A Lattice Reduction Aided Overloaded Multi-user MIMO

We consider overloaded communication in multi user-multiple input multiple output (MU-MIMO) systems in order to further increase the capacity of downlink communication to multiple users. Overloaded communication is a case where the number of receiving antennas is smaller than the number of transmitting streams. In the proposed scheme, overloaded MU-MIMO communication is achieved by precoding with a weight matrix generated based on singular value decomposition. In contrast, we attempt to improve the communication characteristics by non-linear precoding (for example Tomlinson-Harashima Precoding (THP)) to reduce the characteristic difference of each stream. In addition, the non-linear precoding uses Lattice-Reduction to optimize the modulo processing. At the receiver, Lattice-Reduction aided Successive Interference Cancellation (SIC) is performed on the transmitted signal. The Lattice-Reduction improves the orthogonality of the channel portion, resulting in lower spatial correlation and reduced noise enhancement. Bit Error Rate (BER) characteristics were calculated by computer simulation, and the precoding characteristics were evaluated and compared. The results showed that the transmission characteristics of the overloaded MU-MIMO system and the non-linear precoding improved the transmission characteristics.