Method and apparatus for preamble transmission for layer 2 mobility based on the second PDCCH order in mobile wireless communication system

1 . A method performed by a user device, the method comprising:

transmitting, to a base station, capability information associated with the user device;

receiving, from the base station, a first radio resource control (RRC) message, wherein the first RRC message comprises:

at least one configuration parameter associated with a serving cell; and

at least one configuration parameter associated with layer-1/layer-2 triggered mobility (LTM);

receiving, from the base station, a specific downlink control information (DCI) associated with a physical downlink control channel (PDCCH) order, wherein the specific DCI comprises:

a first field comprising a value associated with the PDCCH order;

a second field comprising a value indicating an identifier of an LTM candidate cell;

a third field comprising a value related to power ramping counter; and

a fourth field comprising a value indicating an index of random access preamble;

determining, in case that the value related to power ramping counter in the third field of the specific DCIis set to a first value, to ramp up a preamble transmission power for a random access preamble transmission to the LTM candidate cell; and

based on the index of random access preamble, transmitting, to the LTM candidate cell, a random access preamble.

2 . The method of claim 1 , wherein the transmitting the random access preamble is based on:

at least one preamble-related parameter set configured for the LTM candidate cell; and

a pathloss associated with the LTM candidate cell.

3 . The method of claim 1 , further comprising:

after transmitting the random access preamble, receiving a second message comprising a timing advance value associated with the LTM candidate cell,

wherein:

the identifier of the LTM candidate cell included in the specific DCI is derived from a second identifier of the LTM candidate cell; and

the second identifier of the LTM candidate cell is indicated by the at least one configuration parameter associated with LTM included in the first RRC message.

4 . The method of claim 3 , further comprising:

determining, based on the value comprised in the second field of the specific DCI, a PDCCH order, of a second type, associated with the LTM candidate cell that is different from a PDCCH order, of a first type, associated with the serving cell.

5 . The method of claim 4 , wherein the first RRC message is received via a first cell of a serving cell group, and

wherein the second message is received via the first cell.

6 . The method of claim 5 , wherein the serving cell is the first cell or another serving cell of the serving cell group.

7 . The method of claim 5 , wherein the second message is comprised in a medium access control protocol data unit (MAC PDU), and

wherein the second message comprises a medium access control (MAC) control element (CE) indicating a switching from the first cell to the LTM candidate cell.

8 . The method of claim 1 , wherein the LTM candidate cell is an SpCell of a candidate cell group.

9 . The method of claim 1 , wherein the second message comprises:

a field indicating an identity of the LTM candidate cell;

a timing advance command field indicating the timing advance value that is associated with an amount of timing adjustment; and

a synchronization signal/physical broadcast channel (SS/PBCH) index field.

10 . The method of claim 1 , wherein the specific DCI further comprises a random access preamble index field.

11 . The method of claim 1 , wherein the first RRC message comprises at least one configuration parameter for a candidate mobility group (CMG), wherein the CMG is a candidate cell group comprising a plurality of LTM candidate cells, and wherein the candidate cell group comprises a candidate SpCell.

12 . The method of claim 1 , wherein the at least one configuration parameter associated with LTM comprises an RRC reconfiguration (RRCReconfiguration) message for an LTM candidate cell.

13 . The method of claim 12 , wherein the RRCReconfiguration message for the LTM candidate cell comprises a medium access control (MAC) cell group configuration (MAC-CellGroupConfig) for the LTM candidate cell.

14 . The method of claim 13 , wherein the MAC-CellGroupConfig for the LTM candidate cell comprises at least one of: timing advance group configuration information for the LTM candidate cell; or at least one discontinuous reception (DRX) configuration (DRX-Config) for the LTM candidate cell.

15 . The method of claim 1 , wherein the capability information comprises at least one parameter indicating the user device supports LTM.

16 . The method of claim 1 , wherein the second field of the specific DCI indicates an identifier of the LTM candidate cell.

17 . The method of claim 1 , wherein the first field of the specific DCI is a frequency domain resource assignment field.

18 . The method of claim 1 , further comprising:

determining a subcarrier spacing (SCS) of an uplink transmission from the user device, wherein the SCS is associated with an amount of time alignment for a timing advance group (TAG), and wherein the TAG is associated with the LTM candidate cell.

19 . The method of claim 18 , wherein the uplink transmission comprises a preamble transmission.

20 . The method of claim 1 , wherein size of the identifier of the LTM candidate cell is smaller than size of the second identifier of the LTM candidate cell.