  Many operators have been bullish on the role of millimeter-wave (mmWave)
communications in fifth-generation (5G) mobile broadband because of its
capability of delivering extreme data speeds and capacity. However, mmWave
comes with challenges related to significantly high path loss and
susceptibility to blockage. Particularly, when mmWave communication is applied
to a mobile terminal device, communication can be frequently broken because of
rampant hand blockage. Although a number of mobile phone companies have
suggested configuring multiple sets of antenna modules at different locations
on a mobile phone to circumvent this problem, identifying an optimal antenna
module and a beam pair by simultaneously opening multiple sets of antenna
modules causes the problem of excessive power consumption and device costs. In
this study, a fast antenna and beam switching method termed Fast-ABS is
proposed. In this method, only one antenna module is used for the reception to
predict the best beam of other antenna modules. As such, unmasked antenna
modules and their corresponding beam pairs can be rapidly selected for
switching to avoid the problem of poor quality or disconnection of
communications caused by hand blockage. Thorough analysis and extensive
simulations, which include the derivation of relevant Cram\'{e}r-Rao lower
bounds, show that the performance of Fast-ABS is close to that of an oracle
solution that can instantaneously identify the best beam of other antenna
modules even in complex multipath scenarios. Furthermore, Fast-ABS is
implemented on a software defined radio and integrated into a 5G New Radio
physical layer. Over-the-air experiments reveal that Fast-ABS can achieve
efficient and seamless connectivity despite hand blockage.
