Remote Control of Transmit Beamforming in TDD/MIMO Systems

This paper propose a new control scheme that the base station (BS) controls the terminal´s transmit beamforming in time-division duplex (TDD)/multi-input multi-output (MIMO) systems. In the proposed scheme, the BS transmits pilot signals using proper downlink beamforming to instruct target beamforming to the terminal. Using responses of the pilot signals, the terminal computes weight for transmit beamforming. We theoretically show that the BS can control not only a single terminal´s transmit beamforming but also multiple terminals´ transmit beamforming simultaneously. Furthermore, efficient weight computation at the terminal is investigated to yield accurate transmit beamforming in the presence of noise. Numerical results show that the terminal can yield transmit beamforming close to the target beamforming in noise environments