in detail tx feedback may have two states similarly to ack nack feedback fed back to an enb from an rd for example the two states for the tx feedback may include tx success or tx failure in addition for example when the td performs d2d data transmission to the rd the tx success may be signaled to the enb and when the td does not perform d2d data transmission to the rd the tx failure may be signaled to the enb for example the tx failure may be useful to the case in which a td gives up d2d data transmission in order to transmit and receiving a signal channel with higher priority than d2d data although the td properly receives a d2d trigger a signal channel used for the tx feedback may have the same similar format e g pucch format 1a 1b to a signal channel for ack nack feedback for example different tx feedback states may be mapped to positions of ack and nack on constellation in addition tx feedback may be transmitted after d2d data is transmitted in addition the tx feedback may be transmitted at the same time point as ack nack feedback based on the a n to enb method or transmitted at a time point prior to ack nack feedback.