A base station determines both a transmission interval between scheduling requests which a mobile station transmits before transmitting uplink data and information about radio resources used for transmitting the scheduling requests, based on the status of the mobile station and/or QoS information transmitted from the mobile station. The mobile station generates the scheduling requests. The mobile station controls the transmission of the scheduling requests based on the transmission interval and the radio resources. The mobile station transmits the scheduling requests. The base station detects correlation based on the scheduling requests which are transmitted from the mobile station based on the transmission interval and the radio resources, and feeds delay information back to the mobile station. The mobile station maintains synchronization based on the delay information transmitted from the base station.