Phase Rotation Assisted Interference Exploitation Precoding With Finite Block Length for MU-MIMO Systems

The interference exploitation precoding (IEP) leverages the harmful interference to align at the constructive interference (CI) region via symbol level precoding (SLP), which greatly improves the conventional zero forcing precoding with QPSK modulation or even higher modulations. This letter firstly develops a joint phase rotation structure, considering both the outer phase rotation for multiple layers and the inner phase alignment for IEP with finite block length in multi-user multiple-input multiple-output (MU-MIMO) systems, termed as JPR-IEP. To tackle the problem, a decoupling scheme is presented, which breaks JPR-IEP into two independent steps as DPR-IEP, thus converting the non-convex JPR-IEP to a solvable problem with low complexity. At last, a codebook-assisted DPR-IEP, namely CB-DPR-IEP with less computational complexity and feed-forward overhead is further investigated, which is approved to be the optimal choice considering the performance, the feed-forward and the complexity for practical MU-MIMO systems.