A radio communications system in which a desired signal can be accurately discriminated from interfering signals, even when signals from a plurality of transmitters are received simultaneously, in which a transmitter communicates information using signals that are repeated over predetermined periods. A pulse generator generates pulses having a predetermined repetition period based on an information bit to be communicated, and the pulses generated by the pulse generator are transmitted. A pulse amplitude altering unit controls the amplitude of the pulses to be transmitted in accordance with a predefined pattern under the control of a control unit.