3rd generation partnership project (3GPP) long term evolution (hereinafter, referred to as ‘LTE’) and LTE-advanced (hereinafter, referred to as ‘LTE-A’) communication systems will be schematically described as examples of mobile communication systems applicable to the present disclosure proposed in the specification. 
One or more cells exist in one base station.  One cell is set to one of bandwidths of 1.25 MHz, 2.5 MHz, 5 MHz, 10 MHz, 15 MHz and 20 MHz with respect to one carrier so as to provide a downlink/uplink transmission service to several user equipments (UEs).  In this case, different cells may be set to provide different bandwidths.  One base station controls data transmission/reception for a plurality of UEs.  The base station transmits downlink (DL) scheduling information of DL data to a corresponding UE so as to inform the corresponding UE of information related to time/frequency domains to which data is to be transmitted, encoding, data size, hybrid automatic repeat request (HARQ), etc.  The base station transmits uplink (UL) scheduling information of UL data to the corresponding UE so as to inform the corresponding UE of information related to time/frequency domains that can be used by the corresponding UE, encoding, data size, HARQ, etc.  An interface for transmitting user traffic or control traffic may be used between base stations. 
Although radio communication technology has been developed up to LTE based on wideband code division multiple access (WCDMA), the demands and expectations of users and providers continue to increase.  Since other radio access technologies have also been continuously developed, new technology evolution is required to secure high competitiveness in the future.  The new technology requires decrease in cost per bit, increase in service availability, flexible use of a frequency band, simple structure, open interface, suitable UE power consumption, etc. 
Recently, the standardization of the subsequent technology of the LTE is ongoing in the 3GPP.  In this specification, the technology is called as ‘LTE-A.’ The LTE and LTE-A systems are different from each other in terms of system bandwidths and introduction of relays. 
The LTE-A system aims to support a wideband of a maximum of 100 MHz.  To this end, the LTE-A system uses carrier aggregation or bandwidth aggregation technology which achieves the wideband using a plurality of frequency blocks.  The carrier aggregation enables the plurality of frequency blocks to be used as one large logical frequency band in order to use a wider frequency band.  The bandwidth of each of the frequency blocks may be defined based on the bandwidth of a system block used in the LTE system.  Each of the frequency blocks is transmitted using a component carrier. 
As the carrier aggregation technology is used in the LTE-A system that is a next-generation communication system, it is required to develop a method in which a UE receives a signal from a base station or relay in a system supporting a plurality of carriers.