Methods for supplementary uplink access in wireless systems

A method performed by a wireless transmit/receive unit (WTRU), the method comprising:

• transmitting, to a next generation node B (gNB), a first random access preamble on a first physical random access channel (PRACH) resource of a first uplink (UL) carrier;
• determining that the transmission on the first PRACH resource is unsuccessful;
• transmitting, to the gNB, a second random access preamble on a second PRACH resource of the first UL carrier;
• determining that the transmission on the second PRACH resource is unsuccessful;
• determining that a maximum number of random access retransmissions on the first UL carrier is met;
• transmitting, to the gNB on a second UL carrier, a third random access preamble on a third PRACH resource;
• determining a random access radio network temporary identifier (RA-RNTI) for the second UL carrier, wherein the RA-RNTI is determined at least in part by a carrier offset;
• and
• monitoring for a random access response (RAR) based on the RA-RNTI;
• wherein the first UL carrier and second UL carrier are different UL carriers.