A method for transmitting channel quality information for a downlink channel, the method includes receiving, by a user equipment (UE), configuration information on periodic channel state information (CSI) reporting by higher layer signaling; determining, by the UE, a channel quality information index considering the configuration information on CSI reporting; and transmitting the determined channel quality information index to a base station, wherein the channel quality information index is determined based on a number of available resource element, and wherein an assumption of no resource element allocated for a Channel Status Information-Reference Signal (CSI-RS) is applied when the number of the available resource element is determined.