Random access with new radio unlicensed cells

1. A user equipment that performs wireless communication comprising:

a processor; and

a memory coupled with the processor, the memory comprising executable instructions stored thereon that when executed by the processor cause the processor to effectuate operations comprising:

receiving, from a network node, a configuration including a first threshold with respect to a first counter for falling back to 4-step random access (RA);

based on obtaining an indication of an event, performing RA resource selection;

performing, by a physical layer (PHY) a first sub-band listen-before-talk (LBT) on a selected sub-band associated with the RA resource selection;

based on detecting a channel is busy by the first sub-band LBT, providing, by the PHY layer to a media access control (MAC) layer, a failure indication;

based on the failure indication, incrementing, by the MAC layer, the first counter;

based on detecting that a value of the first counter is not greater than the first threshold, performing, by the PHY layer a second sub-band LBT on the selected sub-band associated with the RA resource selection;

based on detecting a channel is free by the second sub-band LBT, incrementing a second counter and providing one or more parameters to configure a 2-step RA preamble transmission to the PHY layer, the second counter is used to calculate a RA target power for the 2-step RA preamble transmission;

based on the one or more parameters, transmitting a MsgA as the 2-step RA preamble transmission to the network node;

receiving, from the network node, a MsgB as a Random Access Response (RAR) for the 2-step RA preamble transmission, wherein the MsgB is comprised of an indication that a MsgA payload was unsuccessfully decoded and uplink (UL) grant for a Msg3 transmission, wherein the indication that the MsgA payload was unsuccessfully decoded is provided by a field for RA preamble ID in a MAC subheader; and

based on detecting the indication, commencing with step 3 of the 4-step RA by transmitting, to the network node, a Msg3 on UL resources configured in the UL grant, wherein the Msg3 comprises the MsgA payload.

2. The user equipment of claim 1 , the operations further comprising when a channel is indicated as free, transmitting a preamble.

3. The user equipment of claim 1 , the operations further comprising:

when a channel is indicated as free, transmitting a preamble; and

monitoring a physical downlink control channel (PDCCH), wherein the monitoring of the PDCCH is on a BWP on which the preamble was transmitted.

4. The user equipment of claim 3 , the operations further comprising starting random access response window at a first PDCCH occasion as from the end of an Random Access Preamble transmission.

5. The user equipment of claim 1 , wherein the failure indication is a random access preamble (RAP) transmission indication.

6. The user equipment of claim 1 , the operations further comprising:

when a channel is indicated as busy, providing, by the PHY layer to the MAC layer, a failure indication that indicates a failure to transmit the preamble; and

based on the received failure indication, performing, by the MAC layer, another random access resource selection using a second selected sub-band.

7. The user equipment of claim 1 , wherein the step 3 of the 4-step random access procedure has a transmission of a Msg3 payload that corresponds to the MsgA payload.

8. The user equipment of claim 7 , wherein the transmission of the Msg3 payload is performed using uplink resources signaled via the RAR.

9. The user equipment of claim 1 , the operations further comprising receiving a configured threshold from a second apparatus, wherein the second apparatus is a gNB.

10. A base station comprising:

a processor; and

a memory coupled with the processor, the memory comprising executable instructions stored thereon that when executed by the processor cause the processor to effectuate operations comprising:

transmitting, to a user equipment, a configuration including a first threshold with respect to a first counter for falling back to 4-step random access (RA), wherein the first counter is configured to be incremented when a failure indication is detected on a sub-band listen-before-talk (LBT);

monitoring a physical random access channel (PRACH) resource for a MsgA preamble of MsgA for a 2-step random access (RA);

detecting the MsgA preamble on a configured PRACH resource, wherein the MsgA is sent after confirming that a value of the first counter is not greater than the first threshold;

failing to successfully decode a MsgA payload associated with the detected MsgA preamble;

transmitting a MsgB as a Random Access Response (RAR) for the 2-step RA preamble transmission, wherein the MsgB is comprised of an indication that the MsgA payload was unsuccessfully decoded and uplink (UL) grant for a Msg3 transmission, wherein the indication is provided by a field for RA preamble ID in a MAC subheader; and

receiving a Msg3 comprising the MsgA payload on UL resources configured in the UL grant.

11. The base station of claim 10 , wherein the MsgA payload on UL resources configured in the UL grant is received from the user equipment.

12. The base station of claim 10 , the operations further comprising receiving a preamble based on a channel being indicates as free.

13. A method for a network node, the method comprising:

transmitting, to a user equipment, a configuration including a first threshold with respect to a first counter for falling back to 4-step random access (RA), wherein the first counter is configured to be incremented when a failure indication is detected on a sub-band listen-before-talk (LBT);

monitoring a physical random access channel (PRACH) resource for a MsgA preamble of MsgAfor a 2-step random access (RA);

detecting the MsgA preamble on a configured PRACH resource, wherein the MsgA is sent after confirming that a value of the first counter is not greater than the first threshold;

failing to successfully decode a MsgA payload associated with the detected MsgA preamble;

transmitting a MsgB as a Random Access Response (RAR) for the 2-step RA preamble transmission, wherein the MsgB is comprised of an indication that the MsgA payload was unsuccessfully decoded and uplink (UL) grant for a Msg3 transmission, wherein the indication is provided by a field for RA preamble ID in a MAC subheader; and

receiving a Msg3 comprising the MsgA payload on UL resources configured in the UL grant.