A communication system, etc. are provided that can prevent the accuracy of propagation channel estimation from degrading when performing radio communications based on orthogonal frequency division multiplexing (OFDM) by using a plurality of carriers each with a predetermined bandwidth. Radio communications based on an OFDM scheme are performed between a transmitter and a receiver by using a carrier with a prescribed bandwidth in which first signals such as reference signals, for example, are arranged at constant subcarrier intervals. The transmitter, when performing communications with the receiver by using a plurality of such carriers, transmits to the receiver an OFDM signal in which the first signals are arranged at predetermined subcarrier intervals across the plurality of carriers. The receiver extracts the first signals from the OFDM signal received from the transmitter.