METHOD AND APPARATUS FOR MAINTAINING UPLINK TIME ALIGNMENT

1 . An apparatus, configured in a terminal equipment, comprising:

processor circuitry configured to:

maintain uplink time alignment of a serving cell based on one or two timing advance (TA) timers, one TA timer in the one or two TA timers being associated with a timing advance group (TAG), and the serving cell being associated with two TA timers; and

a receiver configured to receive a signal including a timing advance command (TAC) of the serving cell and TAG ID of one or more TAGS, the signal being a random access response (RAR) message or a message B (MSGB);

wherein, the processor circuitry is further configured to start or restart a TA timer in the two TA timers when the signal is received, the TA timer corresponding to a TAG which corresponds to the TAG ID of the one or more TAGS.

2 . The apparatus according to claim 1 , wherein the to start or restart a TA timer in the two TA timers when at least one of the following conditions is satisfied:

a timing advance command (TAC) media access control control element (MAC CE) is received;

a response message of a message A (MSGA) transmission including a cell radio network temporary identifier (C-RNTI) MAC CE is received and the response message contains an absolute TAC; and

a radio resource control (RRC) signaling is received and the RRC signaling indicates a TAG identifier (ID).

3 . The apparatus according to claim 2 , wherein,

the response message contains TAG ID(s) of the one or more TAGS or is associated with the one or more TAGS.

4 . The apparatus according to claim 1 , wherein that one TA timer is associated with a TAG comprises at least one of the following:

one TA timer is associated with a TCI state or a TCI state group or a spatial relationship or a spatial relationship group;

one TA timer is associated with a control resource set (CORESET) or a control resource set pool (CORESETPool);

one TA timer is associated with a downlink reference signal (DL RS) or a DL RS group; and

one TA timer is associated with a physical cell identifier (PCI) or a PCI group different from a PCI of the serving cell.

5 . The apparatus according to claim 3 , wherein being associated with the TAG comprises at least one of the following:

being associated with a TCI state or a TCI state group or a spatial relationship or a spatial relationship group;

being associated with a CORESET or CORESETPool;

being associated with a DL RS or a DL RS group; and

being associated with a PCI or a PCI group different from a PCI of the serving cell.

6 . The apparatus according to claim 1 , wherein,

when the serving cell is a special cell, the TAG is a primary TAG, and the number of the primary TAGs is two.

7 . The apparatus according to claim 1 , wherein when the TA timer expires, the processor circuitry is further configured to:

not perform or stop uplink transmission associated with the TA timer; and/or

not perform or stop uplink transmission corresponding to a TAG associated with the TA timer; and/or

clear configured downlink assignments and configured uplink grants associated with the TA timer; and/or

clear configured downlink assignments and configured uplink grants corresponding to a TAG associated with the TA timer; and/or

clear physical uplink shared channel (PUSCH) resources for a semi-persistent channel state information (CSI) reporting associated with the TA timer; and/or

clear PUSCH resources for a semi-persistent CSI reporting; and/or

flush a hybrid automatic repeat request (HARQ) buffer corresponding to a TAG associated with the TA timer; and/or

flush an HARQ buffer associated with the TA timer.

8 . The apparatus according to claim 7 , wherein that the TA timer expires comprises:

one of the two TA timers expires, and the other TA timer is running.

9 . The apparatus according to claim 1 , wherein when two TA timers associated with a secondary cell expire, the processor circuitry is further configured to:

notify RRC to release uplink configuration of the secondary cell; and/or

clear all configured downlink assignments and configured uplink grants of the secondary cell; and/or

clear all PUSCH resources for a semi-persistent CSI reporting of the secondary cell; and/or

flush all HARQ buffers for the secondary cell.

10 . The apparatus according to claim 9 , wherein,

at least one TA timer associated with a special cell or a primary TAG does not expire or is running.

11 . The apparatus according to claim 1 , wherein when both two TA timers associated with a special cell and/or a primary TAG expire, the processor circuitry is further configured to:

notify RRC to release uplink configurations of all serving cells; and/or

clear all configured downlink assignments and configured uplink grants; and/or

clear all PUSCH resources for a semi-persistent CSI reporting; and/or

consider all running TA timers as expired; and/or

flush all HARQ buffers for all serving cells.

12 . The apparatus according to claim 1 , wherein

the processor circuitry is further configured to maintain uplink time alignment of the serving cell based on a state of a TA timer, wherein the TA timer is associated with the serving cell.

13 . The apparatus according to claim 12 , wherein,

the TA timer is associated with two or more TAGS.

14 . The apparatus according to claim 13 , wherein that the TA timer is associated with two or more TAGs comprises at least one of the following:

the TA timer is associated with two or more TCI states or TCI state groups or spatial relationships or spatial relationship groups;

the TA timer is associated with two or more CORESETs or CORESETPools;

the TA timer is associated with two or more DL RSs or DL RS groups; and

the TA timer is associated with two or more PCIs or PCI groups different from a PCI of the serving cell.

15 . The apparatus according to claim 12 , wherein when the TA timer expires and the serving cell is a special cell, the processor circuitry is further configured to:

notify RRC to release uplink configurations of all serving cells; and/or

clear all configured downlink assignments and configured uplink grants; and/or

clear all PUSCH resources for a semi-persistent CSI reporting; and/or

consider all running TA timers as expired; and/or

flush all HARQ buffers for all serving cells.

16 . The apparatus according to claim 12 , wherein when the TA timer expires and the serving cell is a secondary cell, the processor circuitry is further configured to:

notify RRC to release uplink configuration of the secondary cell; and/or

clear all configured downlink assignments and configured uplink grants of the secondary cell; and/or

clear all PUSCH resources for a semi-persistent CSI reporting of the secondary cell; and/or

flush all HARQ buffers for the secondary cell.

17 . The apparatus according to claim 16 , wherein,

a TA timer associated with the special cell does not expire or is running.

18 . An apparatus, configured in a network device, comprising:

a memory; and

processor circuitry coupled to the memory and configured to:

transmit a signal including a timing advance command (TAC) of a serving cell and timing advance group (TAG) ID of one or more TAGS, the signal being a random access response (RAR) message or a message B (MSGB),

wherein, the uplink time alignment of the serving cell is maintained based on one or two timing advance (TA) timers, one TA timer in the one or two TA timers is associated with the TAG, the serving cell is associated with two TA timers;

wherein, the TA timer corresponding to a TAG which corresponds to the TAG ID of the one or more TAGs.

19 . A communication system comprising:

a terminal equipment; and

a network device,

wherein the network device is configured to transmit a signal including a timing advance command (TAC) of a serving cell and timing advance group (TAG) ID of one or more TAGS, the signal being a random access response (RAR) message or a message B (MSGB),

wherein uplink time alignment of the serving cell is maintained based on one or two timing advance (TA) timers, one TA timer in the one or two TA timers is associated with the TAG, the serving cell is associated with two TA timers, and

wherein the terminal equipment is configured to receive the signal and start or restart a TA timer in the two TA timers when the signal is received, the TA timer corresponding to a TAG which corresponds to the TAG ID of the one or more TAGS.