Integrating packet-level FEC with data carousels for reliable content delivery in satellite broadcast/multicast systems

摘要

One key aspect of digital multimedia broadcasting is the reliable point-to-multipoint distribution of content. Since the capacity and energy constraints in wireless environments do not favour the provision of a return channel for user feedback, the use of partial reliability techniques is often the only realistic option for the reliable transport layer design. In this paper, we focus on the two main reliable transport mechanisms in unidirectional, point-to-multipoint systems, namely packet-level forward error correction (FEC) and data carousels. We approach them as building components of an integrated scheme and investigate its performance via analytical means. Our analysis demonstrates that the network responsiveness, expressed by the average content access time, is optimized for certain packet-level FEC redundancy values. This is clearly different from setting FEC without considering the data carousel dimension, where the FEC redundancy is determined from the probability of recovering the whole file versus FEC overhead trade-off curves. We describe design alternatives for both scheme components, such as different FEC code types, rules for assigning FEC redundancy per carousel item, and ways to retrieve items from the data carousel, and evaluate their impact on the performance of the scheme. Our results suggest that the superposition of FEC on data carousels mitigates the otherwise significant impact of the data item retrieval technique on performance, at least for close-to-optimal FEC settings. On the contrary, the careful selection of FEC code and FEC redundancy assignment rule for data carousel items results in performance gains of up to 11 and 18% for the average content access time and FEC overhead, respectively, depending on the item demand and length distributions.