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This letter proposes a hybrid transmission scheme by combining zero-forcing beamforming (ZFBF) and orthogonal beamforming (OBF) for the multiple-input multiple-output broadcast channel. This method first utilizes ZFBF for only a part of the scheduled users with approximately orthogonal channels. By further constructing orthogonal beamformers in the null space of the ZFBF user channels, it then employs OBF for the rest of users to fully exploit the spatial dimension. Theoretical analysis, as well as simulation results, verify that our scheme outperforms the conventional ZFBF scheme and OBF scheme with user selection.
Date of Publication: January 2009