Optimized block-diagonalization precoding technique using givens rotations QR decomposition

The emerging 5G mobile communication standard aims to increase the throughput and, in the same time, to considerably increase the number of users serviced concurrently (Internet of Things). The key direction for achieving these requirements is to heavily extend the use of the spatial degrees of freedom, especially in the multi-user scenarios. Multi-User Massive MIMO (MU-MIMO) is one of the key technologies that responds well to the 5G needs. However, the use of MU-MIMO in the downlink direction raises the collaborative detection problem at the user side, thus the elimination of the inter-user interference becomes necessary. The paper presents a reduced complexity linear transmitter precoding technique that cancels the inter-user interference in a downlink MU-MIMO system. The reduced complexity is achieved through re-using as many low-level operations as possible. The method is suitable for implementation on any modern processor and proven to be scalable to a Massive MIMO scenario without any loss in performance.