Patent ID: 8385236

Claim:
A user apparatus for use in a mobile communications system, comprising: a unit which determines, using acknowledgement information received from a communications counterpart, whether retransmission is required for a transmitted signal; and a unit which transmits, to the communications counterpart, a signal required to be retransmitted according to a round-trip delay (RTD) which is set in the user apparatus for retransmission control, wherein, the RTD of the user apparatus is arranged to be changed, when the user apparatus enters a region which uses an RTD shorter than the RTD set for the user apparatus, to an integer multiple of the shorter RTD, wherein the integer multiple of the shorter RTD becomes no less than an RTD which is preset for retransmission control, wherein the shorter RTD is six times a transmission time interval (TTI), and wherein the RTD which is preset is 10 TTIs, and the RTD of the user apparatus is changed to 12 TTIs when the user apparatus enters a region which uses the RTD of 6 TTIs.