Increasing demand for higher data rates and channel capacity drives the need to use the available spectrum more efficiently. As a result, 5G wireless systems will use millimeter wave (mmWave) frequency bands to take advantage of wider available bandwidth. In addition, 5G systems deploy large scale antenna arrays to mitigate severe propagation loss in the mmWave band. However, these configurations bring their unique technical challenges.
Spatial multiplexing can be used to create multiple subchannels in the scatterer rich environment so multiple data streams can be transmitted and recovered independently. This is achieved by applying a set of precoding and combining weights derived from the channel matrix. With large antenna arrays, it is not always practical due to cost and power budgets, to apply digital weights on each antenna element. Hybrid beamforming can be used to address this issue.