Timing advance management during layer (L1/L2) triggered mobility (LTM)
The present disclosure describes techniques for timing advance management during layer (L1/L2) Triggered Mobility (LTM). In one aspect, a method comprises obtaining timing advances (TAs) for one or more LTM candidate cells based on indication from a serving gNB-DU and storing the obtained TAs and receiving LTM serving cell switch command to switch from a current serving cell to a target cell. The method further comprises transmitting, a list of candidate cell IDs and the stored TAs corresponding to the list of candidate cell IDs, to the target gNB-DU serving the target cell, in response to the successful completion of the LTM cell switch.
1 . An apparatus comprising:
at least one processor; and
a memory communicatively coupled to the at least one processor, wherein the memory stores processor-executable instructions, which, on execution, cause the at least one processor to:
obtain, by a User Equipment (UE), timing advances (TAs) for one or more Layer (L1/L2) Triggered Mobility (LTM) candidate cells based on an indication from a serving gNodeB Distributed Unit (gNB-DU) and store the obtained TAs;
receive, by the UE, an LTM cell switch command to perform an LTM cell switch from a current serving cell to a target cell, wherein the current serving cell is served by the serving gNB-DU and the target cell is served by a target gNB-DU; and
transmit, by the UE to the target gNB-DU serving the target cell, a list of candidate cell IDs and the stored TAs corresponding to the list of candidate cell IDs in response to a successful completion of the LTM cell switch.
2 . The apparatus of claim 1 , wherein to obtain TAs for the one or more LTM candidate cells, the at least one processor is configured to:
receive, from the serving gNB-DU, a Physical Downlink Control Channel (PDCCH) order to perform uplink synchronization with at least one LTM candidate cell of at least one candidate gNB-DU, wherein the PDCCH order includes a physical cell ID (PCI) of the at least one LTM candidate cell being served by the at least one candidate gNB-DU;
transmit a Random Access Channel (RACH) preamble in a RACH Request message to the at least one candidate gNB-DU serving the at least one LTM candidate cell;
receive a Random Access Response including a TA of the at least one LTM candidate cell either directly from the at least one candidate gNB-DU or via the serving gNB-DU; and
store the TA of the at least one LTM candidate cell based on TA alignment timer.
3 . The apparatus of claim 1 , wherein in response to receipt of the LTM cell switch command to switch from the current serving cell to the target cell, the at least one processor is configured to:
perform, periodically, an intra-frequency L1 measurement for at least one LTM candidate cell;
transmit an intra-frequency L1 measurement report of the at least one LTM candidate cell to the serving gNB-DU;
receive the LTM cell switch command from the serving gNB-DU based on the intra-frequency L1 measurement report, wherein the LTM cell switch command at least includes a physical cell ID (PCI) of the target cell and beam information of the target cell; and
perform the LTM cell switch from the current serving cell to the target cell based on the LTM cell switch command.
4 . The apparatus of claim 1 , wherein to transmit the list of candidate cell IDs and the stored TAs corresponding to the list of candidate cell IDs, the at least one processor is configured to:
transmit, an uplink (UL) Media Access Control (MAC) control element (CE) or a similar L1/L2 command including the list of candidate cell IDs and the stored TAs corresponding to the list of candidate cell IDs, to the target gNB-DU.
5 . The apparatus of claim 1 , wherein the at least one processor is configured to:
transmit, an uplink (UL) Media Access Control (MAC0 control element (CE) or a similar L1/L2 command including the list of candidate cell IDs and the stored TAs corresponding to the list of candidate cell IDs, to the serving gNB-DU.
6 . The apparatus of claim 1 , wherein the at least one processor is configured to:
transmit a Layer 3 (L3) Radio Resource Control (RRC) measurement report to a gNB-Control Unit (CU); and
receive an RRC reconfiguration message including configuration of at least one candidate cell from the gNB-CU.
7 . The apparatus of claim 1 , wherein the serving gNB-DU and the target gNB-DU belong to one of: a different gNB or a same gNB.
8 . A method comprising:
obtaining, by a User Equipment (UE), timing advances (TAs) for one or more Layer (L1/L2) Triggered Mobility (LTM) candidate cells based on an indication from a serving gNodeB Distributed Unit (gNB-DU) and storing the obtained TAs;
receiving, by the UE, an LTM cell switch command to perform an LTM cell switch from a current serving cell to a target cell, wherein the current serving cell is served by the serving gNB-DU and the target cell is served by a target gNB-DU; and
transmitting, by the UE to the target gNB-DU serving the target cell, a list of candidate cell IDs and the stored TAs corresponding to the list of candidate cell IDs in response to a successful completion of the LTM cell switch.
9 . The method of claim 8 , wherein the obtaining the TAs for the one or more LTM candidate cells includes:
receiving, from the serving gNB-DU, a Physical Downlink Control Channel (PDCCH) order for performing uplink synchronization with at least one LTM candidate cell of at least one candidate gNB-DU, wherein the PDCCH order includes a physical cell ID (PCI) of the at least one LTM candidate cell being served by the at least one candidate gNB-DU;
transmitting a Random Access Channel (RACH) preamble to the at least one candidate gNB-DU for the at least one LTM candidate cell;
receiving a Random Access Response including a TA of the at least one LTM candidate cell either directly from the at least one candidate gNB-DU or via the serving gNB-DU; and
storing the TA of the at least one LTM candidate cell based on TA alignment timer.
