A communication system comprising a plurality of movable aerial-floating type communication relay apparatuses that respectively include a relay communication station of performing a service-link radio communication with a terminal apparatus, and plural gateway stations that are respectively configured to perform a feeder-link radio communication with the plurality of the communication relay apparatuses, wherein the communication system comprises a common baseband processing apparatus connected to the plural gateway stations, characterised in that the common baseband processing apparatus is configured to detect, when each of the plurality of movable aerial-floating type communication relay apparatuses fly in a same common area and transmit a feeder link to its respective gateway station, an interference of a reverse link communication between the feeder links due to an interference wave (I_REV) from a relay communication station of another communication relay apparatus, the interference wave (I_REV) interfering with a signal wave (S_REV) of the reverse link communication from the terminal apparatus to the gateway station via the relay communication station of the communication relay apparatus connected to the gateway station, based on plural reception signals received by the plural gateway stations, wherein the common baseband processing apparatus is configured: to perform a reception process of processing plural reception signals received by the plural gateway stations, as reception signals received by plural antennas; to compare a signal-wave reception level and an interference-wave reception level of the reverse link communication for each of the antennas, based on a reception signal of each of the plural antennas obtained in the reception process; and to determine that the interference of the reverse link communication is occurred, when a difference between the signal-wave reception level and the interference-wave reception level becomes equal to or less than a predetermined threshold value, or when a ratio of the interference-wave reception level to the signal-wave reception level becomes equal to or more than a predetermined threshold value. wherein the communication system comprises a common baseband processing apparatus connected to the plural gateway stations, characterised in that the common baseband processing apparatus is configured to detect, when each of the plurality of movable aerial-floating type communication relay apparatuses fly in a same common area and transmit a feeder link to its respective gateway station, an interference of a reverse link communication between the feeder links due to an interference wave (I_REV) from a relay communication station of another communication relay apparatus, the interference wave (I_REV) interfering with a signal wave (S_REV) of the reverse link communication from the terminal apparatus to the gateway station via the relay communication station of the communication relay apparatus connected to the gateway station, based on plural reception signals received by the plural gateway stations, wherein the common baseband processing apparatus is configured: to perform a reception process of processing plural reception signals received by the plural gateway stations, as reception signals received by plural antennas; to compare a signal-wave reception level and an interference-wave reception level of the reverse link communication for each of the antennas, based on a reception signal of each of the plural antennas obtained in the reception process; and to determine that the interference of the reverse link communication is occurred, when a difference between the signal-wave reception level and the interference-wave reception level becomes equal to or less than a predetermined threshold value, or when a ratio of the interference-wave reception level to the signal-wave reception level becomes equal to or more than a predetermined threshold value. to perform a reception process of processing plural reception signals received by the plural gateway stations, as reception signals received by plural antennas; to compare a signal-wave reception level and an interference-wave reception level of the reverse link communication for each of the antennas, based on a reception signal of each of the plural antennas obtained in the reception process; and to determine that the interference of the reverse link communication is occurred, when a difference between the signal-wave reception level and the interference-wave reception level becomes equal to or less than a predetermined threshold value, or when a ratio of the interference-wave reception level to the signal-wave reception level becomes equal to or more than a predetermined threshold value.