Chapter 6 / 6.7 / 6.7.7

6.7.7 Demodulation

There are three types of demodulator for digital modulation:

• Non-coherent demodulators. These do not require carrier phase synchronization and are typically used for schemes such as non-coherent FSK or OOK. They are simpler but exhibit inferior error performance compared with coherent detection.
• Coherent demodulators. These employ carrier recovery to establish a phase reference and perform matched filtering prior to symbol decision. Coherent detection provides optimal performance in AWGN channels and is used for PSK and QAM systems.
• Differentially coherent demodulators. Used with DPSK, these avoid explicit carrier phase recovery by comparing the phase of successive symbols.

Coherent demodulators are more complex but are often preferred to non-coherent demodulators because they have lower error rates and use less power.