A transmitter includes a power measurement unit, a carrier sense unit, and a transmission unit. A first frequency band is allocated to a TDMA system. The power measurement unit measures a receiving power over a part of a first frequency band and a second frequency band. The carrier sense unit continues to check for a certain duration whether the receiving power is smaller than a threshold. The transmission unit generates a transmission signal including a dummy signal and a data signal when the receiving power has been smaller than the threshold for the certain duration. Moreover, the transmission unit transmits the transmission signal using the second frequency band.