Communication system

1. A user equipment performing radio communication with a base station which configures a primary cell and a secondary cell,

wherein the user equipment is configured to be informed, from the primary cell, of a timing advance for use in communicating to the secondary cell, the timing advance indicating an uplink transmission timing alignment value, and

wherein the user equipment is configured to set a timing advance for use in communicating to the primary cell and the timing advance for use in communicating to the secondary cell and perform radio communication via carrier aggregation (CA) simultaneously over the primary cell and the secondary cell based on the set timing advance for each of the primary cell and the secondary cell, wherein the timing advance for use in communicating to the primary cell is different from the timing advance for use in communicating to the secondary cell, the timing advance for use in each of the primary cell and the secondary cell being configured to cause communication from the user equipment to a node in the primary cell and to a node in the secondary cell to arrive at each of the nodes at a same time,

wherein the uplink transmission timing alignment value indicated by the set timing advance for each of the primary cell and the secondary cell indicates an added amount of timing advance or delay for the user equipment to wait before the user equipment sends a radio frequency signal for communication with each of the primary cell and the secondary cell respectively.

2. A base station, which configures a primary cell and a secondary cell, used in a communication system comprising the base station and a user equipment performing radio communication with the base station, the base station comprising:

a transmitter configured to inform, via the primary cell, the user equipment of a timing advance for use in communicating to the secondary cell, the timing advance indicating an uplink transmission timing alignment value; and

a receiver, wherein the transmitter and the receiver are configured to perform communication with the user equipment, such that the user equipment performs communication via carrier aggregation (CA) simultaneously over the primary cell and the secondary cell based on a timing advance for use in communicating to the primary cell and the timing advance for use in communicating to the secondary cell informed to the user equipment, wherein the timing advance for use in communicating to the primary cell is different from the timing advance for use in communicating to the secondary cell, the timing advance for use in each of the primary cell and the secondary cell being configured to cause communication from the user equipment to a node in the primary cell and to a node in the secondary cell to arrive at each of the nodes at a same time,

wherein the uplink transmission timing alignment value indicated by the timing advance for each of the primary cell and the secondary cell indicates an added amount of timing advance or delay for the user equipment to wait before the user equipment sends a radio frequency signal for communication with each of the primary cell and the secondary cell respectively.

3. A user equipment performing radio communication with a base station which configures a primary cell and a secondary cell, the user equipment comprising:

a controller;

a transmitter that receives transmit data from the controller, converts the transmit data to first and second radio frequency signals, sends the first radio frequency signal for communication with the primary cell according to a first timing advance set by the controller, and sends the second radio frequency signal for communication with the secondary cell according to a second timing advance set by the controller, such that the user equipment perform radio communication via carrier aggregation (CA) simultaneously over the primary cell and the secondary cell based on the first timing advance and the second timing advance, wherein the first timing advance is different from the second timing advance, the timing advance for use in each of the primary cell and the secondary cell being configured to cause communication from the user equipment to a node in the primary cell and to a node in the secondary cell to arrive at each of the nodes at a same time; and

a receiver that receives the radio frequency signals, converts the radio frequency signals to received data, and sends the received data to the controller,

wherein the controller is programmed to receive the received data including information regarding at least one of the first timing advance and the second timing advance, the first timing advance indicating a first uplink transmission timing alignment value and the second timing advance indicating a second uplink transmission timing alignment value,

wherein the first uplink transmission timing alignment value indicates a first added amount of timing advance or delay for the user equipment to wait before the transmitter sends the first radio frequency signal for communication with the primary cell, and the second uplink transmission timing alignment value indicates a second added amount of timing advance or delay for the user equipment to wait before the transmitter sends the second radio frequency signal for communication with the secondary cell.

4. The user equipment according to claim 3 , wherein the radio frequency signals including the information regarding the second timing advance received by the receiver are transmitted from the primary cell.

5. The user equipment according to claim 3 , wherein a first distance between the user equipment and the primary cell is different from a second distance between the user equipment and the secondary cell, and the first and second uplink transmission timing alignment values are used to compensate for a difference in radio signal propagation delay timing resulting from the difference between the first distance and the second distance.