“…The contention-based RA procedure is a reference method used in the existing RA scheme and it has difficulty supporting massive connectivity. Therefore, a number of studies on contention-based RA considering the massive RA of 5G have been conducted [ 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 ].…”