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Everything about Hybrid automatic repeat request

Hybrid error-detection and correction code in communications

Hybrid automatic repeat request is a combination of high-rate forward error correction (FEC) and automatic repeat request (ARQ) error-control. In standard ARQ, redundant bits are added to data to be transmitted using an error-detecting (ED) code such as a cyclic redundancy check (CRC). Receivers detecting a corrupted message will request a new message from the sender. In Hybrid ARQ, the original data is encoded with an FEC code, and parity bits are either immediately sent along with the message or only transmitted upon request when a receiver detects an erroneous message. The ED code may be omitted when a code is used that can perform both forward error correction (FEC) in addition to error detection, such as a Reed–Solomon code. The FEC code is chosen to correct an expected subset of all errors that may occur, while the ARQ method is used as a fall-back to correct errors that are uncorrectable using only the redundancy sent in the initial transmission. As a result, hybrid ARQ performs better than ordinary ARQ in poor signal conditions, but in its simplest form this comes at the expense of significantly lower throughput in good signal conditions. There is typically a signal quality cross-over point below which simple hybrid ARQ is better, and above which basic ARQ is better. Wikipedia →

🧭 Start here: a 6-step reading path

  1. Read the overview: Hybrid automatic repeat requestA 5-minute orientation
  2. Skim a recent paper: SemHARQ: Semantic-Aware Hybrid Automatic Repeat Request for Multi-Task Semantic CommunicationsInfluential work since 2022
  3. Pick up a classic book: Data Communications and NetworkingThe most-reprinted book on the subject
  4. Read the landmark paper: Hybrid Automatic Repeat Request (HARQ) in Wireless Communications Systems and Standards: A Contemporary SurveyCited 155 times
  5. Go sideways: Error detection and correctionA closely related topic
  6. Go sideways: Link adaptationA closely related topic

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🗂️ The subject at a glance

  1. Simple hybrid ARQ
  2. Hybrid ARQ with soft combining
  3. Applications

🏆 Landmark papers (most cited)

🆕 Influential since 2022

📚 Books worth reading

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