| In recent years, with the rapid development of IP networks, multimedia applications become more and more widespread. In the actual multimedia communication system, there is a variety of channel noise, therefore channel coding is very important for multimedia communication. Digital fountain codes, with their advantages of free code rate, no feedback, etc., will be one of the most effective channel coding techniques for the multimedia communication. However, under certain circumstances, a portion of the transmission data is more important than the others. Therefore, some scholars add unequal error protection mechanisms to the digital fountain codes which can make the data relatively higher important more redundancy.Firstly, this thesis describes the research background including the development and application of digital fountain codes. Then it introduces the error channel, encoding-decoding principles of two practical digital fountain codes, which are LT codes and Raptor codes. Then, this thesis introduces the existing LT codes and Raptor codes with the property of Unequal Error Protection(UEP).Secondly, this thesis introduces the principle of several existing distribution functions, and analyzes their performance. Then it introduces the existing belief propagation(BP) decoding algorithm and gaussian elimination(GE) algorithm. After analyzing their demerit, the thesis proposes a novel decoding algorithm. The simulation results show that the proposed decoding algorithm obtains better decoding correct rate and lower algorithm complexity than BP decoding algorithm with the same overhead.Thirdly, this thesis analyzes and compares the performance of LT codes and Raptor codess. Then, it analyzes the merit and demerit of the existing UEP fountain schemes, and proposes a new UEP-LT scheme named improved expanding window fountain(iEWF) codes, which is based on the existing expanding window fountain(EWF). The simulation results show that the proposed UEP-LT codes scheme can provide a superior UEP performance, and improve the performance of date less important relatively. Furthermore, the thesis proposes a novel UEP-Raptor codes based on the iEWF. The simulation results show that the proposed UEP-Raptor has obvious UEP performance, which can make the whole performance well.Finally, the thesis researches the encoder and decoder scheme based on the proposed UEP-Raptor codes, which can be used in video communication systems. Then it designs the application of video data packaging and transmission. Apart from them, it designs information delivery strategy and work processes of the system. The test results show the well performance of the video transmission system. The UEP-Raptor decoding can reduce the packet loss rate effectively, and provides the video data unequal error protection. |
