A base station has a time correlation calculating unit for estimating a
variation-with-time characteristic of radio link quality using radio
downlink quality information reported by a mobile station, a target error
rate setting unit for changing over a target error rate adaptively using
this variation-with-time characteristic, and an MCS decision unit for
deciding a modulation scheme and/or encoding rate, in such a manner that
packet error rate becomes equal to the target error rate, using the radio
link quality information as well as reception success/failure information
reported by the mobile station. The base station transmits a packet based
upon the modulation scheme and/or encoding rate decided.