HARQ Using Hierarchical Tree-Structured Physical Channel Identifiers in NOMA-Based Random Access for Multi-Packet Reception

Megumi Asada, Nobuhide Nonaka, Kenichi Higuchi

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review


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

Original languageEnglish
Title of host publication2021 IEEE 94th Vehicular Technology Conference, VTC 2021-Fall - Proceedings
PublisherInstitute of Electrical and Electronics Engineers Inc.
ISBN (Electronic)9781665413688
Publication statusPublished - 2021
Event94th IEEE Vehicular Technology Conference, VTC 2021-Fall - Virtual, Online, United States
Duration: 27 Sep 202130 Sep 2021

Publication series

NameIEEE Vehicular Technology Conference
ISSN (Print)1550-2252


Conference94th IEEE Vehicular Technology Conference, VTC 2021-Fall
Country/TerritoryUnited States
CityVirtual, Online


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