Attitude Information Aided Digital Beamforming in Millimeter-Wave MIMO Systems

Attitude information can be utilized for beam tracking in millimeter-wave (mmWave) analog beamforming. It provides the direction of arrival (DOA) information of the user equipment (UE) when it rotates, and thus, significantly reduces the overhead of beam searching. However, in digital beamforming (DBF), the transceivers are not designed based on DOAs, which makes it more challenging to utilize attitude information to reduce system overhead. In this article, we propose an attitude information aided DBF algorithm. Specifically, based on the clustered channel model, we derive the relationship between channel variation and the attitude of UE during the rotation. Furthermore, it is proved that only the transmitter at UE requires to be redesigned after the rotation, while the receiver at base station does not. Compared with the joint transceiver design, the performance loss is generally trivial. Therefore, we propose an AIA digital transmitter design algorithm for uplink transmission with equal power allocation. The spectral efficiency performance can approximate the optimal joint transceiver design performance without real-time channel state information. We also extend the method to unequal power allocation case and propose the algorithm with water-filling power allocation. Finally, simulation results are presented to examine the effectiveness of proposed algorithms.