Method of configuring timing advance group and/or value of time alignment timer

1. A base station, comprising:

at least one processor; and

at least one memory including computer program code;

the at least one memory and the computer program code configured to, with the at least one processor, cause the base station at least to perform:

transmitting the value of the time alignment timer toward a user equipment via a radio resource control message;

determining whether a secondary cell is a first secondary cell for which the base station configures a timing advance group or the secondary cell is added to an existing timing advance group;

when the secondary cell is determined to be the first secondary cell for which the base station configures the timing advance group, configuring the value of the time alignment timer for the secondary cell;

when the secondary cell is determined to be added to an existing timing advance group, reconfiguring an existing time alignment timer value of a secondary cell belonging to the timing advance group with a time alignment timer value already configured for the timing advance group,

wherein the at least one memory and the computer program code is further configured to, with the at least one processor, cause the base station at least to perform:

determining that the secondary cell is added to an existing timing advance group; and

in response to the determination that the secondary cell is added to an existing timing advance group, reconfiguring an existing time alignment timer value of a secondary cell belonging to the timing advance group with a time alignment timer value already configured for the timing advance group.

2. The base station according to claim 1 , wherein the at least one memory and the computer program code is further configured to, with the at least one processor, cause the base station at least to perform:

determining whether all secondary cells in the timing advance group of the secondary cell are released; and

releasing a configuration of the time alignment timer, if all of the secondary cells are released.

3. The base station according to claim 2 , wherein the at least one memory and the computer program code is further configured to, with the at least one processor, cause the base station at least to perform:

transmitting an instruction to the user equipment to instruct the user equipment to release the configuration of the time alignment timer.

4. A base station, comprising:

at least one processor; and

at least one memory including computer program code;

the at least one memory and the computer program code configured to, with the at least one processor, cause the base station at least to perform:

transmitting the value of the time alignment timer toward a user equipment in a media access control layer signaling;

determining whether a secondary cell is a first secondary cell for which the base station configures a timing advance group or the secondary cell is added to an existing timing advance group;

when the secondary cell is determined to be the first secondary cell for which the base station configures the timing advance group, configuring the value of the time alignment timer for the secondary cell; and

when the secondary cell is determined to be added to an existing timing advance group, reconfiguring an existing time alignment timer value of a secondary cell belonging to the timing advance group with a time alignment timer value already configured for the timing advance group;

wherein the at least one memory and the computer program code is further configured to, with the at least one processor, cause the base station at least to perform:

using a logical channel identifier, identifying a media access control layer control element that identifies the value of the time alignment timer and a corresponding timing alignment group.

5. A method of configuring a timing advance group for a secondary cell, in a base station, the method comprising:

transmitting an initial timing advance group identifier to the secondary cell of the user equipment via a radio link control message or a media access control protocol data unit;

determining whether the timing advance group identifier is valid for the secondary cell;

when the timing advance group identifier is invalid for the secondary cell, then triggering a random access procedure of a user equipment over the secondary cell;

obtaining a timing advance value of the user equipment over the secondary cell according to a result of the random access procedure of the user equipment over the secondary cell;

determining a final timing advance group to which the secondary cell belongs according to the timing advance value and comparing obtained timing advance value with timing advance values pre-stored in the base station

providing the user equipment with an identifier of the final timing advance group;

taking a timing advance group corresponding to the pre-stored timing advance value as the final timing advance group of the secondary cell, when a difference between the obtained timing advance value and any one of timing advance values pre-stored in the base station is within a predetermined range; or taking a timing advance group corresponding to the obtained timing advance value as the final timing advance group of the secondary cell, when a difference between the obtained timing advance value and any one of the timing advance values pre-stored in the base station exceeds the predetermined range,

wherein the base station transmits an identifier of the final timing advance group to the user equipment by any one of the following:

including the identifier of the final timing advance group in a message 2 for transmission to the user equipment, for the user equipment with a contention-free random access; and

including the identifier of the final timing advance group in a message 4 for transmission to the user equipment, for the user equipment with a contention-based random access.