  The orbital angular momentum (OAM) technique provides a new degree of freedom
for information transmissions in millimeter wave communications. Considering
the spatial distribution characteristics of OAM beams, a new OAM spatial
modulation (OAM-SM) millimeter wave communication system is first proposed for
future mobile networks. Furthermore, the capacity, average bit error
probability and energy efficiency of OAM-SM millimeter wave communication
systems are analytically derived for performance analysis. Compared with the
conventional multi-input multi-output (MIMO) millimeter wave communication
systems, the maximum capacity and energy efficiency of OAM-SM millimeter wave
communication systems are improved by 36% and 472.3%, respectively. Moreover,
numerical results indicate that the proposed OAM-SM millimeter wave
communication systems are more robust to path-loss attenuations than the
conventional MIMO millimeter wave communication systems, which makes it
suitable for long-range transmissions. Therefore, OAM-SM millimeter wave
communication systems provide a great growth space for future mobile networks.
