  In this paper, we propose an analog beamsteering approach for enabling
flexible hybrid beamforming design that can achieve performance close to
singular value decomposition (SVD) based digital beamforming with single user
case. As a starting point, assuming the use of a codebook with infinite
precision, we apply transposes of antenna array response matrices as analog
beam-formers at the BS and the UE sides. The resulting effective chan-nel
matrix including both propagation channel and analog beam-formers is shown to
be able to provide a maximal achievable rate very close to SVD based digital
beamforming at low to medium SNR. Next, the impact of a finite size codebook is
analyzed for practical analog beamformer design. A closed-form derivation is
obtained for mapping rate loss to the number of antennas, code-book sizes and
the received SNR. The analysis shows that in or-der to achieve performance
comparable to analog beamforming with infinite precision, the codebook size
should be at least larger than the number of implemented antennas. Therefore,
the pro-posed analog beamforming approach can be designed inde-pendently
without taking digital beamforming into account. Such an approach can lead to
the development of flexible hybrid beam-forming architectures that could adapt
to a changing propagation environment via agile analog beam selection and
maximize spatial multiplexing gain via proper digital beamformer design.
