DocumentCode :
3800990
Title :
Comparison of adaptive beamforming and orthogonal STBC with outdated feedback
Author :
Youngwook Ko;Qian Ma;Cihan Tepedelenlioglu
Author_Institution :
Dept. of Electr. Eng., Arizona State Univ., Tempe, AZ
Volume :
6
Issue :
1
fYear :
2007
Abstract :
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achievable performance of adaptive beamforming (A-BF) and adaptive orthogonal space time block coding (A-OSTBC) with outdated channel feedback.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
Keywords :
"Array signal processing","Feedback","Delay","Transmitting antennas","Antenna feeds","Block codes","Adaptive systems","Diversity methods","Closed-form solution","Bit error rate"
Journal_Title :
IEEE Transactions on Wireless Communications
Publisher :
ieee
ISSN :
1536-1276
Type :
jour
DOI :
10.1109/TWC.2007.05013
Filename :
4114244
Link To Document :
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