10 . The method of claim 8 , wherein in response to receiving the LTM cell switch command to switch from the current serving cell to the target cell, the method comprises:
performing, periodically, an intra-frequency L1 measurement for at least one LTM candidate cell;
transmitting an intra-frequency L1 measurement report of the at least one LTM candidate cell to the serving gNB-DU;
receiving the LTM cell switch command from the serving gNB-DU based on the intra-frequency L1 measurement report, wherein the LTM cell switch command at least includes a physical cell ID (PCI) of the target cell and beam information of the target cell; and
performing the LTM cell switch from the current serving cell to the target cell based on the LTM cell switch command.
11 . The method of claim 8 , wherein the transmitting the list of candidate cell IDs and the stored TAs corresponding to the list of candidate cell IDs includes:
transmitting, an uplink (UL) Media Access Control (MAC) control element (CE) including the list of candidate cell IDs and the stored TAs corresponding to the list of candidate cell IDs, to the target gNB-DU.
12 . The method of claim 8 , further comprising:
transmitting, an uplink (UL) Media Access Control (MAC) control element (CE) or a similar L1/L2 command including the list of candidate cell IDs and the stored TAs corresponding to the list of candidate cell IDs, to the serving gNB-DU.
13 . The method of claim 8 , further comprising:
transmitting a Layer 3 (L3) Radio Resource Control (RRC) measurement report to a gNB-Control Unit (CU); and
receiving an RRC reconfiguration message including configuration of at least one candidate cell from the gNB-CU.
14 . The method of claim 8 , wherein the serving the current serving cell by the serving gNB-DU and the serving the target cell by the target gNB-DU includes one of providing a same gNB for the serving gNB-DU and the target gNB-DU, or providing a first gNB for the serving gNB-DU and a second gNB for the target gNB-DU, wherein the first gNB is different than the second gNB.
15 . A non-transitory computer-readable medium having computer-readable instructions that when executed by a processor causes the processor to perform operations of:
obtaining, by a User Equipment (UE), timing advances (TAs) for one or more Layer (L1/L2) Triggered Mobility (LTM) candidate cells based on an indication from a serving gNodeB Distributed Unit (gNB-DU) and storing the obtained TAs;
obtaining, by the UE, an LTM cell switch command to perform an LTM cell switch from a current serving cell to a target cell, wherein the current serving cell is served by the serving gNB-DU and the target cell is served by a target gNB-DU; and
transmitting, by the UE to the target gNB-DU serving the target cell, a list of candidate cell IDs and the stored TAs corresponding to the list of candidate cell IDs, to the target gNB-DU serving the target cell, in response to a successful completion of the LTM cell switch.
16 . The non-transitory computer-readable medium of claim 15 , wherein the obtaining the TAs for the one or more LTM candidate cells includes:
receiving, from the serving gNB-DU, a Physical Downlink Control Channel (PDCCH) order for performing uplink synchronization with at least one LTM candidate cell of at least one candidate gNB-DU, wherein the PDCCH order includes a physical cell ID (PCI) of the at least one LTM candidate cell being served by the at least one candidate gNB-DU;
transmitting a Random Access Channel (RACH) preamble to the at least one candidate gNB-DU for the at least one LTM candidate cell;
receiving a Random Access Response including a TA of the at least one LTM candidate cell either directly from the at least one candidate gNB-DU or via the serving gNB-DU; and
storing the TA of the at least one LTM candidate cell based on TA alignment timer.
17 . The non-transitory computer-readable medium of claim 15 , wherein in response to receiving the LTM cell switch command to switch from the current serving cell to the target cell, the operations comprise:
performing, periodically, an intra-frequency L1 measurement for at least one LTM candidate cell;
transmitting an intra-frequency L1 measurement report of the at least one LTM candidate cell to the serving gNB-DU;
receiving the LTM cell switch command from the serving gNB-DU based on the intra-frequency L1 measurement report, wherein the LTM cell switch command at least includes a physical cell ID (PCI) of the target cell and beam information of the target cell; and
performing the LTM cell switch from the current serving cell to the target cell based on the LTM cell switch command.
18 . The non-transitory computer-readable medium of claim 15 , wherein the transmitting the list of candidate cell IDs and the stored TAs corresponding to the list of candidate cell IDs includes:
transmitting, an uplink (UL) Media Access Control (MAC) control element (CE) including the list of candidate cell IDs and the stored TAs corresponding to the list of candidate cell IDs, to the target gNB-DU.
19 . The non-transitory computer-readable medium of claim 15 , further comprising:
transmitting, an uplink (UL) Media Access Control (MAC) control element (CE) or a similar L1/L2 command including the list of candidate cell IDs and the stored TAs corresponding to the list of candidate cell IDs, to the serving gNB-DU.
20 . The non-transitory computer-readable medium of claim 15 , further comprising:
transmitting a Layer 3 (L3) Radio Resource Control (RRC) measurement report to a gNB-Control Unit (CU); and
receiving an RRC reconfiguration message including configuration of at least one candidate cell from the gNB-CU.