Physical random access for NR-U
Systems and methods are disclosed for performing random access (RA) in 5G New Radio (NR) systems, including New Radio in unlicensed spectrum (NR-U) systems. A wireless transmit/receive unit (WTRU) may receive a configuration for physical random access channel (PRACH) resources. The WTRU may determine whether to use a first type of PRACH transmission or a second type of PRACH transmission. For the first type of PRACH transmission, the WTRU may select a PRACH resource, without performing listen-before-talk (LBT), immediately following reception of an synchronization signal block (SSB). For the second type of PRACH transmission, the WTRU may randomly select the PRACH resource associated with the SSB, and perform a first LBT on the selected PRACH resource. The WTRU may transmit a PRACH preamble in the selected PRACH resource. The WTRU may perform a second LBT for random access response (RAR) reception for hidden node detection.
1. A wireless transmit/receive unit (WTRU), the WTRU comprising:
a transceiver; and
a processor;
the transceiver configured to receive configuration information indicating physical random access channel (PRACH) resources;
the processor and the transceiver configured to transmit a PRACH preamble using one of the indicated PRACH resources;
the processor and the transceiver configured to perform a listen-before-talk (LBT) procedure for hidden node detection before monitoring for a random access response (RAR); and
on a condition that the RAR is not received successfully, the transceiver is configured to:
on a condition that a hidden node is detected, retransmit the PRACH preamble without power ramping;
on a condition that a hidden node is not detected, retransmit the PRACH preamble with power ramping; and
on a condition that the RAR is received successfully, the transceiver is configured to transmit a RACH message.
2. The WTRU of claim 1 , wherein the processor is configured to determine whether to transmit the PRACH preamble using a first type of PRACH transmission or a second type of PRACH transmission based on at least one of a service type or a service requirement.
3. The WTRU of claim 2 , wherein the service type or the service requirement include latency and performance.
4. The WTRU of claim 2 , wherein the processor is configured to determine to use the first type of PRACH transmission for a low latency service type or service requirement and the processor is configured to determine to use the second type of PRACH transmission for an enhanced mobile broadband (eMBB) service type or service requirement.
5. The WTRU of claim 1 , wherein the transceiver is configured to retransmit the PRACH preamble after a time delay.
6. The WTRU of claim 1 , wherein the transceiver is further configured to receive a RACH message 2 (Msg2) from a base station.
7. The WTRU of claim 1 , wherein the transceiver is configured to transmit the PRACH preamble in a RACH message 1 (Msg1).
8. The WTRU of claim 1 configured to perform RA in a New Radio unlicensed spectrum (NR-U) system.
9. The WTRU of claim 2 , the processor and the transceiver configured to, on a condition that the second type of PRACH transmission is used:
randomly select a PRACH resource from the indicated PRACH resources,
perform a first LBT procedure on the randomly selected PRACH resource,
transmit a PRACH preamble in the randomly selected PRACH resource; and
perform a second LBT procedure for hidden node detection before monitoring for a random access response (RAR).
10. A method performed by a wireless transmit/receive unit (WTRU), the method comprising:
receiving configuration information indicating physical random access channel (PRACH) resources;
transmitting a PRACH preamble using one of the indicated PRACH resources;
performing a listen-before-talk (LBT) procedure for hidden node detection before monitoring for a random access response (RAR); and
on a condition that the RAR is not received successfully:
retransmitting, on a condition that a hidden node is detected, the PRACH preamble without power ramping; and
retransmit, on a condition that a hidden node is not detected, the PRACH preamble with power ramping.
11. The method of claim 10 , further comprising determining whether to transmit the PRACH preamble using a first type of PRACH transmission or a second type of PRACH transmission based on at least one of a service type or a service requirement.
12. The method of claim 11 , wherein the service type or the service requirement include latency and performance.
13. The method of claim 11 , wherein the first type of PRACH transmission is used for a low latency service type or service requirement and the second type of PRACH transmission is used for an enhanced mobile broadband (eMBB) service type or service requirement.
14. The method of claim 10 , further comprising:
on a condition that the RAR is received successfully, transmitting a RACH message.
15. The method of claim 14 , wherein the PRACH preamble is retransmitted after a time delay.
16. The method of claim 14 , further comprising:
receiving a RACH message 2 (Msg2) from a base station.
17. The method of claim 10 , wherein the PRACH preamble is transmitted in a RACH message 1 (Msg1).
18. The method of claim 10 performed in a New Radio unlicensed spectrum (NR-U) system.
19. The method of claim 11 , comprising: on a condition that the second type of PRACH transmission is used:
randomly selecting a PRACH resource from the indicated PRACH resources; performing a first LBT procedure on the randomly selected PRACH resource;
transmitting a PRACH preamble in the randomly selected PRACH resource; and
performing a second LBT procedure for hidden node detection before monitoring for a random access response (RAR).