Hi,
When explaining the demodulation process of an amplitude modulated digital signal, I haven't find any article about how a receiver retrieves the "correct" levels for decoding the signal without error. In a binary (On/off) modulation it is not an issue however if there are more than two amplitude values then how the receiver knows that the signal it's receiving is a '01' and not a '11' that was attenuated by distance (assuming a purely amplitude modulated digital signal) ?
I can see several ways of doing it but I didn't find how it's done in a real system :
- the transmission of a synchronization word that will be recognised as such by the receiver and used as a reference;
- the use of an AGC that will amplify the received signal to a normalized level (but then how the AGC work ?);
Thank you in advance for your answer. I apologise if the question is either not in the correct subsection of the forum or if it was answered before (and I didn't find the information).
When explaining the demodulation process of an amplitude modulated digital signal, I haven't find any article about how a receiver retrieves the "correct" levels for decoding the signal without error. In a binary (On/off) modulation it is not an issue however if there are more than two amplitude values then how the receiver knows that the signal it's receiving is a '01' and not a '11' that was attenuated by distance (assuming a purely amplitude modulated digital signal) ?
I can see several ways of doing it but I didn't find how it's done in a real system :
- the transmission of a synchronization word that will be recognised as such by the receiver and used as a reference;
- the use of an AGC that will amplify the received signal to a normalized level (but then how the AGC work ?);
Thank you in advance for your answer. I apologise if the question is either not in the correct subsection of the forum or if it was answered before (and I didn't find the information).