The disclosure is directed to method of transmitting a reference signal used by a wireless device in an unlicensed spectrum for a LTE-LAA communication system, and a wireless communication device using the same method. In one of the exemplary embodiments, the method would include not limited to receiving, via a first wireless receiver tuned to a licensed spectrum, a control message which at least indicates a pattern of a reference signal to be received; receiving, via a second wireless receiver tuned to an unlicensed spectrum, a first message which comprises the reference signal in the unlicensed spectrum; performing a measurement of the reference signal; generating a feedback based on the measurement of the reference signal; and transmitting, via a wireless transmitter tuned to the licensed spectrum, a second message which comprises the feedback of the reference signal in the licensed spectrum.