Method for transmitting and receiving message for random access in multi beam system

A method for transmitting and receiving a message for a random access (RA) with a base station by user equipment in a multi beam system, the method comprising:

• receiving a synchronization signal (SS) block including a synchronization signal from the multi beam of the base station;
• determining a physical random access channel (PRACH) resource through which a message 1 of a RA procedure is transmitted based on information about an association mapping between the SS block and the PRACH resource;
• and
• transmitting the message 1 to the base station by using the determined PRACH resource.

A method for transmitting and receiving a message for a random access (RA) with user equipment (UE) by a base station in a multi beam system, the method comprising:

• transmitting a synchronization signal (SS) block including a synchronization signal by performing beam sweeping for a multi beam;
• receiving a message 1 of an RA procedure from the UE;
• determining an optimal transmission beam to be used to transmit a message 2 of the RA procedure based on information about an association mapping between the SS block and a preamble index of a preamble included in the message 1;
• and
• transmitting the message 2 by using the optimal transmission beam.