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Glossary

HARQ (Hybrid ARQ, Hybrid Automatic Repeat Request) in 3GPP: meaning and where it is specified

Published 2026-10-16Updated 2026-10-16

At a glance

Term
HARQ
Stands for
Hybrid ARQ, Hybrid Automatic Repeat Request
Defined in
3GPP TR 21.905 V19.2.0, clause 4
Used in
TS 25.302, TS 25.308, TS 38.300

In plain words

HARQ means "Hybrid ARQ, Hybrid Automatic Repeat Request", the short form listed in 3GPP TR 21.905. In TS 25.302, HARQ information lets the UE identify the process for an HS-DSCH transport block, while FDD E-DCH derives the HARQ process implicitly. TS 25.308 assigns its HARQ entity responsibility for handling the HARQ protocol, and TS 38.300 describes up to two simultaneous high or low priority HARQ-ACK codebooks.

Source: 3GPP TR 21.905 V19.2.0, clause 4. © 3GPP Organizational Partners (ARIB, ATIS, CCSA, ETSI, TSDSI, TTA, TTC). Official text: https://www.3gpp.org/ftp/Specs/archive/21_series/21.905/21905-j20.zip

Sources

  1. 3GPP TR 21.905 V19.2.0, clause 4. © 3GPP Organizational Partners (ARIB, ATIS, CCSA, ETSI, TSDSI, TTA, TTC). Official text: https://www.3gpp.org/ftp/Specs/archive/21_series/21.905/21905-j20.zip
  2. 3GPP TS 25.302 V19.0.0, clause 7.1.13. © 3GPP Organizational Partners (ARIB, ATIS, CCSA, ETSI, TSDSI, TTA, TTC). Official text: https://www.3gpp.org/ftp/Specs/archive/25_series/25.302/25302-j00.zip
  3. 3GPP TS 38.300 V16.22.0, clause 5.3.5.4. © 3GPP Organizational Partners (ARIB, ATIS, CCSA, ETSI, TSDSI, TTA, TTC). Official text: https://www.3gpp.org/ftp/Specs/archive/38_series/38.300/38300-gm0.zip
  4. 3GPP TS 25.308 V19.0.0, clause 6.1.4. © 3GPP Organizational Partners (ARIB, ATIS, CCSA, ETSI, TSDSI, TTA, TTC). Official text: https://www.3gpp.org/ftp/Specs/archive/25_series/25.308/25308-j00.zip

How this page was made

The facts box comes straight from the 3GPP TDoc list and specification archive as indexed by 3GPP Scout. An AI model (GPT-6 Luna) wrote the paragraph and named the source of each sentence. Code checked every quote word for word against the stored source text and every number against the cited source. A second AI model from another company (Claude Opus 5.5) reviewed the paragraph against the same sources. The 3GPP documents themselves govern.