Date Added: Oct 2012
In this paper, an Orthogonal Projection SIgnal Alignment (OP-SI) scheme is proposed for Multiple-Input and Multiple-Output (MIMO) relay systems, and the user performance is studied with and without perfect Channel State Information (CSI). Particularly, the authors focus on an important scenario in cellular systems, where the base station exchanges messages with multiple users via a relay. By jointly designing the pre-coding matrices at the base station and the relay, information exchanging can be accomplished within two time slots. When the perfect CSI is available, closed form expressions of ergodic sum rate are developed for the proposed scheme, where they can demonstrate that the proposed scheme yields a better performance than the existing zero-forcing signal alignment scheme.