Comparison of adaptive beamforming and orthogonal STBC with outdated feedback

Youngwook Ko, Qian Ma, Cihan Tepedelenlioglu

Research output: Contribution to journalArticlepeer-review

8 Scopus citations


We compare the achievable performance of adaptive beamforming (A-BF) and adaptive orthogonal space time block coding (A-OSTBC) with outdated channel feedback. We extend our single user setup to multiuser diversity systems employing adaptive modulation, and illustrate the impact of feedback delay on the multiuser diversity gain with either A-OSTBC or A-BF. Using closed-form expressions for spectral efficiency and average BER of a multiuser diversity system derived in this paper, we prove that the A-BF scheme outperforms the A-OSTBC scheme with no feedback delay. However, when the feedback delay is large, the A-OSTBC scheme achieves better performance due to the reduced diversity advantage of A-BF. We observe that more transmit antennas bring higher spectral efficiency for BF. With small feedback delay, this becomes inverted using OSTBC, due to the effect of channel-hardening. Interestingly, however, we show that A-OSTBC with multiple users enjoys improved spectral efficiency when the number of transmit antennas is increased and the feedback delay is significant.

Original languageEnglish (US)
Pages (from-to)20-25
Number of pages6
JournalIEEE Transactions on Wireless Communications
Issue number1
StatePublished - Jan 2007


  • Adaptive modulation
  • Beamforming
  • Multi-antenna systems
  • Multiuser diversity
  • Orthogonal space-time block coding

ASJC Scopus subject areas

  • Computer Science Applications
  • Electrical and Electronic Engineering
  • Applied Mathematics


Dive into the research topics of 'Comparison of adaptive beamforming and orthogonal STBC with outdated feedback'. Together they form a unique fingerprint.

Cite this