Opportunistic relay selection with outdated csi: Outage probability and diversity analysis

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In this paper, we analyze the outage probability and diversity order of opportunistic relay selection in a scenario based on decode and forward and where the available channel state information (CSI) is outdated. The study is conducted analytically by obtaining a closed-form expression for the outage probability, which is defined as the probability that the instantaneous capacity is below a target value. We derive high-SNR approximations for the outage probability. By doing so, we demonstrate that the diversity order of the system is reduced to 1 when CSI is outdated, being this behavior independent of the level of CSI accuracy. A physical explanation for this extreme loss of diversity is provided along with numerical results to support the analytical study. © 2006 IEEE.
Original languageEnglish
Article number5089967
Pages (from-to)2872-2876
JournalIEEE Transactions on Wireless Communications
Publication statusPublished - 1 Jun 2009


  • Cooperative communications
  • Diversity gain
  • Opportunistic relay selection
  • Outdated CSI


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