Generalized HARQ Protocols with Delayed Channel State Information and Average Latency Constraints

Kasper Fløe Trillingsgaard, Petar Popovski

Research output: Contribution to journalJournal articleResearchpeer-review

11 Citations (Scopus)
259 Downloads (Pure)

Abstract

In many wireless systems, the signal-to-interference-and-noise ratio that is applicable to a certain transmission, referred to as channel state information (CSI), can only be learned after the transmission has taken place and is thereby delayed (outdated). In such systems, hybrid automatic repeat request (HARQ) protocols are often used to achieve high throughput with low latency. This paper put forth the family of expandable message space (EMS) protocols, that generalize the HARQ protocol and allow for rate adaptation based on delayed CSI at the transmitter (CSIT). Assuming a block-fading channel, the proposed EMS protocols are analyzed using dynamic programming. When full delayed CSIT is available and there is a constraint on the average decoding time, it is shown that the optimal zero outage EMS protocol has a particularly simple operational interpretation and that the throughput is identical to that of the backtrack retransmission request (BRQ) protocol. We also devise EMS protocols for the case in which CSIT is only available through a finite number of feedback messages. The numerical results demonstrate that BRQ approaches the ergodic capacity quickly compared with HARQ, while EMS protocols with only three and four feedback messages achieve throughputs, that are only slightly worse than that of BRQ.

Original languageEnglish
Article number7814295
JournalI E E E Transactions on Information Theory
Volume64
Issue number2
Pages (from-to)1262-1280
Number of pages19
ISSN0018-9448
DOIs
Publication statusPublished - Feb 2018

Keywords

  • Backtrack retransmission request
  • Delayed channel state information
  • Dynamic programming
  • Hybrid automatic repeat request
  • Low latency

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