  Beamforming is an indispensable feature for millimeter wave (mmWave) wireless
communications in order to compensate for the severe path loss incurred due to
high frequency operation. In this paper, we introduce a novel framework to
evaluate the spectral efficiency (SE) of non-line-of-sight(NLOS) mmWave links
with optimal analog beamforming. Optimality here implies the joint selection of
antenna beams at the transmitter and receiver which simultaneously maximize the
received power. We develop a mathematical framework based on the extended
Saleh-Valenzuela channel model to embody the impact of optimal analog
beamforming into the performance metrics for NLOS mmWave links. Practical
mmWave channels are characterized by sparsity in terms of number of multi-path
components; we exploit this feature to derive upper and lower bounds on SE of
beamformed directional links. Simulation results reveal that the proposed
approach is fairly accurate to model beamformed links in most practical
operating scenarios. We also study the impact of overhead due to antenna beam
training on the throughput (TP) of a link and obtain an approximate solution
for optimal antenna half power beamwidth which maximizes TP.
