Digital Modulation techniques may be classified into coherent (or) Non-coherent techniques, depending on whether the receiver is equipped with a phase-recovery circuit (or) not.
| Coherent digital modulation techniques (or) systems | Non-coherent digital Modulation techniques (or) systems /Envelope detection. |
| 1. In this scheme, the local carrier generated at the receiver is phase locked with the carrier at the transmitter.
i.e, phase lock exists between Transmitter and Receiver. |
1. There exists no such phase lock between Transmitter and Receiver.
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| 2. This is also called Synchronous detection. | 2. This is known as Non-synchronous detection. |
| 3. complexity increases in terms of designing of the receiver. | 3. less complexity in terms of designing the receiver.
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| 4. probability of error decreases.
Examples:- coherent ASK, PSK, and FSK systems. |
4. error probability increases.
examples:-Non-coherent ASK, PSK, and FSK systems. |
