High-performance cooperative demodulation with decode-and-forward relays

Tairan Wang, Alfonso Cano, Georgios B Giannakis, J. Nicholas Laneman

Research output: Contribution to journalArticlepeer-review

582 Scopus citations


Cooperative communication systems using various relay strategies can achieve spatial diversity gains, enhance coverage, and potentially increase capacity. For the practically attractive decode-and-forward (DF) relay strategy, we derive a high-performance low-complexity coherent demodulator at the destination in the form of a weighted combiner. The weights are selected adaptively to account for the quality of both source-relaydestination and source-destination links. Analysis proves that the novel coherent demodulator can achieve the maximum possible diversity, regardless of the underlying constellation. Its error performance tightly bounds that of maximum-likelihood (ML) demodulation, which provably quantifies the diversity gain of ML detection with DF relaying. Simulations corroborate the analysis and compare the performance of the novel decoder with existing diversity-achieving strategies including analog amplify-andforward and selective-relaying.

Original languageEnglish (US)
Pages (from-to)1427-1438
Number of pages12
JournalIEEE Transactions on Communications
Issue number7
StatePublished - Jul 2007

Bibliographical note

Funding Information:
Paper approved by S. N. Batalama, the Editor for Spread Spectrum and Estimation of the IEEE Communications Society. Manuscript received August 5, 2005; revised March 12, 2006 and August 3, 2006. This work was supported in part by the U.S. Army Research Laboratory under the Collaborative Technology Alliance Program, Cooperative Agreement DAAD19-01-2-0011, in part by the Spanish government under Grant TEC2005-06766-C03-01/TCM, and in part by the NSF Grant ECS03-29766. This paper was presented in part at the 39th Asilomar Conference on Signals, Systems, and Computers, Pacific Grove, CA, November 2005.


  • Decode-and-forward (DF)
  • Diversity gain
  • Full diversity
  • Relay channel
  • Relaying protocol
  • User cooperation


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