Performance limitation of closed-loop transmit antenna diversity over fast Rayleigh fading channels

Recently, transmit antenna diversity (TAD) has been considered as a key technique to improve the capacity of wireless systems over a fading channel. A type of TAD is closed-loop TAD, which utilizes channel conditions. Closed-loop TAD has a drawback caused by the feedback delay under u fast fading channel environment. If the channel information is outdated due to the feedback delay, the performance can be severely degraded. In this correspondence, we find the bit error rate (BER) of the closed-loop TAD with the feedback delay for a time-variant Rayleigh fading channel. For example, it is observed that there is about 2-dB degradation at the BER of 10-2when four transmit antennas are used, and the feedback delay is 5 ms with the updating rate 400 Hz.