Design Of Fountain Codes With Unequal Error Protection Property

With the further development of mobile communication and Internet, multimedia transmission on the basic of image and video gradually becomes the major task of future communication service. However, high packet loss rate, time-variant channel charac-teristic and the heterogeneous client in the process of network communication seriously limit the multimedia transmission and decrease the communication reliability. There-fore, how to reduce the bit error rate (BER) of data transmission and the impact on the reception performance has become one of key problems in the study of multimedia com-munication. Digital fountain coding is a novel forward error correction (FEC) coding technology. Unlike traditional fixed-rate schemes, digital fountain codes are rateless, have low coding complexity and can obtain better performance without the need of feedback, so such codes have been widely investigated by the coding industry.Firstly, we introduced normal fountain codes (i.e., LT codes and Raptor codes) and other fountain codes with unequal error protection (UEP) property. From the per-spectives of asymptotic analysis and practical finite-length simulation, respectively, we further studied the main impact factors on the performance of fountain codes, and com-paratively analyzed the advantages and disadvantages of several existing typical UEP fountain codes.Secondly, to reduce the high coding complexity and improve the performance (e.g., UEP property) of previous duplicate UEP scheme, we proposed an efficient scheme to construct fountain codes that can provide UEP property. We implemented various rate low-density parity-check (LDPC) codes instead of the first duplication process, i.e., re-peat and replaced the high-complexity classical robust soliton distribution (RSD) by low constant average degree distributions with high intermediate symbol recovery rates (ISRR). We verified that it is impossible to improve the performance by increasing ex-panding factor in both the duplicate UEP scheme and our proposed scheme while uti-lizing the weaker degree distributions with constant average degree. Compared to other schemes, our scheme had lower complexity for the same decoding performance. Simu-lation results demonstrated that our scheme can obtain better error-resilient performance, especially for the smaller input information length. Comparison of peak signal-noise ra- tio (PSNR) performance showed that, for moderate input length, our scheme can provide a better basic video quality at lower overhead.Due to the rateless property, fountain codes still can obtain better performance without the need for the feedback. However, because of duplex communication in the communication networks (e.g., Internet and mobile communication network), it is very easy to obtain the feedback channel and restrict the feedback to a single bit per source block. And the transmission of such feedback message would not have great impact on the communication. Therefore, we studied the impact of feedback in the form of an acknowledgment, which is a single bit per source block, in EWF codes. Additionally, we proposed a practical prediction model to calculate the successful decoding overhead in corresponding prioritized data. This model applied to the scenario without/with feed-back. Asymptotic analysis and simulation results showed that, compared with standard EWF codes, our proposed EWF codes with feedback can obtain a lower average over-head of successful decoding in LIB, and the proposed prediction model is effective.