5G‐NR Radio Interface – MIMO and Beamforming

The multiple input multiple output (MIMO) mechanism improves radio data rate by performing spatial multiplexing of multiple signals. Beamforming is a complementary mechanism to MIMO. Beamforming logically reduces the beam opening angle and limits the level of interference between cells. Elevation beamforming allows a beam to be directed in a specific way, for example, a beam pointing either up or down. The transmission modes implementing beamforming and the multi user‐MIMO mechanism require good correlation between the antennas. The MIMO mechanism and the beamforming mechanism are based on knowledge of the propagation channel. Symbols produced by modulation are distributed over spatial layers, and then precoded before being assigned to resource elements by antenna port. Only the orthogonal frequency division multiplexing signal allows the MIMO mechanism to operate up to four spatial layers or the beamforming mechanism by digital precoding.