Optimal selective feedback policies for opportunistic beamforming

Tharaka Samarasinghe, Hazer Inaltekin, Jamie S. Evans

Research output: Contribution to journalArticle

20 Citations (Scopus)

Abstract

This paper studies the structure of downlink sum-rate maximizing selective decentralized feedback policies for opportunistic beamforming under finite feedback constraints on the average number of mobile users feeding back. First, it is shown that any sum-rate maximizing selective decentralized feedback policy must be a threshold feedback policy. This result holds for all fading channel models with continuous distribution functions. Second, the resulting optimum threshold selection problem is analyzed in detail. This is a nonconvex optimization problem over finite-dimensional Euclidean spaces. By utilizing the theory of majorization, an underlying Schur-concave structure in the sum-rate function is identified, and the sufficient conditions for the optimality of homogenous threshold feedback policies are obtained. Applications of these results are illustrated for well-known fading channel models such as Rayleigh, Nakagami, and Rician fading channels. Rather surprisingly, it is shown that using the same threshold value at all mobile users is not always a rate-wise optimal feedback strategy, even for a network in which mobile users experience statistically the same channel conditions. For the Rayleigh fading channel model, on the other hand, homogenous threshold feedback policies are proven to be rate-wise optimal if multiple orthonormal data carrying beams are used to communicate with multiple mobile users simultaneously.

Original languageEnglish
Pages (from-to)2897-2913
Number of pages17
JournalIEEE Transactions on Information Theory
Volume59
Issue number5
DOIs
Publication statusPublished - May 2013
Externally publishedYes

Keywords

  • Majorization
  • opportunistic beamforming (OBF)
  • selective feedback
  • sum-rate
  • vector broadcast channels

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