  Medium-scale or large-scale receive antenna array with digital beamforming
can be employed at receiver to make a significant interference reduction, but
leads to expensive cost and high complexity of the RF-chain circuit. To deal
with this issue, a classic analog-and-digital beamforming (ADB) structure was
proposed in the literature for greatly reducing the number of RF-chains. Based
on the ADB structure, we in this paper propose a robust hybrid ADB scheme to
resist directions of arrival (DOAs) estimation errors. The key idea of our
scheme is to employ null space projection (NSP) in analog beamforming domain
and diagonal loading (DL) method in digital beamforming domain. Simulation
results show that the proposed scheme performs more robustly, and moreover, has
a significant improvement on the receive signal to interference plus noise
ratio (SINR) compared to NSP ADB scheme and DL method.
