Fountain codes over fading relay channels

This paper discusses cooperative protocols based on fountain codes in a relay network. Unlike traditional fixed-rate codes, fountain codes are capable of adapting the bit rate to the channel realization blindly, i.e., without channel information at the transmitter. This makes them attractive in fading wireless channels. We first describe several rateless cooperative protocols, and then implement them using Raptor codes (a type of fountain code) and 16-QAM over a slow, deeply-interleaved fading relay channel. Given no delay constraints, the achievable rate of these protocols are found when the source and relay are close to each other, and when the relay is half-way between the source and destination. Furthermore, to reduce decoding complexity, we propose a soft-decision version of the adaptive demodulation (ADM) method recently introduced in the literature at each receiver. Finally, we analyze the practical scenario of data streaming with delay constraints, and find that the time-division (TD) protocol retains its relative superiority over the space-time one.