Virtual Pairing for Power-Level Collision Mitigation in IRSA-NOMA

Irregular Repetition Slotted ALOHA with Non-Orthogonal Multiple Access (IRSA-NOMA) suffers from power-level collisions where insufficient received power separation prevents successive interference cancellation (SIC) from resolving colliding users, rendering slots undecodable. This letter proposes Irregular Repetition Virtual Pairing NOMA (IR-VP-NOMA), which applies virtual pairing to resolve these collisions through decoder-side bandwidth partitioning. When received power separation falls below the SIC threshold due to similar channel conditions, the slot bandwidth is divided into orthogonal sub-bands for frequency-domain separation. Simulations demonstrate PLR reduction exceeding 99% at collision-dominated loads and 53.8% throughput improvement, with no additional overhead.