Downlink beam-forming method using STBC for mobile propagation environments

Space division multiple access (SDMA) is an attractive candidate for increasing the channel capacity. In an SDMA system, signals from multiple terminals are spatially separated and this feature enables terminals to use the same frequency and the same timing. However, even slight channel estimation error significantly affects the transmission quality in the downlink. We propose a new closed-loop SDMA downlink beam-forming method that employs transmission diversity for multi-beams and mitigates the influence of multi-path fading. The effectiveness with respect to angular spread and the Doppler frequency is evaluated in computer simulations and the proposed method is shown to achieve an signal-to interference-plus-noise-ratio (SINR) that is 3-dB higher than that of the conventional scheme in a flat fading environment.