Performance Analysis of Transmit Diversity Systems with Multiple Antenna Replacement

There are usually rate loss and power spreading effects associated with transmit diversity systems based on orthogonal space-time block coding (OSTBC). Proper antenna selection scheme can help more effectively utilize the transmit antenna and transmission power in such systems. In this paper, we propose a new antenna selection scheme for such systems based on the idea of antenna switching. In particular, targeting at reducing the number of pilot channels and RF chains, the transmitter now replaces the antennas with the lowest received SNR with unused ones if the output SNR of space time decoder at the receiver is below a certain threshold. With this new scheme, not only the number of pilot channels and RF chains to be implemented is decreased, the average amount of information feedback is also reduced. To analyze the performance of this scheme, we derive the exact integral form expression for the probability density function (PDF) of the received SNR. We show through numerical examples that the proposed scheme offers better performance than traditional OSTBC systems using all available transmitting antenna, with a small amount of information feedback. We also examine the effect of different antenna configuration and feedback delay.