Downlink radio resource control message transmission in 2-step random access
Apparatuses, systems, and methods for a wireless device to perform 2-step random access procedures. The disclosure identifies techniques for transmitting and receiving downlink connection configuration information, such as a radio resource control message, in a 2-step random access procedure.
1. A method for operating a base station, the method comprising:
transmitting random access configuration information for 2-step random access;
receiving, from first and second user equipment devices (UEs), first and second initial messages of 2-step random access, MsgA, according to the random access configuration information; and
transmitting, in response to the first and second initial messages of 2-step random access, MsgA:
a first response message for the first UE, the first response message including a fallback random access response (RAR); and
a second response message for the second UE, the second response message including:
a first sub protocol data unit (subPDU), of a protocol data unit (PDU), the first subPDU comprising a success RAR and a subheader indicating that a downlink (DL) radio resource control (RRC) message is included in the second response message; and
a second subPDU of the PDU including the DL RRC message, wherein the second subPDU successively follows the first subPDU.
2. The method of claim 1 , wherein the subheader does not include a random access preamble ID (RAPID) field.
3. The method of claim 2 , wherein the success RAR includes the RAPID field.
4. The method of claim 1 , wherein the DL RRC message comprises an RRC setup message.
5. The method of claim 1 , wherein the DL RRC message follows all RAR messages in a MsgB.
6. The method of claim 1 , further comprising:
determining that a respective one of the first or second UEs did not receive a respective one RAR message; and
performing a retransmission of the respective one RAR message.
7. The method of claim 1 , wherein the PDU is scheduled by random access radio network temporary identifier (RA-RNTI).
8. A method for operating a user equipment device (UE), the method comprising:
receiving random access configuration information for 2-step random access;
transmitting an initial message of 2-step random access, MsgA, according to the random access configuration information; and
receiving a response message including:
a first sub protocol data unit (subPDU), of a protocol data unit (PDU), the first subPDU comprising a success RAR and a subheader indicating that a downlink (DL) radio resource control (RRC) message is included in the response message; and
a second subPDU of the PDU including the DL RRC message, wherein the second subPDU successively follows the first subPDU.
9. The method of claim 8 , wherein the subheader does not include a random access preamble ID (RAPID) field.
10. The method of claim 9 , wherein the success RAR includes the RAPID field.
11. The method of claim 8 , wherein the DL RRC message comprises an RRC setup message.
12. The method of claim 8 , wherein the DL RRC message follows all RAR messages in a MsgB.
13. The method of claim 8 , wherein the PDU is scheduled by random access radio network temporary identifier (RA-RNTI).
14. An apparatus, comprising:
a processor configured to cause a base station to:
transmit random access configuration information for 2-step random access;
receive, from at least a first user equipment device (UE), at least one first message (MsgA) of the 2-step random access according to the random access configuration information; and
transmit a MsgB in response to the at least one first message (MsgA), the MsgB including a first sub protocol data unit (subPDU) of the MsgB including a success random access response (successRAR) for the first UE and immediately followed by a second subPDU including a radio resource control (RRC) message for the first UE, wherein the first subPDU includes a first subheader in addition to the successRAR.
15. The apparatus of claim 14 , wherein the first subheader indicates whether the first subPDU includes backoff indication.
16. The apparatus of claim 14 , wherein the RRC message is scheduled by a random access radio network temporary identifier (RA-RNTI).
17. The apparatus of claim 14 , wherein the first subPDU does not include an RRC message.
18. The apparatus of claim 14 , wherein the RRC message comprises an RRC setup message.
19. The apparatus of claim 14 , wherein the RRC message follows all random access response (RAR) messages in the MsgB.
20. The apparatus of claim 14 , wherein the processor is further configured to cause the base station to:
determine that a second UE did not receive a corresponding random access response (RAR) message; and
perform a retransmission of the corresponding RAR message.