A unified derivation and cutoff rate analysis of transmit diversity

We present a framework for systematically studying transmit diversity schemes with various levels of feedback about the channel coefficients from the receiver to the transmitter. We define a simple optimality criterion with respect to which we show that traditional schemes designed by conventional wisdom are optimal and also show that when only the channel gains are fed back the switched-time scheme is optimal. We then determine the channel cutoff rates for the different transmit diversity schemes.