A method for transmitting signals by a medium access control (MAC) entity of a transmission end in a wireless communication system is disclosed. The method includes steps of receiving a protocol data unit (PDU) from a Radio Link Control (RLC) layer; transmitting a signal including the PDU based on a specific coverage enhanced (CE) level to a network; when a transmission of the signal to a network is failed, determining whether a current CE level is changed or not from the specific CE level; if the current CE level is changed from the specific CE level, transmitting an indication requesting a retransmission of the PDU, to the RLC layer; receiving the PDU from the RLC layer; and transmitting a signal including the PDU based on the current CE level to the network.