  Multi-beam selection is one of the crucial technologies in hybrid beamforming
systems for frequency-selective fading channels. Addressing the problem in the
frequency domain facilitates the procedure of acquiring observations for analog
beam selection. However, it is difficult to improve the quality of the
contaminated observations at low SNR. To this end, this paper uses an idea that
the significant observations are sparse in the time domain to further enhance
the quality of signals as well as the beam selection performance. By exploiting
properties of channel impulse responses and circular convolutions in the time
domain, we can reduce the size of a Toeplitz matrix in deconvolution to
generate periodic true values of coupling coefficients plus random noise
signals. An arithmetic mean of these signals yields refined observations with
minor noise effects and provides more accurate sparse multipath delay
information. As a result, only the refined observations associated with the
estimated multipath delay indices have to be taken into account for the analog
beam selection problem.
