Fountain Codes

In Chapter 11, we address an alternative paradigm for erasure coding that exploits feedback from (multiple) receivers to the transmitter. Here, the receivers are assumed to be interested in the same content, and the transmission takes place over a broadcast channel. The feedback is employed to adapt “on the fly” the coding rate to the channel conditions. This approach, which shares several similarities with the framework of rate-compatible codes with hybrid automatic retransmission query ARQ, relies on the so-called fountain codes. Two well-established classes of fountain codes are discussed, namely the class of LT codes (strongly related to LDPC codes) and the class of Raptor codes.