Transmit optimization for frequency division duplex multi-antenna systems

This paper proposes a transmission scheme for frequency division duplex (FDD) multi-antenna systems. The proposed scheme achieves rates close to capacity without requiring explicit feedback of channel state information (CSI) from the receiver. For FDD systems, the conventional assumption is that the channels on the forward and reverse links are completely uncorrelated and hence the transmitter has to rely on feedback from the receiver in order to implement any transmit optimization. However, this assumption of completely uncorrelated channels on the two links is not always a valid assumption. It is argued that in several situations, specifically those in which the base station antenna array is situated high above the terrain, there is partial correlation between the two links. This paper presents a transmission scheme that exploits this correlation between the forward and reverse links in a multi-antenna FDD system. The scheme is designed to be robust in that the performance degrades gracefully in the absence of any correlation between the two links. Simulations show that the proposed scheme indeed achieves near-optimal performance under many different channel conditions.