Low-Complexity Coding and Spreading for Unsourced Random Access

We propose a low-complexity unsourced random access (URA) transmission scheme where the data payload, encoded by an error-reduction code, undergoes repetition, permutation, and spreading. An approach to perform spatial graph coupling of the URA messages via randomized message delays is also presented. The proposed system, in either block or coupled form, outperforms the existing URA counterparts in the high multi-user interference regime and provides a substantial increase in the supported multi-user loads. A choice of stronger, albeit more complex, error-correction code allows for performance improvements at lower system loads. Finally, system performance predictions via a state-evolution analysis are also demonstrated.