A communication system and an oscillation signal provision method based thereon are provided. In the communication system, a high frequency oscillator generates a first high frequency signal upon receipt of an enable signal. The first high frequency signal is commonly shared by a first module and a second module. The first module is coupled to the high frequency oscillator, operating in either busy or idle mode, wherein the first module operates at the first high frequency signal when in busy mode. The second module converts the first high frequency signal to a second high frequency signal and operates at the second high frequency signal when in busy mode.