Expanding-Window Zigzag Decodable Fountain Codes for Scalable Multimedia Transmission

In this paper, we present a coding method called expanding-window zigzag decodable fountain code with unequal error protection property (EWF-ZD UEP code) to achieve scalable multimedia transmission. The key idea of the EWF-ZD UEP code is to utilize bit-shift operation and expanding-window strategy to improve the decoding performance of the high-priority data without performance deterioration of the low-priority data. To provide more protection for the high-priority data, we precode the different importance level using LDPC codes of varying code rates. The generalized variable nodes of different importance levels are further grouped into several windows. Each window is associated with a selection probability and a bit-shift distribution. The combination of bit-shift and symbol exclusive-or operations is used to generate an encoded symbol. Theoretical and simulation results on input symbols of two importance levels reveal that the proposed EWF-ZD UEP code exhibits UEP property. With a small bit shift, the decoding delay for recovering high-priority input symbols is decreased without degrading the decoding performance of the low-priority input symbols. Moreover, according to the simulation results on scalable video coding, our scheme provides better basic video quality at a lower proportion of received symbols compared to three state-of-art UEP fountain codes.