Investigation on precoding techniques in E-UTRA and proposed adaptive precoding scheme for MIMO systems

Codebook based multiple-input multiple-output (MIMO) precoding can significantly improve the system spectral efficiency with limited feedback and has been accepted as one of the most promising techniques for the Evolved UTRA (E-UTRA). In this paper, firstly, we investigate precoding techniques through system-level simulation in EUTRA environment including various precoding modes, precoding methods and codebooks. Then, to further exploit the system performance in universal environments, an adaptive MIMO precoding scheme is proposed, in which different precoding modes including single-user MIMO (SU-MIMO) and multiple-user MIMO (MU-MIMO), precoding methods including unitary precoding (UP) and zero-forcing beamforming (ZF-BF) for MU-MIMO, and codebooks including Grassmannian codebook and DFT codebook for MU-MIMO with ZF-BF, are semi-statically switched based on long-term information, system load and channel statistics. Particularly, the proposed scheme is much feasible for practical systems and the increase of signaling overhead can be negligible. Finally, it can be seen from the simulation results that, compared with conventional schemes with fixed precoding technique, proposed adaptive scheme can yield much improvement on spectral efficiency.