Reliable and Efficient Download Delivery with Raptor Codes

In this work we address reliable file delivery over mobile broadcast networks using Raptor Codes. We assume a point-to-multipoint (broadcast) transmission, where original source symbols are protected by additional parity symbols. Despite the good performance of Raptor codes, reliable delivery cannot be guaranteed due to the statistics in heterogeneous receiver environments. Therefore, a second phase, where individual users are allowed to complete their delivery by performing individual repair sessions, must be conducted. Our main contribution are two algorithms, one allowing to find a minimum set of source symbols to be requested in the post-delivery, and one allowing to find a sufficient number of consecutive repair symbols, guaranteeing successful recovery. These post-repair methods fully exploit the properties of these codes. Selected simulations verify the good performance of file distribution with Raptor codes as well as the algorithms for file repair in case of file distribution to more than one user.