Layered block diagonalization for base station cooperated multiuser MIMO with partial channel state information feedback

This paper proposes a layered block diagonalization (BD) precoding method for downlink multiuser multiple-input multiple-output (MIMO) transmission employing multiple base station (BS) cooperation where some of the instantaneous channel state information (CSI) feedback between the user equipment and the respective BSs are missing depending on the location of the user equipment. In the layered BD method, the inter-user interference from the channel for which the set of BSs knows the instantaneous CSI is eliminated as in the conventional BD method with perfect CSI feedback. However, since some of the instantaneous CSI is not obtained at the BSs, the inter-user interference from these channels without the knowledge of the instantaneous CSI is allowed. To minimize the inter-user interference from the BS-unknown channel and to utilize fully the available transmission power, the layered BD method adaptively controls the set of BSs used for the signal transmission for a particular user in user-by-user manner, based on the CSI feedback state of that user and the other users. The layered BD method maximizes the power efficiency of the respective users in a partial instantaneous CSI feedback scenario, while maintaining the nulling of the inter-user interference in all of the BS-known MIMO channels. A computer simulation is conducted to verify the effectiveness of the proposed method from the viewpoint of the achievable throughput. The results show that the proposed layered BD method expands the user throughput region compared to that of the conventional approaches when accommodating the partial instantaneous CSI feedback scenario.