METHOD AND APPARATUS FOR LAYER1/LAYER2 TRIGGERED MOBILITY (LTM) IN WIRELESS NETWORKS
A method performed by a User Equipment (UE) for a Layer1/Layer2 Triggered Mobility (LTM) operation is provided. The method receives, from a source cell, an LTM cell switch command Medium Access Control (MAC) Control Element (CE) including a Timing Advance Command (TAC) field. The method switches from the source cell to a target cell in response to receiving the LTM cell switch command MAC CE. In a case that the TAC field is set to an invalid value, the method performs a Random Access (RA) procedure with the target cell upon switching to the target cell, where a type of the RA procedure depends on whether the LTM cell switch command MAC CE further includes a Contention-Free Random Access (CFRA)-related field. In a case that the TAC field is set to a valid value, the method skips the RA procedure with the target cell upon switching to the target cell.
1 . A method performed by a User Equipment (UE) for a Layer1/Layer2 Triggered Mobility (LTM) operation, the method comprising:
receiving, from a source cell, an LTM cell switch command Medium Access Control (MAC) Control Element (CE) comprising a Timing Advance Command (TAC) field;
determining whether the LTM cell switch command MAC CE further comprises a Contention-Free Random Access (CFRA)-related field;
switching from the source cell to a target cell in response to receiving the LTM cell switch command MAC CE;
in a case that the TAC field is set to an invalid value, performing a Random Access (RA) procedure with the target cell upon switching to the target cell, wherein a type of the RA procedure depends on whether the LTM cell switch command MAC CE comprises the CFRA-related field; and
in a case that the TAC field is set to a valid value, skipping the RA procedure with the target cell upon switching to the target cell.
2 . The method of claim 1 , wherein:
the type of the RA procedure is a CFRA type in a case that the LTM cell switch command MAC CE comprises the CFRA-related field, and
the type of the RA procedure is a Contention-Based Random Access (CBRA) type in a case that the LTM cell switch command MAC CE does not comprise the CFRA-related field.
3 . The method of claim 1 , wherein the CFRA-related field comprises at least one of a preamble index, a mask index, and a Synchronization Signal/Physical Broadcast Channel (SS/PBCH) Block (SSB) index.
4 . The method of claim 1 , wherein the invalid value is ‘FFF’ in hexadecimal notation.
5 . The method of claim 1 , wherein the valid value corresponds to an index of a Timing Advance (TA) value for the target cell.
6 . The method of claim 1 , wherein the LTM cell switch command MAC CE further comprises an indication field for indicating whether the LTM cell switch command MAC CE comprises the CFRA-related field.
7 . The method of claim 1 , wherein performing the RA procedure with the target cell comprises:
monitoring a Downlink Control Information (DCI) format with Cyclic Redundancy Check (CRC) scrambled by a Random Access-Radio Network Temporary Identifier (RA-RNTI), a Message B-RNTI (MsgB-RNTI), or a Temporary Cell-RNTI (TC-RNTI) in a search space on the target cell.
8 . A User Equipment (UE) for a Layer1/Layer2 Triggered Mobility (LTM) operation, the UE comprising:
at least one processor; and
at least one non-transitory computer-readable medium coupled to the at least one processor and storing one or more computer-executable instructions that, when executed by the at least one processor, cause the UE to:
receive, from a source cell, an LTM cell switch command Medium Access Control (MAC) Control Element (CE) comprising a Timing Advance Command (TAC) field;
determine whether the LTM cell switch command MAC CE further comprises a Contention-Free Random Access (CFRA)-related field;
switch from the source cell to a target cell in response to receiving the LTM cell switch command MAC CE;
in a case that the TAC field is set to an invalid value, perform a Random Access (RA) procedure with the target cell upon switching to the target cell, wherein a type of the RA procedure depends on whether the LTM cell switch command MAC CE comprises the CFRA-related field; and
in a case that the TAC field is set to a valid value, skip the RA procedure with the target cell upon switching to the target cell.
9 . The UE of claim 8 , wherein:
the type of the RA procedure is a CFRA type in a case that the LTM cell switch command MAC CE comprises the CFRA-related field, and
the type of the RA procedure is a Contention-Based Random Access (CBRA) type in a case that the LTM cell switch command MAC CE does not comprise the CFRA-related field.
10 . The UE of claim 8 , wherein the CFRA-related field comprises at least one of a preamble index, a mask index, and a Synchronization Signal/Physical Broadcast Channel (SS/PBCH) Block (SSB) index.
11 . The UE of claim 8 , wherein the invalid value is ‘FFF’ in hexadecimal notation.
12 . The UE of claim 8 , wherein the valid value corresponds to an index of a Timing Advance (TA) value for the target cell.
13 . The UE of claim 8 , wherein the LTM cell switch command MAC CE further comprises an indication field for indicating whether the LTM cell switch command MAC CE comprises the CFRA-related field.
14 . The UE of claim 8 , wherein performing the RA procedure with the target cell comprises:
monitoring a Downlink Control Information (DCI) format with Cyclic Redundancy Check (CRC) scrambled by a Random Access-Radio Network Temporary Identifier (RA-RNTI), a Message B-RNTI (MsgB-RNTI), or a Temporary Cell-RNTI (TC-RNTI) in a search space on the target cell.
15 . A Base Station (BS) for a Layer1/Layer2 Triggered Mobility (LTM) operation, the BS comprising:
at least one processor; and
at least one non-transitory computer-readable medium coupled to the at least one processor and storing one or more computer-executable instructions that, when executed by the at least one processor, cause the BS to:
transmit, to a User Equipment (UE), via a source cell associated with the BS, an LTM cell switch command Medium Access Control (MAC) Control Element (CE) comprising a Timing Advance Command (TAC) field, wherein the UE:
determines whether the LTM cell switch command MAC CE further comprises a Contention-Free Random Access (CFRA)-related field,
switches from the source cell to a target cell in response to receiving the LTM cell switch command MAC CE,
in a case that the TAC field is set to an invalid value, performs a Random Access (RA) procedure with the target cell upon switching to the target cell, wherein a type of the RA procedure depends on whether the LTM cell switch command MAC CE comprises the CFRA-related field, and
in a case that the TAC field is set to a valid value, skips the RA procedure with the target cell upon switching to the target cell.
16 . The BS of claim 15 , wherein:
the type of the RA procedure is a CFRA type in a case that the LTM cell switch command MAC CE comprises the CFRA-related field, and
the type of the RA procedure is a Contention-Based Random Access (CBRA) type in a case that the LTM cell switch command MAC CE does not comprise the CFRA-related field.
17 . The BS of claim 15 , wherein the CFRA-related field comprises at least one of a preamble index, a mask index, and a Synchronization Signal/Physical Broadcast Channel (SS/PBCH) Block (SSB) index.
18 . The BS of claim 15 , wherein the invalid value is ‘FFF’ in hexadecimal notation.
19 . The BS of claim 15 , wherein the valid value corresponds to an index of a Timing Advance (TA) value for the target cell.
20 . The BS of claim 15 , wherein the LTM cell switch command MAC CE further comprises an indication field for indicating whether the LTM cell switch command MAC CE comprises the CFRA-related field.