TY - JOUR
T1 - Comparison of adaptive beamforming and orthogonal STBC with outdated feedback
AU - Ko, Youngwook
AU - Ma, Qian
AU - Tepedelenlioglu, Cihan
N1 - Funding Information:
Manuscript received January 25, 2005; revised May 23, 2005 and November 15, 2005; accepted January 10, 2006. The associate editor coordinating the review of this paper and approving it for publication was H. Jafarkhani. The work in this paper was supported by NSF Career Grant No. CCR-0133841. Portions of this work have appeared in [1] and [2].
PY - 2007/1
Y1 - 2007/1
N2 - 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achievable performance of adaptive beamforming (A-BF) and adaptive orthogonal space time block coding (A-OSTBC) with outdated channel feedback.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.
AB - 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achievable performance of adaptive beamforming (A-BF) and adaptive orthogonal space time block coding (A-OSTBC) with outdated channel feedback.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.
KW - Adaptive modulation
KW - Beamforming
KW - Multi-antenna systems
KW - Multiuser diversity
KW - Orthogonal space-time block coding
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U2 - 10.1109/TWC.2007.05013
DO - 10.1109/TWC.2007.05013
M3 - Article
AN - SCOPUS:33947606945
SN - 1536-1276
VL - 6
SP - 20
EP - 25
JO - IEEE Transactions on Wireless Communications
JF - IEEE Transactions on Wireless Communications
IS - 1
ER -