A communication device includes a radio transceiver and a processor. The radio transceiver is configured to transmit or receive wireless signals and includes a collision detection device. The collision detection device is configured to detect energy in a wireless communication channel during a first time interval before a packet is transmitted by the radio transceiver and accordingly generate a detection result. The first time interval covers a period of time for the radio transceiver to switch from a receiving state to a transmitting state. The processor is configured to adjust at least one transmission parameter according to the detection result.