按优先级预编码：一种适用于RaptorQ码的UEP方案
Precoding by Priority: A UEP Scheme for RaptorQ Codes
摘要：
Raptor码是第一类具有线性时间编码和译码的喷泉码。在诸如第三代合作伙伴计划（3GPP）和数字视频广播的标准中推荐这些码。RaptorQ码是Raptor码的扩展，具有更好的编码效率和灵活性。标准Raptor和RaptorQ代码是系统的，具有相同的数据错误保护。然而，在诸如MPEG传输的许多应用中，存在对不等错误保护（UEP）的需要：即，一些数据符号与其他数据符号相比需要更高的纠错能力。我们提出了一种方法，我们称之为基于优先级的预编码比（PBPR），以实现UEP系统的RaptorQ和Raptor码。我们的UEP假设源块中的所有符号属于相同的重要性类。UEP通过根据源块中的信息符号的优先级改变预编码符号的数量来实现。PBPR为具有不同重要性类别的源块提供具有相同数量的解码开销符号的UEP。我们证明了一致的改进，在较高的重要性类的纠错能力相比，较低的重要性类在整个范围内的信道擦除概率。我们还表明，PBPR不会导致解码和编码时间的显着增加相比，标准的实现。
英文摘要：
Raptor codes are the first class of fountain codes with linear time encoding and decoding. These codes are recommended in standards such as Third Generation Partnership Project (3GPP) and digital video broadcasting. RaptorQ codes are an extension to Raptor codes, having better coding efficiency and flexibility. Standard Raptor and RaptorQ codes are systematic with equal error protection of the data. However, in many applications such as MPEG transmission, there is a need for Unequal Error Protection (UEP): namely, some data symbols require higher error correction capabilities compared to others. We propose an approach that we call Priority Based Precode Ratio (PBPR) to achieve UEP for systematic RaptorQ and Raptor codes. Our UEP assumes that all symbols in a source block belong to the same importance class. The UEP is achieved by changing the number of precode symbols depending on the priority of the information symbols in the source block. PBPR provides UEP with the same number of decoding overhead symbols for source blocks with different importance classes. We demonstrate consistent improvements in the error correction capability of higher importance class compared to the lower importance class across the entire range of channel erasure probabilities. We also show that PBPR does not result in a significant increase in decoding and encoding times compared to the standard implementation.
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