HARQ Using Hierarchical Tree-Structured Random Access Identifiers in NOMA-Based Random Access

We propose an efficient hybrid automatic repeat request (HARQ) method that simultaneously achieves packet combining and resolution of the collisions random access identifiers (RAIDs) during retransmission in a non-orthogonal multiple (NOMA)-based system. Here, RAID functions as separator for received packets use same channel NOMA. An example this is scrambling code used 4G 5G systems. Since users independently select from candidate set prepared by system, decoding fails when RAID. Random reselection each user attempting can resolve collision; however, between previous retransmitted not possible case because base station receiver does know relationship previously transmitted packet. To address problem, we HARQ employs novel hierarchical tree-structured groups which transmission has one-to-one with RAIDs retransmission. The proposed resolves at randomly reselecting dedicated transmission. known station, achieved simultaneously. Computer simulation results show effectiveness method.