Digital Modulation Techniques (Coherent and Non-Coherent Digital Modulation Techniques)

Coherent Vs Non Coherent Modulation (Introduction)

On the Basis of presence of Phase-Recovery circuit, we can classify digital modulation techniques into coherent or non coherent techniques.

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The job of the phase recovery circuit is to keep the oscillators supplying locally generated carrier wave at the receiver; in synchronizm to the oscillator supplying carrier wave at the transmitting end.
Actually, We use carrier waves at the transmitting and receiving ends both and for coherent detection these two Carriers should be in synchronism. Here synchronism means, synchronization in both frequency and phase.

Coherent Digital Modulation Technique

This technique employs coherent detection, the local carrier wave which is generated at the receiver is phase locked with the carrier at the transmitter.
Hence both the oscillators (carrier waves) are synchronized in both frequency and phase.
In coherent digital modulation technique, The error probability decreases but the system becomes complex.

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Non Coherent Digital Modulation Technique

In non coherent digital modulation technique, there is no need for the two carriers (at transmitter and receiver) to be phase locked.
Although in non-coherent technique the system becomes simple but the error probability increases which is in contrast to the coherent detection method.

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Advantages and disadvantages of digital communication system
Need and benefits of modulation
Sampling theorem and reconstruction (sampling and quantization)
Digital modulation techniques (coherent and non-coherent digital modulation techniques)
Digital modulation techniques (ASK, FSK, PSK, BPSK)/amplitude, frequency and phase shift keying)
Generation of binary phase shift keying (BPSK generation) -block diagram of binary phase shift keying (BPSK)
Quadrature amplitude modulation (QAM)/ QAM transmitter and QAM receiver block diagram
Quadrature phase shift keying modulation (QPSK) basics, waveform and benefits
Pulse code modulation (PCM) vs differential pulse code modulation (DPCM)