Cognitive medium access: Exploration, exploitation, and competition

Lifeng Lai, Hesham El Gamal, Hai Jiang, H. Vincent Poor

Research output: Contribution to journalArticlepeer-review

239 Scopus citations


This paper considers the design of efficient strategies that allow cognitive users to choose frequency bands to sense and access among multiple bands with unknown parameters. First, the scenario in which a single cognitive user wishes to opportunistically exploit the availability of frequency bands is considered. By adopting tools from the classical bandit problem, optimal as well as low complexity asymptotically optimal solutions are developed. Next, the multiple cognitive user scenario is considered. The situation in which the availability probability of each channel is known is first considered. An optimal symmetric strategy that maximizes the total throughput of the cognitive users is developed. To avoid the possible selfish behavior of the cognitive users, a game-theoretic model is then developed. The performance of both models is characterized analytically. Then, the situation in which the availability probability of each channel is unknown a priori is considered. Low-complexity medium access protocols, which strike an optimal balance between exploration and exploitation in such competitive environments, are developed. The operating points of these low-complexity protocols are shown to converge to those of the scenario in which the availability probabilities are known. Finally, numerical results are provided to illustrate the impact of sensing errors and other practical considerations.

Original languageEnglish (US)
Pages (from-to)239-253
Number of pages15
JournalIEEE Transactions on Mobile Computing
Issue number2
StatePublished - Feb 2011

All Science Journal Classification (ASJC) codes

  • Software
  • Computer Networks and Communications
  • Electrical and Electronic Engineering


  • Bandit problem
  • Cognitive radio
  • Exploitation
  • Exploration
  • Medium access


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