Enhanced unequal error protection coding scheme of Luby transform codes

摘要

A Luby transform (LT) coding scheme providing unequal error protection (UEP) is proposed. As an enhanced method, the proposed UEP-LT coding scheme can be easily applied to the existing UEP rateless codes to achieve further bit error rate (BER) performance improvement. In the proposed UEP-LT encoder, a number of the so-called fixed symbols are added to the original source symbols. The level of importance of them can be assigned as that of any subset of the original source symbols. When the encoded symbols are generated, the proposed encoder only XOR the original source symbols. Therefore the efficiency of the UEP-LT codes remains unchanged. It is found that this can benefit the belief propagation decoding. Using the And–Or tree analysis technique, the asymptotic BER performance of the proposed method is analysed in detail. Compared with some existing UEP rateless codes, the asymptotic BERs of the proposed UEP-LT codes are much lower when the parameters are properly chosen. Besides, the proposed method needs less decoding iterations to converge, which means the source symbols can be recovered earlier. Simulation results show that the BER performances are improved when the proposed scheme is applied to the existing UEP rateless codes.