Method and device for performing fast fallback in order to avoid link disconnection in wireless access system supporting millimeter wave (mmWave)

A user equipment (UE) for performing fast fallback in a wireless access system supporting millimeter wave (mmWave), the UE comprising:

• a transmitter;
• a receiver;
• and
• a processor that controls the transmitter and the receiver to support fast fallback,
• wherein the processor:
• controls the transmitter and the receiver to establish radio resource control (RRC) connections with each of an mmWave base station (BS) and a legacy BS,
• controls the receiver to receive downlink data from the mmWave BS,
• controls the receiver to receive, from the legacy BS, information related to resources to be allocated for the fast fallback, wherein the information is received periodically and includes downlink transmit power strength information of the legacy BS,
• detects whether non-line of sight (NLoS) transition occurs in an mmWave link with the mmWave BS,
• determines whether to transmit a fallback request message based on the downlink transmission power strength information of the legacy BS in order to perform a fast fallback to the legacy BS in response to the NLoS transition being detected, and
• controls the receiver to receive downlink data from the legacy BS after the fallback request message is transmitted and the fast fallback to the legacy BS is performed,
• wherein the UE maintains the RRC connection with the mmWave BS after performing the fast fallback to the legacy BS.