Bounds and protocols for a rate-constrained relay channel

Ashutosh Sabharwal, Urbashi Mitra

Research output: Contribution to journalArticlepeer-review

8 Scopus citations


In this correspondence, a relay rate-constrained variation of the three-node relay channel is introduced and studied. In the rate-constrained relay channel, the relay cannot reliably decode or encode beyond a rate constraint ̄R. A cut-set upper bound, and rate-constrained variations of decode-and-forward and estimate-and-forward protocol are derived. It is observed that relative performance of the unconstrained protocols does not predict relative performance of the constrained protocols; that is, estimate-and-forward almost always offers superior performance for small rate constraints. A new metric, denoted as the relay efficiency, measures the slope at which the relay channel rate increases over the relay-less channel. While the cut-set upper bound has a relay efficiency of one for the Gaussian relay channel at ̄R = 0, the two new protocols do not. Finally, it is shown that an effective relay rate constraint can be computed for general relay protocols. To demonstrate this concept, a Markovian amplify-and-forward protocol, in which the relay does not perform any explicit encoding or decoding, is examined and compared to the introduced rate-constrained protocols.

Original languageEnglish (US)
Pages (from-to)2616-2624
Number of pages9
JournalIEEE Transactions on Information Theory
Issue number7
StatePublished - Jul 2007


  • Amplify-and-forward
  • Decode-and-forward
  • Estimate- and-forward
  • Rate-constrained channels
  • Relay channel

ASJC Scopus subject areas

  • Information Systems
  • Computer Science Applications
  • Library and Information Sciences


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