A communication device capable of operating in a first and a second communications systems includes a radio signal transceiver module, a first reception module for receiving signals from the first communications system, a first transmitting module for transmitting signals to the first communications system, a second reception module for receiving signals from the second communications system, a second transmitting module for transmitting signals to the second communications system, a first filtering unit coupled to the first transmitting module for filtering out signals in an overlapping frequency band between the first transmitting module and the second reception module, and a second filtering unit coupled to the second transmitting module for filtering out signals in an overlapping frequency band between the second transmitting module and the first reception module.