In the case of digital QAM, a definite number of minimum of two phases and least of two amplitudes are employed. The modulated waves are merged and the consequent waveform is a composite form of both PSK (Phase Shift Keying) and ASK (Amplitude Shift Keying) techniques or PM (Phase Modulation) and AM (Amplitude Modulation) (in the analog case). There are two sinusoid carrier wave does not remain in phase with each other exhibiting the difference of 90° and therefore called quadrature carriers or quadrature components.
In order to transmit two analog message signals/two digital bit streams, it modulates the amplitude of the two carrier waves with the help of amplitude shift keying (ASK). QAM (Quadrature Amplitude Modulation) is the combination of analog and digital modulation method. On the other hand, QAM is a group of ASK and PSK.īER is the percentage of the faulty bits as per the total number of transmitted, received and processed bits in a certain period of time which is equivalent to signal-to-noise ratio in an analog system. The QPSK is very much similar to the PSK the only difference between PSK and QPSK is that in basic PSK the phase shift occurs in every 180° degrees while in QPSK the phase shift occurs in multiple of 90°. Among these modulation techniques, we are going to compare the two, QAM and QPSK. This emerged the development of the encoding or modulation techniques named as PSK, FSK, ASK, QPSK and QAM, to convert the digital data into analog signals. Modulation requires the alteration of any of the three characteristics (i.e., amplitude, frequency and phase) of the carrier wave.
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