A communication system is provided. The communication system includes a communication device receiving a state signal from at least one remote terminal unit (RTU), generating signal quality data for the state signal, and transmitting, to a control device, the generated signal quality data and the received state signal. The control device generates state estimation data for each of the at least one RTU on a basis of the state signal received from the communication device, corrects the signal quality data transmitted from the communication device according to at least one preset condition, and changes the generated state estimation data on a basis of the corrected signal quality data and the received state signal.