  The initial access is required to establish a connection between millimeter
wave access point (AP) and users. The large isotropic pathloss at high
frequencies can be mitigated by the use of highly directional antennas.
However, it complicated the initial access procedures and increased the
latency, defying one of the major low latency objective of 5G systems. Beam
training algorithms are developed for the AP as well as for the users to find
the desired beam quickly and reduce the initial access delay. But, these beam
training protocols have to be run very frequently due to outage events, user's
mobility and period of sleep cycles.
