Data rate dependent control channel allocation

When a base station generates an FCM, the base station detects the use rate of a transmission buffer and decides how slots of a frame of an uplink channel are structured. When the use rate of the transmission buffer is high, the base station designates the number of ACTSs to 0 so that the base station does not accept registration requests and so forth from mobile stations. When the use rate of the transmission buffer is low, the base station designates the number of ACTSs to 1. When the number of mobile stations is large as in a large convention hall, the base station generates TDMA frames each of which has only ACTSs. The base station can decide the number of ATCSs corresponding to the probability of which registration requests and so forth from mobile stations collide.