Apparatuses and methods for beam identification through the physical random access channel (PRACH) and efficient PRACH resource utilization

1. A User Equipment (UE), comprising:

a wireless transceiver, configured to perform wireless transmission and reception to and from a cellular station; and

a controller, configured to select a downlink reference signal associated with a candidate beam among a plurality of downlink reference signals comprising Channel State Information-Reference Signal (CSI-RS) resources, Synchronization Signal (SS) blocks, or Physical Broadcast Channel (PBCH) blocks, determine one set from a plurality of sets of Physical Random Access Channel (PRACH) preambles and RACH occasions for the selected downlink reference signal according to an association configured between the downlink reference signals and PRACH resources, and use the determined set of PRACH preamble and RACH occasion to perform a PRACH transmission to the cellular station via the wireless transceiver,

wherein the association between the downlink reference signal and the PRACH resource indicates the downlink reference signal selected by the UE to the cellular station,

wherein the association between the downlink reference signal and the candidate beam indicates the candidate beam to the cellular station, and

wherein the cellular station identifies the candidate beam indicated by the UE based on determination of the PRACH resource.

2. The UE of claim 1 , wherein the candidate beam is used for beam failure recovery or for a handover from a cell to another cell.

3. The UE of claim 1 , wherein the PRACH resources comprises the PRACH preambles, the RACH occasions, or a combination thereof, and the association is configured between the downlink reference signals and the PRACH preambles, the RACH occasions, or a combination thereof.

4. The UE of claim 1 , wherein, when the PRACH transmission comprises transmitting a first PRACH preamble using a first RACH occasion which corresponds to the selected downlink reference signal, the first PRACH preamble is used for one purpose; and when the PRACH transmission comprises transmitting the first PRACH preamble using a second RACH occasion which corresponds to another downlink reference signal, the first PRACH preamble is used for another purpose.

5. The UE of claim 4 , wherein, when the first PRACH preamble is transmitted on a serving beam, the first PRACH preamble serves as a scheduling request or an acknowledgement (ACK) or non-acknowledgement (NACK) signal, and when the first PRACH preamble is transmitted on the candidate beam, the first PRACH preamble serves as a request for beam failure recovery.

6. The UE of claim 1 , wherein the association configured between the downlink reference signals and the PRACH resources associates one CSI-RS resource, SS block, or PBCH block to one set of PRACH resource, or associates multiple CSI-RS resources, SS blocks, or PBCH blocks to one set of PRACH resource.

7. The UE of claim 6 , wherein, when the association configured between the downlink reference signals and the PRACH resources associates multiple CSI-RS resources, SS blocks, or PBCH blocks to one set of PRACH resource, the controller is further configured to transmit an uplink transmission to the cellular station via the wireless transceiver for identifying which one of the multiple CSI-RS resources, SS blocks, or PBCH blocks is associated with the candidate beam.

8. The UE of claim 6 , wherein the association configured between the downlink reference signals and the PRACH resources associates one CSI-RS resource, SS block, or PBCH block to one set of PRACH resource, by at least one of: Code Division Multiplexing (CDM), Frequency Division Multiplexing (FDM), and Time Division Multiplexing (TDM).

9. A method for beam identification through a PRACH, executed by a UE wirelessly connected to a cellular station, the method comprising:

selecting a downlink reference signal associated with a candidate beam among a plurality of downlink reference signals comprising CSI-RS resources, SS blocks, or PBCH blocks;

determining one set from a plurality of sets of PRACH preambles and RACH occasions for the selected downlink reference signal according to an association configured between the downlink reference signals and PRACH resources; and

using the determined set of PRACH preamble and RACH occasion to perform a PRACH transmission to the cellular station,

wherein the association between the downlink reference signal and the PRACH resource indicates the downlink reference signal selected by the UE to the cellular station,

wherein the association between the downlink reference signal and the candidate beam indicates the candidate beam to the cellular station, and

wherein the cellular station identifies the candidate beam indicated by the UE based on determination of the PRACH resource.

10. The method of claim 9 , wherein the candidate beam is used for beam failure recovery or for a handover from a cell to another cell.

11. The method of claim 9 , wherein the PRACH resources comprises the PRACH preambles, the RACH occasions, or a combination thereof, and the association is configured between the downlink reference signals and the PRACH preambles, the RACH occasions, or a combination thereof.

