Deterministic perturbation gradient approximation for transmission subspace tracking in FDD-CDMA

Multiple antenna transmission promises to bring substantial capacity benefits to wireless communication systems. Knowledge of the channel can be used to further improve the communication. In frequency division duplex channels, such knowledge can be obtained using feedback. The feedback bandwidth is limited, hence efficient feedback of such channel information to the transmitter is required. This paper proposes one such method based on subspace tracking principles. A perturbation vectors is used to approximate the gradient of the cost function. Simulation results show good performance when there is temporal or spatial correlation in the channel.