Practical rateless cooperation in multiple access channels using multiplexed Raptor codes

In this paper we develop practical rateless coded cooperation strategies for a two-user multiple access channel. At the heart of our practical strategies lie Raptor codes concatenated with a space-time code, and an iterative decoding procedure to jointly recover the two users' messages at the base station. Since cooperation in multiple access channels is known to be particularly beneficial when considering the outage probability at low SNRs, or equivalently at low transmission rates, we simulate our strategies at a transmission rate of 0.25 bits/sample. Experiments indicate that our schemes perform very close to the theoretical limit, with the performance gap being less than 0.55 dB.