12. The method of claim 9 , wherein, when the PRACH transmission comprises transmitting a first PRACH preamble using a first RACH occasion which corresponds to the selected downlink reference signal, the first PRACH preamble is used for one purpose; and when the PRACH transmission comprises transmitting the first PRACH preamble using a second RACH occasion which corresponds to another downlink reference signal, the first PRACH preamble is used for another purpose.

13. The method of claim 12 , wherein, when the first PRACH preamble is transmitted on a serving beam, the first PRACH preamble serves as a scheduling request or an ACK or NACK signal, and when the first PRACH preamble is transmitted on the candidate beam, the first PRACH preamble serves as a request for beam failure recovery.

14. The method of claim 9 , wherein the association configured between the downlink reference signals and the PRACH resources associates one CSI-RS resource, SS block, or PBCH block to one set of PRACH resource, or associates multiple CSI-RS resources, SS blocks, or PBCH blocks to one set of PRACH resource.

15. The method of claim 14 , further comprising:

when the association configured between the downlink reference signals and the PRACH resources associates multiple CSI-RS resources, SS blocks, or PBCH blocks to one set of PRACH resource, transmitting an uplink transmission to the cellular station for identifying which one of the multiple CSI-RS resource, SS blocks, or PBCH blocks is associated with the candidate beam.

16. The method of claim 9 , wherein the association configured between the downlink reference signals and the PRACH resources associates one CSI-RS resource, SS block, or PBCH block to one set of PRACH resource, by at least one of: CDM, FDM, and TDM.

17. A cellular station, comprising:

a wireless transceiver, configured to perform wireless transmission and reception to and from a UE; and

a controller, configured to receive a PRACH transmission which utilizes a PRACH resource from the UE via the wireless transceiver, determine one of a plurality of downlink reference signals comprising CSI-RS resources, SS blocks, or PBCH blocks according to an association configured between the downlink reference signals and the PRACH resource, and identify a candidate beam associated with the determined downlink reference signal,

wherein the association between the downlink reference signal and the PRACH resource indicates the downlink reference signal selected by the UE to the cellular station,

wherein the association between the downlink reference signal and the candidate beam indicates the candidate beam to the cellular station, and

wherein the cellular station identifies the candidate beam indicated by the UE based on determination of the PRACH resource, wherein the PRACH transmission comprising a PRACH preamble transmitted on a RACH occasion, and the association is configured between the downlink reference signals and the PRACH preamble, the RACH occasion, or a combination thereof.

18. The cellular station of claim 17 , wherein the candidate beam is identified for beam failure recovery, or for a handover from a cell to another cell.

19. The cellular station of claim 17 , wherein the association configured between the downlink reference signals and the PRACH resource associates one CSI-RS resource, SS block, or PBCH block to one set of PRACH resource, or associates multiple CSI-RS resources, SS blocks, or PBCH blocks to one set of PRACH resource.

20. A method for beam identification through a PRACH, executed by a cellular station wirelessly connected to a UE, the method comprising:

receiving a PRACH transmission which utilizes a PRACH resource from the UE;

determining one of a plurality of downlink reference signals comprising CSI-RS resources, SS blocks, or PBCH blocks according to an association configured between the downlink reference signals and the PRACH resource; and

identifying a candidate beam associated with the determined downlink reference signal,

wherein the association between the downlink reference signal and the PRACH resource indicates the downlink reference signal selected by the UE to the cellular station,

wherein the association between the downlink reference signal and the candidate beam indicates the candidate beam to the cellular station, and

wherein the cellular station identifies the candidate beam indicated by the UE based on determination of the PRACH resource, wherein the PRACH transmission comprising a PRACH preamble transmitted on a RACH occasion, and the association is configured between the downlink reference signals and the PRACH preamble, the RACH occasion, or a combination thereof.

21. The method of claim 20 , wherein the candidate beam is identified for beam failure recovery, or for a handover from a cell to another cell.

22. The method of claim 20 , wherein the association configured between the downlink reference signals and the PRACH resource associates one CSI-RS resource, SS block, or PBCH block to one set of PRACH resource, or associates multiple CSI-RS resources, SS blocks, or PBCH blocks to one set of PRACH resource.