ACHIEVING EXPONENTIAL DIVERSITY ORDER IN RAYLEIGH FADING CHANNELS

We consider the problem of optimal power allocation in an MISO system with perfect/partial channel state information (CSI) at the transmitter and perfect CSI at the receiver. Unlike other recent work, we consider power allocation in space and time. In addition to providing substantial reduction in BER, this control surprisingly provides exponential diversity order for a Rayleigh fading channel. However, when the CSI is not perfect at the transmitter, we obtain only polynomial diversity order which nevertheless may still be higher than the usually assumed maximal diversity or-