Method and apparatus for uplink time alignment in a wireless communication system
A method and apparatus are disclosed. In an example from the perspective of a User Equipment (UE), the UE receives a first signaling indicating a configuration of a first cell, wherein the first cell is associated with a first timing advance group (TAG). The UE receives a second signaling indicative of addition of the first cell as a first Serving Cell. In response to the second signaling, the UE (i) adds the first cell as the first Serving Cell, and (ii) determines whether to initiate a random access procedure based on the second signaling, and/or based on whether the first cell is associated with a first valid timing advance value.
1 . A method of a User Equipment (UE), the method comprising:
receiving a first signaling indicating a configuration of a first cell, wherein the first cell is associated with a first timing advance group (TAG);
receiving a second signaling indicative of (i) switching a SpCell of the UE to the first cell and (ii) a timing advance information; and
in response to the second signaling:
switching the SpCell of the UE to the first cell; and
determining whether to initiate a random access procedure on the first cell based on at least whether the timing advance information is valid.
2 . The method of claim 1 , wherein:
at least one of the first signaling or the second signaling is indicative of:
a TAG associated with the timing advance information.
3 . The method of claim 1 , comprising:
applying the timing advance information associated with the first cell in response to the second signaling if the timing advance information is valid.
4 . The method of claim 1 , comprising:
applying the timing advance information associated with the first cell after adding the first cell as a first Serving Cell.
5 . The method of claim 1 , comprising:
initiating the random access procedure based on at least a determination that the timing advance information associated with the first cell is invalid.
6 . The method of claim 1 , comprising:
not initiating the random access procedure based on the timing advance information associated with the first cell being valid.
7 . The method of claim 1 , wherein:
the timing advance information indicates whether to initiate the random access procedure.
8 . The method of claim 1 , wherein:
switching the SpCell of the UE to the first cell comprises applying the configuration of the first cell.
9 . The method of claim 1 , wherein:
the first signaling is indicative of a second configuration of a second cell, wherein the second cell is associated with a second TAG.
10 . The method of claim 9 , wherein:
the second signaling is indicative of addition of the second cell as a second Serving Cell; and
the method comprises adding the second cell as the second Serving Cell in response to the second signaling.
11 . The method of claim 9 , wherein:
the determination, in response to the second signaling, of whether to initiate the random access procedure on the second cell is based on whether the second cell is associated with a second valid timing advance value.
12 . The method of claim 11 , comprising:
initiating the random access procedure on the second cell based on a determination that:
the timing advance information associated with the first cell is valid; and
no valid timing advance value is associated with the second cell.
13 . The method of claim 9 , wherein:
the second signaling is indicative of at least one of:
a second valid timing advance value associated with the second cell; or
a TAG associated with the second valid timing advance value.
14 . The method of claim 9 , wherein:
at least one of the first signaling or the second signaling is indicative of at least one of:
the timing advance information and a second valid timing advance value associated with the second cell; or
a TAG associated with the timing advance information and a TAG associated with the second valid timing advance value.
15 . The method of claim 1 , wherein:
the second signaling comprises a Medium Access Control (MAC) Control Element (CE).
16 . A User Equipment (UE), the UE comprising:
a control circuit;
a processor installed in the control circuit; and
a memory installed in the control circuit and operatively coupled to the processor, wherein the processor is configured to execute a program code stored in the memory to perform operations, the operations comprising:
receiving a first signaling indicating a configuration of a first cell, wherein the first cell is associated with a first timing advance group (TAG);
receiving a second signaling indicative of (i) switching a SpCell of the UE to the first cell and (ii) a timing advance information; and
in response to the second signaling:
switching the SpCell of the UE to the first cell; and
determining whether to initiate a random access procedure on the first cell based on at least whether the timing advance information is valid.
17 . The UE of claim 16 , wherein:
at least one of the first signaling or the second signaling is indicative of
a TAG associated with the timing advance information.
18 . The UE of claim 16 , the operations comprising:
initiating the random access procedure based on at least a determination that the timing advance information associated with the first cell is invalid.
19 . The UE of claim 16 , the operations comprising:
not initiating the random access procedure based on the timing advance information associated with the first cell being valid.
20 . The UE of claim 16 , wherein:
the timing advance information indicates whether to initiate the random access procedure.