The processor includes a cyclic variation processor (12) and a channel variation processor (14).

Therefore, receiving performance of a receiving system whose channel variation is significant can be enhanced.

Accordingly, it is possible to cope with a serious channel variation while applying robustness to the mobile service data.

A dynamic adjustment scheme adapts quickly to channel variation characteristics where adjustment values depend on the target data packet completion rates that maximizes the effective throughput.

Accordingly, the mobile station of the OFDM system that is robust to channel variation and various fading environments may be provided to efficiently perform the automatic gain control.