Full rank spatial channel estimation at millimeter wave systems

Spatial channel estimation (CE) for hybrid beamforming architecture is one of the crucial challenges for millimeter wave (mmW) links. The limited beamwidth makes the CE incapable of resolving multiple channel paths from the same cluster when the angular spread is less than or equal to the beamwidth. Therefore, how to efficiently obtain reliable links which provide maximum spatial degree-of-freedom gain for data transmission is the key technology. To this end, a novel CE method to estimate full rank array response matrices is presented. The full rank array response matrices lead to the full rank reconstructed channel matrix, which provides the maximum spatial degree-of-freedom gain of the sparse mmW channels. Compared with the previously proposed CE methods which use transmit or receive diversity rather than spatial degrees of freedom, the proposed one shows significant increase of data rates as SNR is getting larger.