The vast amount of spectrum available in the underutilized millimeter-wave (mmWave) frequency bands is considered as one of the key enablers for the demanded tremendous increase in the capacity of future cellular networks. In contrast to the frequencies traditionally used for mobile communications, the higher frequencies of the mmWave frequency bands lead to a higher free space omnidirectional path loss. To overcome the huge free space omnidirectional path loss, the deployment of a very large number of antennas at the base station (BS), known as massive MIMO, is crucial.
Due to the large antenna gains achievable by the large number of antennas, more energy can be transmitted and received through narrower directed beams, which can compensate for the high free space omnidirectional path loss. Therefore, massive MIMO makes the communication in the underutilized mmWave frequency bands viable and mmWave communications can increase the amount of usable spectrum.
In our research, we focus on hybrid precoding for mmWave communications, which, in contrast to the traditional fully digital precoding, moves a part of the signal processing from the digital to the analog domain and is one possibility for reducing the complexity, power consumption and costs resulting from the large number of antennas. In particular, we develop new hybrid precoding algorithms, which design the hybrid precoders for the hybrid analog and digital signal processing. Here, our main interest lies in hybrid precoding algorithms for a scenario with multiple users served by the BS that achieve a high sum rate and have a low computational complexity at the same time.