Electronics and Communication Engineering - Communication Systems - Discussion

Coherent detection requires the phase information of the carrier phase. This can be achieved either by sending a carrier from a transmitter or by using a local oscillator at the receiver that is phase locked with the transmitter. Thus there exists a phase difference between the two which has to be estimated and corrected for detection. In non-coherent detection, no phase information is required. Since PM is required to continually change the phase of the carrier, therefore, non-coherent detection which does not require phase information can't be used to detect it. To detect PM one must use phase information as the message is present in phase information.

For non-coherent detection, information should be send in amplitude and frequency. If we send information in phase the carrier is not recovered at the receiver and in PSK information is send in phase.

In PSK, the information is dubbed into the phase of the carrier signal, however non coherent detection does not need the phase information of signal. Thus it can't demondulate.

Non-coherent detection is not possible in PSK and FSK because the receiver needs to know the carrier phase and frequency, respectively, to demodulate the signal accurately.

Non-coherent detection is not possible because at the receiver end the same frequency should be used as that of at the transmitter end, And coherency maintenance is must.

With respect to phase when we talk, detection is random in nature and mapping of information cannot be done correctly, so we need exact estimation and detection process.

Non-coherent detection process doesn't need receiver to be phase locked with transmitted carrier. As the main objective is phase itself, so how could we determine PSK!

When the receiver exploits knowledge of the carrier's phase to detect the signal. The process is called coherent detection.

Because in PSK modulation technique the phase of the modulated is changed according to the phase of the baseband signal.

Phase always indicates the exact position of the signal. So we need exact phase we need synchronous the modulation.