Before revision: An additional technique called Quadrature Amplitude Modulation (QAM) has also been proposed, where both amplitude and phase of the sinusoidal voltage are keyed simultaneously in order to increase the possible number of symbols , some other modulation techniques also available all are depend on the performance parameters as per the required application .
After revision: An additional technique called Quadrature Amplitude Modulation (QAM) has also been proposed, where both amplitude and phase of the sinusoidal voltage are keyed simultaneously in order to increase the possible number of symbols .