TRANSMITTER, RECEIVER, RADIO COMMUNICATIONS SYSTEM, AND PROGRAM

PROBLEM TO BE SOLVED: To increase data signal transmission efficiency at frequency hopping.SOLUTION: A transmitter 10 for changing a frequency bandwidth, used for data signal transmission, within a plurality of frequency bandwidths, according to elapsed time, is provided. A transmission part 11 transmits a first data signal 31a in a first frequency bandwidth D, at a first time period T, and transmits a second data signal 31b in a second frequency bandwidth D, at a second time period Twhich is after the first time period T. The transmission part 11 transmits a known signal 32, used for gain control at reception of the second data signal 31b by a receiver 20, before transmission of the second data signal 31b. A control part 12 controls the transmission part 11 so as to transmit the known signal 32, concurrently with the first data signal 31a, in the second frequency bandwidth D, at the first time period T.