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retrieving I & Q components from a complex signal

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rmreddy

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hello everyone,
i have generated a complex signal by mutiplying the real part of a symbol with cosine of carrier frequency and imaginary part by sine of carrier frequency.
com_signal=real(symbol)*cos(2*pi*fc*) + imag(symbol)*sin(2*pi*fc*t)). at the transmitter end

now, the problem is how to retrieve back the I & Q components at the reciever end.
i have done the coding on matlab.

help me guys..
 

First down convert frequency carrier component and then

Ich =real(com_signal); and Qch = imag(com_signal);

symbol = Ich + j*Qch;

Anyway i'm not sure hope someone for more clarity. :D
 

you have to multiply by coherent quadrature
carrier signals and lowpass filter the resulting
2 signals
 

Hi
sin and cos are orthogonal, so if you downconvert your signal with cos(wt) and filter it, real part is extracted. if you downconvert your signal with sin(wt) and filter it, imag part is extracted.
 

hey thanks dude, very good link .. almost all my doubts have been cleared ...
 

hi,
as you have stated, multiplying complexsignal with cos(theta) to retrieve inphase component and by sin(theta) to retrieve Q component ... and then passing through LPF of cut-off frequency - fc, .. this will work well if the noise introduced by the channel is a function of phase or frequency but not a DC noise ...

i have problem while trying to retrieve the signal assuming i have a DC component corrupted by the DC noise ,....
 

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