission. The traditional disadvantage of LDPC's decoding algorithm is the long time delay result from much iteration. It is intolerable for the Mobile TV who demands real-time transmission. Therefore, this paper proposes an adaptive iterative algorithm. By simulation, it shows that this algorithm can reduce the average number of iterations to reduce the decoding difficult and shorten the delay time. So it can guarantee the transmission of CMMB.