Breaking spectrum gridlock with cognitive radios: An information theoretic perspective

Andrea Goldsmith, Syed Ali Jafar, Ivana Maric, Sudhir Srinivasa

Research output: Contribution to journalArticlepeer-review

2068 Scopus citations


Cognitive radios hold tremendous promise for increasing spectral efficiency in wireless systems. This paper surveys the fundamental capacity limits and associated transmission techniques for different wireless network design paradigms based on this promising technology. These paradigms are unified by the definition of a cognitive radio as an intelligent wireless communication device that exploits side information about its environment to improve spectrum utilization. This side information typically comprises knowledge about the activity, channels, codebooks, and/or messages of other nodes with which the cognitive node shares the spectrum. Based on the nature of the available side information as well as a priori rules about spectrum usage, cognitive radio systems seek to underlay, overlay, or interweave the cognitive radios' signals with the transmissions of noncognitive nodes. We provide a comprehensive summary of the known capacity characterizations in terms of upper and lower bounds for each of these three approaches. The increase in system degrees of freedom obtained through cognitive radios is also illuminated. This information- theoretic survey provides guidelines for the spectral efficiency gains possible through cognitive radios, as well as practical design ideas to mitigate the coexistence challenges in today's crowded spectrum.

Original languageEnglish (US)
Article number4840529
Pages (from-to)894-914
Number of pages21
JournalProceedings of the IEEE
Issue number5
StatePublished - May 2009
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • General Computer Science
  • Electrical and Electronic Engineering


  • Capacity
  • Cognitive radio
  • Degrees of freedom
  • Interweave
  • Overlay
  • Side information
  • Underlay


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