[Problem] According to conventional techniques, a modulation class is determined on the basis of past communication environment information stored at a base station, and the modulation class cannot be determined with consideration of a communication environment in which a signal is retransmitted. Thus, with the conventional techniques, a modulation and coding scheme cannot be determined with consideration of the communication environment in which the signal is retransmitted.[Solution] An embodiment of this communication system has a control unit that determines a first modulation and coding scheme to be applied to a signal on the basis of information about predicted first communication quality when a signal is transmitted at a first timing and information about predicted second communication quality when the signal is retransmitted at a second timing.