Low-complexity coding scheme to approach multiple-access channel capacity

A very simple coding scheme, called multi-user repetition-aided irregular repeat-accumulate (IRA) code, is proposed to approach the multiple-access channel (MAC) capacity. The main idea is that not only parity checks, which are generated by an IRA encoder, but also repetitions are used in each user's codeword to reduce the coding and decoding complexities. Repetition is a simple way to construct a low-rate code and is shown to be beneficial for multi-user decoding iteration. It is shown that there is a maximum allowable fraction of repetitions in codewords, below which channel capacity can always be approached by optimizing the degree distribution of the IRA encoder. As users increase, the maximum allowable fraction of repetitions increases, and therefore, very low encoding and decoding complexities are required.