| Comparing to other frequency band broadcasting systems, the one under 30MHz has unique superiority. The AM broadcasting system under 30MHz in our country is a analog system, while it has established a digital one in Europe since June, 2003. Because of the need of development and the pressure of competition, it is imperative to carry on the digital transformation in our country. Channel coding is one of the key technique of digital AM broadcasting system. According to the system specification of DRM given by ETSI, the channel coding scheme applied to the system is a set of combination schemes of the multilevel coding and modulation. It is a flexible mechanism which makes it possible to choose different coding method and constellation according to different data channel or channel condition.Simulation platform is established in matlab to realize the channel coding scheme described in the standard of DRM. One of the channel coding scheme is choosen to research. In this scheme robustness B, spectrum of 10kHz, SM64QAM, total rate of 1/2 is used. Decoding performances of PDL, iMSD, hard-decision and soft-decision are compared and analyed. The simulation shows that this channel coding scheme with soft-decision and iterative multilevel coding could preferably improve the symbol error rate. It can obtain a gain of 4.5dB in channel of Gauss and 9.5dB in channel of Rice. Additionally, performance of bit error rate of component code with SM64QAM and HMsym64QAM is tested. It is concluded that the multilevel coding scheme has specific property of unequal error protection.The background and significance of this project are introduced in the beginning of the paper. Then the channel coding's task, principle, common forms are introduced, the concept of coding modulation technique are introduced on emphasis. The channel coding scheme is introduced and realization of modules are given in Chapter 3, including energy dispersal, partition of bitstream, component encoding, bit interleaving, signal constellation and mapping, MSC cell interleaving. The performance is analysed, the property of the multilevel coding scheme is explained and the system frequency band efficiency is calculated. Summarize is given in the end, which includes a technical problem and the orientation of the next work. |
