I. Introduction
THE improvement of the downlink capacity is one of the main challenges of the wireless systems, and closed-loop techniques are known to have the potential to solve the problem. As a well-known example, Transmit Adaptive Array is part of the 3GPP standard. In a downlink closed-loop system, the transmitter receives the required CSI (Channel State Information) through a limited-capacity feedback channel from the receiver. The feedback data is a low-rate bitstream resulting from rough quantization of the CSI at the receiver. There are three major imperfections which affect the closed-loop systems: feedback delay, feedback error, and sub-optimal reconstruction. Feedback delay has been shown to drastically affect the performance of closed-loop systems [1], especially at high mobile speeds.