phase detection am signal

Question

Hi,

i've implemented, in VHDL language, an iq demodulator for AM signal with the classic method of multiplying the input signal by sine and cosine, low pass filter and then SQRT(I^2 + Q^2).

Now i need to add a functionality to my demodulator.

Input signal could change phase and i should be able to detect this fact.

How can implement this feature in my design?

Can i use my IQ demodulator to do this thing?

Could you help me?

Thanks

altera_forum · Answer

Your IQ demod provides phase of received signal. But why AM needs phase detection?

altera_forum · Answer

--- Quote Start ---

Your IQ demod provides phase of received signal. But why AM needs phase detection?

--- Quote End ---

The signal that i've to demodulate is in figure below

http://www.alteraforum.com/forum/attachment.php?attachmentid=11167&stc=1

the phase of that signal could change as in figure below

http://www.alteraforum.com/forum/attachment.php?attachmentid=11168&stc=1

the input signal could be also

http://www.alteraforum.com/forum/attachment.php?attachmentid=11169&stc=1

i do not understand how detect phase change... before or after fir filter?

could you explain me better? thanks

altera_forum · Answer

The first two signals are on off keying OOK (a simple form of amplitude modulation).

The third signal seems as phase modulated BPSK (Not AM)

For OOK you need to read amplitude if it is well away from zero. In fact you don't need to square root (I^2+Q^2).

For BPSK you need to map output of demod to I constellations, there will be 180 degrees ambiguity of phase but this can be dealt with by using known data pattern from transmitter.

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phase detection am signal

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