Random access in new radio (NR) and other beamforming systems
A wireless transmit/receive unit (WTRU) may receive, from a base station, information concerning an association between synchronization signal/physical broadcast channel (SS/PBCH) block transmissions and physical random access channel (PRACH) resources. In an example, each SS/PBCH block transmission may be associated with a transmission beam of the base station. The WTRU may receive the SS/PBCH block transmissions and select one of the transmissions. Further, the WTRU may compare a reference signal received power (RSRP) associated with the selected transmission to a threshold. The WTRU may then determine between performing a random access procedure of a first type and a second type based on the comparison. Also, the WTRU may select a PRACH resource based on the selected transmission and the information concerning the association between the transmissions and the PRACH resources. Moreover, the WTRU may transmit a PRACH preamble, for the determined random access procedure, using the selected PRACH resource.
1. A method performed by a wireless transmit/receive unit (WTRU), the method comprising:
receiving, from a base station, information concerning an association between a plurality of synchronization signal/physical broadcast channel (SS/PBCH) block transmissions and a plurality of physical random access channel (PRACH) resources, wherein each of the plurality of SS/PBCH block transmissions is associated with a transmission beam of the base station;
receiving the plurality of SS/PBCH block transmissions;
comparing a reference signal received power (RSRP) associated with one of the plurality of the SS/PBCH block transmissions to a threshold;
determining between random access procedure of a first type and a random access procedure of a second type based on the comparison;
selecting a PRACH resource based on the one of the plurality of the SS/PBCH block transmissions and the information concerning the association between the plurality of SS/PBCH block transmissions and the plurality of PRACH resources; and
transmitting a PRACH preamble, for the determined random access procedure of the first type or random access procedure of the second type, using the selected PRACH resource.
2. The method of claim 1 , wherein the random access procedure of the first type is a four-step random access procedure and the random access procedure of the second type is a two-step random access procedure.
3. The method of claim 2 , wherein the two-step random access procedure includes a first step including transmitting a physical uplink shared channel (PUSCH) transmission and a second step including receiving a message in a control channel search space.
4. The method of claim 3 , wherein the PUSCH transmission is a grant-less PUSCH transmission.
5. The method of claim 3 , wherein the PUSCH transmission includes a radio resource control (RRC) connection request.
6. The method of claim 3 , wherein the first step of the two-step random access procedure further includes the transmission of the PRACH preamble.
7. The method of claim 2 , wherein the four-step random access procedure includes a first step including transmitting a random access preamble, a second step including receiving a random access response, a third step including transmitting a PUSCH transmission and a fourth step including receiving a contention resolution message.
8. The method of claim 1 , wherein the plurality of PRACH resources include one or more of PRACH preamble sequences, time resources and frequency resources.
9. The method of claim 1 , further comprising determining an SS/PBCH block time index for the one of the plurality of the SS/PBCH block transmissions.
10. The method of claim 1 , further comprising determining a transmission beam for uplink transmission based on the one of the plurality of the SS/PBCH block transmissions.
11. The method of claim 10 , wherein the PRACH preamble is transmitted using the determined transmission beam.
12. A wireless transmit/receive unit (WTRU) comprising:
a transceiver; and
a processor operatively coupled to the transceiver; wherein:
the transceiver is configured to receive, from a base station, information concerning an association between a plurality of synchronization signal/physical broadcast channel (SS/PBCH) block transmissions and a plurality of physical random access channel (PRACH) resources, wherein each of the plurality of SS/PBCH block transmissions is associated with a transmission beam of the base station;
the transceiver is configured to receive the plurality of SS/PBCH block transmissions;
the processor is configured to compare a reference signal received power (RSRP) associated with one of the plurality of the SS/PBCH block transmissions to a threshold;
the processor is configured to determine between a random access procedure of a first type and a random access procedure of a second type based on the comparison;
the processor is configured to select a PRACH resource based on the one of the plurality of the SS/PBCH block transmissions and the information concerning the association between the plurality of SS/PBCH block transmissions and the plurality of PRACH resources; and
the transceiver is configured to transmit a PRACH preamble, for the determined random access procedure of the first type or random access procedure of the second type, using the selected PRACH resource.
13. The WTRU of claim 12 , wherein the random access procedure of the first type is a four-step random access procedure and the random access procedure of the second type is a two-step random access procedure.
14. The WTRU of claim 13 , wherein the two-step random access procedure includes a first step including transmitting a physical uplink shared channel (PUSCH) transmission and a second step including receiving a message in a control channel search space.
15. The WTRU of claim 14 , wherein the PUSCH transmission is a grant-less PUSCH transmission.
16. The WTRU of claim 14 , wherein the PUSCH transmission includes a radio resource control (RRC) connection request.
17. The WTRU of claim 14 , wherein the first step of the two-step random access procedure further includes the transmission of the PRACH preamble.
18. The WTRU of claim 13 , wherein the four-step random access procedure includes a first step including transmitting a random access preamble, a second step including receiving a random access response, a third step including transmitting a PUSCH transmission and a fourth step including receiving a contention resolution message.
19. The WTRU of claim 12 , wherein the plurality of PRACH resources include one or more of PRACH preamble sequences, time resources and frequency resources.
20. The WTRU of claim 12 , wherein the processor is further configured to determine a SS/PBCH block time index for the one of the plurality of the SS/PBCH block transmissions.
21. The WTRU of claim 12 , wherein the processor is further configured to determine a transmission beam for uplink transmission based on the one of the plurality of the SS/PBCH block transmissions.
22. The WTRU of claim 21 , wherein the PRACH preamble is transmitted using the determined transmission beam.