中文摘要：

在多媒体传输、深空通信等应用中，由于数据的重要性程度不同，需要喷泉码具有不等差错保护的特性，根据数据重要性给予不同程度的保护。对基于块复制的不等差错保护喷泉码的机制进行了理论分析，提出了改进的信息符号选取策略，让度1编码符号全部在重要信息比特中选取，一定数量的度2编码符号分别在重要信息比特和次要信息比特中选取，从局部上提升对重要信息比特的保护。仿真结果表明，相比于现有的基于块复制的不等差错保护喷泉码，改进方法在进一步提高重要信息比特保护的同时没有降低对次要信息比特的保护，且有更好的不等恢复时间性能。

英文摘要：

In several applications such as multimedia transmission and deep space communications, some data may need more protection than the rest because of the dif{ercnt importance of the data. Such applica- tions raise the need for fountain codes with unequal error protection （UEP）. The operation mechanism of the unequal error protected fountain codes based on block duplication is analyzed, and an improved selec- tion strategy of information symbols is proposed to improve the protection of more important bits （MIB） in local area. Degree 1 encoded symbols are selected from MIB and a certain number of degree 2 encoded symbols are chosen from MIB and less important bits（LIB）, respectively. Simulation results show that compared with the existing method, the proposed scheme perform better on decoding MIB without reduc- ing the decoding of LIB while reserving a better unequal recovery time （URT） property.