In practical downlink multiuser MIMO channels, users' channels are non-orthogonal, which results in inter-user interference and in turn degrades system performance. In this paper, a new subspace-domain linear transmit preprocessing technique is proposed in enhancing users' spatial separation and suppressing inter-user interference. The authors show by simulations that sum rate is significantly improved and its saturation is avoided. In downlink MU-MIMO channels, sum capacity can be significantly improved by allowing simultaneous transmission to multiple users and applying pre-coding to minimize inter-user interference. Aiming at maximizing the achievable data rate, a great number of linear pre-coding algorithms have been proposed.