Coherent demodulation, why isn't the phase of the carrier wave known or constant?

Thread Starter

abdulwahab.hajar

Joined Jun 14, 2016
93
Hello everyone

So as I understand in coherent demodulation, it is necessary to obtain the carrier phase in order to demodulate the received signal (is this to generate a carrier wave with a matching phase in order to be used in the matching filter to detect the received symbol?), so if this is true, why isn't the phase of the carrier wave at the transmitter constant or known, or is it known initially but changes or is affected drastically when it is transmitted through the channel?

Or maybe there is some something that I'm completely missing? Kindly enlighten me.

Thank you
 

KeithWalker

Joined Jul 10, 2017
679
Hello everyone

So as I understand in coherent demodulation, it is necessary to obtain the carrier phase in order to demodulate the received signal (is this to generate a carrier wave with a matching phase in order to be used in the matching filter to detect the received symbol?), so if this is true, why isn't the phase of the carrier wave at the transmitter constant or known, or is it known initially but changes or is affected drastically when it is transmitted through the channel?

Or maybe there is some something that I'm completely missing? Kindly enlighten me.

Thank you
Wikpedia explains it far clearer than I could:
https://en.wikipedia.org/wiki/Carrier_recovery
 
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