Process loads of a base station and a mobile station are reduced when setting a group with respect to a plurality of mobile stations. The base station stores group information corresponding to a group assignable to a wireless device in association with the wireless device. The base station transmits group information to the wireless device through a relay station according to an authentication request from the wireless device. The base station generates call information defining a group requesting participation. The base station transmits call information to the wireless device through the relay station. The wireless device determines whether the group defined by call information and received from the base station includes the group corresponding to group information. The wireless device participates in the group determined to be included. The wireless device performs a data communication with other wireless devices participating in the group through the relay station.