User equipment transmits signals in consideration of a time alignment timer

摘要

A method for transmitting and receiving signals in consideration of a time alignment timer (TAT), which a user equipment (UE) runs after receiving a time alignment command (TAC) from a base station (BS) S1201. The UE performs initial transmission or retransmission of an uplink signal S1204 using wireless resources corresponding to an uplink grant signal received from the BS S1202 only when the TAT of the UE is running S1203. Similarly, the UE does not transmit a HARQ feedback signal to a BS for a downlink signal received from the BS when the TAT of the UE is not running (fig.13). Since the UE is not always located at a fixed position, the transmission timing of the UE changes, so when a TAC is received from the BS, the UE assumes that the TAC is valid only for a specific time, i.e. the UE assumes that it is in time synchronisation with the BS only when the TAT is running.