Random access channel collision during timing adjustment acquisition for layer 1 or layer 2 triggered mobility
Various aspects of the present disclosure generally relate to wireless communication. In some aspects, a user equipment (UE) may initiate a first random access channel (RACH) procedure with a serving cell of the UE. The UE may receive, prior to terminating the first RACH procedure, a trigger for a second RACH procedure with a candidate cell of the UE. The UE may initiate the second RACH procedure with the candidate cell. Numerous other aspects are described.
1 . A user equipment (UE) for wireless communication, comprising:
a memory; and
one or more processors, coupled to the memory, configured to:
initiate a first random access channel (RACH) procedure with a serving cell of the UE;
receive, prior to terminating the first RACH procedure, a trigger for a second RACH procedure with a candidate cell of the UE; and
initiate the second RACH procedure with the candidate cell, wherein the one or more processors, to initiate the second RACH procedure, are configured to transmit a physical RACH transmission to the candidate cell after the first RACH procedure has terminated.
2 . The UE of claim 1 , wherein the one or more processors, to initiate the second RACH procedure, are configured to initiate the second RACH procedure in accordance with a capability, of the UE, indicating whether the UE supports multiple concurrent RACH procedures.
3 . The UE of claim 1 , wherein the one or more processors are further configured to defer transmission of the physical RACH transmission until after the first RACH procedure has terminated.
4 . The UE of claim 1 , wherein the one or more processors are further configured to receive a random access response (RAR) from the candidate cell, wherein the RAR is indicated as being associated with the second RACH procedure by at least one of:
a receive beam of the RAR,
a radio network temporary identifier to which the RAR is addressed, or
a frequency on which the RAR is received.
5 . The UE of claim 1 , wherein the one or more processors are further configured to receive a random access response (RAR) from the serving cell, wherein the RAR is indicated as being associated with one of the first RACH procedure or the second RACH procedure by at least one of:
a random access preamble identifier of the RAR,
a medium access control RAR included in the RAR,
a format of the RAR,
an identifier of the candidate cell included in the RAR, or
an identifier of the UE, for the candidate cell, included in the RAR.
6 . The UE of claim 1 , wherein the one or more processors are further configured to receive medium access control signaling, from the serving cell, including an indication of the candidate cell and a timing adjustment for the candidate cell.
7 . The UE of claim 1 , wherein the second RACH procedure is associated with a Layer 1 or Layer 2 triggered mobility handover to the candidate cell.
8 . A network node for wireless communication, comprising:
a memory; and
one or more processors, coupled to the memory, configured to:
perform at least part of a first random access channel (RACH) procedure with a serving cell of a user equipment (UE);
transmit, prior to terminating the first RACH procedure, a trigger for a second RACH procedure with a candidate cell of the UE; and
receive, from the UE after the first RACH procedure has terminated, a physical RACH transmission to initiate the second RACH procedure.
9 . The network node of claim 8 , wherein the one or more processors are further configured to transmit a random access response (RAR), associated with the second RACH procedure, to the UE, wherein the RAR is indicated as being associated with the second RACH procedure by at least one of:
a random access preamble identifier of the RAR,
a medium access control RAR included in the RAR,
a format of the RAR,
an identifier of the candidate cell included in the RAR, or
an identifier of the UE, for the candidate cell, included in the RAR.
10 . The network node of claim 8 , wherein the one or more processors are further configured to transmit medium access control signaling including an indication of the candidate cell and a timing adjustment for the candidate cell.
11 . The network node of claim 8 , wherein the second RACH procedure is associated with a Layer 1 or Layer 2 triggered mobility handover to the candidate cell.
12 . The network node of claim 8 , wherein the one or more processors are further configured to receive, from the UE, capability information indicating whether the UE supports multiple concurrent RACH procedures.
13 . The network node of claim 12 , wherein the capability may indicate whether the UE can receive a random access response (RAR) carrying a timing advance (TA) from the serving cell, the candidate cell, or both.
14 . A method of wireless communication performed by a user equipment (UE), comprising:
initiating a first random access channel (RACH) procedure with a serving cell of the UE;
receiving, prior to terminating the first RACH procedure, a trigger for a second RACH procedure with a candidate cell of the UE; and
initiating the second RACH procedure with the candidate cell, further comprising transmitting a physical RACH transmission to the candidate cell after the first RACH procedure has terminated.
15 . The method of claim 14 , wherein initiating the second RACH procedure further comprising initiating the second RACH procedure in accordance with a capability, of the UE, indicating whether the UE supports multiple concurrent RACH procedures.
16 . The method of claim 14 , further comprising deferring transmission of the physical RACH transmission until after the first RACH procedure has terminated.
17 . The method of claim 14 , further comprising receiving a random access response (RAR) from the candidate cell, wherein the RAR is indicated as being associated with the second RACH procedure by at least one of:
a receive beam of the RAR,
a radio network temporary identifier to which the RAR is addressed, or
a frequency on which the RAR is received.
18 . The method of claim 14 , further comprising receiving a random access response (RAR) from the serving cell, wherein the RAR is indicated as being associated with one of the first RACH procedure or the second RACH procedure by at least one of:
a random access preamble identifier of the RAR,
a medium access control RAR included in the RAR,
a format of the RAR,
an identifier of the candidate cell included in the RAR, or
an identifier of the UE, for the candidate cell, included in the RAR.
19 . The method of claim 14 , further comprising receiving medium access control signaling, from the serving cell, including an indication of the candidate cell and a timing adjustment for the candidate cell.
20 . The method of claim 14 , wherein the second RACH procedure is associated with a Layer 1 or Layer 2 mobility handover to the candidate cell.
21 . A method of wireless communication performed by a network node, comprising:
performing at least part of a first random access channel (RACH) procedure with a serving cell of a user equipment (UE);
transmitting, prior to terminating the first RACH procedure, a trigger for a second RACH procedure with a candidate cell of the UE; and
receiving, from the UE after the first RACH procedure has terminated, a physical RACH transmission to initiate the second RACH procedure.
22 . The method of claim 21 , further comprising transmitting a random access response (RAR), associated with the second RACH procedure, to the UE, wherein the RAR is indicated as being associated with the second RACH procedure by at least one of:
a random access preamble identifier of the RAR,
a medium access control RAR included in the RAR,
a format of the RAR,
an identifier of the candidate cell included in the RAR, or
an identifier of the UE, for the candidate cell, included in the RAR.
23 . The method of claim 21 , further comprising transmitting medium access control signaling including an indication of the candidate cell and a timing adjustment for the candidate cell.
24 . The method of claim 21 , wherein the second RACH procedure is associated with a Layer 1 or Layer 2 triggered mobility handover to the candidate cell.
25 . The method of claim 21 , further comprising:
receiving, from the UE, capability information indicating whether the UE supports multiple concurrent RACH procedures.
26 . The method of claim 25 , wherein the capability may indicate whether the UE can receive a random access response (RAR) carrying a timing advance (TA) from the serving cell, the candidate cell, or both.