As an example of a mobile communication system, to which the present invention is applicable, a 3rd Generation Partnership Project Long Term Evolution (3GPP LTE) communication system will be schematically described.
FIG. 1 is a schematic diagram showing a network architecture of an Evolved Universal Mobile Telecommunications System (E-UMTS) as an example of a mobile communication system. The E-UMTS is an evolved version of the existing Universal Mobile Telecommunications System (UMTS) and basic standardization thereof is in progress under the 3GPP. In general, the E-UMTS is also referred to as a Long Term Evolution (LTE) system. For details of the technical specifications of the UMTS and the E-UMTS, refer to Release 7 and Release 8 of “3rd Generation Partnership Project; Technical Specification Group Radio Access Network”, respectively.
Referring to FIG. 1, the E-UMTS mainly includes a User Equipment (UE) 120, base stations (BSs) (or eNBs or eNode Bs) 110a and 110b, and an Access Gateway (AG) which is located at an end of a network (E-UTRAN) and which is connected to an external network. Generally, the BS can simultaneously transmit multiple data streams for a broadcast service, a multicast service and/or a unicast service.
One or more cells may exist for one BS. The cell provides a downlink or uplink transmission service to several UEs using any one of bandwidths of 1.4, 3, 5, 10, 15 and 20 MHz. Different cells may be set to provide different bandwidths. A BS controls data transmission or reception to or from a plurality of UEs. The BS transmits downlink scheduling information to a UE with respect to downlink (DL) data so as to inform the UE of time/frequency domain, coding, data size, Hybrid Automatic Repeat and reQuest (HARQ) associated information of data to be transmitted, or the like. The BS transmits uplink scheduling information to a UE with respect to uplink (UL) data so as to inform the UE of time/frequency domain, coding, data size, HARQ associated information used by the UE, or the like. An interface for transmitting user traffic or control traffic can be used between BSs. A Core Network (CN) may include the AG, a network node for user registration of the UE, or the like. The AG manages mobility of a UE on a Tracking Area (TA) basis. One TA includes a plurality of cells.
Wireless communication technology has been developed to reach the LTE based on Wideband Code Division Multiple Access (WCDMA), but demands and expectations of users and providers have continuously increased. In addition, since other aspects of wireless access technology continue to evolve, new advances are required to remain competitive in the future. There is a need for reduction in cost per bit, service availability increase, the use of a flexible frequency band, a simple structure and an open type interface, appropriate power consumption of a UE, etc.
Recently, standardization of the successor to LTE is in progress under the 3GPP. In the present specification, the above technology is referred to as “LTE-Advanced” or “LTE-A”. The LTE system and the LTE-A system are different from each other in a system bandwidth difference. The LTE-A system is to support a maximum wideband of 100 MHz. The LTE-A system uses carrier aggregation or bandwidth aggregation technology to achieve a wideband using a plurality of component carriers. In the carrier aggregation, in order to use a wider frequency band, the plurality of component carriers is treated as one large logic frequency band. The bandwidth of each component carrier may be defined based on the bandwidth of a system block used in the LTE system. In the present specification, the component carrier may be a component carrier for carrier aggregation or a central carrier of the component carrier according to context.